THE  PROPERTY  OF, 


7' 


* 


MEIDICAL    SCHOOL 


i 

/' 


PRINCIPLES 


OF 


HUMAN    PHYSIOLOGY, 

WITH  THEIR    CHIEF  APPLICATIONS   TO    PATHOLOGY,   HYGIENE, 
AND  FORENSIC  MEDICINE. 

ESPECIALLY  DESIGNED  FOR  THE  USE  OF  STUDENTS. 


BY 


WILLIAM  B.  jgARPENTER,  M.D.,  F.R.S., 

FULLERIAN  PROFESSOR  OF  PHYSIOLOGY  IN  THE  ROYAL  INSTITUTION  OF   GREAT  BRITAIN; 

LECTURER  ON   NATURAL   HISTORY   AND   COMPARATIVE   ANATOMY   AT   ST.  THOMAS' 

HOSPITAL,   AND   CORRESPONDING   MEMBER   OF  THE   NATIONAL 

INSTITUTE   OF   THE  UNITED   STATES. 


Second  ^merfcnn,  from  tjje  last  Hontjon  IJQftfon. 
WITH  NOTES  AND  ADDITIONS. 


BY 


MEREDITH   CLYMER,  M.  D., 

PHYSICIAN  TO 

THE   PHILADELPHIA  HOSPITAL; 
FELLOW    OF   THE   COLLEGE   OF   PHYSICIANS.  ETC. 


WITH  TWO   HUNDRED  AND  SIXTEEN  WOOD-CUT  AN 


L  E  A  JA  N,i; 


1845. 


ILLUSTRATIONS. 


. 

ENTERED  according  to  Act  of  Congress,  in  the  year  1845,  by 

LEA  AND  BLANCHARD, 
In  the  Office  of  the  Clerk  of  the  District  Court  for  the  Eastern  District  of  Pennsylvania. 


'  PRIMERS. 


'2 


TO 

WILLIAM  PULTENEY  ALISON, 

M.D.,  F.R.S.E.,  &c.  &c. 

PROFESSOR  OF  THE  PRACTICE  OF  MEDICINE  OF  THE  UNIVERSITY  OF   EDINBURGH. 


MY  DEAR  SIR, 

I  take  the  liberty  of  inscribing  the  following  Work  to  you,  as  an 
expression  of  my  grateful  remembrance  of  the  value  of  your  instructions, 
of  my  respect  for  those  intellectual  faculties  which  render  you  pre-emi- 
nent amongst  the  Medical  Philosophers  of  our  time,  and  of  my  admiration 
for  those  moral  excellencies  which  call  forth  the  warm  regard  of  all  who 
are  acquainted  with  your  character. 

In  many  parts  of  this  Treatise  you  will  find  that  doctrines,  which  you 
have  long  upheld  in  opposition  to  almost  the  whole  Physiological  world, 
are  defended  with  such  resources  as  I  could  command ;  and  that,  in 
many  instances,  such  convincing  evidence  of  their  truth  has  been 
afforded  by  recent  observations,  that  further  opposition  to  them  would 
now  seem  vain.  And  if  I  have  presumed  to  differ  from  you  on  some 
points,  it  has  been  in  the  spirit  of  that  independence  which  you  have 
uniformly  encouraged  in  your  pupils;  yet  with  a  distrust  of  my  own 
judgment,  wherever  it  came  into  collision  \*ith  YQ^fl^ 

That  you  may  long  be  spared  to  be  the  ornam^B  iBbur  University, 
and  the  honour  of  your  City,  is  the  earnest  wish  ^^ 

Dear  Sir, 

Your  obliged  Pupil, 

WILLIAM  B.  CARPENTER. 
Ripky,  Surrey,  Sept.  20;  1844. 


t.348. 


PREFACE  OF  THE  AMERICAN  EDITOR. 


"THE  peculiar  character  of  Dr.  Carpenter's  £ Human  Physiology,' 
particularly  adapts  it  to  the  wants  of  the  medical  student.  The  close 
connection  between  Physiology  and  the  practical  branches  of  medicine, 
has  been  throughout  the  work  carefully  borne  in  mind,  and  their  inti- 
mate relations  pointed  out.  The  present  Treatise  will  be  found  to  be  a 
concise,  yet  comprehensive  exposition  of  the  actual  condition  of  physi- 
ological science,  conceived  and  executed  in  an  acute  and  philosophical 
spirit.  With  much  that  is  profound  and  original,  the  Author  has  pre- 
sented all  the  received  or  probable  facts  of  the  Science  of  Life,  in  a 
well-digested  and  lucid  manner,  deducing  from  them  legitimate  infer- 
ences, and  carefully  abstaining  from  the  discussion  of  controverted 
questions,  and  never  hazarding  any  startling  hypothesis." 

The  above  opinion  was  expressed  by  the  Editor  in  the  Preface  to  the 
First  American  Edition  of  this  work.  The  universal  favour  with  which 
it  has  been  received,  and  the  rapid  sale  of  a  very  large  impression,  are 
proofs  that  his  judgment  was  neither  erroneous  nor  too  partial.  It  is 
now  generally  conceded  in  this  country  and  in  England,  that  Dr.  Car- 
penter's "Principles  of  Human  Physiology"  is  one  of  the  best  digested, 
most  complete  and  compendious  expositions  of  the  Science  of  Life  in 
its  actual  state,  that  has  yet  been  written,  and  admirably  adapted  to  the 
purposes  of  the  medical  student.  9^^k 

In  preparing  the  present  edition,  no  pains  have^^^BApared  to  render 
it  complete  in  all  respects.  Besides  other  sources,  1f$e  Editor  has  availed 
himself  of  much  valuable  matter  contained  in  the  excellent  Annual 
Report  on  the  Progress  of  Anatomy  and  Physiology  in  the  British  and 
Foreign  Medical  Review  for  January,  1845.  He  has  also  introduced 
about  eighty  additional  wood-cut  illustrations,  which,  being  accom- 
panied with  very  copious  references,  will,  he'  trusts,  materially  add  to 
the  value  of  the  work  as  a  text-book. 

The  new  matter  added  by  the  American  Editor  is  in  smaller  type, 
and  is  distinguished  thus  [ — M.  C.]  The  new  cuts  are  included  be- 
tween brackets,  thus  [  ]. 

No.  230  Spruce  St., 

Philadelphia,  April,  1845. 


X  PREFACE  TO  THE  SECOND  EDITION. 

4.  Observations  on  the  Nature  and  Destination  of  the  Food  of  Animals ;  principally 
based  on  Prof.  Liebig's  views,  $§  430—434. 

5.  Mr.  Goodsir's  researches  on  the  absorbent  Cells  of  the  Intestinal  Villi,  §§  461,  462. 

6.  Researches  of  Mr.  Addison  and  M.  Bourgery  on  the  structure  of  the  Lungs,  §  525. 

7.  Researches  of  MM.  Andral  and  Gavarret,  and  of  Prof.  Scharling,  on  Respiration, 
.§  534  note,  and  §  544. 

8.  The  chapter  on  Nutrition,  including  the  history  of  the  Chyle,  Blood  and  Tissues, 
almost  wholly  re-written;  so  as  to  include  the  results  of  the  most  recent  observations  on 
these  subjects,  and  the  views  to  which  the  Author  has  been  led  by  them. 

9.  The  doctrine  of  Secretion  by  Cells,  as  developed  by  Henle,Goodsir  and  others,  §  651. 

10.  The  researches  of  Mr.  Bowman  on  the  structure  and  functions  of  the  Malpighian 
bodies  of  the  Kidney,  §§  667,  668. 

11.  The  account  of  the  constitution  of  Urine  lately  given  by  Liebig,  §§  673 — 678. 

"12.  The  inquiries  of  Dr.  Lehmann,  respecting  the  influence  of  diet  on  the  constitution 
of  the  Urinary  Secretion,  §§  679,  680. 

13.  The  researches  of  Dr.  Evans  on  the  structure  of  the  Spleen,  §§  708,  709. 

14.  The  inquiries  of  Dr.  Buchanan  on  the  changes  in  the  Blood  produced  by  admixture 
of  Chyle,  §§  714  note,  715. 

15.  The  investigations  of  Chossat  on  the  effects  of  Inanition,  §  730. 

16.  The  results  of  M.  Raciborski's  inquiries  in  regard  to  the  relation  between  the 
periods  of  Conception  and  Menstruation,  §  742. 

17.  The  researches  of  Dr.  Ritchie,  into  the  various  conditions  of  the  Ovaria,  §  744. 

Many  other  additions,  not  of  sufficient  importance  to  be  thus  specified, 
are  scattered  throughout  the  work ;  and  in  many  instances  these  are  the 
result  of  the  Author's  own  investigations.  He  has  particularly  directed, 
his  attention  to  the  settlement  of  points  which  appeared  to  him  to  have 
been  left  doubtful  by  others  ;  and  hence  will  sometimes  be  found  to 
have  expressed  his  views  with  a  degree  of  confidence  which  the  evi- 
dence adduced  by  them  may  scarcely  appear  to  warrant. 

Notwithstanding  the  attacks  which  have  been  made  on  Dr.  Barry's 
views  respecting  the  Reproductive  process,  by  Prof.  Bischoff  and  Mr. 
Wharton  Jones,  tl^Author  has  not  felt  it  desirable  to  modify  in  any 
great  degree,  t^e^^ount  he  had  previously  given  of  that  Function, 
chiefly  on  Dr.  Barry's  authority.  It  happens  that  he  is  well  convinced, 
by  his  own  observations,  of  Dr.  B.'s  accuracy  on  some  of  the  leading 
points  which  have  been  most  strongly  objected  to;  and  he  feels  the 
more  confidence,  therefore,  in  regard  to  the  rest.  He  may  also  advert  to 
the  very  remarkable  confirmation,  which  has  been  afforded  to  Dr.  B.'s 
statements  regarding  the  early  changes  that  take  place  within  the  germi- 
nal vesicle,  by  the  parallel  researches  of  Mr.  H.  S.  Goodsir  on  the  ova 
of  Acephalocysts  (Trans,  of  Roy.  Soc.  of  Edinb.,  vol.  xv.).  He  cannot 
but  regret  that  the  subject  has  been  discussed  with  so  much  acrimony 
of  feeling,  and  with  so  much  more  desire  to  find  fault  than  to  elicit 
Truth. 

In  regard  to  certain  subjects  which  have  excited  much  attention  since 
the  appearance  of  the  First  Edition,  the  Author  may  be  permitted  to 


PREFACE  TO  THE  SECOND  EDITION.  XI 

remark  that  he  has  found  less  occasion  to  introduce  alterations  or  addi- 
tions than  might  have  been  expected  ;  for  the  general  doctrine  respecting 
the  connection  of  the  waste  of  the  Organic  structure  with  its  functional 
activity,  and  the  dependence  of  the  excreting  processes  upon  the  disin- 
tegration of  the  bodily  framework, — which  have  been  considered  novel 
features  in  the  Animal  Chemistry  of  Prof.  Liebig,  had  been  very  clearly 
set  forth  by  himself.  He  cannot  but  think  that  the  value  of  that  able 
Chemist's  actual  contributions  to  Physiological  Science  have  been  con- 
siderably overrated  ;  though  none  can  estimate  more  highly  than  he  does, 
the  importance  of  the  path  of  inquiry  which  Prof.  L.  has  opened  up. 

The  only  point  in  which  any  considerable  fault  has  been  found  writh 
this  work,  in  the  criticisms  offered  by  the  Medical  Journals,  has  respect 
to  the  arrangement  of  its  subjects.  It  seems  to  be  the  general  opinion 
that  the  consideration  of  the  Organic  Functions  should  precede  that  of 
the  Functions  of  Animal  Life,  on  account  of  the  greater  complexity  of 
the  latter.  The  Author's  reasons  for  the  course  he  has  adopted  will  be 
found  in  §  82 ';  and  he  would  only  add  here  that  the  reader  who  is  so 
disposed  will  find  no  difficulty  in  passing  at  once  from  the  General  View 
of  the  Functions  (Chap.  II.)  to  the  Second  Division  of  the  book,  com- 
mencing with  Chap.  VIII.;  deferring  the  consideration  of  the  Nervous 
System  and  its  operations  until  the  last.  It  is  the  Author's  own  opinion, 
however,  that  this  latter  class  of  phenomena  is,  as  now  understood,  the 
least  complex  of  the  two. 

He  has  only  further  to  notice,  that  a  considerable  number  of  new 
Woodcuts,  and  a  new  Plate,  have  been  added  to  the  present  Edition. 

Ripley,  Surrey,  Sept.  21th,  1844. 


LIST  OF  WOODCUT  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Structure  of  the  Star-fish,  after  Tiedemann     -                                                 -  37 

2.  External  aspect  of  Aplysia,  after  Rang            -  38 

3.  Structure  of  Aplysia,  after  Cuvier        -                                                                -  40 

4.  Section  of  Cockchafer,  after  Strauss-Durckheim        ....  42 

5.  Comparative  view  of  the  base  of  the  Skull  of  Man,  and  of  the  Orang  Outan, 

after  Owen               -                        ...                                    -  61 

6.  Comparative  view  of  the  Skeletons  of  Man  and  the  Orang,  after  Owen         -  62 

7.  Structure  of  Nerve-tubes,  after  Wagner          .....  91 

8.  Primitive  fibres  and  globules  of  ganglia,  after  Wagner  92 

9.  Primitive  fibres  and  ganglionic  globules  of  Human  brain,  after  Purkinje      -  92 

10.  Nervous  system  of  Aplysia,  after  Cuvier        -                         ...  106 

11.  Nervous  system  of  Larva  of  Sphinx  Ligustri,  after  Newport             -            -  108 

12.  Portion  of  Ganglionic  tract  of  Polydesmus  maculatus,  after  Newport            -  109 

13.  Parts  of  Nervous  System  of  Articulata,  after  Newport                                     -  113 

14.  Stomato-gastric  system  of  Gryllotalpa  vulgaris,  after  Brandt                          -  114 

15.  View  of  the  Great  Sympathetic  Nerve                                                                 -  120 

16.  Nervous  centres  in  Frog,  after  Leuret             .....  123 

17.  Transverse  sections  of  Spinal  Cord  at  different  points,  after  Solly     -            -  123 

18.  A  transverse  section  of  Spinal  Marrow                       -            -            -  124 

19.  Structure  of  the  Spinal  Cord,  according  to  Stilling      -                        -            -  125 

20.  A  posterior  superior  view  of  the  Pons  Varolii,  Cerebellum,  &c.         -            -  127 

21.  A  posterior  view  of  ;he  Medulla  Oblongata     -----  127 

22.  An  anterior  view  of  the  Medulla  Oblongata    -----  128 

23.  Course  of  the  Motor  tract,  after  Sir  C.  Bell      -            -                                     -  129 

24.  Course  of  the  Sensory  tract,  after  Sir  C.  Bell              -                                     -  130 

25.  A  lateral  view,  of  the  Spinal  Marrow,  &c.,  of  a  new-born  infant         -            -  131 

26.  A  posterior  view  of  the  Medulla  Spinalis        -----  131 

27.  Brains  of  Fox-Shark,  Cod,  and  Pike,  after  Leuret      -            -            -  159 

28.  Human  Embryo,  showing  rudiments  of  Encephalon,  after  Wagner  -            -  160 

29.  Brain  of  Turtle,  after  Solly      -                                     -----  161 

30.  Brain  of  Buzzard,  after  Leuret                        .....  161 

31.  Brain  of  Human  Embryo,  at  12th  week,  after  Tiedemann      -  162 

32.  Brain  of  Rabbit,  after  Leuret   -  162 

33.  Base  of  the  Cerebrum  and  Cerebellum,  with  their  nerves       -            -            -  163 

34.  First  pair,  or  Olfactory  Nerves                         .....  164 

35.  Portio  Mollis  of  Seventh  Pair,  or  Auditory  Nerve       -                        -            -  167 

36.  Diagram  of  the  distribution  of  the  Fifth  Pair                                        -            -  168 

37.  Distribution  of  the  Fifth  Pair               ....                         -  168 
'38.  Diagram  of  the  distribution  of  the  Facial  Nerve         ....  170 

39.  Diagram  of  the  distribution  of  the  Eighth  Pair            ....  172 

40.  Distribution  of  the  Glosso-Pharyngeal,  Pneumogastric,and  Spinal  Accessory 

Nerves,  or  Eighth .Pair        -                        -                                    -            -  172 

41.  Course  and  distribution  of  the  Hypo-Glossal  or  Ninth  Pair    -            -  181 

42.  View  of  the  Third,  Fourth,  and  Sixth  Pair      -                        -            -            -  183 

43.  Longitudinal  Section  of  Eye     -                                                   ...  242 

44.  Horizontal  Section  of  Eye  Ball                                                   -            -            -  243 

45.  Magnified  view  of  outer  surface  of  Retina  of  Frog,  after  Treviranus              -  245 

46.  Do.                of  inner  surface                        .....  245 

47.  Portion  of  the  Retina  of  an  Infant,  magnified                                                   •  246 

48.  Imaginary  Plan  of  the  Cochlea                                                                            -  257 

49.  Axis  of  Cochlea  and  Lamina  Spiralis                                                               -  257 

20 


XXVI  LIST  OF  WOODCUT  ILLUSTRATIONS. 

FIG.  PAGE 

50.  Section  of  the  Cochlea,  after  Breschet                                    -  -  258 

51.  Papillae  of  Auditory  nerve  in  Mouse,  after  Treviranus  -  259 

52.  Auditory  Nerve  taken  out  of  Cochlea  -  259 

53.  Magnified  view  of  Lamina  Spiralis  ------  259 

54.  Soft  parts  of  the  Vestibule     -  -  260 

55.  Ampulla  of  the  External  Semi-circular  Membranous  Canal  -  260 

56.  Labyrinth  laid  open,  after  Breschet  -                         -  261 

57.  Labyrinth  of  the  Left  Side     -  -            -  265 

58.  Left  Ear  in  its  natural  state   -                                      ...  267 

59.  Anterior  view  of  the  External  Ear,  Meatus  Auditorius,  &c.  -            -  267 

60.  Fasciculus  of  fibres  of  Voluntary  Muscle,  after  Baly  -  271 

61.  Portion  of  Human  Muscular  Fibre,  separating  into  disks,  after  Bowman    -  272 

62.  Cleavage  of  Striped  Elementary  Fibres         -  -  272 

63.  Fibre  of  Human  Muscle  broken  across,  after  Bowman         -  -  273 

64.  Transverse  Section  of  Muscular  fibres  of  Teal  after  Bowman  -  274 

65.  Fragment  of  Muscular  fibre  from  Heart  of  Ox,  after  Bowman  -  275 

66.  Muscular  fibre  of  Dytiscus,  contracted  in  the  centre,  after  Bowman  -  276 

67.  Muscular  fibre  of  Skate,  in  different  stages  of  contraction,  after  Bowman    -  277 

68.  Attachment  of  Tendon  to  Muscular  fibre,  after  Bowman       -  -  278 

69.  Stages  of  the  development  of  Striped  Muscular  Fibre,  after  Bowman  -  278 

70.  Another  view  of  the  development  of  Muscular  Fibre  -  279 

71.  Terminating  loops  of  Nerves  in  Muscles,  after  Burdach       -  -  282 

72.  Thyroid  and  Cricoid  Cartilages         -  297 

73.  Side-views  of  Larynx,  after  Willis    -  -  297 

74.  Posterior  and  Anterior  views  of  the  left  Arytenoid  Cartilage  -  298 

75.  Bird's-eye  view  of  Larynx  from  above,  after  Willis  -  298 

76.  Vertical  Section  of  the  Larynx           -            -                         -  -  298 

77.  Diagram  of  the  direction  of  the  muscular  forces  of  the  Larynx,  after  Willis  299 

7®'    (  Artificial  Larynx,  after  Willis       -  -  303 

80.  View  of  the  Organs  of  Digestion  in  their  whole  length  -  326 

81.  Muscles  of  the  Tongue,  Palate,  Larynx  and  Pharynx  -  328 

82.  Front  view  of  the  Stomach  distended             -----  333 

83.  Interior  of  the  Stomach                                                 -            -  -  333 

84.  Interior  of  the  Stomach  and  Duodenum         -  -  334 

85.  Vessels  of  Intestinal  Villus  of  Hare,  after  Dollinger              -  -            -  346 

86.  Do.            Do.                 of  Man,  after  Krause       -  346 

87.  Commencement  of  Lacteal  in  Villus,  after  Krause  -  -  346 

88.  Web  of  Frog's  Foot,  after  Wagner    -  -  359 

89.  Do.                     more  highly  magnified,  after  Wagner  -            -  360 

90.  First  appearance  of  blood-vessels  in  Germinal  Membrane,  after  Wagner    -  361 

91.  Diagram  of  Heart       -                                      -            -  -  368 

92.  Haemadynamometer  of  Poisseuille    -            -            .            -  371 

93.  Lung  of  Triton,  slightly  magnified,  after  Wagner     -  -  392 

94.  Portion  of  the  same  more  highly  magnified,  after  Wagner    -  -  392 

95.  Capillary  circulation  in  Lung  of  living  Triton,  after  Wagner  -  392 

96.  Portion  of  Lung  of  Pig,  after  Wagner            ...  -  393 

97.  Development  of  Lungs,  after  Rathke              ...  394 

98.  Larynx,  Trachea  and  Bronchiae         -            -  -  394 

99.  Bronchiae  and  Blood-vessels  of  the  Lungs     -            -            -  -  395 

100.  Corpuscle  of  Human  Blood,  after  Wagner    -            -  -  428 

101.  Corpuscles  of  Frog's  Blood,  after  Wagner    -            -            -  -  428 

102.  Production  of  Blood-corpuscles  in  Chick,  after  Wagner       -  -  432 

103.  Circulation  of  oval  and  colourless  corpuscles,  in  venous  trunk  of  Frog's 

foot,  after  Wagner                                                    -  -  434 

104.  Shape  of  Fat  Vesicles  in  close  pressure         ...  .  468 

105.  Blood-vessels  of  Fat                                                      -  -  468 

106.  Fat  Vesicles  from  an  emaciated  subject        -  -  469 

107.  Examples  of  Cilia      -  -  472 

108.  Magnified  view  of  Human  Hair        -                        -  -  475 

109.  Magnified  view  of  a  Hair  from  the  beard                   -•  -  475 

110.  Root  of  a  Hair  of  the  beard,  magnified          -  -  476 

1 1 1.  Follicle  of  a  Hair  of  the  Beard,  with  Arteries  -  476 

112.  Nutrient  vessels  of  Cartilage,  after  Toynbee  -^    478 

113.  Minute  structure  of  Bone,  after  Wilson         -----  481 


LIST  OF  WOODCUT  ILLUSTRATIONS.  XXV11 

FIG.  PAGE 

114.  Transverse  section  of  a  long  Bone    -                                     ...  -482 

115.  Transverse  section  of  a  Tibia                         .....  482 

116.  Haversian  Canals  in  a  long  Bone      ......  483 

117.  Scapula  of  a  Foetus,  showing  the  process  of  ossification       -            -            -  483 

118.  Vertical  section  of  Cartilage               -                                      ...  484 

119.  Longitudinal  section  of  an  Incisor  and  Molar  Tooth                           -            -  488 

120.  Vertical  section  of  an  adult  Bicuspid                                                   -            -  488 

121.  Section  of  an  imperfectly  developed  Incisor                                        -           •-  489 

122.  Hexagonal  Terminations  of  Fibres  of  Enamel          -            -            -  489 
]  23.  Fibres  of  Enamel  viewed  sideways    -                                                   -  '489 

124.  Vertical  section  of  Bicuspid,  highly  magnified           ....  489 

125.  Main  Tubes  of  Dental  Bone  -                         ...                         -  490 

126.  Ramifications  of  the  Tubes  of  Dental  Bone                                                       -  490 

127.  Transverse  Section  of  Crown  of  Bicuspid,  highly  magnified            -            -  490 
128..  Position  of  the  Main  Tubes  near  the  Root  of  Bicuspid                      -            -  490 

129.  First  stage  of  formation  of  Teeth,  after  Goodsir        -                                      -  492 

130.  Diagram  illustrating  subsequent  stages  of  formation  of  Teeth,  after  Goodsir  492 

131.  Do.                                Do.                                Do.                                       -  493 

132.  Elements  of  Areolar  Tissue                -                                      ...  498 

133.  Development  of  Areolar  Tissue,  after  Schwann        -                                      -  498 

134.  Inferior  Surface  of  the  Liver              ....                         .  512 

135.  Three  Coats  of  the  Gall  Bladder        ...                         -            -  513 

136.  Gall  Bladder  distended,  with  vessels  injected             ....  513 

137.  Nucleated  Cells  of  Parenchyma  of  Liver       -  514 

138.  Lobules  of  Liver,  with  branches  of  Hepatic  vein,  after  Kiernan       -            -  515 

139.  Nucleated  Cells  forming  Parenchyma  of  Liver,  after  Bowman        -            -  515 

140.  Horizontal  section  of  Lobules,  showing  the  arrangement  of  their  vessels, 

after  Kiernan         -                                                                                    '  -  515 

141.  Do.                                      Do.             bile-ducts,  after  Kiernan  516 

142.  Lobules  in  a  state  of  Anaemia,  after  Kiernan                                                   -  518 

143.  Do.      in  first  stage  of  hepatic-venous  congestion,  after  Kiernan  -            -  518 

144.  Do.      in  second  stage  of  do.           -                        ....  519 

145.  Do.      in  a  state  of  Portal  venous  congestion,  after  Kiernan          -            -  519 

146.  Hepatic  Cells  loaded  with  Fat,  after  Bowman                                                  -  520 

147.  Right  Kidney,  with  Renal  Capsule     ......  525 

148.  Section  of  Kidney,  after  Wilson        ....                         .  525 

149.  Half  a  Kidney,  divided  vertically       ......  525 

150.  Kidney  divided  vertically,  with  Arteries  injected       ....  525 

151.  Section  of  a  Pyramid  of  Malpighi       -                                                               -  527 

152.  Kidney  of  new-born  Infant,  after  Wagner     -----  528 

153.  Extremity  (1)  of  Tubulus  Uriniferus,  after  Wagner                                        -  528 

154.  Section  of  small  portion  of  Kidney,  after  Wagner     -                                      -  529 

155.  Structure  of  Malpighian  body,  after  Bowman                                                   -  530 

156.  Diagram  of  Circulation  in  the  Kidney,  after  Bowman                                   -  530 

157.  Corpora  Wolffiana,  after  Muller        -                                                             -  530 

158.  Mammary  Gland        -                         ...                         .            .  541 

159.  Vertical  Section  of  Mammary  Gland                          ....  541 

160.  Distribution  of  Milk-ducts  in  Mammary  Gland,  after  Sir  A.  Cooper             -  541 

161.  Termination  of  Milk-ducts  in  Follicles,  after  Sir  A.  Cooper                            -  543 

162.  Lobule  of  Parotid  Gland,  after  Wagner         -                        ...  549 

163.  The  Testicle  injected  with  Mercury               -  552 

164.  Minute  structure  of  the  Testis                                     ....  552 

165.  Human  Testis,  injected  with  Mercury,  after  Lauth  -                         -            -  553 

166.  Diagram  of  the  structure  of  the  same            .....  553 

167.  Sudoriferous  Gland,  after  Wagner     ------  555 

168.  Cutaneous  Glands  of  external  Meatus  Auditorius,  after  Wagner      -            -  557 

169.  Mesocolon  in  connection  with  Mesentery      -                                      -  558 

170.  Gastric  Glands  in  Human  Stomach,  after  Wagner                                          -  558 

171.  The  same,  from  another  part,  after  Wagner                                                     -  558 

172.  Entrances  to  Secreting  Tubes,  after  Boyd     -                                                   -  558 

173.  Villi  and  Follicles  of  LieberkQhn  on  surface  of  Ileum                                   -  559 

174.  Mucous  coat  of  Small  Intestines,  as  altered  in  Fever,  after  Boehm                -  560 

175.  One  of  the  Glandulae  Solitariae  of  Peyer,  from  the  Large  Intestine,  after  Boehm  560 

176.  Conglomerate  Glands  of  Brunner,  after  Boehm        -                                      -  560 

177.  Glands  of  Peyer  on  Small  Intestine    -                                                             -  561 


XXV111  LIST  OF  WOODCUT  ILLUSTRATIONS. 

FIG.  PAGE 

178.  Patch  of  aggregated  Peyerian  Glands,  from  Ileum,  after  Boehm       -  561 

179.  Section  of  Thymus  Gland,  after  Sir  A.  Cooper                                                 -  565 

180.  Section  of  Uterus,  showing  formation  of  Decidua  Vera,  after  Wagner         -  601 

181.  Do.           "more  advanced,  after  Wagner      -                         -  601 

182.  Diagram  illustrating  position  of  Embryo  in  Ovum,  after  Wagner     -            -  613 

183.  Do.                  more  advanced,  the  Amnion  beginning  to  form            -  613 

184.  Do.  still  more  advanced,  the  Allantois  beginning  to  appear, 

after  Wagner     -                                    ...                       .  615 

185.  Do.                 at  a  later  time,  the  Amnion  fully  formed,  after  Wagner  615 

186.  Section  of  Uterus,  showing  the  Ovum,  Membranes,  &c.,  after  Wagner        -  616 

187.  Diagram  illustrating  the  Foetal  Circulation                -                                    -  618 

188.  Curve  representing  the  relative  Viability  of  Human  Male  and  Female  at 

different  ages          ...                        .                                    _  g25 

189.  Do.  Do.         Heights  and  Weights  of  the  Human  Male 

and  Female  at  different  ages,  after  Quetelet          -                                     .  626 

Also, 
Two  Lithographic  Plates  with  27  Figures. 


FROM  THE  PREFACE 


TO 


THE  FIRST  EDITION. 


THE  composition  of  such  a  Treatise  as  the  following  was  a  part  of  the 
original  plan  of  the  Author,  when  he  first  came  before  the  Public  as  a 
writer  on  Physiology.  Being  desirous,  however,  of  making  his  first 
essay  in  the  path  which  had  been  previously  the  most  incompletely 
explored,  he  deemed  it  better  to  await  the  verdict  upon  this  before  pro- 
ceeding further ;  and  he  was  not  without  hope  that  some  Writer,  more 
fully  competent  to  the^task,  might  in  the  mean  time  take  up  the  subject 
of  Human  Physiology  in  such  a  way  as  to  leave  nothing  for  the  Student 
to  desire.  This,  however,  has  not  been  accomplished.  The  previously- 
existing  Treatises  upon  it,  which  have  been  every  year  becoming  more 
antiquated,  have  not  been  replaced  by  any  works  that  can  be  considered 
as  at  the  same  time  sufficiently  elevated  in  their  character,  to  represent 
the  present  condition  of  Physiological  Science, — sufficiently  compendi- 
ous in  their  bulk  for  the  limited  time  at  the  disposal  of  most  Students, — 
and  sufficiently  practical  in  their  tendency  to  lead  their  readers  to  the 
useful  applications  of  the  facts  and  principles  they  place  before  them. 
This  is  not  the  opinion  of  the  Author  alone,  but  that  of  numerous  expe- 
rienced Teachers  throughout  the  country;  and  he  has  been  led  to  regard 
the  present  as  a  good  time  for  carrying  his  purpose  into  execution. 

The  plan  and  objects  of  his  Treatise  may  be  gathered  from  the  pre- 
ceding statement  of  the  reasons  which  have  occasioned  its  production. 
In  this,  as  in  his  previous  work,  it  has  been  his  object  to  place  the 
Reader  in  the  possession  of  the  highest  principles,  that  can  be  regarded 
as  firmly  established,  in  each  department  of  the  Science ;  and  to  explain 
and  illustrate  these  by  the  introduction  of  as  many  important  facts  as 
could  be  included  within  moderate  limits.  In  every  instance  he  has 
endeavoured  to  make  his  statements  clear  and  precise,  without  being 
formal  or  dogmatical ;  and  definite  enough  to  admit  of  practical  appli- 
cation, without  appearing  to  be  unimprovable  by  further  inquiry.  Phy- 
siology is  essentially  a  science  of  progress ;  and  it  must  happen  that 
2 


XIV  PREFACE. 

much  of  what  is  now  regarded  as  established  truth,  will  need  great 
modification  to  be  brought  into  accordance  with  the  results  of  new 
inquiries.  It  is  very  desirable,  therefore,  that  the  Student  should  not 
be  made  to  think  so  confidently  of  his  acquirements  as  to  be  indisposed 
to  receive  new  information,  even  though  it  should  tend  to  diminish  their 
value. 

The  present  Treatise  is  to  be  regarded  as  complete  in  itself,  and  as 
quite  independent  of  the  Author's  "Principles  of  General  and  Compara- 
tive Physiology."  That  it  may  be  so,  he  has  inserted  an  introductory 
chapter  on  the  "Place  of  Man  in  the  Scale  of  Being,"  and  numerous 
references  to  the  Comparative  Physiology  of  the  lower  Animals.  Still 
he  does  not  hesitate  to  express  the  opinion  that,  the  greater  the  amount 
of  the  Student's  previous  general  knowledge  of  the  Science,  the  better 
will  he  be  prepared  to  enter  upon  any  department  of  it,  especially  that 
peculiarly  complex  and  difficult  branch,  the  Physiology  of  Man.  On 
every  topic  it  has  been  the  Author's  aim  to  present  the  latest  and  most 
satisfactory  information  within  his  reach ;  and  he  believes  that  the 
Volume  contains  much  that  will  be  new  to  the  Physiologist,  whose 
reading  has  not  been  tolerably  extensive.  Its  materials  have  been  but 
little  derived  from  other  Systematic  Treatises  on  the  subject;  and  it  will 
not  be  found  to  bear,  as  a  whole,  any  considerable  resemblance  to  those 
already  before  the  public.  The  Author  has  rather  endeavoured  to  bring 
together  the  valuable  facts  and  principles,  scattered  through  the  best  of 
the  numerous  Monographs  that  have  been  recently  published  on  special 
divisions  of  Physiology  and  Medicine;  and  to  reduce  these  disjecta 
membra  to  that  systematic  form,  which  they  can  only  be  rightly  made  to 
assume,  when  brought  into  relation  with"  each  other,  and  shown  to  be 
subservient  to  principles  of  still  higher  generality.  In  regard  to  this, 
as  to  his  former  Treatise,  the  Author  believes  that  he  may  claim  a 
somewhat  higher  character  than  that  of  the  mere  Compiler ;  and  that 
even  the  well-read  Physiologist  will  find  in  it  many  facts  and  deductions 
which  have  not  been  previously  brought  before  him  in  the  same  form. 

In  apportioning  the  amount  of  space  to  be  devoted  to  each  division 
of  the  subject,  the  Author  has  had  in  view  its  practical  relations,  much 
more  than  its  merely  scientific  interest;  and  he  has  on  this  account 
bestowed  a  much  larger  share  on  the  Organs  of  Animal  life  than  some 
may  think  just,  when  compared  with  the  narrow  limits  within  which 
other  important  topics  are  discussed.  But  he  has  endeavoured  to  keep 
always  in  view,  that  he  is  writing  for  the  guidance  of  the  Student  who 
is  to  become  a  Practitioner,  rather  than  for  him  who  makes  the  pursuit 
of  Science  his  professed  object;  and  that  much  that  is  of  the  highest 
interest  to  the  latter,  is  comparatively  valueless  to  the  former.  Hence 


PREFACE.  XV 

many  topics  of  great  scientific  interest  are  entirely  passed  over ;  and  it 
is  hoped  that  such  omissions  will  not  be  accounted  as  faults  in  the  esti- 
mation of  those,  who  dread  lest  the  attention  of  the  Student  should  be 
too  much  drawn  off  by  the  seducing  novelties  of  Science,  from  his  less 
attractive,  but  more  important  objetts. 

For  a  large  part  of  his  illustrations  the  Author  is  indebted  to  the 
valuable  and  beautiful  Icones  Physiologies  of  Prof.  Wagner.  The 
sources  of  all  are  indicated. 

In  conclusion,  the  Author  would  repeat  what  he  has  already  had 
occasion  to  state ; — that  in  a  work  involving  many  details,  it  is  not  to 
be  expected  that  no  error  should  have  crept  in ;  but  that  he  has  endea- 
voured to  secure  correctness,  by  relying  only  upon  such  authorities  as 
appeared  to  him  competent,  and  by  comparing  their  statements  with 
such  general  principles  as  he  considers  well  established.  For  the  truth 
of  those  principles  he  holds  himself  responsible ;  for  the  correctness  of 
the  details,  he  must  appeal  to  those  from  whom  they  are  derived,  and 
to  whom  he  has  generally  referred.  He  hopes  that  he  will  not  be  found 
unwilling  to  modify  either,  when  they  have  been  proved  to  be  errone- 
ous; nor  indisposed  to  profit  by  criticism,  when  administered  in'  a 
friendly  spirit. 

Bristol,  Feb.  1,  1842. 


TABLE  OF  CONTENTS. 


INTRODUCTION. 

GENERAL  VIEW  OF    THE    CONNECTION  OF   PHYSIOLOGY  WITH  OTHER  BRANCHES  OF 

MEDICINE,  25 31. 

CHAPTER  I. 

ON    THE    PLACE    OF    MAN    IN    THE    SCALE    OF    BEING,   32 68. 

PAGE 

1.  Distinction  between  Animals  and  Plants         -  32 

2.  General  sub-divisions  of  the  Animal  Kingdom                        -  34 

3.  General  characters  of  Radiata             ......  35 

4.  General  characters  of  Mollusca          -                        -  37 

5.  General  characters  of  Articulata                                                           -  41 

6.  General  characters  of  Vertebrata         -  43 

7.  General  characters  of  Fishes               ......  46 

8.  General  characters  of  Reptiles  47 

9.  General  characters  of  Birds     -                                                 ...  50 

10.  General  characters  of  Mammalia        -                                     ...  54 

11.  Chief  sub-divisions  of  Mammalia        ......  57 

12.  Characteristics  of  Man                         ......  60 

CHAPTER  II. 

GENERAL   VIEW    OF    THE    FUNCTIONS,    69 88. 

.1.  Of  Vital  Actions,  and  their  mutual  dependence  69 

2.  Functions  of  Vegetative  Life                                                     -  76 

3.  Functions  of  Animal  Life        ...                        .  85 

CHAPTER  III. 

FUNCTIONS   OF    THE    NERVOUS    SYSTEM,    88 224. 

1.  General  Summary       ....  88 

2.  Elementary  Structure  of  the  Nervous  System  90 

3.  Elementary  Functions  of  Nervous  Structure              -  93 

4.  Mode  of  determining  the  Functions  of  Nerves                        -            -  96 

5.  Nature  of  the  Changes  in  the  Nervous  System           •  98 

6.  Comparative  Anatomy  and  Physiology  of  the  Nervous  System                      -  100 

7.  Nervous  System  of  Vertebrata                                                                          •  118 

8.  Functions  of  the  Spinal  Cord                           -                                                 -  132 

9.  Respiratory  Movements                                                                                     -  139 
10.  Deglutition  and  Defecation      .....  145 


XV111  CONTENTS. 

PAGE 

11.  Protecting  Agency  of  the  Spinal  Cord                         -            --          .            -  153 

12.  Other  Functions  of  Spinal  Cord                       .....  155 

13.  Comparative  Anatomy  of  the  Encephalon       -                        -            -            -  158 

14.  Functions  of  the  Cephalic  Nerves       -                        ....  164 
15. 'Motor  Nerves  of  the  Orbit        .......  182 

16.  Consensual  Movements  of  the  Eye     -                                    -            -            -  186 

17.  General  Functions  of  the  Encephalon                         -            -            .            -  191 

18.  Functions  of  the  Tubercula  Quadrigemina,  &c.;  Emotional  and  Instinctive  Actions  191 

19.  Functions  of  the  Cerebellum                                          ....  jgg 

20.  Functions  of  the  Cerebrum      -                                                 ...  204 

21.  General  Recapitulation  and  Pathological  Applications           -            -            -  216 

CHAPTER  IV. 

OF    SENSATION    AND    THE    ORGANS    OF    THE    SENSES,   224 270. 

1.  Of  Sensation  in  General           -            -                                     ...  224 

2.  Sense  of  Touch                                                             ....  234 

3.  Sense  of  Taste                                                                                        .            .  237 

4.  Sense  of  Smell             -                                                             r  238 

5.  Sense  of  Vision            ...                                                             .  240 

6.  Sense  of  Hearing         -                                                             ...  255 

CHAPTER  V. 

OF    MUSCULAR   CONTRACTILITY,    270 296. 

1.  Of  Contractility  in  General      -                                                 ...  270 

2.  Muscles  of  Animal  Life                                                            .                        -  271 

3.  Muscles  of  Organic  Life                                                                                    -  279 

4.  Properties  of  Muscular  Fibre               -                                                             -  280 

5.  Energy  and  Rapidity  of  Muscular  Contraction                                                 -  290 

6.  Applications  of  Muscular  Power                                                                       -  292 

7.  Sensibility  of  Muscles                                                                                            -  295 

CHAPTER  VI. 

OF  THE  VOICE  AND  SPEECH,  296 312. 

1.  The  Larynx  and  its  Actions     -                                                               -            -  296 

2.  Of  Articulate  Sounds  307 

CHAPTER  VII. 

INFLUENCE    OF    THE    NERVOUS    SYSTEM    ON   THE    ORGANIC    FUNCTIONS,  312 319. 

CHAPTER  VIII. 

ON   DIGESTION    AND    NUTRITIVE    ABSORPTION,    320 357. 

1.  Nature  and  Destination  of  the  Food  of  Animals                                              -  320 

2.  Mastication  and  Deglutition     ...                                    -  327 

3.  Action  of  the  Stomach                                                                                       -  329 

4.  Action  of  the  Intestinal  Tube                                                                            -  335 

5.  Nature  of  Chymification                                                                                    -  336 

6.  Lacteal  and  Lymphatic  Absorption     -                                                 -  345 


CONTENTS.  XIX 

• 

PAGE 

7.  Absorption  by  the  General  Surface     -  -        348 

8.  Supply  of  Food  required  by  Man         -  -        353 

CHAPTER  IX. 

OF    THE    CIRCULATION,    358—388. 

1.  Of  the  Circulation  in  General  -        358 

2.  Action  of  the  Heart      -  -        363 

3.  Causes  influencing  the  Circulation  in  the  Arteries  and  Capillaries  -        373 

4.  Of  the  Venous  Circulation       -  -            -        384 

5.  Peculiarities  of  the  Circulation  in  different  parts        -  -                    387 

CHAPTER  X. 

ON    RESPIRATION,    388 413 

1.  Nature  of  the  Function;  and  Provisions  for  its  Performance  -        388 

2.  Chemical  Phenomena  of  Respiration  -        400 

3.  Effects  of  Respiration  on  the  Blood     -  -        403 

4.  Exhalation  and  Absorption  by  the  Lungs                 >   -  -                                 411 

CHAPTER  XI. 

ON    NUTRITION,   413—507. 

1.  Organizable  Principles             ....  .                    413 

2.  Formation  of  Cells       -  -        418 

3.  Elaboration  of  Chyle  and  Lymph        ...  .        423 

4.  Physical  and  Vital  Properties  of  the  Blood      -  -        427 

5.  Pathological  changes  in  the  Blood       -  -        446 

6.  Origin  of  the  Solid  Tissues. — Reparative  processes  ...        451 

7.  Varying  Activity  of  the  Nutritive  processes  -         457 

8.  Abnormal  forms  of  the  Nutritive  process        -  -        460 

9.  Formation  of  the  Tissues         -  -        463 

CHAPTER  XII. 

OF    SECRETION,    507 567. 

1.  Of  Secretion  in  General            ...  .        50? 

2.  The  Liver.— Secretion  of  Bile  -        511 

3.  The  Kidneys.— Secretion  of  Urine       -  -        524 

4.  Mammary  GJand. — Secretion  of  Milk  -        540 

5.  Salivary  Glands  and  Pancreas             ...  .        549 

6.  Lachrymal  Gland         -  -        551 

7.  The  Testis.— Spermatic  Fluid  -        551 

8.  Cutaneous  and  Mucous  Follicles         -  -                     554 

9.  The  Spleen,  and  Supra-Renal  Capsules  -        562 
10.  Thymus  and  Thyroid  Glands  -        565 

CHAPTER  XIII.* 

GENERAL    REVIEW    OF    THE    NUTRITIVE    PROCESSES,  567—585. 

1.  Review  of  the  Nutritive  processes,  with  practical  applications  •        567 

2.  Animal  Heat    - 573 


XX  CONTENTS. 

CHAPTER  XIV. 

OF    REPRODUCTION,    585—627. 

PAGE 

1.  General  character  of  the  Function  -                                                           -  585 

2.  Action  of  the  Male       -  -  587 

3.  Action  of  the  Female  -  59° 

4.  Development  of  the  Embryo    -  -  610 


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EXPLANATION   OF    PLATES. 


PLATE  I. 

The  first  16  Figures  in  this  Plate  are  from  Dr.  Barry's  Embryological  Researches  in  the 
Philosophical  Transactions  for  1837,  1839  and  1840. 

FIG. 

1.  A  very  early  stage  of  the  formation  of  the  Ovum ;  the  vesicles,  the  largest  of  which 

measures  only  1-1 125th  of  an  inch,  are  seen  in  the  midst  of  dark  granules  or 
globules  (§  740). 

2.  A  stage  somewhat  more  advanced;   the  vesicles  are  surrounded  by  envelops  of 

smaller  vesicles,  amongst  which  the  granules  are  still  seen  (§  740). 

3.  A  still  later  stage ;  a  central  vesicle,  a,  is  seen,  with  a  spot,  b,  upon  its  walls,  and 

surrounded  with  numerous  granules;  this  has  now  evidently  become  the  Germi- 
nal Vesicle  (§  740). 

4.  Ovisacs  from  Human  Ovum,  l-200th  of  an  inch,  and  upwards,  in  diameter;  the 

largest  exhibits  the  Germinal  Vesicle,  a,  very  distinctly  (§  740). 

5.  Ovisac  from  Cat,  showing  its  contents  when  near  matarity;  a,  ovisac;  b,  its  con- 

tained granules ;  c,  zona  pellucida;  d,  granules  of  the  yolk;  e,  germinal. vesicle ; 
/,  germinal  spot;  magnified  440 diameters  (§  739). 

6.  Ovum  of  Rabbit  at  the  periphery  of  the  Graafian  follicle,  with  part  of  the  membrana 

granulosa  removed;  g, g,  membrana  granulosa;  ov,  ovulum;  r,  retinacula  (§§ 
740,  744). 

7.  Ovum  with  its  tunica  granulosa  and  retinacula,  removed  from  the  Graafian  follicle; 

a,  germinal  vesicle;  b,  germinal  spot;  c,  zona  pellucida;  d,  globules  of  the  yolk; 
r,  r,  retinacula ;  t  g,  tunica  granulosa  (§  740). 

8.  Graafian  follicle  discharging  its  Ovum,  ov,  to  which  the  tunica  granulosa,  t  g,  and  re- 

tinacula, r,  r,  remain  attached  (§  744). 

9.  Ovarium  Ovum  in  preparation  for  fecundation ;  a,  germinal  spot,  beginning  to  resolve 

itself  into  cells  at  its  margin ;  b,  germinal  vesicle ;  c,  elliptical  cells  in  the  place 
of  the  yolk;  d,  zona  pellucida.  100  Diameters  (§  745). 

10.  Ovum  nearly  ready  for  fecundation:  a, germinal  spot  more  fully  developed  into  cells, 

of  which  concentric  layers  occupy  the  germinal  vesicle  bf  c,  elliptical  discs  or 
cells;  d,  zona  pellucida;  e,  outer  layer  of  cells  of  yolk  (§  745). 

11.  Fecundated  Ovum  of  nine  hours;  the  germinal  vesicle,  having  returned  to  the  centre 

of  the  ovum,  is  concealed  by  the  large  elliptical  discs,  which  fill  the  cavity  of 
the  zona  pellucida  (§§  745,  746). 

12.  Plan  of  one  of  these  discs  or  cells:  its  nucleus,  «,  has  developed  itself  into  con- 

centric rings  of  cells :  and  in  the  most  fully  developed  of  these,  the  nucleus,  b, 
is  seen  to  be  commencing  the  same  kind  of  evolution.  In  the  centre  of  the 
original  nucleus,  a  pellucid  spot,  the  nucleolus  of  Schwann  and  Schleiden,  is 
observed  (§  745). 

13.  Ovum  from  the  Uterus,  measuring  about  l-68th  of  an  iocb  in  diameter:  a,  pair  of 


XX11  EXPLANATION  OF  PLATES. 

FIG. 

cells  now  occupying  the  greater  part  of  the  germinal  vesicle  b,-  c,  zona  pellu- 
cida:  d,  chorion,  a  new  envelop,  separated  from  the  last  by  the  fluid  it  has  ab- 
sorbed (§  746). 

14.  Ovum,  of  which  the  essential  part,  a,  the  pair  of  cells  occupying  the  germinal  vesicle, 

has  advanced  further  than  in  the  last  case;  the  other  contents  of  the  germinal 
vesicle  have  undergone  liquefaction.  The  chorion  is  here  incipient:  and  the 
remains  of  the  cells  of  which  it  is  composed  are  seen  at  cho  (§  747). 

15.  More  advanced  ovum;  the  cavity  of  the  germinal  vesicle  filled  with  cells,  a,  that 

have  originated  in  the  two  represented  in  the  last  figure;  these  cells  have 
nuclei,  b,  which  are  undergoing  a  corresponding  process  of  evolution  into 
secondary  cells;  c  and  d  as  in  Fig.  13  (§  758). 

16.  Ovum  in  a  state  rather  more  advanced;  a,  central  cell  of  the  germinal  mass,  now 

come  to  the  surface,  and  showing  the  nucleus  b  with  a  pellucid  centre,  from 
which  most  of  the  embryonic  structures  are  developed;  c, cavity  in  the  germinal 
mass,  caused  by  the  approach  of  its  peripheral  cells  to  the  enclosing  membrane, 
d  (§  758). 

17.  Formation  of  the  Membrana  Decidua;  a,  a,  a,  villi  of  the  mucous  membrane^of  the 

uterus;  b,  substance  secreted  between  and  upon  these;  c,  uterine  vessels  pro- 
longed into  the  decidua  and  forming  loops.  After  Baer. 

18.  Human  Spermatozoa;  a,  seminal  granules.    After  Wagner  (§  735). 

19.  Cyst  of  evolution.    After  Wagner  (§  735). 

20.  Capsular  bundle  of  Spermatozoa,  just  previous  to  their  separation.    After  Wagner 

(§  735). 

21.  Globules  fiom  the  Chyle;  a,  ordinary  globules;  b,  a  globule  (cytoblastl)  surrounding 

itself  with  an  envelop  (a  forming  cell?);  c,  minute  molecules  of  chyle;  d,a  co- 
•    lourless  corpuscle  from  the  blood.    After  Wagner  (§  563). 

22.  Particles  of  Blood  undergoing  multiplication:  a,  b,  c,  d, e,  successive  stages.    After 

Barry  (§  576). 

23.  Extremity  of  one  of  the  tufts  of  fetal  vessels  forming  the  Placenta ;  this  includes 

(like  a  branchial  tuft)  an  artery  and  vein.    After  Reid  (§  749). 

24.  Plan  of  the  structure  of  the  Placenta,  according  to  Dr.  J.  Reid's  view  of  it ;  a,  a,  por- 

tion of  substance  of  uterus ;  b,  b,  b,  b,  section  of  uterine  sinuses,  some  of  them 
opening  on  the  inner  surface  into  the  cavity  of  the  placenta ;  c,  curling  artery 
of  uterus ;  d,  d,  ramifications  of  foetal  vessels,  some  of  them  sending  down  pro- 
longed tufts  which  dip  into  the  uterine  sinuses  (§  749). 


PLATE  II. 

25.  Uterine  Ovum  of  Rabbit,  showing  the  Area  Pellucida,  with  the  annular  nucleus  of 

the  embryonic  cell  (Fig.  14,  6)  now  elongated.  In  the  clear  space  enclosed  by 
this  is  a  well-marked  dark  groove,  occupying  the  position  in  which  the  nervous 
centres  are  subsequently  to  be  developed.  The  cephalic  extremity  of  this  is 
already  rounded  and  the  caudal  extremity  pointed.  After  Bischoff  (§  760). 

26.  More  advanced  ovum,  showing  the  incipient  formation  of  the  Vertebral  column  ;  and 

the  dilatation  of  the  primitive  groove  at  its  anterior  extremity.  After  Bischoff 
(§  760). 

27.  More  advanced  embryo,  seen  on  its  ventral  side,  and  showing  the  first  development 

of  the  Circulating  apparatus.    Around  the  Vascular  Area  is  shown  the  terminal 


PL  ATE  11. 


My.  27 


EXPLANATION  OF  PLATES.  XX111 

sinus,  a,  a,  a.  The  blood  returns  from  this  by  two  superior  branches,  b,  6,  and 
two  inferior,  c,  c,  of  the  omphalo-raeseraic  veins,  to  the  heart,  d;  which  ,  at 
this  period,  a  tube  curved  on  itself,  and  presenting  the  first  indication  of  a 
division  into  cavities.  The  two  aortic  trunks  appear,  in  the  abnormal  region, 
as  the  inferior  vertebral  arteries,  e,  e;  from  which  are  given  off  the  omphalo- 
meseraic  arteries, /,/,  which  form  a  net-work  that  distributes  the  blood  over 
the  vascular  area.  In  the  cephalic  region  is  seen  the  anterior  cerebral  vesi- 
cles, with  the  two  ocular  vesicles,  g.  After  Bischoff  (§  762). 


INTRODUCTION. 


GENERAL    VIEW    OF    THE    CONNECTION    OF    PHYSIOLOGY    WITH    OTHER   BRANCHES 

OF    MEDICINE. 

1.  THE  object  of  the  Science  of  Physiology  is  to  bring-  together,  in  a  sys- 
tematic form,  the  phenomena  which  normally  present  themselves  during  the 
existence  of  living  beings ;  and  to  classify  and  compare  these,  in  such  a  man- 
ner as  to  deduce  from  them  the  general  laws  or  principles,  by  which  they  are 
regulated.     In  order  to  attain  a  correct  knowledge  of  the  latter,  a  very  exten- 
sive comparison  is  requisite.     Principles,  which  might  seem  of  paramount 
importance  in  regard  to  one  group  of  living  beings,  are  often  found,  on  a  more 
general  review,  to  be  quite  subordinate.     For  example,  the  predominance  of 
the  Nervous  System  in  the  higher  classes  of  Animals,  and  its  evidently  close 
connection  with  many  of  the  functions  of  life,  have  led  several  physiologists  to 
the  opinion,  that  its  influence  is  essential  to  the  performance  of  the  functions 
of  Nutrition,  Secretion,  &c. :  but,  on  turning  our  attention  to  the  Vegetable 
kingdom,  in  which  nothing  analogous  to  a  nervous  system  can  be  proved  to 
exist,  we  find  these  functions  going  on  with  even  greater  activity  than  in 
Animals.     It  is  clear,  therefore,  that  they  may  be  performed  without  it ;  and 
on  a  closer  examination  of  the  phenomena  presented  by  Animals,  it  is  seen 
that  they  may  be  explained  equally  well,  or  even  better,  on  the  principle  that 
the  nervous  system  has  a  powerful  influence  on  these  actions,  than  on  the  idea 
that  it  affords  a  condition  essential  to  them.     This  is  only  one  out  of  many 
instances  which  it  would  be  easy  to  adduce,  in  proof  of  the  necessity  of  bring- 
ing together  all  the  phenomena  of  the  same  kind,  in  whatever  class  of  living 
beings  they  may  be  presented,  before  we  erect  any  general  principles  in 
Physiology. 

2.  The  object  of  the  present  work,  however,  is  not  to  follow  out  such  an 
investigation,  but  to  show  the  detailed  application  of  the  principles,  of  which 
Physiological  Science  may  now  be  said  to  consist,  to  the  phenomena  exhibited 
by  the  Human  being,  during  what  may  be  called  his  normal  life.     Every  one 
knows  the  difficulty  of  defining  the  two  conditions  health  and  disease.     The 
former  may  be  said  to  be  that  state  in  which  the  various  actions  of  life  are 
normally  or  regularly  performed ;  and  the  latter  to  result  from  a  disturbance 
or  irregularity  in  these  actions,  constituting  an  abnormal  state.     But  this  is 
only  substituting  one  term  for  another ; — the  difficulty  remains  the  same. 
Many  variations  occur,  within  the  limits  of  what  must  be  called  in  some  per- 
sons the  normal  state,  which  in  others  must  be  regarded  as  abnormal  actions. 
Thus  in  most  adults  the  pulse  averages  about  70;.  but  it  is  easily  raised  by 
exercise  to  90,  without  any  injurious  consequences  ;  and  such  must  be  regarded 
as  a  normal  or  physiological  state.     But  we  occasionally  meet  with  instances 
in  which  the  usual  pulse  is  not  quicker  than  40 ;  and  for  this  to  rise  to  90 
might  indicate  a  very  alarming  state  of  the  system ;  since  there  are  individuals 

3 


26  CONNECTION  OF  PHYSIOLOGY  WITH 

in  whom  such  a  pulse  would  be  equivalent  to  one  of  140,  in  a  person  whose 
circulation  was  in  health  of  the  average  rapidity.  Thus  an  abnormal  state  in 
any  individual  can  frequently  be  ascertained  only  by  comparison  with  his 
normal  condition.  This  is  a  difficulty  from  which  we  can  never  hope  to  make 
a  complete  escape  ;  for  it  is  the  peculiar  character  of  living  beings,  to  exhibit 
such  variations  in  their  phenomena,  resulting  from  the  number  of  concurrent 
causes  which  are  involved  in  the  production  of  these ;  a  slight  alteration  in 
any  one  of  which  will  most  seriously  affect  the  general  result.  Upon  the 
distinction  between  normal  and  abnormal  life,  however,  is  founded  that  of  the 
two  sciences — Physiology  and  Pathology.  These  are  very  closely  related  to 
each  other ;  and  neither  can  be  pursued  with  the  prospect  of  complete  success, 
except  in  connection  \vith  the  other. 

3.  The  relation  between  the  sciences  of  Physiology  and  Pathology  on  the 
one  hand,  and  the  various  departments  of  the  Ars  Medendi  on  the  other,  may 
be  shown  within  a  brief  compass ;  and  it  is  perhaps  desirable  to  point  them 
out  here,  in  order  to  place  the  importance  of  these  sciences  in  its  proper  light. 
Science  must  strictly  be  said  to  consist  of  general  principles,  embodying  the 
phenomena  which  present  themselves  to  the  observer,  in  any  particular  de- 
partment of  observation ;  and  a  science  is  perfect,  in  so  far  as  its  collection  of 
facts  is  reducible  to  these  general  laws,  the  ascertainment  of  which  enables  us 
to  extend  our  knowledge  of  similar  facts.     An  Art  is,  properly  speaking,  the 
application  of  a  science  to  practical  purposes,  consisting  of  a  set  of  rules  de- 
duced from  its  principles ;  and  its  perfection  will  be  exactly  proportional  to 
that  of  the  science  upon  which  it  rests.     The  most  perfect  of  all  sciences  is 
astronomy ;  all  its  leading  phenomena  may  be  reduced  to  one  general  prin- 
ciple ;  and  phenomena,  previously  unobserved,  have  been  predicted  as  the 
necessary  results  of  that  principle.     The  Art  of  Navigation  is  a  collection  of 
rules,  framed  by  those  who  were  profoundly  conversant  with  the  principles  of 
the   science ;  but   capable  of  being   employed   by  those  whose   knowledge 
extends  no  further  than  to  the  mode  of  applying  them.     When,  however,  the 
science  has  not  this   degree  of  perfection,  the  art  has  not  this  independent 
character.      In  Chemistry,  for  example,  many  principles  of  high  generality 
have  been  attained ;  and  yet  unknown  phenomena  cannot  be  predicted  from 
them  with  certainty  (in  a  great  variety  of  cases  at  least),  owing  to  the  number 
of  other  conditions  by  which  they  may  be  affected.     Hence  no  art  founded 
upon  this  science  can  be  supplied  with  any  other  than  very  limited  rules.     In 
the  case  of  dyeing,  for  example,  great  improvement  has  been  effected  by 
chemical  knowledge  ;  but  the  greater  part  of  its  rules  are  empirical,  that  is  to 
say,  founded  on  a  limited  induction,  not  comprehended  in  more  general  prin- 
ciples, and  therefore  quite  uncertain  in  their  results.     Thus,  if  a  new  Animal 
or  Vegetable  dye  were  discovered,  the  modes  of  fixing-  and  discharging  it,  and 
of  varying  its  shades  of  colour,  wrould  have  to  be  determined  by  experiment, 
before  it  could  be  brought  into  advantageous  employment.     We  can  neverthe- 
less imagine,  and  (from  the  recent  great  advance  in  Organic  Chemistry)  in 
some   degree  anticipate,  the  period,  when  chemical  science  shall  be  so  far 
advanced,  that  a  simple  analysis  of  the  material  (supplying  data  corresponding 
to  the  solar  or  lunar  observations  of  the  navigator)  may  enable  the  manufac- 
turer, by  a  reference  to  his  code  of  rules,  to  avail  himself  to  the  fullest  extent 
of  its  capabilities,  without  being  himself  aware  of  the  principles  upon  which 
those  rules  are  founded. 

4.  An  Art,  then,  will  be  scientific  or  empirical  (that  is,  its  rules  will  be 
based  upon  general  principles,  or  upon  induction  from  a  limited  experience), 
in  proportion  to  the  comprehensiveness  of  the  laws  that  have  been  attained  in 
the  Science  on  which  it  rests.     This  distinction,  however,  has  nothing  to  do 
with  the  certainty  or  uncertainty  of  its  application  in  particular  instances. 


OTHER  BRANCHES  OF  MEDICINE.  27 

An  art  may  be  entirely  empirical,  and  yet  be  perfect  so  far  as  it  goes ;  but  no 
unknown  cases  are  provided  for,  no  contingencies  foreseen.  It  is  in  its  adap- 
tation to  these,  that  the  triumph  of  a  scientific  over  an  empirical  art  manifests 
itself;  and  in  proportion  as,  from  the  nature  of  the  subjects  embraced  by  it,  a 
greater  or  less  variety  of  novel  cases  presents  itself,  in  that  proportion  is  its 
superiority  more  evident.  It  was  well  observed  by  Lord  Bacon,  that  "it  is  the 
office  and  excellence  of  all  sciences  to  shorten  the  long  turnings  and  windings 
of  experience."  The  deficiency  of  higher  or  more  comprehensive  laws  should 
not  prevent  us  from  making  cautious  use  of  those  we  already  possess ;  and, 
where  the  demands  of  mankind  require  that  an  art  should  be  practised  even 
in  its  imperfect  condition,  we  must  be  content  with  such  means  of  satisfying 
them  as  lie  within  our  reach.  Contentment,  however,  by  no  means  involves 
a  tacit  acquiescence  in  the  infirmities  of  our  condition ;  and  the  man  of  noble 
and  elevated  mind  will  not  only  aim  at  the  perfection  of  his  science,  from  that 
abstract  love  of  knowledge,  which  is,  as  Sir  H.  Davy  has  beautifully  remarked, 
"in  its  ultimate  and  perfect  development,  the  love  of  infinite  wisdom  and  un- 
bounded power,  or  the  love  of  God,"  but  may  also  safely  cherish  the  belief,  that 
every  contribution  which  he  makes  to  general  laws  will  ultimately  have  its 
practical  bearing  on  the  condition  of  humanity. 

5.  In  no  department  of  inquiry  is  it  more  necessary  to  keep  these  princi- 
ples in  view,  than  in  that  which  relates  to  the  phenomena  of  Vitality.     The 
changes  which  characterize  living  beings,  and  which  in  their  totality  constitute 
the  Life  of  these,  are  as  capable  of  being  referred  to  general  laws,  expressive 
of  their  uniform  conditions,  as  are  phenomena  of  any  other  kind.     But  there 
are  many  causes  which  render  the  attainment  of  these  laws  so  difficult,  that  at 
present  we  cannot  assign  to  Biology  (a  term  which  may  be  advantageously 
employed  for  the  science  of  Vital  Action,  including  Physiology  and  Pathology), 
a  high  rank  amongst  the  sciences.     Hence  the  rules  of  any  arts  which  are 
founded  upon  it,  can  be  only  in  part  regarded  as  possessing  that  certainty 
which  it  is  desirable  they  should  have.     Some  there  are,  which  are  derived 
from  laws  of  such  high  generality,  that  we  cannot  imagine  any  cause  which 
can  interfere  with  their  application.     For  example,  it  is  one  of  these  facts  of 
universal  application,  that  a  large  mixture  of  carbonic  acid  in  the  medium  to 
which  the  circulating  fluid  is  exposed  for  aeration,  is  prejudicial  to  life ;  and 
an  obvious  rule  thence  follows.     But  it  is  not  a  fact  of  equal  universality,  that 
a  dose  of  a  purgative  medicine  will  induce  increased  action  of  the  bowels ;  for 
there  may  be  many  conditions  of  the  system  in  which  this  shall  not  occur. 
The  physician,  in  directing  the  ventilation  of  a  room,  would  be  guided  by  a 
high  scientific  principle ;  whilst  in  administering  a  medicine,  he  is  working 
upon  an  induction  derived  from  a  comparatively  limited  experience. 

6.  The  art  which  most  directly  springs  out  of  the  science  of  Physiology,  is 
that  of  Hygiene,  which  may  be  defined  as  a  system  of  rules  for  the  preserva- 
tion of  the  body  in  health,  deduced  from  the  principles  by  which  its  actions 
are  governed.     Were  the  science  of  Physiology  perfect,  the  art  would  require 
little  skill  for  its  practice;  this,  however,  is  far  from  being  the  case.     Its  rules 
are  at  present  founded,  in  great  part,  upon  too  limited  an  induction  to  deserve 
the  title  of  universal;  and  their  operation  is  frequently  interfered  with  by  a 
number  of  causes,  of  whose  mode  of  action  we  are  almost  entirely  ignorant. 
Still  much  has  been  done,  by  calling  public  attention  to  those,  of  which  the 
general  importance  is  acknowledged,  in  preserving  the  body  in  health  by 
removing  the  causes  of  disease ;  as  the  increased  value  of  human  life,  shown 
by  statistical  returns,  abundantly  testifies.     And  the  Physiologist  can  readily 
point  out  many  more,  which  have  not  yet  received  the  attention  that  their 
importance  deserves.     The  term  Hygiene  is  sometimes  used  to  include  the 
art  of  restoring  as  well  as  preserving  health,  by  the  use  of  means  not  strictly 


28  CONNECTION  OF  PHYSIOLOGY  WITH 

to  be  regarded  as  medical,  e.  g.,  the  regulation  of  diet,  temperature,  &c.;  but 
this  employment  of  it  is  not  strictly  correct,  such  treatment  being  properly  a 
part  of  Therapeutics,— an  art  which  stands  in  the  same  relation  to  Hygiene, 
that  Pathology  bears  to  Physiology.  In  proportion  as  the  science  of  Physio- 
logy is  perfected,  will  the  simplicity  and  certainty  of  its  practical  applications 
increase;  and  though  we  may  not  anticipate  a  return  of  patriarchal  longevity, 
yet  the  experience  of  the  last  century  has  amply  shown,  that  every  general 
increase  of  attention  to  its  simple  and  universally-acknowledged  truths,  is 
attended  with  a  prolongation  of  life,  and  contributes  to  that  not  less  important 
object — its  emancipation  from  disease.  Hence  the  establishment  of  the  rules 
of  Hygiene  may  be  considered  as  the  most  direct  practical  benefit,  afforded  by 
the  pursuit  of  Physiological  science. 

7.  In  the  assistance  which  it  affords,  however,  in  the  establishment  of  the 
principles  of  Pathology,  the  importance  of  Physiology  is  by  no  means  inferior; 
and  it  is   surprising  how  much  the  relation  of  the  two  has  been  neglected. 
That  the  knowledge  of  the  normal  actions  of  a  living  system  is  essential  to 
success,  in  the  investigation  of  the  causes  and  mode  of  cure  of  its  irregulari- 
ties,— seems  almost  a  self-evident  proposition.     We  should  all  think  it  absurd 
for  a  person  to  attempt  to  repair  a  watch  or  a  steam-engine  that  might  be 
acting  wrongly,  without  being  acquainted  with  the  uses  of  the  several  parts  of 
its  structure,  both  singly  and  in  combination  with  each  other.     He  might 
have  such  an  acquaintance  with  their  form  and  mechanical  arrangement,  as 
might  enable  him  to  delineate  them,  or  even  to  construct  the  counterpart  of 
the  whole  machine,  without  being  able  to  put  it  into  successful  operation. 
Just  so  it  is  with  an  anatomist,  who  regards  the  mere  acquaintance  with  the 
structure  of  the  human  body  as  a  sufficient  guide  in  the  treatment  of  disease. 
But  this  is  really  of  little  assistance  in  any  thing  but  surgical  operations ; 
that  which  we  require  to  know,  for  the  rectification  of  morbid  phenomena, 
being  the  normal  history  of  those  phenomena,  and  the  conditions  on  which 
they  are  dependent.     The  neglect  of  physiological  science  as  an  adjunct  to 
the  ars  medendi,  may  probably  be  in  part  attributed  to  the  facility  with  which 
striking  curative  effects  may  often  be  produced,  by  the  application  of  empi- 
rical rules  only.     Thus  a  person  usually  healthy,  who  is  suffering  from  head- 
ache, feverishness  and  constipation, — the  effects  of  an  overloaded  alimentary 
canal, — may  be  pretty  certainly  relieved  by  a  brisk  purge  ;  or  a  stout  child, 
wrho  is  suffering  from  cough,  tightness  of  the  chest,  and  heat  and  dryness  of 
skin,  resulting  from  recent  exposure  to  cold  and  damp,  by  a  strong  dose  of 
an  antimonial.     These  are  results  with  which  every  tyro  is  well  acquainted  ; 
they  are  based  upon  ordinary  experience,  and,  if  applied  without  further  con- 
sideration of  their  rationale,  are  strictly  empirical.     The  case  might  be  com- 
pared to  that,  in  which  a  person  unacquainted  with  the  construction  or  prin- 
ciples of  action  of  a  watch  or  a  steam-engine,  alters  its  rate  of  movement,  by 
shifting  a  lever  or  opening  a  cock.     But,  though  usually  successful,  excep- 
tional cases  will  occur,  in  which  unexpected  results  will  follow  ;  and  the 
merely  empirical  practitioner  is  baffled  and  confounded.     For  these,  some- 
thing more  is  requisite ;  and  no  treatment  can  be  successful,  otherwise  than 
by  an  accidental  coincidence,  in  which  the  causes  of  the  derangement  are  not 
carefully  inquired  into,  and  their  operation  understood.     And  how  can  their 
operation,  in  producing  a  disturbance  of  the  system,  be  comprehended,  when 
its  regular  actions  are  not  even  known, — far  less,  their  principles  ascertained? 

8.  The  study  of  Physiology,  being  the  inquiry  into  the  phenomena  of  nor- 
mal life  and  the  conditions  of  those  phenomena,  requires  a  knowledge  of  the 
two  sets  of  causes  which  must  be  concerned  in  them, — the  organized  struc- 
ture or  mechanism,  possessed  of  certain  properties, — and  the  agents  or  sti- 
muli, by  whose  operation  on  this  mechanism  its  properties  are  made  to  de- 


OTHER  BRANCHES  OF  MEDICINE.  29 

velop  themselves  in  the  production  of  phenomena.  These  require  to  be 
separately  considered ;  just  in  the  same  manner  as  when,  in  examining  the 
action  of  a  steam-engine,  we  inquire  into  its  mechanical  structure,  and  the 
effects  upon  it  of  the  agencies  by  which  it  is  put  in  operation.  Now  in  the 
study  of  Pathology,  or  the  science  of  diseased  action,  we  have  to  attend,  in 
the  same  manner,  to  two  sets  of  conditions.  On  the  one  hand,  we  have  to 
make  ourselves  acquainted  with  the  characters  of  all  the  external  agents, 
which  can  produce  a  deleterious  effect  upon  the  living  body,  whether  their 
operation  be  mechanical,  chemical,  or  more  directly  vital ;  as  well  as  with  the 
results  of  the  suspension,  partial  or  complete,  of  the  conditions  by  which  its 
healthy  action  is  maintained.  On  the  other  side,  we  have  to  investigate  the 
changes  of  structure  which  manifest  themselves  in  the  body  itself,  the  causes 
by  which  these  are  produced,  and  the  new  results  which  they  will  themselves 
occasion.  Now  one  of  the  chief  difficulties  in  the  pursuit  of  Pathological 
Science  results  from  this, — that  we  are  at  present  so  imperfectly  acquainted 
with  the  conditions  required  for  normal  action,  that  we  cannot  ascertain  what 
those  changes  are,  in  which  the  derangement  primarily  consists.  Hence  we 
are  in  constant  danger  of  mistaking  the  more  evident  changes,  which  are 
often  but  secondary  results  of  the  morbid  action,  for  the  real  source  of  the  dis- 
ease. For  example,  we  are  not  yet  sufficiently  acquainted  with  the  condi- 
tions necessary  for  the  transmission  of  nervous  influence,  to  be  able  to  state 
when  those  conditions  are  interfered  with ;  hence  a  great  extent  of  morbid 
alteration  not  unfrequently  presents  itself,  in  the  parts  which  we  know  to  be 
concerned  in  this  operation,  without  such  symptoms  as  we  should  expect  to 
correspond  with  it ;  and,  on  the  other  hand,  we  frequently  observe  during  life 
most  decided  deviations  from  the  ordinary  sequence  of  nervous  phenomena, 
which  we  cannot  attribute  to  any  change  of  structure  that  we  can  discover 
after  death.  Here,  then,  is  a  case  in  which  Pathology  must  necessarily  be 
imperfect,  until  Physiology  has  greatly  advanced  ;  and  numbers  of  similar 
instances  might  be  pointed  out.  Again,  it  would  be  easy  to  show  the  direct 
benefit  which  the  Physician  has  derived  from  the  Physiologist,  by  reference 
to  the  same  class  of  phenomena ;  but  for  this  we  may  refer  to  the  subsequent 
part  of  this  Treatise,  in  which  the  chief  practical  applications  of  late  discove- 
ries as  to  the  Functions  of  the  Nervous  System,  will  be  set  forth.  It  will  be 
scarcely  questioned,  then,  that  the  Science  of  Pathology  has  so  direct  and 
immediate  a  dependence  upon  that  of  Physiology,  that  the  former  cannot  be 
pursued  with  a  fair  prospect  of  success,  without  a  knowledge  both  of  the 
principles  and  of  the  chief  phenomena  of  the  latter. 

9.  Another  illustration  may  be  useful.  Few  Pathologists  regard  any  mor- 
bid process  as  better  understood  than  that  of  Inflammation ;  and  yet  scarcely 
any  two  are  agreed  as  to  its  real  nature.  By  some,  its  essential  condition  is 
stated  to  be  a  contraction  or  a  dilatation  of  the  capillary  vessels;  and  this 
alteration  is  supposed  by  one  to  result  from  an  exalted— and  by  another  from 
a  diminished — degree  of  vitality  in  their  walls.  Others,  again,  regarding 
Inflammation  as  an  affection  of  the  sensory  rather  than  of  the  organic  func- 
tions, have  imagined  its  seat  to  be  in  the  nervous  system.  Now  it  may  be 
stated  with  tolerable  confidence,  that  no  theoretical  view  of  the  nature  of 
Inflammation  has  exerted  any  beneficial  influence  on  its  treatment ;  and  that 
all  the  rules  of  practice  to  which  we  trust  for  the  cure,  are  founded  on  expe- 
rience alone.  It  is  therefore  evident,  that  there  must  be  something  very  faulty 
in  the  mode  of  cultivation,  since  the  fruits  yielded  by  a  domain  so  fertile  of 
phenomena  are  thus  useless ;  and  the  Physiologist  has  not  much  difficulty  in 
pointing  out  several  sources  of  error  thaf  have  resulted  from  the  insufficient 
acquaintance  possessed  by  most  Pathologists,  with  those  normal  actions  of 
which  Inflammation  is  a  disturbed  form.  Thus,  he  can  show  that  Innamma- 


30  CONNECTION  OF  PHYSIOLOGY  WITH 

tion  is  not  primarily  a  disorder  of  the  function  of  Circulation,  but  rather  of 
Nutrition,  the  vascular  apparatus  being  only  secondarily  affected ;  so  that  no 
observations  on  the  state  of  the  vessels,  and  on  the  movement  of  the  blood 
through  them,  give  us  any  real  information  as  to  the  nature  of  the  morbid 
action.  Further,  he  is  aware  that  no  inferences  can  be  valid,  that  are 
founded  on  experiments  made  on  the  cold-blooded  Vertebrata,  since  in  them 
the  true  Inflammatory  state  can  with  difficulty  be  induced :  and  also,  that  the 
nervous  system  cannot  be  an  element  in  the  primary  phenomena  of  Inflam- 
mation, since  these  are  manifested  by  beings  that  do  not  possess  it.  It  will 
hereafter  be  pointed  out,  that,  by  attention  to  the  principles  of  Physiology,  our 
knowledge  of  the  real  character  of  this  and  of  many  other  morbid  processes, 
is  now  being  rapidly  increased ;  and  that  it  is  at  the  same  time  acquiring  a 
degree  of  definiteness,  which  cannot  but  lead  to  important  improvements  in 
practice. 

10.  As  Hygiene,  or  the  art  of  preserving  health,  arises  out  of  the  science 
of  Physiology,  so  does  the  Therapeutic  art  depend  upon  the  science  of  Patho- 
logy;  or,  to  use  language  rendered  venerable  by  its  antiquity,  the  ars  medendi, 
to  be  perfect,  must  be  guided  by  the  ratio  medendi.     The  term  Therapeutics, 
however,  is  sometimes  used  to  denote  that  division  of  the  Science  of  Pathology, 
which  concerns  the  principles  of  the  application  of  curative  agents  to  the 
treatment  of  disease.     There  is  no  real  ground,  however,  for  distinguishing 
this  as  any  other  than  a  section  of  Pathology ;  or  for  considering  the  practical 
use  of  these  principles  as  any  thing  but  an  Art.     As  Life,  in  the  healthy 
condition,  is  known  to  be  maintained  by  the  operation  of  external  agents  upon 
organized  tissues  endowed  with  vital  properties, — so  is  it  found  that,  in  dis- 
eased states  of  the  system,  such  a  change  takes  place  in  the  character  of  these 
actions,  as  adapts  them  to  its  altered  circumstances ;  thus,  in  a  febrile  con- 
dition, when  any  increase  of  stimulus  would  be  injurious,  there  is  no  longer  an 
appetite  for  food.     Moreover,  it  is  found  that  by  the  regulation  of  the  natural 
actions,  or  the  substitution  of  new  ones,  the  diseased  condition  may  frequently 
be  controlled,  and  the  normal  action  restored.     Hence  the  inquiry  into  the 
curative  influence  of  external  agents  upon  the  phenomena  of  disease,  is  as  much 
a  part  of  the  Science  of  Pathology,  as  the  study  of  the  influence  of  the  ordinary- 
vital  stimuli,  in  producing  the  normal  actions  of  the  system,  is  a  division  (as  it 
is  universally  allowed  to  be)  of  the  Science  of  Physiology.     If  this  inquiry  had 
terminated  in  the  discovery  of  general  principles,  all  difficulty  would  be  removed 
from  the  Therapeutic  art,  as  soon  as  the  perplexities  of  diagnosis  had  been  over- 
come ;   and,  in  proportion  as  such  are  approached,  and  our  knowledge  of  the 
essential  nature  of  diseased  actions  is  extended,  will  be  the  facility  and  the 
success  of  our  curative  treatment. 

11.  In  the  mean  time  the  practitioner  must  be  content  to  follow  a  middle 
course.     His  aim  must  be  to  avoid,  on  the  one  hand,  confiding  too  exclusively 
in  general  principles,  however  stable  and  comprehensive  he  may  imagine 
them  to  be,  until  he  is  satisfied  that  he  knows,  not  only  the  principle  itself, 
but  the  subordinate  laws  which  regulate  or  modify  its  application  to  individual 
cases.     Long  after  the  highest  laws  of  motion  had  been  established  by  New- 
ton, no  astronomer  could,  on  the  faith  of  them,  have  predicted  the  situation  of 
a  planet,  with  more  than  an  approximation  to  certainty ;  the  law  of  attraction 
had  to  be  applied  in  numberless  modes  not  contemplated  by  its  discoverer, 
before  perfect  accuracy  could  be  attained.     There  is  great  danger,  then,  in 
the  present  state  of  the  science  of  Pathology,  in  trusting  to  principles  which  we 
may  consider  unassailable,  as  our  sole  guides  in  the  practice  of  our  art ;  and 
hence  it  is  not  always  the  scientific  practitioner,  as  he  is  emphatically  termed, 
who  is  the  most  successful  in  his  treatment.     On  the  other  hand,  to  apply  a 
particular  mode  of  treatment  to  a  particular  set  of  symptoms,  without  inquiring 


OTHER  BRANCHES  OF  MEDICINE. 

into  the  cause  of  those  symptoms,  merely  on  account  of  its  having  been  suc- 
cessful in  some  case  that  appeared  analogous,  is  a  mode  of  practice  completely 
empirical.  Yet  such  a  plan  is  constantly  being  pursued.  But  as  soon  as  we 
begin  to  inquire  into  the  cause  of  the  morbid  action,  and  seek  to  remove  or 
counteract  this,  by  the  application  of  remedial  means,  which  experience  has 
shown  to  be  effectual  for  such  an  object,  we  are  really  acting,  to  a  certain 
extent,  on  scientific  principles.  The  recorded  experience  of  ages,  in  its  con- 
densed form,  must  of  necessity  assume  the  appearance  of  general  rules  of 
practice ;  and  it  is  in  the  application  of  these  rules  to  individual  cases,  and  in 
the  distinction  of  those  phenomena  whose  causes  are  subservient  to  them, 
from  those  which  are  beyond  their  pale  and  which  require  a  mode  of  treat- 
ment altogether  different,  that  the  sagacity  of  the  practitioner  most  displays 
itself.  The  rational  empiricism  which  prevails  in  this  country  at  the  present 
day,  is  a  mode  of  practice  that  may  be  regarded  as  best  combining  the  advan- 
tages of  scientific  knowledge  and  of  recorded  experience.  The  value  of  facts 
as  the  only  sure  basis  of  general  principles  is  duly  appreciated;  and  yet 
there  is  no  indisposition  to  make  trial  of  such  principles  when  announced, 
and  to  abide  by  them  so  far  as  they  appear  practically  available.  This  is  the 
only  method  in  which  the  young  practitioner  can  hope  to  succeed.  The 
increased  attention  at  present  paid  to  diagnosis,  will  frequently  enable  him  to 
determine  the  real  nature  of  the  malady  with  much  more  precision  than  a 
man  of  age  and  experience  can  do,  who  has  not  kept  pace  with  the  progress 
of  medical  science ;  whilst  the  latter  will  have  decidedly  the  advantage  in  the 
application  of  therapeutic  means,  especially  in  those  obscure  cases  that  most 
require  that  tact  which  can  only  be  gained  by  long  and  attentive  observation. 
12.  The  numerical  method,  which  is  at  present  much  valued  by  many,  as  a 
guide  in  the  Study  and  Practice  of  Medicine,  is  simply  a  statistical  arrange- 
ment of  the  phenomena  presented  by  various  diseases,  with  a  view  of  deter- 
mining the  frequency  of  their  occurrence,  their  connections  with  each  other, 
and  the  influence  of  various  modes  of  treatment  upon  them.  Its  advantages 
in  substituting  an  accurate  and  definite  record  of  facts,  for  the  vague  state- 
ments which  we  so  frequently  meet  with,  are  unquestionable.  Yet  we  must 
be  careful  not  to  attach  too  much  importance  to  the  results  afforded  by  it.  They 
have  a  tendency  to  lead  to  the  substitution  of  empirical  rules  for  scientific 
principles ;  and  if  too  exclusively  followed,  therefore,  will  tend  to  the  retardation 
of  Pathology.  If  the  practitioner  is  led  to  reason  thus  on  every  particular 
instance, — "  In  nine-tenths  of  the  cases  exhibiting  these  symptoms,  such-and- 
such  a  treatment  is  successful;  therefore  I  shall  adopt  this  treatment  in  the 
present  one," — he  is  acting  on  a  most  grossly  empirical  system.  A  general 
law  admits  of  no  exceptions ;  and  if  such  appear  to  present  themselves,  they 
must  be  due  to  some  cause  interfering  with  its  operation.  His  object  ought  to 
be  rather,  therefore,  to  ascertain  what  plan  of  treatment  is  constantly  successful 
in  each  form  of  disease;  in  other  words,  to  determine  that  invariable  sequence 
of  cause  and  effect,  on  which  alone  general  principles  or  laws  can  be  erected ; 
and  in  order  to  do  this,  he  must  carefully  analyze  the  unsuccessful  cases,  and 
ascertain  in  what  their  conditions  differed  from  the  rest,  so  as  to  be  able  to 
determine  positively  to  which  head  he  is  to  refer  the  case  before  him,  and  to 
be  guided  in  his  treatment  accordingly.  In  this  manner  he  will  advance  the 
Science ;  whilst  in  the  other  he  is  reducing  the  Art  to  its  lowest  condition.* 

*  For  a  lucid  analysis  of  the  value  of  the  numerical  method,  Dr.  Symonds's  Retrospec- 
tive Address  (at  the  Liverpool  Meeting  of  the  Provincial  Medical  Association)  may  be 
advantageously  consulted. 


32 


CHAPTER  I. 


ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 


Distinction  "between  Animals  and  Plants. 

13.  IN  entering  upon  the  general  survey  of  the  Animal  Kingdom,  which  it 
is  desirable  to  take,  before  we  consider  in  detail  any  particular  member  of  it, 
the  question  naturally  arises, — how  is   the  Animal  distinguished  from  the 
Vegetable  ?     There  is  no  difficulty  in  replying  to  this,  if  we  keep  in  view 
merely  the  higher  tribes  of  each  division;  no  one,  for  example,  would  be  in 
any  danger  of  confounding  a  Whale  with  a  Palnij  or  an  Elephant  with  an 
Oak.     It  is  when  we  descend  to  the  opposite  extremity  of  the  scale,  that  we 
encounter  the  greatest  difficulty ;  from  the  circumstance,  that  the  distinguish- 
ing characters  of  each  kingdom  disappear,  one  after  another,  until  we  are 
reduced  to  those  which  seem  common  to  both.    So  completely  is  this  the  case, 
that  there  are  many  tribes,  which  cannot,  in  the  present  state  of  our  know- 
ledge, be  referred  with  certainty  to  either  one  division  or  the  other.     We  are 
accustomed  to  think  of  Animals  as  beings,  which  not  only  grow  and  reproduce 
themselves,  but  also  possess  the  power  of  spontaneously  moving  from  place 
to  place,  and  are  conscious  of  impressions  made  upon  them:  and  we  usually 
regard  Plants  as  beings  which  are  entirely  destitute  of  sensibility  and  of  the 
power  of  spontaneous  motion, — going  through  all  their  processes  of  growth, 
reproduction,  and  decay,  alike  unconscious  of  pleasure  and  of  pain,  and  devoid 
of  all  power  of  voluntarily  changing  their  condition.     Such  a  definition  is  pro- 
bably the  most  correct  that  we  can  employ ;  but  great  difficulties  lie  in  the  way 
of  its  application.     There  are  many  tribes  which  possess  a  general  structure 
more  allied  to  that  of  beings  known  to  be  Animals,  than  to  that  of  any  Plants ; 
and  which  yet  present  no  decided  indications  either  of  sensibility  or  of  volun- 
tary power.     Such  is  the  Sponge,  the  fabric  of  which  closely  corresponds 
with  that  of  many  Alcyonian  Polypes,  whose  animality  is  undoubted;  and  yet 
neither  observation  nor  experiment  has  ever  succeeded  in  proving  that  the 
Sponge  feels  or  spontaneously  moves.     Yet  there  are  no  known  Vegetables, 
to  which  it  presents  any  near  resemblance.     On  the  other  hand,  there  are 
many  vegetables  that  perform  evident  movements,  which,  at  first  sight,  appear 
to  be  spontaneous,  as  if  they  indicated  sensibility  on  the  part  of  the  being  that 
performs  them.     Such  movements,  however,  can  in  some  instances  (as  in  that 
of  the  Sensitive-Plant,  or  of  the  Venus's  Fly-trap),  be  referred  to  a  sort  of 
mechanism,  the  action  of  which  does  not  involve  sensibility,  and  which  may 
be  compared  with  the  many  movements  (such  as  that  of  the  heart)  that  are 
constantly  taking  place  in  the  bodies  of  the  highest  animals,  without  their 
consciousness;  and  in  other  cases  (as  in  the  Oscillalorise)  they  are  so  rhythm- 
ical, as  to  impress  the  observer  with  the  idea,  that  they  are  rather  the  result 
of  some  physical,  than  of  any  mental,  influence.     In  this  respect  they  corre- 
spond with  the  motions  of  the  constantly-vibrating  cilia,  which  cover  the  sur- 
face of  the  mucous  membranes  of  Animals. 

14.  However  difficult  it  may  be  for  us,  owing  to  our  imperfect  knowledge, 


DISTINCTION  BETWEEN  ANIMALS  AND  PLANTS.  33 

to  ~4raw  the  line  in  individual  cases,  it  cannot  be  doubted  that  a  boundary 
<'x1st;  and  in  general  a  very  simple  mark  will  suffice  to  establish  the 
distmchoiv.  This  mark  is  the  presence  or  absence  of  a  stomach  or  internal 
cavitji/flh*  the  reception  of  food.  The  possession  of  a  stomach  cannot  be 
regarded,  however,  as  in  itself  an  essential  distinction  between  the  two  king- 
doms (as  some  have  represented  it) ;  for  its  presence  is  merely  a  result,  so  to 
speak,  of  tlje  nature  of  the  food  of  Animals,  and  of  the  mode  in  which  it  is 
obtained.  Vegetables  are  dependent  for  their  support,  upon  those  materials 
only  which  they  obtain  from  the  surrounding  elements ;  carbonic  acid,  water, 
and  ammonia,  duly  supplied  to  them,  with  a  small  quantity  of  certain  mineral 
ingredients,  afford  all  the  conditions  they  require,  for  the  production  of  the 
most  massive  fabrics,  and  the  greatest  variety  of  secretions.  But  these  same 
elements,  if  supplied  to  Animals,  could  not  be  converted  by  them  into  the 
materials  of  organized  structures  ;  for  they  can  only  employ  as  food  substances 
which  have  bee.n  already  organized ;  and  they  are  consequently  dependent, 
either  directly  or  indirectly,  upon  the  Vegetable  kingdom,  for  their  means  of 
support.  Now  they  cannot  incorporate  any.  alimentary  substance  into  their 
own  tissues,  until  it  has  been  reduced  to  the  fluid  form ;  hence  they  need  the 
means  of  effecting  this  reduction,  which  are  supplied  by  the  stomach.  Again, 
they  cannot  be  always  in  immediate  relation  with  their  food ;  they  have  to 
go  in  search  of  it,  and  need  a  store-room  in  which  it  may  be  deposited  during 
the  intervals ;  this  purpose  also  is  supplied  by  the  stomach.  It  is  evident,' 
moreover,  that  the  powers  of  voluntary  locomotion  and  sensation,  which  Ani- 
mals enjoy,  are  connected  with  the  peculiar  nature  of  the  food  they  require ; 
for  if  they  were  fixed  in  the  ground,  like  Plants,  they  would  not  be  able  to 
obtain  that  which  they  require  for  their  support.  It  is  true  that  there  are 
some  which  seem  almost  rooted  to  one  spot ;  but  these  have  the  power  of 
bringing  their  food  within  their  reach,  though  they  cannot  go  in  search  of  it. 
Such  is  the  case  with  many  Polypes,  which  use  their  outspread  tentacula  for 
this  purpose ;  and  with  the  lower  Mollusca,  which  can  create  currents  by 
means  of  ciliary  action. 

15.  A  distinction  might  probably  be  erected  between  the  Animal  and  Vege- 
table kingdoms,  upon  the  mode  in  which  the  first  development  of  the  germ 
takes  place.  The  seed  of  the  Plant,  at  the  time  of  fertilization,  principally 
consists  of  a  store  of  nourishment  prepared  by  the  parent  for  the  supply  of  the 
germ,  Avhich  is  introduced  into  the  midst  of  it.  The  same  may  be  said  of  the 
egg  of  the  Animal.  In  both  instances,  the  first  development  of  the  germ  is 
into  a  membranous  expansion,  which  absorbs  the  alimentary  materials  with 
which  it  is  in  contact ;  and  it  prepares  these  by  assimilation,  for  the  nourish- 
ment of  the  embryonic  structure,  the  most  important  parts  of  which, — in  the 
higher  classes  of  Animals  and  in  Phanerogamic  Plants,  the  only  permanent 
parts — are  in  its  centre.  Now  in  Plants,  this  membranous  expansion  (the 
single  or  double  cotyledon)  absorbs  -by  its  outer  surface,  which  is  applied  to 
the  albumen  of  the  seed,  and  takes  it  more  or  less  completely  into  its  own 
substance.  In  Animals,  this  expansion  is  developed  in  such  a  manner,  that 
it  surrounds  the  albumen,  enclosing  it  in  a  sac,  the  inner  surface  only  of  which 
is  'concerned  in  absorption.  The  sac  is,  then,  the  temporary  stomach  of  the 
embryonic  structure  ;  it  becomes  the  permanent  stomach  of  the  Radiata  ;  but 
in  the  higher  classes,  only  a  portion  of  it  is  retained  in  the  fabric  of  the  adult, 
— the  remainder  being  cast  offj  like  the  cotyledon  of  Plants,  as  soon  as  it  has 
performed  its  function.  Thus,  then,  the  first  nisus  of  Animal  development  is 
towards  the  formation  of  a  stomach,  for  the  internal  reception  and  digestion  of 
food ;  whilst  the  first  processes  of  Vegetable  evolution  tend  to  the  production 
of  a  frond-like  membrane,  which,  like  the  permanent  frond  of  the  lower  classes 
of  Plants,  absorbs  nourishment  by  its  expanded  surface  only. 


34  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

16.  Some  Physiologists  have  asserted,  that  the  nature  of  the  respiratory 
process  affords  a  ground  of  distinction  between  Animals  and  Plants  ; — oxygen 
being  absorbed,  and  carbonic  acid  evolved,  by  the  former, — and  a  converse 
change  being  effected  in  the  surrounding  air  by  the  latter.     It  is  not  correct, 
however,  to  designate  this  converse  change  as  a  consequence  of  the  respiratory 
process  ;  for  in  Plants,  as  in  Animals,  there  is  a  continual  absorption  of  oxy- 
gen and  evolution  of  carbonic  acid,  which  constitute  the  function  of  respira- 
tion ;  but  the  effects  of  this  change  are  masked  (as  it  were)  by  those  of  the 
process  of  fixation  of  carbon  from  the  atmosphere,  which  only  takes  place 
under  the  influence  of  sun-light,  and  which  is  much  more  analogous  to  the 
digestion  of  Animals.     The  most  valid  distinction,  in  doubtful  cases,  seems 
likely  to  be  founded  on  the  chemical  constitution  of  the  tissues  themselves. 
In  the  Plant,  the  whole  of  the  organized  structure,  when  freed  from  the  pro- 
ducts of  secretion  which  are  deposited  in  it,  (many  of  these  containing  the 
same  proportion  of  nitrogen  as  exists  in  animal  flesh,  §  454,)  is  found  to  have 
the  same  composition  with  starch ;  being  formed  of  oxygen,  hydrogen,  and 
carbon  only.     In  the  Animal,  on  the  other  hand,  the  organized  tissues  all  con- 
tain azote  as  part  of  their  proper  substance  ;  non-azotized  compounds,  such  as 
fatty  matter,  being  merely  deposited  in  these,  as  products  of  secretion.    Hence 
if  the  chemical  composition  of  the  organized  tissues  themselves  can  be  cor- 
rectly determined,  the  Vegetable  or  Animal  nature  of  a  doubtful  body  may  be 
ascertained.     By  this  test  the  long-disputed  question  of  the  nature  of  the  true 
Corallines  has  been  set  at  rest ;  their  tissue,  when  freed  from  the  lime  depo- 
sited in  it,  being  found  to  have  the  composition  of  that  of  Plants.* 

General  Subdivisions  of  the  Jlnimal  Kingdom. 

17.  The  Animal  kingdom  was  formerly  divided  into  two  primary  groups, — 
the  Vertebrated  and  the  Invertebrated;  the  former  comprising  those  which  are 
distinguished  by  the  possession  of  a  jointed  spinal  column,  consisting  of  a 
number  of  internal  bones  termed  vertebrae  ;  and  the  latter  including  all  those 
animals,  which  are  destitute  of  this  support.     It  was  pointed  out  by  Cuvier, 
however,  that,  among  the  Invertebrata,  there  are  three  types  of  organization, 
as  distinct  from  each  other,  as  any  of  them  are  from  the  Vertebrata ;  and  he 
accordingly  distributed  the  whole  under  four  primary  divisions  or  sub-king- 
doms :  of  these,  the  VERTEBRATA  rank  highest ;  next,  the  ARTIUULATA  and  the 
MOLLUSCA,  which  are  both  inferior  in  degree  of  organization  to  the  Vertebrata, 
but  are  superior  to  the  lowest  group,  the  RADIATA,  which  contains  those  ani- 
mals that  border  most  closely,  both  in  external  aspect,  and  in  general  character, 
upon  the  Vegetable  kingdom.     The  members  of  these  groups  are  readily  sepa- 
rated from  each  other  by  the  structure  of  their  skeletons,  or  organs  of  support 
and  protection  ;  as  well  as  by  many  other  characters.     In  the  Vertebrata,  the 
skeleton  consists  of  a  number  of  internal  jointed  bones,  which  are  clothed  by 
the  muscles  that  are  attached  to  them  and  move  them ;  these  bones  are  tra- 
versed by  blood-vessels  and  absorbents,  and  are  to  be  regarded  as  in  all  re- 
spects analogous  to  the  other  living  tissues  of  the  body.     In  the  Articulata,  the 
soft  parts  are  supported  by  a  hard  external  envelope,  which  is  of  corresponding 
form  on  the  two  sides  of  the  median  line,  and  is  divided  into  several  pieces, 
jointed  or  articulated  together  by  a  membrane,  in  Such  a  manner  as  still  to 
allow  of  free  motion  ;  and  the  muscles,  which  are  numerous  and  complex,  are 
attached  to  the  interior  of  these.     In  the  Mollusca,  the  whole  body  is  quite 
soft ;  and  many  species  exist,  in  which  it  has  no  external  protection :  in .  a 
large  proportion  of  the  group,  however,  the  surface  has  the  power  of  exuding 

*  See  London  Physiological  Journal,  vol.  i.,  p.  29,  and  Comptes  Rendus,  July  3,  1843. 


GENERAL  CHARACTERS  OF  RADIATA.  35 

shelly  matter,  so  as  to  form  a  protective  habitation,  within  which  the  animal 
can  withdraw  its  body,  but  which  is  by  no  means  to  be  regarded  as  a  part  of 
it,  and  does  not  exhibit  any  definite  type  of  form.  In  the  Radiata,  all  the  parts 
are  arranged  in  a  circular  manner,  the  mouth  being  in  the  centre ;  some  of 
them  are  protected  by  firmly-jointed  external  skeletons,  like  those  of  the  Arti- 
culata  ;  whilst  others  deposit  calcareous  matter  in  the  centre  of  their  soft  fleshy 
structures,  as  if  sketching  out  the  internal  skeleton  of  the  Vertebrata.  The 
skeletons  of  most  of  the  Invertebrata  differ,  however,  from  those  of  Vertebrate 
animals,  in  this  important  character, — that  they  are  not  permeated  by  vessels, 
and  are  formed  only  by  a  superficial  deposition.  Hence  they  are  termed  extra- 
vascular  :  and  it  is  an  obvious  result  of  an  arrangement  of  this  kind,  that  parts 
once  formed  are  never  changed,  except  by  the  ordinary  processes  of  decay,  and 
that  they  can  only  be  extended  by  addition  to  their  exterior ;  whilst  in  Verte- 
brata, the  bones  are  subject  to  alterations  of  any  kind,  whether  of  removal  or 
addition,  throughout  their  entire  substance.  It  is  not  correct  to  regard  them, 
however,  as  destitute  of  vitality  ;  since  they  consist,  in  all  instances,  of  a  regu- 
larly-organized tissue,  in  which  the  mineral  matter,  where  such  exists,  is 
deposited ;  and  in  several  cases  they  are  traversed  by  tubes,  which  seem  to 
convey  a  fluid  destined  for  their  nutrition,  if  not  actual  blood.  Structures  of 
this  kind  are  on  the  same  footing  with  the  dentine  and  enamel  of  the  teeth  of 
Vertebrata,  (§§  633,  634) ;  to  which  they  sometimes  bear  a  very  strong  resem- 
blance. A  more  detailed  account  of  the  general  structure  of  these  sub-king- 
doms will  now  be  given,  beginning  with  the  lowest. 

General  characters  of  Radiata. 

18.  The  RADIATA  possess  many  points  of  affinity  with  the  Vegetable  king- 
dom ;  and  of  these,  the  circular  arrangement  of  their  parts  is  one  of  the  most 
evident.  Many  species  of  Sea-Anemone,  for  instance,  present  an  appearance 
so  much  resembling  that  of  various  composite  blossoms,  as  to  have  been  com- 
monly termed  Animal-flowers, — a  designation  to  which  they  further  seem 
entitled,  from  the  small  amount  of  sensibility  they  manifest,  and  the  evident 
influence  of  light  upon  their  opening  and  closing.  But  it  is  in  the  tendency 
to  the  production  of  compound  fabrics, — each  containing  a  number  of  indivi- 
duals, which  have  the  power  of  existing  independently,  but  which  are  to  a 
certain  degree  connected  with  one  another, — that  we  recognize  the  greatest 
affinity  in  structure  between  this  group  and  the  Vegetable  kingdom.  Every 
tree  is  made  up  of  a  large  number  of  buds,  which  are  composed  of  leaves  ar- 
ranged round  a  common  axis ;  each  bud  has  the  power  of  preserving  its  own 
life,  and  of  reproducing  the  original  structure,  when  removed  from  the  parent 
stem,  if  placed  in  circumstances  favourable  to  its  growth  ;  and  yet  all  are  con- 
nected in  the  growing  tree,  by  a  system  of  vessels,  which  forms  a  communica- 
tion between  them.  This  is  precisely  the  nature  of  those  structures,  which 
are  formed  by  the  animals  of  the  class  that  may  be  regarded  as  the  most  charac- 
teristic of  the  group.  Every  mass  of  coral  is  the  skeleton  of  a  compound 
animal,  consisting  of  a  number  of  polypes,  connected  together  by  a  soft  flesh, 
in  which  vessels  are  channeled  out ;  these  polypes  are  capable  of  existing 
separately,  since  each  one,  when  removed  from  the  rest,  can  in  time  produce  a 
massive  compound  fabric,  like  that  of  its  parent ;  but  they  all  contribute  to  the 
maintenance  of  the  composite  structure,  so  long  as  they  are  in  connection  with 
it.  In  some  instances,  the  skeleton  is  stony,  and  is  formed  by  the  deposition 
of  calcareous  matter, — either  in  the  centre  of  each  fleshy  column,  so  as  to  form 
a  solid  stem, — or  on  its  exterior,  so  as  to  form  a  tube.  In  other  cases,  it  is  horny; 
and  then  it  may  be  a  flexible  axis,  or  a  delicate  tube.  Both  the  stony  and 
horny  corals  frequently  possess  the  form  of  plants  or  trees :  and  as  their  skele- 


36  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

tons  are  often  found  with  no  obvious  traces  of  the  animals  to  which  they  be- 
longed, they  have  been  accounted  Vegetable  growths.  This  idea  receives 
confirmation  from  examination  of  their  intimate  structure  ;  for  they  are  com- 
posed of  a  tissue  which  bears  more  resemblance  to  the  cellular  tissue  of  Plants 
than  to  the  areolar  tissue  of  the  higher  Animals.  There  is  not  the  least  doubt, 
however,  as  to  the  Animal  origin  of  the  greatest  part  of  these  plant-like  struc- 
tures ;  and  one  group  only,  that  of  Corallines,  remains  a  source  of  much 
perplexity  to  the  Naturalist. 

19.  The  affinity,  however,  between  the  lowest  Radiata  and  Plants,  in  regard 
to  the  vital  phenomena  they  exhibit,  is  still  more  close  than  that  manifested 
by  their  structure.     Although,  in  the  higher  groups,  movements  may  be  con- 
stantly witnessed,  which  evidently  indicate  consciousness  and  voluntary  power, 
this  js  far  from  being  the  case  in  the  lower.     There  are  many  tribes,  whose 
reception  of  food,  growth,  and  reproduction,  are  not  known  to  be  accompanied 
by  any  phenomena  which  distinctly  indicate  their  animal  character.     The 
most  violent  lacerations  produce  no  signs  of  sensibility ;  and  the  movements 
they  occasionally  exhibit  have  not  so  much  of  a  spontaneous  character  as  those 
which  are  performed  by  many  plants.     This  is  the  case,  for  example,  with  the 
Sponge  tribe,  and  also  with  a  number  of  microscopic  species."    So  doubtful  is 
the  nature  of  these  beings,  that  their  Animal  or  Vegetable  character  is  rather 
to  be  decided  by  their  affinity  with  species  known  to  belong  to  one  or  the 
other  kingdom,  than  in  any  other  way. 

20.  It  is  very  different,  however,  in  regard  to  the  higher  Radiata.     Even 
among  the  Zoophytes  (as  the  plant-like  animals  just  alluded  to  are  commonly 
termed)  there  are  some  species  which  are  unattached  during  the  whole  period 
of  their  lives,  and  have  a  power  of  voluntarily  moving  from  place  to  place, 
such  as  is  never  possessed  by  plants.     And  in  the  highest  class,  the  Echino- 
dermata,  including  the  Star-fish,  Sea  Urchin,  &c.,  we  meet  with  a  considerable 
degree  of  complexity  of  structure,  and  a  corresponding  variety  of  actions.    Still, 
except  in  those  species  which  connect  this  group  with  others,  the  same  cha- 
racter of  radial  or  circular  symmetry  is  maintained  throughout ;  and  in  no  ani- 
mal is  it  more  remarkable  than  in  the  common  Star-fish.     It  is  exhibited  alike 
in  its  internal  conformation  and  external  aspect.     The  mouth,  placed  in  the 
centre  of  the  disk,  leads  to  a  stomach  which  occupies  the  greatest  part  of  the 
cavity  of  the  body ;  and  this  sends  prolongations  into  the  (arms  which  are 
exactly  alike  in  form),  and  occupy  a  precisely  similar  position  in  every  one. 
Each  arm  is  furnished,  on  its  under  side,  with  a  curious  apparatus  for  locomo- 
tion, consisting  of  a  series  of  short  elastic  tubes,  which  are  prolonged  through 
apertures  in  the  hard  envelop,  from  a  series  of  vesicles  placed  along  the  floor 
(as  it  may  be  termed)  of  the  ray.     The  system  of  vessels  for  absorbing  nutri- 
ment and  conveying  it  through  the  system,  is  also  disposed  upon  the  same 
plan  ;  and  the  same  may  be  said  of  the  nervous  system,  and  of  the  only  organs 
of  special  sensation  which  this  animal  appears  to  possess, — the  rudimentary 
eyes,  of  which  one  is  found  at  the  extremity  of  each  ray. 

21.  Amongst  other  results  of  the  repetition  of  similar  organs,  so  remarkable 
in  this  group,  is  this, — that  one  or  more  of  them  may  be  removed  without  per- 
manent injury  to  the  whole  structure,  and  may  even  develop  themselves  into 
an  entire  fabric.     Thus  in  the  Star-fish,  instances  are  known  of  the  loss  of  one, 
two,  three,  and  even  four  rays,  which  have  been  gradually  reproduced ;  the 
whole  process  appearing  to  be  attended  with  little  inconvenience  to  the  animal. 
In  some  species  of  isolated  Polypifera,  such  as  the  common  Sea- Anemone,  and 
Hydra  (Fresh-water  Polype),  this  power  of  reproduction  is   much  greater. 
The  Hydra  may  be  cut  into  a  large  number  of  pieces  (it  is  said  as  many  as 
40),  of  which  every  one  shall  be  capable  of  developing  itself  in  time  into  a  per- 
fect polype.    The  Sea- Anemone,  when  divided  either  transversely  or  vertically, 


GENERAL  CHARACTERS  OF  MOLLUSCA. 


Fig.  1. 


• 


Asterias  aurantiaca,  with  the  upper  side  of  the  hard  envelope  removed:  a,  central  stomach;  b,  coeca  upon 
its  upper  surface,  probably  answering  to  the  liver;  c,  e,  coecal  prolongations  of  stomach  into  rays;  c'.c',  the 
same  empty  ;  d,  the  same  opened;  e,  under  surface,  showing  vesicles  of  feet;/,  vesicles  contracted,  showing 
skeleton  between  them. 

still  lives ;  and  each  half  produces  the  other,  so  as  to  re-form  the  perfect  ani- 
mal. This  is  another  character,  which  shows  the  affinity  of  the  Radiata  to  the 
Vegetable  kingdom ;  and  there  is  yet  another,  derived  from  their  mode  of  re- 
production. In  many  Polypifera,  we  observe  a  propagation  by  buds,  in  all 
respects  conformable  to  that  which  plants  effect,  and  quite  different  from  the 
regular  multiplication  by  distinct  germs.  This  gemmiparous  reproduction,  as 
it  is  called,  takes  place,  not  only  in  the  compound  Polypifera,  whose  plant- 
like  structures  are  extended  by  it,  but  also  in  some  isolated  species,  such  as 
the  Hydra ;  from  the  body  of  which,  one  or  more  young  polypes  bud  forth  at 
the  same  time ;  and  these  buds  may  themselves  put  forth  another  generation, 
previously  to  their  separation  from  their  parent.  This  kind  of  reproduction  is 
not  seen  anywhere  else,  in  the  whole  Animal  kingdom,  except  in  a  few  of 
the  lowest  Mollusca  and  Articulata,  which  border  most  closely  on  the  Radiata. 

General  characters  of  Mollusca. 

22.  The  range  of  Animal  forms  comprehended  in  the  sub-kingdom  MOL- 
LUSCA is  so  great,  that  it  would  be  difficult  to  include  them  in  any  positive 
definition,  which  should  be  applicable  to  all.  They  present  few  traces  of  the 
circular  disposition  of  organs  around  the  mouth,  which  is  characteristic  of  the 
Radiated  classes;  and  we  seldom  meet  with  any  marked  approach  to  the 
4 


38  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

elongation  of  the  body,— still  seldomer  with  any  indication  of  that  division 
into  segments,  which  are  the  chief  peculiarities  of  the  Articulata.  It  is  by 
the  absence  of  these,  and  of  any  trace  of  the  Vertebrated  structure,  that  the 
Mollusca  are  most  readily  defined.  The  variety  of  form  which  they  present 
is  less  surprising,  when  it  is  considered,  that  the  bulk  of  their  bodies  is  almost 
entirely  made  up  by  organs  of  nutrition ;  and  the  organs  of  sensation  and  loco- 
motion which  they  possess,  are  subservient  to  the  supply  of  these.  We  find, 
in  the  lowest  tribes  of  this  group,  living  beings  which  are  fixed  to  one  spot 
during  all  but  the  earliest  period  of  their  lives ;  and  which  scarcely  possess 
within  themselves  so  much  power  of  movement  as  that  enjoyed  by  the  in- 
dividual Polypes  in  a  compound  polypidom ;  and  yet  these  exhibit  a  complex 
and  powerful  digestive  apparatus,  a  regular  circulation  of  blood,  and  an  active 
respiration.  We  never  find,  throughout  the  whole  Animal  kingdom,  that  the 
apparatus  of  organic  life  is  arranged  on  any  definite  plan  of  its  own ;  its  con- 
formation is  adapted  to  the  type  which  predominates  in  the  structure  of  each 
group,  and  which  is  principally  manifested  in  the  disposition  of  the  locomotive 
organs.  Thus,  the  stomach  of  the  Star-fish  is  circular,  and  sends  a  prolongation 
into  each  ray ;  whilst  the  digestive  cavity  of  the  Articulata  is  prolonged  into  a 
tube.  In  the  Mollusca,  there  is  no  such  definite  type,  the  apparatus  of  nutri- 
tion having  the  predominance  over  that  of  locomotion ;  and  the  form  of  the 
body  is,  therefore,  extremely  variable.  The  relative  places,  even  of  the  most 
important  organs  (such  as  the  gills),  are  found  to  undergo  complete  changes, 
as  we  pass  from  one  tribe  to  another ;  although  their  general  structure  is  but 
little  altered. 

23.  The  lower  Mollusca  may  be  characterized  as  consisting  merely  of  a  bag 
of  viscera ;  they  have  not  even  any  prominence  for  the  mouth,  nor  any  organs 
of  special  sense,  such  as  would  distinguish  a  head;  and  they  are  entirely  desti- 
tute of  symmetry, — the  radiated  arrangement  of  parts  seen  in  the  lower  tribes 
being  absent,  as  well  as  the  bi-lateral  correspondence  which  is  characteristic 
of  the  higher.  In  the  more  elevated  Mollusca,  however,  which  possess  not 
merely  sensitive  tentacula,  but  eyes  and  even  organs  of  smell  and  hearing,  we 
find  these  disposed  in  a  symmetrical  manner;  so  that  the  head,  which  is  the 
part  concerned  peculiarly  in  animal  life,  does  present  a  bi-lateral  equality  of 
parts,  even  when  the  remainder  of  the  body  wants  it.  Further,  in  the  more 
active  among  the  higher  classes,  we  find  this  bi-lateral  symmetry  showing 
itself  in  the  exterior  of  the  whole  body  ;  evidently  bearing  a  pretty  close  rela- 
tion to  its  degree  of  locomotive  power.  It  is  most  evident  and  complete  in 
the  Cephalopoda  (Cuttle-fish  tribe);  many  of  which  are  adapted  to  lead  the 
life  of  Fishes,  and  resemble  them  in  the  general  form  of  the  body,  and  in 
the  structure  of  many  of  the  individual  organs.  It  is  also  manifested  in  many 

Fig.  2. 


Aplysia  depilans ;  a,  branchiae  or  gills. 


GENERAL  CHARACTERS  OF  MOLLUSCA.  39 

of  the  shell-less  Gasteropoda,  such  as  the  Slug,  or  the  Aplysia  (Sea-Hare) ; 
as  will  be  seen  by  the  accompanying  representation  of  a  species  of  the  latter. 
But  this  symmetry  does  not  extend  to  the  arrangement  of  the  internal  organs ; 
and  appears  to  be  only  designed  to  adapt  the  body  for  more  convenient  loco- 
motion. 

24.  As  a  group,  however,  the  Mollusca  are  to  be  characterized  rather  by 
the  absence  than  by  the  possession,  of  any  definite  form ;  and  there  is  a  cor- 
responding absence  of  any  regular  organs  of  support,  by  which  such  a  form 
could  be  maintained.     The  name  they  have  received  designates  them  as  soft 
animals ;  and  this  they  are  pre-eminently,  as  every  one  knows  who  has  taken 
a  Slug  between  his  fingers.     The  shell,  where  it  exists,  is  to  be  regarded  rather 
in  the  light  of  an  appendage,  designed  for  the  mere  protection  of  the  body, 
and  deriving  its  shape  from  the  latter, — than  as  a  skeleton,  giving  attachment 
to  muscles,  and  regulating  the  form  of  the  whole  structure.     It  is  in  no  in- 
stance a  fixed  point  for  the  muscles  of  locomotion ;  and  it  is  only,  indeed,  where 
the  body  is  uncovered  by  a  shell  or  where  a  locomotive  organ  may  be  pro- 
jected beyond  it,  that  any  active  movements  can  be  executed.     This  locomotive 
organ, — the  foot  as  it  is  commonly  termed,— is  nothing  else  than  a  fleshy 
mass,  formed  by  the  increased  development  of  the  muscular  portion  of  one  part 
of  the  general  envelope  of  the  body,  termed  the  mantle  in  which  the  visceral 
mass  is  loosely  included.     The  mantle  is  not  essentially  different  from  the  skin 
of  other  animals ;  but  it  is  usually  thicker,  possessing  a  considerable  amount 
of  muscular  fibre  interwoven  with  it,  and  its  surface  having  frequently  a  glan- 
dular character.     This  general  muscular  envelope  is  the  only  locomotive  organ 
possessed  by  a  large  proportion  of  the  Mollusca;  but  its  contractile  properties 
are  usually  greatest  at  some  particular  spot,  where  it  is  thickened  into  a  sort 
of  disk,  by  the  alternate  contraction  and  extension  of  which  the  animal  can 
slowly  propel  itself;  this  is  well  seen,  by  causing  a  Snail  or  Slug  to  crawl  over 
a  piece  of  glass,  so  that  the  under  surface  of  the  disk  may  be  seen  whilst  it 
is  in  operation.     The  general  character  of  their  locomotion,  however,  is  well 
expressed  by  the  term  sluggish;  and  there  are  scarcely  any  among  the  typical 
Mollusca,  whose  activity  is  such  as  to  demand  for  them  any  higher  appellation. 

25.  The  general  development  of  their  organs  of  Nutrition,  however,  is  much 
higher  than  is  met  with  among  the  Articulata;  and,  in  proportion  to  that  of 
the  organs  of  Locomotion,  it  is  much  greater  than  will  be  elsewhere  observed 
throughout  the  Animal  kingdom.     The  justice  of  this  statement  will  be  made 
evident  by  a  slight  examination  of  the  adjoined  figure,  in  which  the  interior 
structure  of  the  Jlplysia,  showing  the  general  character  of  that  of  the  group, 
is  displayed.     The  only  set  of  muscles  which  this  animal  possesses,  is  that 
connected  with  the  mouth,  which  it  is  able  to  push  forwards  or  to  draw  back ; 
and  which  possesses  considerable  powers  of  mastication,  and  is  furnished  with 
large  salivary  glands.     The  nervous  centres  (of  which  more  will  be  said  here- 
after) are  seen  to  be  principally  disposed  around  the  oesophagus.     The  whole 
digestive  apparatus  is  observed  to  be  very  complex  and  highly-developed ;  the 
liver  alone  occupies  a  considerable  part  of  the  cavity.     The  heart  has  distinct 
muscular  walls,  and  is  divided  into  a  separate  auricle  and  ventricle ;  and  a 
large  respiratory  organ  is  developed  for  the  aeration  of  the  blood.     The  posi- 
tion of  the  gills,  which  are  external  to  the  cavity,  but  which  are  concealed  in 
part  by  a  fold  of  the  mantle,  and  in  part  by  the  rudimentary  shell,  is  seen  at 
«,  Fig.  2.     The  generative  apparatus,  also,  is  highly  developed.     Yet  with 
all  this  complex  organization,  the  locomotive  power  of  tfye  animal  is  not  much 
greater  than  that  of  the  Slug ;  no  other  means  being  provided  for  the  purpose, 
than  the  contractility  of  the  general  envelope,  which  is  greatest  on  the  under 
side  of  the  body. 

26.  The  blood  of  the  Mollusca  is  white,  and  the  number  of  corpuscles  in 
it  is  small.     Their  temperature  is  low,  being  seldom  more  than  one  or  two 


40 


ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 


degrees  above  that  of  the  surrounding  medium ;  but  many  of  them  are  capa- 
ble of  being  subject  to  extreme  variations  of  heat  and  cold,  without  their  vita- 
lity being  thereby  destroyed.  Their  respiration  is  for  the  most  part  aquatic ; 
and  is  performed  by  means  of  gills,  over  which  a  current  of  water  is  con- 
stantly being  propelled,  by  the  vibration  of  the  cilia  that  cover  their  surface. 
Many  of  them  are  dependent  on  the  same  current  for  their  supplies  of  food ; 
part  of  the  water  so  introduced  being  taken  into  the  stomach ;  and  a  part  flow- 
ing over  the  res^ratory  surface.  The  higher  tribes,  however,  go  in  search 
of  their  food,  and  have  instruments  of  mastication  for  reducing  it;  but  in 
these,  as  in  the  former,  the  anal  orifice  of  the  intestine  opens  into  the  passage, 
through  which  the  current  that  has  passed  over  the  respiratory  organs  finds 
egress ;  so  that  the  faBcal  matter  from  the  former,  and  the  fluid  that  has  served 

Fig.  3. 


t- 


Aplysia  cut  open,  showing  the  viscera;  a,  upper  part  of  oesophagus;  b,  pen's;  c.  c,  salivary  glands;  d, 
superior  or  cephalic  ganglion ;  e,  e,  inferior,  or  subcesophageal  ganglia ;  /,  termination  of  oesophagus ;  g.  g.  first 
stomach;  h,  third  stomach;  i,  second  stomach;  k,  intestine;  Z,  I,  Z,  liver:  771,  posterior  ganglion;  n,  aorta; 
o,  hepatic  artery;  y,  ventricle  of  heart;  g,  auricle;  r,  s,  branchiae ;  t}  testis;  w,  lower  part  of  intestine  ;  «, 
ovary ;  w,  anus. 


GENERAL  CHARACTERS  OF  ARTICULATA.  41 

the  purpose  of  the  latter,  are  discharged  together.  Although  very  voracious, 
when  supplies  of  food  come  in  their  way,  most  of  the  Mollusca  are  capable 
of  fasting  for  long  intervals,  where  none  offer  themselves, — a  fact  which  is 
readily  explained  by  that  general  inertness  of  their  vital  processes,  which  has 
been  stated  to  be  the  characteristic  of  the  group. 

General  characters  of  Articulata. 

27.  The  members  of  the  sub-kingdom  ARTICULATA  are  distinguished  for 
the  most  part,  by  characters  which  are  exactly  opposed  tfj  those  just  enume- 
rated.   Their  characteristic  form  is  easily  defined;  and  in  no  instance  is  there 
any  wide  departure  from  it.     The  body  is  more  or  less  elongated,  and  pre- 
sents throughout  a  most  exact  bi-lateral  symmetry.     It  is  completely  enclosed 
in  an  integument  of  greater  density  than  the  rest  of  the  structure,  which  is 
divided  into  distinct  rings  or  segments ;  these,  being  held  together  by  a  flexi- 
ble membrane,  allow  considerable  freedom  of  motion,  whilst  they  firmly  pro- 
tect the  soft  parts,  and  afford  attachment  to  numerous  muscles.     It  is  in  the 
Centipede,  arid  other  such  animals,  that  this  division  into  segments  is  most 
distinctly  and  regularly  marked.     In  the  lower  Articulata,  such  as  the  Leech 
and  the  Earth-worm,  the  integument  is  altogether  so  soft,  that  the  intervals  of 
the  articulations  are  not  very  distinct  from  the  rings  themselves ;  and  in  the 
highest  Crustacea  and  Arachmda,  the  segments  are  so  closely  united  together, 
as  to  be  in  some  instances  scarcely  recognizable.     In  the  former,  the  move- 
ments of  the  body  are  entirely  effected  by  its  own  flexion ;  whilst  in  the  latter, 
they  are  committed  to  members  developed  for  that  special  purpose.     These 
members  also  have  an  articulated  external  skeleton.     The  bulk, of  the  body 
in  the  Articulata  is  made  up  of  the  muscles,  by  which  the  several  segments, 
and  their  various  appendages,  are  put  in  motion ;  these  muscles  have  their 
fixed  points  on  the  interior  of  the  hard  envelope,  just  as  they  are  attached  in 
vertebrated  animals  to  the  exterior  of  the  bones ;  and  they  form  a  system  of 
great  complexity. 

28.  The  development  of  the  organs  of  Nutrition  in  Articulata  would  seem 
to  be  altogether  subservient  to  that  of  the  Locomotive  apparatus, — their  func- 
tion being  chiefly  to  supply  the  muscles  with  the  aliment  necessary  to  main- 
tain their  vigour.     The  power  of  these  muscles  is  so  great  in  proportion  to 
their  size,  that  in  energy  and  rapidity  of  movement,  some  of  the  Articulated 
tribes  surpass  all  other  animals.     Their  movements  are  directed  by  organs  of 
sensation,  which,  although  not  developed  on  so  high  a  plan  as  those  of  some 
Mollusca,  are  evidently  very  acute  in  their  powers.     There  are  very  few  in- 
stances of  Articulated  animals  being  in  any  way  restrained  as  to  freedom  of 
locomotion ;  and  these  are  found  in  a  single  group,  the  Cirrhopoda  or  Barnacle 
tribe,  which  connects  this  sub-kingdom  with  the  last.     In  general,  they  roam 
freely  abroad  in  search  of  food,  and  are  supplied  with  prehensile  organs  for 
capturing  their  prey,  and  with  a  complex  masticating  apparatus  for  reducing 
it.     Their  actions  are  evidently  directed  almost  solely  by  instinctive  propensi- 
ties, which  are  adapted  to  meet  every  ordinary  contingency,  being  of  similar 
character  in  each  individual  of  the  same  species,  and  presenting  but  little  ap- 
pearance of  ever  being  modified  by  intelligence.     Hence  these  animals  seem 
like  machines,  contrived  to  execute  a  certain  set  of  operations;  many  of  them 
producing  immediate  results,  which  even  Man,  by  the  highest  efforts  of  his 
reason,  has  found  it  difficult  to  attain.* 

29.  All  the  Articulata,  save  a  few  of  the  very  lowest  species,  possess  a  dis- 
tinct head  at  one  end  of  the  body,  furnished  with  organs  of  special  sensation, 

*  Reference  is  here  especially  made  to  the  celebrated  problem  of  Miraldi  (§  155). 

4* 


ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

and  with  lateral  jaws  for  the  prehension  and  reduction  of  food;  and  their 
movements,  being  principally  guided  by  the  special  senses,  take  place  in  this 
direction.  The  bi-lateral  symmetry  of  the  body  is  not  confined  to  its  exte- 
rior; for  it  prevails  most  completely  in  the  whole  muscular  apparatus;  and 
even  the  organs  of  nutrition  present  more  distinct  traces  of  it  than  are  to  be 
seen  elsewhere.  The  compact  heart  of  the  Mollusca,  for  instance,  is  here  re- 
placed by  a  long  tube,  the  dorsal  vessel,  placed  on  the  median  line;  and  the 
respiratory  organs,  which  are  usually  diffused  through  the  whole  system,  are 
uniform  on  the  two  sides.  Even  the  intestinal  canal  partakes  of  this  sym- 
metry ;  in  some  Species  it  runs  straight  from  end  to  end  of  the  body ;  and  even 
where  it  is  otherwise  disposed,  its  appendages  are  nearly  equal  on  the  two 
sides.  The  respiration  of  this  group  is  for  the  most  part  aerial;  and  the  appa- 
ratus for  the  purpose  consists  of  a  series  of  chambers  or  tubes,  which  are  dis- 
persed or  extended  through  the  whole  body.  By  this  means,  the  air,  the 
blood,  and  the  tissue  to  be  nourished,  are  all  brought  into  contact  at  the  same 
points ;  and  a  much  less  vigorous  circulation  is  required,  therefore,  than  would 
otherwise  be  needed.  The  whole  apparatus  of  nutrition  is  comprised  within 
a  comparatively  small  part  of  the  body ;  and  the  bulk  of  the  organs  which 
compose  it,  is  never  at  all  comparable  with  that  which  we  ordinarily  find  in 
the  Mollusca.  Thus,  the  liver,  which  in  the  Oyster  forms  a  large  part  of  the 
whole  substance,  is  often  scarcely  recognizable  as  such  in  the  Insect ;  and  the 
intestinal  tube  seldom  makes  many  convolutions  in  its  course  from  one  extre- 
mity to  the  other.  The  blood  is  usually  white,  as  in  the  other  Invertebrated 
classes ;  but  it  contains  a  larger  number  of  corpuscles  than  are  seen  in  that  of 
most  of  the  Mollusca.  The  temperature  varies  to  a  certain  degree  with  that 
of  the  atmosphere  ;  but  there  are  many  Insects  that  have  the  power  of  gene- 
rating a  large  amount  of  independent  heat,  which  is  strictly  proportionable  to 
the  quantity  of  oxygen  converted  by  them  into  carbonic  acid  in  the  respiratory 
process.  All  the  actions  of  the  Articulata  are  performed  with  great  energy  ; 
and,  at  the  time  of  the  most  rapid  increase  of  the  body,  the  demand  for  food 
is  so  great,  that  a  short  suspension  of  the  supply  of  aliment  is  fatal.  They 
are  capable,  however,  of  being  submitted  to  the  influence  of  very  extreme 
temperatures,  with  little  permanent  injury. 

30.  The  adjoining  figure,  which  displays  the  muscular  apparatus  of  the 

Fig.  4. 


Section  of  the  trunk  of  Melolontha  vulgaris  (after  Strauss-Durckheim),  showing  the  complexity  of  the 
muscular  system.    The  first  segment  of  the  thorax  (2)  is  chiefly  occupied  by  the  muscles  of  the  head,  and^ 
by  those  of  the  first  pair  of  legs.    The  second  and  third  segments  (3  and  4)  contain  the  very  larg€  muscles 
of  the  wings,  and  those  of  the  other  two  pairs  of  legs.    The  chief  muscles  of  the  abdomen  are  the  long 
dorsal  and  abdominal  recti,  which  move  the  several  segments  one  upon  another. 


GENERAL  CHARACTERS  OF  VERTEBRATA.  43 

interior  of  the  body  of  a  Cock-chafer,  will  give  an  idea  of  its  complexity  and 
variety,  and  of  the  large  portion  of  the  trunk  which  is  occupied  by  it ;  and 
will  also  show  the  division  of  the  skeleton  into  segments,  the  number  of  which 
in  Insects  is  limited  to  thirteen.  These  are  nearly  equal  and  similar  to  each 
other  in  the  Larva  ;  but,  in  the  perfect  Insect,  the  three  behind  the  head  are 
united  into  the  thorax,  to  which  the  legs  and  wings  are  attached ;  and  the 
remainder  form  the  abdomen,  which  has  little  concern  in  locomotion. 

General  characters  of  Vertebrata. 

31.  In  none  of  the  three  preceding  divisions  of  the  Animal  kingdom,  does 
the  Nervous   System  attain  such  a  degree  of  development,  as  to  give  it  that 
predominance  in  the  whole  fabric,  which  it  evidently  possesses  in  VERTE- 
BRATA.    In  the  Radiata  and  Mollusca,  its  functions  are  obviously  restricted^to 
the  maintenance  of  the  nutritive  operations ;  and  to  the  guidance  of  the  ani- 
mal, by  means  of  its  sensory  endowments,  in  the  choice  of  food,  as  well  as  (in 
some  instances)  in  the  search  for  an  individual  of  the  opposite  sex :  in  the 
Articulata,  its  purpose  appears  similar,  but  is  carried  into  effect  in  a  different 
manner,  the  locomotive  organs  being  the  parts  chiefly  supplied  by  it.     In  the 
Vertebrata,  on  the  other  hand,  the  development  of  all  the  other  organs  appears 
to  be  subordinate  to  that  of  the  Nervous  System ;  their  object  being  solely  to 
give  to  it  the  means  of  the  exercise  of  its  powers.     This  statement  is  not,  of 
course,  as  applicable  to  the  lower  Vertebrata  as  it  is  to  the  higher  ;  but  it  is 
intended  to  express  the  general  character  of  the  group.     The  predominance 
of  the  nervous  system  is  manifested,  not  only  in  the  increased  size  of  its  cen- 
tres, but  also  in  the  special  provision  which  we  here  find,  for  the  protection  of 
these  from  injury.     In  the  invertebrated  classes,  wherever  t&e  nervous  system 
is  enclosed  in  any  protective  envelope,  that  envelope  serves  equally  for  the 
protection  of  the  whole  body.     This  is  the  case,  for  example,  in  regard  to  the 
spiny  integument  of  the  Star-Fish,  the  shell  of  the  Mollusca,  and  firm  jointed 
rings  of  the  Insect.     The  only  exceptions  occur  in  a  few  tribes,  in  which  the 
nervous  system  is  much  concentrated ;  and  in  which  the  general  organization 
approaches  that  of  the  Vertebrata.*     In  Vertebrated  animals,  we  find  that  the 
skeleton  essentially  consists  of  a  series  of  parts,  which  are  destined  to  enclose 
the  nervous  centres,  and  to  give  attachment  on  their  exterior  to  the  muscles  by 
which  the  body  is  moved:  hence  it  may  be  termed  the  neuro-skeleton;  in 
contra-distinction  to  the  dermo-skeleton,  which  envelops  the  whole  body  .iff' 
many  Invertebrata,  being  formed  on  the  basis  of  their  integument.     The  tis- 
sues, bone  and  cartilage,  of  which  the  former  is  composed,  are  more  closely 
connected  with  the  vascular  system,  than  are  the  hard  parts  of  Invertebrata ; 
and  are  consequently  more  capable  of  undergoing  interstitial  change. 

32.  In  considering  the  essential  character  of  the  skeleton  of  Vertebrata,  we 
should  look'  at  its  simplest  forms, — those  in  which  it  has  the  least  number  of 
superadded  parts.     We  find  these  in  the  Serpent  tribe  among  Reptiles,  and 
in  the  Eel  and  its  allies  among  Fish.     If  we  examine  their  skeletons,  we  per- 
ceive that  the  Spinal  Column,  with  the  cranium  at  its  anterior  extremity,  con- 
stitutes the  essential  part  of  the  vertebrated  framework ;  and  that  the  develop- 
ment of  members  is  secondary  to  this.     The  Spinal  Column  usually  consists 
of  a  number  of  distinct  bones,  the  Vertebrae  ;   each  of  which  is  perforated  by 
a  large  aperture,  in  such  a  manner  that,  when  the  whole  is  united,  a  continu- 

*  Thus,  in  the  highest  Crustacea,  there  is  an  internal  projection  from  the  shell,  on 
each  side  of  the  median  line,  which  forms  a  sort  of  arch  enclosing  the  ventral  cord ;  and 
in  the  naked  Cephalopoda,  the  nervous  centres  are  supported,  and  in  part  protected,  by 
cartilaginous  plates,  which  are  evidently  the  rudiments  of  the  internal  skeleton  of  the 
Vertebrata. 


44  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

ous  tube  is  formed  for  the  lodgment  of  the  spinal  cord.  The  Cranium,  which 
it  bears  at  its  upper  end,  is  in  reality  formed  of  the  same  elements  as  the 
vertebras,  instead  of  differing  from  them  completely  in  structure,  as  we  might 
be  led  to  suppose  by  examination  of  its  most  developed  forms  only.  The 
object  of  this  enlargement  is  to  enclose  the  brain,  or  mass  of  cephalic  ganglia, 
which  attains  a  greatly  increased  size  in  the  Vertebrata ;  and  also  to  afford 
support  and  protection  to  the  organs  of  special  sense,  which  are  far  more 
highly  developed  among  them  than  elsewhere.  The  true  nature  of  the  cra- 
nium is  best  seen  in  those  animals,*in  which  the  brain  bears  but  a  small  pro- 
portion to  the  spinal  cord,  such  as  the  lower  Reptiles  and  Fishes ;  and  an 
examination  of  its  structure  in  these  satisfactorily  proves  the  reality  of  this 
view,  which  is  further  borne  out  by  the  history  of  its  development,  and  of  that 
of  its  contained  parts,  in  the  higher  Vertebrata. 

,  33.  The  Vertebral  column,  at  its  opposite  extremity,  is  usually  contracted 
instead  of  being  dilated, — forming  a  tail,  or  a  rudiment  of  one,  from  which  the 
nervous  centres  are  entirely  withdrawn  ;  the  development  of  the  tail  is  com- 
monly seen  to  be  in  an  inverse  proportion  to  that  of  the  cranium.  To  this 
column,  the  ribs  and  extremities  are  merely  apendages,  which  we  find  more 
or  less  developed  in  the  various  tribes,  and  often  entirely  absent ;  whilst  the 
vertebral  column  is  never  wanting,  although  reduced  in  some  species  to  a  very 
rudimentary  state.  It  is  interesting  to  compare  its  various  conditions  with 
those  which  have  been  noticed  in  the  external  skeleton  of  the  Articulata.  In 
the  lowest  animals  of  the  group,  locomotion  is  pri»cipally  or  even  entirely  per- 
formed by  flexion  of  the  body  itself ;  and  here,  as  in  the  warm  tribe,  we  find 
the  skeleton  extremely  flexible,  the  whole  being  comparatively  soft,  and  its 
divisions  indistinct.  This  is  the  case,  for  example,  in  the  Lamprey  and  other 
Cyclostome  fishes ;  in  which  there  is  no  distinct  division  into  vertebrae,  the 
spinal  column  scarcely  possessing  even  the  density  of  cartilage.  In  propor- 
tion, however,  as  distinct  members  are  developed,  and  the  power  of  locomotion 
is  committed  to  them,  we  find  the  firmness  of  the  spinal  column  increasing, 
and  its  flexibility  diminishing ;  and  in  Birds, — in  which,  as  in  Insects,  the 
movements  of  the  body  through  the  air  are  effected  by  muscles  which  must 
have  very  firm  points  of  support, — the  vertebral  column  is  much  consolidated 
by  the  union  of  its  different  parts,  so  as  to  form  a  solid  frame-work.  As  a 
general  rule,  then,  the  mobility  of  the  extremities,  and  the  firmness  of  the  ver- 
tebral column,  vary  in  a  like  proportion.  The  number  of  these  extremities  in 
Vertebrata  never  exceeds  four  and  two  of  them  are  not  unfrequently  absent. 
The  power  of  locomotion  is  not  developed  to  nearly  the  same  proportional  ex- 
tent as  in  the  Articulata  ;  the  swiftest  Bird,  for  example,  not  passing  through 
nearly  so  many  times  its  own  length  in  the  same  period,  as  a  large  proportion 
of  the  Insect  tribes  :  but  it  is  far  greater  than  that  which  is  characteristic  of  the 
Mollusca ;  and  there  is  no  species  that  is  fixed  to  one  spot,  without  the  power 
of  changing  its  place.  On  the  other  hand,  the  highest  Mollusca  approach  them 
very  nearly  in  the  development  of  organs  of  special  sense,  of  which  Verte- 
brata almost  invariably  possess  all  four  kinds, — sight,  hearing,  smell,  and  taste. 
34.  The  perfection  of  the  Articulate  structure  has  been  shown  to  consist  in 
the  development  of  those  powers  which  enable  the  animal  to  perform  actions 
denoting  the  highest  instinctive  faculties.  That  of  the  Vertebrata  evidently 
tends  to  remove  the  animal  from  the  dominion  of  undiscerning,  uncontrollable 
instinct ;  and  to  place  all  its  operations  under  the  dominion  of  an  intelligent 
will.  We  no  longer  witness  in  these  operations  that  uniformity,  which  has 
been  mentioned  as  so  remarkable  a  characteristic  of  instinctive  actions.  There 
is  evidently,  among  the  higher  Vertebrata  especially,  a  power  of  choice  and  of 
determination,  guided  by  a  perception  of  the  nature  of  the  object  to  be  attained, 
and  of  the  means  to  be  employed,  constituting  the  simplest  form  of  the  reason- 


GENERAL  CHARACTERS  OF  VERTEBRATA.  45 

ing  faculty ;  and  the  amount  of  this  bears  so  close  a  relation  with  the  deve- 
lopment of  the  brain,  that  it  is  scarcely  possible  to  regard  the  two  as  uncon- 
nected. In  Man,  whose  brain  is  far  larger  in  proportion  to  his  size,  as  well 
as  more  complex  in  its  structure,  than  that  of  any  other  animal,  the  reasoning 
faculties  attain  the  highest  perfection  that  we  know  to  be  anywhere  manifested 
by  them  in  connection  with  a  material  instrument ;  the  instinctive  propensities 
are  placed  under  their  subjection ;  and  all  his  acts,  excepting  those  imme- 
diately required  for  the  maintenance  of  his  organic  functions,  are  put  under 
their  control.  It  is  to  Man,  therefore,  that  what  was  just  now  stated,  of  the 
predominance  of  the  neryous  system  in  Vertebrata,  particularly  applies  ;  but 
the  same  may  be  noticed,  though  in  a  less  striking  degree,  throughout  the 
group.  Not  only  is  the  influence  of  the  nervous  system  to  be  traced  in  the 
sensible  movements  which  they  perform,  but  also  in  various  modifications  of 
the  organic  functions,  which  take  place  under  the  influence  of  particular  states 
of  mind,  and  the  occurrence  of  which  there  is  no  reason  to  suspect  in  the  lower 
tribes  of  animals.  These  are  even  much  more  striking  in  Man  than  in  the 
lower  Vertebrata ;  indeed,  the  comparative  slightness  of  the  influence  of  the  mind 
upon  the  body,  is  one  of  the  causes  which  render  the  lower  Mammalia  more 
able  than  Man  is,  to  recover  from  the  effects  of  severe  injuries.  The  Mollusca 
seem  to  grow  like  plants  ;  their  massive  organs  increasing  by  their  own  sepa- 
rate vitality,  and  being  but  little  dependent  upon  each  other.  Even  the  act 
of  respiration,  which  is  in  most  animals  performed  by  a  series  of  distinct  mus- 
cular contractions,  is  there  principally  effected  through  the  medium  of  the 
cilia  which  clothe  the  respiratory  surface.  'But  in  the  Vertebrata,  the  nervous 
system  possesses  a  distinct  and  independent  rank ;  its  offices  are  those  which 
more  particularly  constitute  the  active  life  of  the  animal ;  the  organic  func- 
tions have  for  their  chief  object,  the  maintenance  of  the  nervous  and  muscular 
apparatus  in  the  conditions  requisite  for  their  activity,  and,  in  consequence, 
all  these  different  kinds  of  apparatus  are  so  interwoven  together,  that  their 
mutual  dependence  is  very  close. 

35.  The  foregoing  remarks  will  be  found  to  have  an  important  bearing  on 
the  details  subsequently  to  be  given,  respecting  the  functions  of  the  nervous 
system  in  Man ;  and  it  is  desirable  to  set  out  with  clear  ideas  on  this  subject, 
since  there  is  no  department  of  Physiology,  regarding  which  more  error  is 
prevalent.     There  is  no  valid  reason  for  believing,  that  the  organic  functions 
in  Animals,  any  more  than  the  corresponding  changes  in  Plants,  are  dependent 
on  the  nervous  system  for  their  performance  ;  but  common  observation  shows, 
that  they  are  much  influenced  by  it  in  the  higher  animals ;  and  from  such  a 
comparison  as  that  which  has  been  just  now  briefly  made,  it  would  appear 
that  the  higher  the  general  development  of  the  nervous  system,  the  closer  is 
their  relation  with  it. 

36.  This  general  character  of  the  Vertebrata  harmonizes  well  with  what 
may  be  observed,  on  a  cursory  glance  at  the  structure  of  their  bodies,  of  the 
proportion  between  the  organs  of  Nutritive  and  those  of  Animal  life.     The 
former,  contained  in  the  cavities  of  the  trunk,  are  highly  developed  ;  but,  as 
in  the  Mollusca,  they  are  for  the  most  part  unsymmetrically  disposed.     Of  the 
latter,  the  nervous  system  and  organs  of  the  senses  occupy  the  head ;  whilst 
the  muscles  of  locomotion  are  principally  connected  with   the  extremities : 
both  are  symmetrical,  as  in  the  Articulata;  but,  whilst  that  part  of  the  nervous 
centres,  which  is  the  instrument  of  reason,  is  very  largely  developed,  the  por- 
tion which  is  specially  destined  to  locomotion,  together  with  the  muscular 
system  itself,  bears  much  the  same  proportion  to  the  whole  bulk  of  the  body, 
as  it  does  in  the  Articulated  series.     Hence  we  observe  that  the  Vertebrata 
unite  the  unsymmetrical  apparatus  of  nutrition,  characteristic  of  the  Mollusca, 
with  the  symmetrical  system  of  nerves  and  muscles  of  locomotion,  which  is 


46  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

the  prominent  characteristic  of  the  Articulata ;  both,  however,  being  rendered 
subordinate  to  the  great  purpose  to  be  attained  in  their  fabric, — the  develop- 
ment of  an  organ,  through  which  intelligence  peculiarly  manifests  itself.  For 
the  operations  of  this,  a  degree  of  general  perfection  is  required,  which  is  not 
met  with  elsewhere.  The  higher  Vertebrata  have  a  power  of  constantly 
keeping  the  temperature  of  the  body  up  to  a  point,  which  it  can  only  attain 
occasionally,  and  under  peculiar  circumstances,  in  the  Articulata,  and  which 
it  never  reaches  in  the  Mollusca.  This  involves  an  energetic  performance  of 
the  functions  of  respiration  and  circulation ;  and  these  again  require  consider- 
able activity  of  digestion.  All  the  Vertebrata  have  red  blood,  which  is  pro- 
pelled through  the  system  by  a  distinct  muscular  heart ;  and  the  number  of 
corpuscles,  which  any  given  amount  of  the  fluid  contains,  bears  a  nearly  con- 
stant proportion  to  the  ordinary  temperature  of  the  animal.  They  are  further 
distinguished  from  Articulata  by  a  character  which  seems  of  little  importance, 
but  which  is  very  constant  in  each  group.  Whilst  the  mouth  of  the  latter  is 
furnished  with  two  or  three  pairs  of  jaws  which  open  sideways,  that  of  the 
former  has  never  more  than  one  pair  of  jaws,  which  are  placed  one  above  or 
before  the  other;  and  these  jaws  are  usually  armed  with  teeth,  which  are  very 
analogous  in  their  structure  to  bone. 

General  characters  of  Fishes. 

37.  The  Vertebrata  are  subdivided  into  classes,  principally  according  to 
their  mode  of  performing  the  functions  of  respiration  and  reproduction.  -Thus, 
FISHES  are  at  once  separated  from  all  other  groups,  from  the  circumstance  of 
their  being  adapted,  like  the  aquatic  Invertebrata,  to  aerate  their  blood  by 
gills;  and  being  hence  enabled  to  inhabit  water  during  their  whole  lives, 
without  the  necessity  of  coming  to  the  surface  to  breathe.  The  low  amount 
of  their  respiration  prevents  their  bodies  from  ever  attaining  a  temperature 
much  above  that  of  the  surrounding  medium;  hence  they  are  spoken  of  as 
cold-blooded.  Further,  they  are  oviparous ;  an  ovum  or  egg  being  deposited 
by  the  parent,  from  which,  in  due  time,  the  young  makes  its  way;  or  if,  as 
sometimes  happens,  the  ovum  is  retained  within  the  body  of  the  parent 
until  it  is  hatched,  the  young  animal,  though  produced  alive,  is  not  subse- 
quently dependent  upon  its  parent  for  support.  In  many  respects,  the  organ- 
ization of  Fishes  is  not  much  advanced  beyond  that  of  the  higher  Mol- 
lusca. Their  respiratory  apparatus  has  the  same  character;  and  the  organs 
by  which  the  blood  is  depurated  of  its  superfluous  azote,  rather  correspond 
with  the  temporary  Corpora  Wolffiana  of  higher  animals,  than  with  their 
true  kidneys  (§  669,  670).  The  vertebral  column  itself  is  often  very  imper- 
fectly developed;  in  a  large  proportion  of  the  group,  the  skeleton  is  cartila- 
ginous only;  and  in  the  lowest  species,  it  does  not  even  manifest  a  distinct 
division  into  vertebrae.  Living  habitually  in  an  element  which  is  nearly  of 
the  same  specific  gravity  with  their  own  bodies,  Fishes  have  no  weight  to  sup- 
port, and  have  only  to  propel  themselves  through  the  water.  Accordingly  we 
find  their  structure  adapted  rather  for  great  freedom  of  motion  than  for  firm- 
ness and  solidity;  and  as  progressive  motion  is  chiefly  effected  by  the  lateral 
action  of  the  spine,  the  vertebrae  are  so  united  as  to  move  very  readily  upon 
one  another.  Instead  of  being  articulated  together  by  surfaces  nearly  flat, 
as  in  Mammalia,  or  by  ball-and-socket  joints,  as  in  Serpents,  they  have  both 
their  surfaces  concave ;  and  these  glide  over  a  bag  of  fluid  (the  representa- 
tive of  the  invertebral  substance  in  the  higher  animals)  which  is  interposed 
between  each  pair.  The  tail  is  flattened  vertically;  so  as,  by  its  lateral 
stroke,  to  propel  the  Fish  through  the  water.  By  this  character,  true 
Fishes  are  distinguished  from  those  aquatic  Mammalia,  which  are  adapted  to 


GENERAL  CHARACTERS  OF  REPTILES.  47 

inhabit  their  element,  and  which  commonly  receive  the  same  designation;  for 
the  latter,  being  air-breathing  Animals,  are  obliged  to  come  frequently  to  the 
surface  to  respire ;  and  their  tail  is  flattened  horizontally,  to  enable  them  to  do 
this  with  facility.  The  lateral  surface  of  the  body  of  Fish  is  further  extended 
above,  by  the  projection  of  the  dorsal  fin,  which  is  supported  on  prolongations 
of  the  spines  of  the  vertebras ;  and  below,  by  the  abdominal  fin,  which  also  is 
placed  on  the  median  line ;  these  will,  of  course,  increase  the  power  of  the 
lateral  stroke  of  the  body,  and  can  only  be  moved  with  the  spine.  The  pec- 
toral and  ventral  fins  on  the  other  hand, — the  former  of  which  answer  to  the 
superior  extremities,  and  the  latter  to  the  inferior  extremities  of  Man, — serve, 
by  their  independent  movements,  rather  as  steering  than  as  propelling  organs ; 
and  they  also  assist  in  raising  and  depressing  the  animal  through  the  water. 
The  scales  with  which  the  bodies  of  all  Fishes  are  covered,  are  frequently  of 
a  bony  hardness,  and  sometimes  form  a  firmly-jointed  casing,  in  which  the 
trunk  is  completely  enclosed  ;  this  is  especially  the  case,  when  the  internal 
skeleton  is  imperfectly  developed ;  so  that  here  we  have  an  approach  to  the 
character  of  the  Invertebrata. 

38.  The  swimming-bladder,  as  it  is  commonly  termed,  of  the  Fish,  is  not 
an  organ  sui  generis  ;  but  is  ascertained,  by  comparison  with  the  pulmonary 
sacs  of  the  lower  Reptiles,  to  be  a  rudimentary  lung.     It  does  not,  however, 
give  any  assistance  in  the  aeration  of  the  blood,  except  in  a  few  instances ;  but 
seems  to  be  in  general  subservient  to  the  elevation  and  depression  of  the  body 
in  its  element.     The  heart  of  the  Fish  is  extremely  simple  in  its  construction 
containing  two  cavities  only;  and  the  course  of  the  circulation  is  equally  simple. 
The  blood,  which  returns  from  the  body  in  a  venous  condition,  is  received  into 
the  single  auricle  or  recipient  cavity ;  and  from  this  it  passes  into  the  ventricle 
or  propellent  cavity.     The  latter  forces  it  into  a  large  trunk,  which  subdivides 
into  branches  that  are  distributed  to  the  branchial  arches  on  each  side ;  and  in 
these  it  undergoes  aeration.     Being  collected  from  the  gills  by  returning  ves- 
sels, the  blood,  now  become  arterial  in  its  character,  is  transmitted  to  the  large 
systemic  trunk,  the  aorta,  by  which  it  is  distributed  through  the  system, — 
returning  again  to  the  heart,  when  it  has  passed  through  the  organs  and  tissues 
of  the  body.     Hence  it  is  evident  that  the  whole  of  the  blood  passes  through 
the  gills  before  it  goes  a  second  time  to  the  system ;  by  which  the  imperfection 
of  the  aerating  process  itself  is  in  some  degree  compensated.     There  is  a 
special  provision,  too,  for  renewing  by  muscular  power  the  stratum  of  water 
in  contact  with  the  gills ;   continual  currents  being  sent  over  them  from  the 
pharynx,  with  which  their  cavity  communicates.     It  is  worth  noticing,  that 
whilst,  in  the  Osseous  Fishes,  there  is  a  single  large  external  gill-opening  on 
either  side,  with  a  valve-like  operculum  or  gill-cover,  there  are,  in  the  Cartila- 
ginous Fishes,  several  slits  on  each  side  of  the  neck,  one  corresponding  with 
each  branchial  arch.     Similar  apertures  in  the  neck  may  be  seen  in  the  em- 
bryo of  Man  and  of  other  Mammalia,  as  well  as  of  Birds  and  Reptiles,  at  the 
time  that  the  circulation  is  in  the  condition  of  that  of  the  Fish, — the  heart 
possessing  only  two  cavities,  and  the  blood  being  first  propelled  through  a  series 
of  branchial  arches. 

General  characters  of  Reptiles. 

39.  The  class  of  REPTILES  is  oviparous  and  cold-blooded,  like  that  of  Fishes ; 
but  the  animals  belonging  to  it  are  formed  to  breathe  air,  and  to  inhabit  the 
surface  of  the  earth, — the  few  which  are  adapted  to  make  the  water  their 
dwelling,  being. obliged  to  come  to  the  surface  to  breathe.     Although  they 
breathe  air,  however,  their  respiration  is  not  usually  so  energetic  as  that  of 
Fishes;  and  their  general  activity  is  much  less.     The  heart  possesses  three 


48  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

cavities,  one  of  which  receives  the  blood  from  the  lungs,  and  another  from  the 
general  system;  the  arterial  and  the  venous  blood  contained  in  these  two 
auricles  respectively,  are  transmitted  to  the  third  or  propelling  cavity,  the 
ventricle,  where  they  are  mixed;  and  the  half-arterialized  fluid  is  then  trans- 
mitted to  the  system  at  large,  a  part  being  sent  to  the  lungs.  Thus  only  a 
portion  of  the  blood  expelled  from  the  heart  is  exposed  to  the  influence  of  the 
air ;  and  that  which  is  transmitted  to  the  body  is  very  imperfectly  arterialized. 
In  some  of  the  higher  Reptiles,  as  the  Crocodile,  the  ventricle  is  double,  as 
in  the  superior  Vertebrata ;  and  the  course  of  the  circulation  is  so  arranged, 
that  pure  arterial  blood  shall  go  to  the  head,  where  it  is  most  required, 
whilst  a  mixed  fluid  is  sent  to  the  rest  of  the  body.  This  plan  exactly  cor- 
responds with  the  one  which  is  adopted  in  the  circulation  of  the  Human 
foetus,  from  the  time  of  the  formation  of  the  four  cavities  in  its  heart,  and  of 
the  permanent  system  of  vessels,  up  to  the  period  of  birth.  The  imperfect 
arterialization  of  the  blood  in  Reptiles  causes  a  great  degree  of  general  inert- 
ness in  their  functions.  Their  motions  are  principally  confined  to  crawling  and 
swimming  ;  their  general  habits  are  sluggish,  and  their  sensations  are  obtuse ; 
and  their  nutritive  functions  are  very  slowly  performed.  Hence  they  can 
exist  for  a  long  time  with  a  very  feeble  exercise  of  these  functions,  under  cir- 
cumstances that  would  be  fatal  to  animals  in  which  they  are  performed  with 
greater  activity.  In  cold  and  temperate  climates,  they  pass.the  whole  winter 
in  a  state  of  torpidity;  and  at  other  seasons,  they  may  be  kept  during  a  long 
time  from  their  due  supplies  of  food  and  air,  without  appearing  to  suffer  much 
inconvenience. 

40.  In  regard  to  the  structure  of  their  skeleton,  and  the  external  form  of  the 
body,  there  is  a  considerable  difference  among  the  sev'eral  orders  of  Reptiles. 
Thus,  Tortoises,  Lizards  and  Serpents,  differ  from  each  other  so  widely,  that  a 
common  observer  would  separate  them  completely ;  and  yet  they  not  only  agree 
in  all  the  foregoing  characters,  but  pass  into  one  another  by  links  of  transition  so 
gradual,  that  it  is  even  difficult  to  classify  them.  They  differ,  however,  more 
in  the  configuration  of  the  accessory  parts  than  in  the  structure  of  the  essential 
portion  of  the  skeleton, — the  spinal  column.  This  is  characterized  by  the 
ball-and-socket  articulation  of  the  vertebrae,  each  vertebra  liaving  one  surface 
convex,  and  the  other  concave,  a  structure  which  is  more  strongly  marked  in 
Serpents,  whose  movements  are  performed  chiefly  by  the  flexion  of  the  spinal 
column  itself,  than  it  is  in  the  other  tribes.  The  chief  characteristic  of  the 
Tortoise  tribe,  is  the  shell  or  case  in  which  the  body  is  contained.  The  upper 
arch  of  this  shell,  termed  the  carapace,  is  formed  by  a  bony  expansion  from 
the  edges  of  the  ribs,  which  is  covered  by  a  set  of  horny  plates,  that  are  to  be 
regarded  (like  smaller  scales)  as  epidermic  appendages.  The  under  portion, 
termed  the  plastron,  is  composed  of  the  sternum,  which  is  in  like  manner 
extended  laterally.  In  the  land-tortoises,  this  usually  forms  a  complete  floor; 
but  in  the  aquatic  species,  a  part  is  commonly  absent,  the  interval  being  filled 
up  by  cartilage  and  membrane.  The  skeleton  of  the  Lizards  is  formed  more 
upon  the  general  plan  of  that  of  Mammalia,  but  may  be  readily  distinguished 
from  it.  The  sternum  is  usually  prolonged  over  the  front  of  the  abdomen, 
and  the  ribs  are  continued  through  a  much  larger  part  of  the  spinal  column ; 
of  these  abdominal  ribs,  the  white  lines  across  the  recti  muscles  in  the  higher 
Vertebrata  are  evidently  the  rudiments.  In  the  higher  Lizards,  the  power  of 
locomotion  is  almost  entirely  delegated  to  the  extremities ;  but  in  the  less  typi- 
cal species,  the  body  and  tail  are  much  prolonged,  so  as  to  present  a  serpenti- 
form  aspect ;  and  first  one  pair  of  feet,  and  then  the  other  disappear,  until  the 
form  is  altogether  that  of  the  Serpent.  Even  in  Serpents,  however,  rudiments 
of  extremities  are  frequently  to.  be  found;  but  their  mode  of  progression  is  very 
different,  and  these  rudiments  are  of  no  assistance  to  them.  The  most  re- 


GENERAL  CHARACTERS  OF  REPTILES.  49 

markable  feature  in  the  Serpent's  skeleton,  besides  the  absence  of  legs,  and 
the  large  number  of  ribs  and  vertebrae,  is  the  deficiency  of  a  sternum ;  through 
the  absence  of  this,  the  extremities  of  the  ribs  are  free,  and  they  become  in 
fact  the  fixed  points,  on  which  the  animal  crawls,  when  advancing  slowly  for- 
wards, in  a  manner  which  bears  a  strong  resemblance  to  the  progression  of  the 
Centipede. 

41.  Although  the  configuration  of  the  cranium  varies  much  in  the  different 
orders  of  Reptiles,  yet  there  is  a  remarkable  agreement  in  certain  general 
characters,  and  in  the  general  degree  of  development.     It  consists  of  a  much 
larger  number  of  parts  than  are  to  be  found  in  the  cranium  of  adult  Birds  or 
Mammalia ;  each  principal  bone  being  subdivided,  as  it  were,  into  smaller 
ones.     This  condition  exactly  corresponds  with  that  which  may  be  observed 
during  the  process  of  ossification  in  higher  Vertebrata ;  for  each  of  the  larger 
bones  of  the  cranium  is  formed  from  several  centres  of  ossification ;  so  that,  if 
the  cranium  of  a  foetus  or  young  infant  be  macerated,  it  will  fall  into  a  number 
of  pieces  nearly  corresponding  with  those  of  the  Reptile's  skull.    The  different 
orders  of  Reptiles  have  a  close  agreement  in  various  other  points ;  especially 
in  the  degree  of  development  of  their  several  organs  of  nutrition.     Thus,  in  all 
of  them,  the  lungs,  though  commonly  of  large  size,  are  so  little  subdivided,  as 
really  to  expose  but  a  small  extent  of  surface.     The  glandular  structures,  too, 
are  formed  upon  a  much  more  simple  type  than  is  characteristic  of  the  warm 
blooded  Vertebrata.     They  all  agree,  moreover,  in  having  the  body  covered 
with  scales ;  which,  though  generally  small,  are  sometimes  large  flattened 
plates. 

42.  Between  Fishes  and  true  Reptiles,  there  is  a  group  that  remarkably 
combines  the  characters  of  both ;  being  composed  of  animals  which  come  forth 
from  the  egg  in  the  condition  of  Fishes,  but  which  afterwards  attain  a  form 
and  structure  closely  corresponding  with  that  of  true  Reptiles.     This  group, 
consisting  of  the  Frog  and  its  allies,  is  sometimes  associated  as  an  order  (Ba- 
trachia)  of  the  class  of  Reptiles ;  and  is  sometimes  made  to  rank  as  a  distinct 
class,  the  Amphibia.     The  Tadpole  or  larva  of  the  Frog  is  in  every  essential 
respect  a  Fish.     Its  respiration  and  circulation,  its  digestion  and  nutrition,  its 
locomotion  and  sensation,  are  entirely  accordant  with  those  of  Fishes.     The 
body  is  destitute  of  members  for  progression,  but  is  propelled  through  the 
water  by  the  lateral  undulations  of  the  spinal  column,  which  is  articulated  in 
the  same  manner  as  is  that  of  Fishes.     At  a  certain  period,  a  metamorphosis 
commences,  in  which  almost  every  organ  in  the  body  undergoes  an  essential 
change.     Lungs  are  developed,  which  take  the  place  (in  regard  to  their"  func- 
tion) of  the  gills ;  and  the  latter  are  atrophied.     The  auricle  of  the  heart  is 
divided  into  two ;  and  the  circulation  is  performed  on  the  plan  of  that  of  the 
true  Reptile.     Two  pairs  of  members  are  usually  formed,  to  which,  when  they 
are  fully  developed,  the  power  of  progression  is  committed, — the  tail  disappear- 
ing ;  in  some  species,  however,  the  tail  remains,  and  the  extremities  are  small. 
The  digestive  system  undergoes  a  remarkable  alteration, — the  intestinal  canal, 
which  was  previously  of  enormous  length  in  proportion  to  the  body,  being  now 
considerably  shortened,  in  accordance  with  the  different  kind  of  food  on  which 
the  animal  has  to  subsist.     The  mode  of  articulation  of  the  spinal  column,  also, 
undergoes  a  change,  which  brings  it  to  the  type  of  that  of  Reptiles.     On  the 
whole,  there  scarcely  appears  sufficient  reason  for  separating  these  animals,  in 
their  adult  condition,  from  the  class  of  Reptiles.     The  most  important  point  of 
difference  is  the  nakedness  of  the  skin,  by  which  the  Batrachia  may  be  at  once 
distinguished,  even  when  their  external  configuration  approaches  that  of  Rep- 
tiles in  general.     In  this  manner,  the  common  Salamander  or  Water-Newt 
may  be  recognized  as  belonging  to  this  group,  though  we  should  otherwise 
have  placed  it  among  the  Lizards ;  and  the  Ccecilia,  which  has  the  form  of 

5 


50  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

the  Serpent,  is  in  like  manner  known  to  be  really  allied  to  the  Frog.  An 
acquaintance  with  the  history  of  these  animals  confirms  such  an  arrangement, 
by  showing  that  the  Salamander  and  the  Coecilia*  undergo  a  metamorphosis ; 
breathing  by  gills,  and  having  the  general  structure  of  Fishes,  in  the  early 
part  of  their  lives. 

43.  Besides  those  animals,  however,  which  attain  the  condition  of  perfect 
Reptiles,  this  group  contains  several  whose  development  is  arrested,  as  it  were, 
in  an  intermediate  or  transition  state  ;  their  adult  form  presenting  a  remarka- 
ble mixture  of  the  characters  of  the  two  classes,  which  they  thus  connect. 
This  is  the  case  in  the  Proteus,  Siren,  and  other  less  known  species,  which 
retain  their  gills  through  the  whole  of  their  lives,  whilst  their  lungs  are  at  the 
same 'time  developed ;  so  that,  as  they  can  respire  in  either  air  or  water,  they 
are  the  only  true  amphibious  animals.     In   their  entire  organization,  they 
correspond  with  the  Tadpole  of  the  Frog  at  an  advanced  period  of  its  metamor- 
phosis ;  and  it  is  a  most  interesting  fact  (which  has  been  established  by  the 
experiments  of  Dr.  W.  F.  Edwards)  that  if  Tadpoles  be  kept  in  such  a  man- 
ner as  to  be  freely  supplied  with  food,  and  exposed  to  a  constantly-renewed 
current  of  water,  but  be  secluded  from  light  and  from  the  direct  influence  of 
the  solar  heat,  they  will  continue  to  grow  as  Tadpoles ;  their  metamorphosis 
being  checked.     The  metamorphosis  of  the  Batrachia  closely  corresponds  with 
that  of  Insects ;  the  young  animal,  in  each  case,  at  the  time  of  its  emersion 
from  the  egg,  having  a  resemblance,  in  all  essential  particulars,  to  a  class  be- 
low that  to  which  it  is  ultimately  to  belong.     This  kind  of  metamorphosis  is 
by  no  means  confined  to  them,  however ;  for  the  gradual  extension  of  our 
knowledge  of  the  early  history  of  different   tribes  of  animals,  is  constantly 
bringing  to  light  new  facts  of  the  same  kind.     The  Polypes  and  lower  Mollus- 
ca,  for  instance,  come  forth  from  the  egg,  and  swim  about  for  some  time,  in  a 
condition  which  can  scarcely  be  termed  animal;  for  there  is  not  even  a  mouth 
leading  to  a  digestive  cavity,  nor  are  there  any  other  organs  of  locomotion  than 
the  cilia,  the  action  of  which  is  involuntary.     And,  in  tracing  the  development 
of  the  Human  embryo,  we  shall  find  that  it  undergoes  a  series  of  progressive 
changes  equally  remarkable; — the  principal  difference  being,  that  these  changegf 
are  not  so  arranged  in  harmony  with  each  other,  as  to  cause  the  embryo  to 
present,  at  any  one  time,  the  combination  of  characters  which  belong  to  the 
Fish,  Reptile,  &c.,  or  to  enable  it  to  sustain  an  independent  existence. 

General  characters  of  Birds. 

44.  From  Reptiles  to  BIRDS,  the  transition  would  seem  rather  abrupt ;  since 
the  latter  class  is,  in  almost  every  respect,  the  opposite  of  the  former.     Never- 
theless it  would  seem  to  have  been  affected  by  the  now  extinct  Pterodactylus, 
which  combined  in  a  most  remarkable  degree  the  characters  of  the  two  groups. 
Birds  are,  like  Fishes  and  Reptiles,  oviparous  Vertebrata;  but  they  differ 
essentially  from  both,  in  being  themselves  warm-blooded,  and  in  the  assistance 
which  they  afford  by  their  own  heat  in  the  development  of  the  ovum.     Birds 
correspond  with  Mammalia,  in  possessing  a  heart  with  four  cavities,  and  a 
complete  double  circulation ;  by  which  the  whole  of  the  blood,  that  has  circu- 
lated through  the  body,  is  exposed  to  the  influence  of  the  air,  before  being 
again  transmitted  to  the  system.     This  high  amount  of  oxygenation  of  the 
blood  is  accompanied  by  great  activity  and  energy  of  all  the  organic  functions, 
acuteness  of  the  senses,  and  rapid  and  powerful  locomotion ;  as  well  as  by  the 
evolution  of  a  degree  of  heat,  superior  to  that  which  we  ordinarly  meet  with 
among  the  Mammalia.     The  temperature  of  Birds  ranges  from  about  104°  to 

*  This  fact,  in  regard  to  the  Ccecilia,  has  only  been  recently  substantiated.    See  Annals 
of  Natural  History,  May  1841. 


GENERAL  CHARACTERS  OF  BIRDS.  51 

The  lowest  is  in  the  aquatic  species,  whose  general  activity  is  much 
less  than  that  of  the  tribes,  which  spend  most  of  their  time  in  the  air ;  the 
highest  is  among  those  distinguished  for  the  rapidity  and  energy  of  their  flight, 
such  as  the  Swallow. 

45.  Birds  have  been  denominated,  and  not  inappropriately,  the  Insects  of  the 
Vertebrated  series.     As  in  the  animals  of  that  class,  we  find  the  whole  struc- 
ture peculiarly  adapted  to  motion,  not  in  water,  nor  upon  solid  ground,  but  in 
the  elastic  and  yielding  air.     It  is  impossible  to  conceive  any  more  beautiful 
series  of  adaptions  of  structure  to  conditions  of  existence,  than  that  which  is 
exhibited  in  the  conformation  of  the  Bird,  with  reference  to  its  intended  mode 
of  life.     In  order  to  adapt  the  Vertebrated  animal  to  its  aerial  residence,  its 
body  must  be  rendered  of  as  low  specific  gravity  as  possible.     It  is  further 
necessary  that  the  surface  should  be  capable  of  being  greatly  extended  ;  and 
this  by  some  kind  of  appendage  that  should  be  extremely  light,  and  at  the 
same  time  possessed  of  considerable  resistance.     The   degree  of  muscular 

'  power  required  for  support  and  propulsion  in  the  air,  involves  the  necessity  of 
a  very  high  amount  of  respiration  (§  392),  for  which  it  has  been  seen  that  an 
express  provision  exists  in  Insects ;  and  as  the  general  activity  of  the  vital 
processes  depends  greatly  upon  the  high  temperature  which  this  energetic 
respiration  keeps  up,  a  provision  is  required  for  keeping  in  this  heat,  and  not 
allowing  it  to  be  carried  away  by  the  atmosphere  through  which  the  Bird  is 
rapidly  flying. 

46.  The  first  and  third  of  these  objects, — the  lightening  of  the  body,  and 
the  extension  of  the  respiratory  surface, — are  beautifully  fulfilled  in  a  mode, 
which  will  be  found  to  correspond  with  the  plan  adopted  for  the  same  purpose 
in  Insects.     The  air  which  enters  the  body,  is  not  restricted  to  a  single  pair  of 
air-sacs  or  lungs  placed  near  the  throat ;  but  is  transmitted  from  the  true  lungs, 
to  a  series  of  large  air-cells,  disposed  in  the  abdomen  and  in  various  other  parts 
of  the  body.     Even  the  interior  of  the  bones  is  made  subservient  to  the  same 
purpose  ;  being  hollow,  and  lined  with  a  delicate  membrane,  over  which  the 
blood-vessels  are  minutely  distributed.    In  this  manner,  the  respiratory  surface 
is  greatly  extended ;  whilst,  by  the  large  quantity  of  air  introduced  into  the 
mass,  its  specific  gravity  is  diminished.     The  subservience  of  the  cavities  in 
the  bones  to  the  respiratory  function,  is  curiously  shown  by  the  fact,  which 
has  been  ascertained  both  accidentally  and  by  a  designed  experiment,  that, 
if  the  trachea  of  a  Bird  be  tied,  and  an  aperture  be  made  in  one  of  the  long 
bones,  it  will  respire  through  this. 

47.  The  other  two  objects, — the  extension  of  the  surface,  and  the  retention 
of  the  heat  within  the  body, — are  also  accomplished  in  combination,  by  a  most 
beautiful  and  refined  contrivance,  the  covering  of  feathers.  Like  hair  or  scales, 
feathers  are  to  be  regarded  as  appendages  to  the  cutis ;  the  stem  is  formed 
from  it  by  an  apparatus,  which  may  be  likened  to  a  hair-bulb  on  a  very  large 
scale ;  but  there  are  some  additional  parts  for  the  production  of  the  laminse, 
which  form  the  vane  of  the  feather,  and  which  are  joined  to  the  stem  during 
its  development.     These  laminae,  when  perfectly  formed,  are  connected  by 
minute  barbs  at  their  edges,  which  hook  into  one  another,  and  thus  give  the 
necessary  means  of  resistance  to  the  air.     The  substance  «of  which  feathers 
consists,  is  a  very  bad  conductor  of  heat ;  and  when  they  are  lying  one  over 
the  other,  small  quantities  of  air  are  included,  which  still  further  obstruct  its 
transmission  by  their  non-conducting  power.     Thus  the  two  chief  objects  are 
fulfilled  ; — power  of  resistance  and  slow  conducting  properties  being  obtained, 
in  combination  with  lightness  and  elasticity.     At  the  two  extremes  of  the  class, 
however,  we  meet  with  remarkable  modifications  in  the  typical  structure^  of 
feathers.     In  the  Penguin,  those  which  cover  the  surface  of  the  wings  have 
a  strong  resemblance  to  scales  ;  and  the  wings  are  not  employed  to  raise  this 


52  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

Bird  in  the  air,  but  only  to  propel  it  through  water  (as  fins  would  do)  by  their 
action  on  the  liquid.  On  the  other  hand,  in  the  Ostrich  tribe,  the  laminae  of 
the  feather  are  quite  distinct  from  each  other,  and  no  longer  form  a  con- 
tinuous surface ;  so  that  the  feathers  more  resemble  branching  hairs.  Here 
the  wings  are  almost  or  completely  absent ;  the  birds  of  this  tribe  being  con- 
stantly upon  the  ground,  propelling  themselves  by  running,  and  approaching 
the  Mammalia  in  many  points  of  their  conformation. 

48.  The  bony  framework  of  Birds  presents  many  remarkable  adaptations  to 
the  same  purposes.     In  the  first  place  it  is  to  be  remarked,  that  the  faculty  of 
locomotion  is  here  entirely  delegated  to  the  extremities ;  and  that  the  skeleton 
of  the  trunk  must  be  consolidated,  in  proportion  to  the  power  with  which  they 
are  to  be  endowed,  in  order  to  afford  their  muscles  a  firm  attachment  (§  33.) 
Just  as  the  segments  of  the  external  skeleton  of  the  Articulata,  therefore,  are 
consolidated  in  Insects,  do  we  find  that  the  vertebral  column  and  its  appen- 
dages are  firmly  knit  together,  in  the  upper  part  of  the  trunk  of  Birds.     The 
vertebrae  are  closely  united  to  each  other ;  and  the  ribs  are  connected  with 
the  sternum  by  bony  prolongations  of  the  latter,  instead  of  by  cartilages.     This 
union  is  so  arranged,  that  the  state  of  expansion  is  natural  to  the  thorax,  whilst 
that  of  contraction  is  forced.     Reptiles  possess  but  a  very  imperfect  mechan- 
ism for  inflating  their  lungs.     Being  destitute  of  a  diaphragm,  they  are  obliged 
to  force  air  into  the  chest,  by  a  process  resembling  deglutition  ;  so  that,  strange 
as  it  may  appear,  a  reptile  may  be  suffocated  by  holding  its  mouth  open.    The 
diaphragm  is  absent  among  Birds,  as  among  Reptiles  ;  except  in  a  few  species 
which  most  nearly  approach  the  Mammalia.     But  its  deficiency  is  compen- 
sated by  this  contrivance,  which  keeps  the  lungs  and  air-sacs  always  full, 
except  when  the  Bird,  by  a  muscular  effort,  expels  the  air  from  them,  in  order 
that  they  may  be  re-filled  by  a  fresh  supply.     By  this  means,  also,  the  specific 
gravity  of  the  body  is  more  constantly  diminished  than  it  could  be  if  the  lungs 
had  been  subjected  to  the  constantly-alternating  contractions  and  expansions 
which  they  perform  in  Mammalia.     It  is  worthy  of  remark,  that  the  air  which 
enters  the  bones  and  the  air-sacs,  passes  through  the  lungs  both  on  its  entrance 
and  return ;  so  as  to  yield  to  their  capillaries  all  the  oxygen  which  they  can 
take  from  it,  and  of  which  the  blood  that  it  has  elsewhere  met  with  has  not 
deprived  it.     It  is  only  in  the  lungs  that  it  meets  with  purely  venous  blood  ; 
for  they  alone  receive  the  branches  of  the  pulmonary  artery  ;  the  vessels  which 
are  distributed  upon  the  respiratory  surface  of  the  air-sacs  and  bones  being  a 
part  of  the  systemic  circulating  apparatus.     Hence  we  may  regard  this  curi- 
ous provision,  as  being  partly  designed  for  the  aeration  of  the  blood  in  its 
course  through  the  system,  (this,  it  will  be  remembered,  being  the  sole  mode 
in  which  the  function  is  performed  in  Insects,)  and  partly  for  supplying  the 
lungs  with  air  as  from  a  reservoir,  during  the  violent  actions  of  flight. 

49.  The  articulation  of  the  anterior  extremity  with  the  trunk  exhibits  a 
peculiar  provision  for  strength  and  power  which  we  find  in  no  other  Verte- 
brata.     The  two  clavicles  are  united  together  on  the  central  line,  forming  the 

furcula  or  merry-thought ;  and  the  use  of  this  is  to  keep  the  shoulders  apart, 
notwithstanding  the  opposing  force  exerted  by  the  pectoral  muscles  in  the 
action  of  flight.  It  is  generally  firm,  and  its  angle  open  in  proportion  to  the 
power  of  the  wings.  Besides  this  bone,  there  is  another  connecting  the  ster- 
num with  the  scapula  on  each  side ;  this  is  the  coracoid  bone,  which  in  Man 
and  other  Mammalia  is  scarcely  developed,  being  merely  a  short  process  which 
dose  not  reach  the  sternum.  The  sternum  of  Birds  usually  exhibits  a  very 
remarkable  development  on  the  median  line  ;  an  elevated  keel  or  ridge  being 
seen  on  it,  which  serves  for  the  attachment  of  the  powerful  muscles  that  de- 
press the  wings.  In  the  great  development  of  the  sternum,  Birds  have  some 
analogy  with  the  Turtle  tribe  (which  they  also  resemble  in  the  deficiency  of 


GENERAL  CHARACTERS  OF  BIRDS. 

teeth,  and  in  the  development  of  a  horny  covering  to  the  jaws) ;  but  in  these, 
the  lateral  elements  of  the  sternum  are  the  parts  most  developed,  whilst  in 
Birds  it  is  the  central  portion  which  exhibits  the  peculiarity.  From  the  depth 
of  the  keel  of  the  sternum,  a  judgment  may  be  formed  of  the  thickness  of  the 
pectoral  muscles,  and  thence  of  the  powers  of  flight ;  in  the  Ostrich  tribe, 
where  the  wings  are  not  sufficiently  developed  to  raise  the  bird  off  the  ground, 
the  sternum  is  quite  flat,  as  in  the  Mammalia.  The  want  of  flexibility  in  the 
trunk  is  counterbalanced  by  the  length  and  flexibility  of  the  neck ;  the  num- 
ber of  cervical  vertebrae  is  very  considerable,  varying  from  12  to  23, — the 
highest  number  being  present  in  the  Swan  tribe.  They  are  so  articulated, 
that  the  head  can  be  turned  completely  round,  or  moved  in  any  direction. 
The  anterior  extremities  of  Birds  being  solely  adapted  to  sustain  them  in 
flight,  the  posterior  are  necessarily  modified  for  their  support  on  the  ground. 
They  are  usually  placed  rather  far  back ;  but  the  spine  has  a  position  more 
inclined  than  horizontal,  so  that  the  weight  may  not  be  altogether  thrown  for- 
wards. The  trunk  is  supported  on  the  thighs  by  powerful  muscles ;  and 
there  is  another  series,  which  passes  from  the  lower  part  of  the  spine  continu- 
ously to  the  toes,  turning  over  the  knee  and  heel,  in  such  a  manner  that  the 
flexion  of  these  joints  shall  tighten  the  tendons ;  by  this  contrivance,  the 
simple  weight  of  the  body  flexes  the  toes,  and  Birds  are  thus  enabled  to  main- 
tain their  position  during  sleep,  without  any  active  muscular  effort. 

50.  Not  only  do  Birds  resemble  Insects  in  their  general  structure  and  mode 
of  life,  but  also  in  the  peculiar  development  of  the  instinctive  powers.    Under 
the  direction  of  these,  the  place  for  their  nest  appears  to  be  selected;  their 
materials  collected ;  the  nests  themselves  built,  and  the  young  reared  in  them ; 
the  migrations  are  performed;  and  many  curious  stratagems  are  employed  to 
obtain  food.     It  is  sufficient  to  indicate  these  in  general  terms;  since  it  is  well 
known,  that  the  habits  of  Birds  have  peculiarities  restricted  to  each.species ;  and 
that  in  all  the  individuals  of  each  species,  they  are  as  precisely  alike  as  their 
circumstances  will  admit.     Nevertheless,  there  is  observed  in  Birds  a  degree 
and  kind  of  adaptation  to  varying  conditions,  which  Insects  do  not  possess, 
and  which  display  an  amount  of  intelligence  far  superior  to  what  is  found  in 
that  class  (§  280).     This  is  evinced  also  in  their  educability ;  for  no  animal 
can  be  taught  to  perform  actions  which  are  not  natural  to  it,  unless  it  possesses 
in  a  considerable  degree  the  powers  of  memory  and  association,  at  least,  if 
not  some  of  the  higher  mental  faculties,  such  as  the  power  of  perceiving  and 
comparing  the  relations  of  ideas.     Moreover,  in  the  domesticability  of  many 
tribes  of  Birds,  \ve  see  this  educability  combined  with  a  degree  of  that  higher 
form  of  attachment  to  Man,  which  is  so  strikingly  exhibited  by  certain  spe- 
cies of  Mammalia.     The  development  of  the  senses  of  Birds  varies  in  differ- 
ent tribes,  according  to  the  mode  in  which  they  are  adapted  to  obtain  their 
prey.     The  sight  is  almost  always  extremely  acute,  and  is  their  chief  means 
of  seeking  food ;  and  where  this  would  be  of  comparatively  little  service,  as 
in  the  nocturnal  rapacious  birds,  it  is  compensated  by  a  much  higher  deve- 
lopment of  the  faculty  of  hearing  than  is  usual  amongst  other  tribes.     The 
senses  of  smell,  taste,  and  touch,  do  not  seem  to  be  usually  very  acute  in 
Birds ;  but  there  are  particular  tribes,  in  which  each  of  these  is  more  deve- 
loped than  in  the  rest. 

51.  As  might  be  expected  from  their  analogy  with  Insects,  the  development 
of  the  organs  of  nutrition  (excepting  that  of  the  respiratory -organs)  is  much 
less  striking  in  Birds  than  is  that  of  the  locomotive  apparatus.     The  whole 
cavity  of  the  trunk,  especially  in  Birds  distinguished  for  their  powers   of 
flight,  is  small  in  comparison  with  that  of  the  body ;  but  what  is  wanting  in 
the  size  of  the  organs,  is  made  up  in  their  energy  of  function.     Hence  the 
demand  for  food  is  more  active  in  them  than  in  any  other  class  of  animals. 

5* 


54  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

It  is  interesting  to  observe,  that  there  is  more  bi-lateral  symmetry  in  the 
arrangement  of  the  viscera  than  we  usually  find  in  the  higher  Vertebrata. 
This  is  evidently  connected  with  their  active  locomotive  powers ;  as  it  is  ob- 
viously necessary  that  the  two  sides  of  the  body  should  be  balanced  with  per- 
fect equality,  and  that  their  energy  should  be  exactly  correspondent.  The 
lungs  and  air-sacs  are  precisely  similar  in  size  and  situation  on  the  two  sides ; 
consequently  the  heart  is  placed  on  the  median  line ;  and  the  mode  of  origin, 
from  the  aorta,  of  the  trunks  supplying  the  head  and  upper  extremities,  is 
alike  on  the  two  sides.  The  liver,  also,  is  less  symmetrical  than  we  usually 
find  it  in  the  Mammalia. 

52.  It  has  been  remarked,  that  the  assistance  afforded  by  the  parent,  in  the 
development  of  the  young,  is  greater  in  Birds  than  in  the  lower  Vertebrata ; 
but  is  less  than  in  Mammalia.     Whilst  Reptiles  and  Fishes  show  little  or 
no  concern  for  their  eggs  after  they  have  deposited  them,  Birds  sedulously 
tend  them,  affording  them  not  only  protection  but  warmth,  by  means  of  their 
powerful  heat-producing  apparatus.     The  yolk-bag  of  the  Bird's  egg  is  so 
suspended  in  the  midst  of  the  white  albumen,  that,  when  the  egg  is  laid  upon 
its  side,  it  will  always  rise  to  the  highest  part  of  it;  and  the  relative  weight 
of  the  several  parts  is  further  adjusted  in  such  a  manner,  that  the  cicatricula 
or  germ-spot  shall  always  be  at  the  point  nearest  the  shell,  so  as  to  come  into 
the  closest  proximity  with  the  source  of  heat,  and  also  to  be  in  the  most  imme- 
diate relation  with  the  surrounding  air.     There  are  some  birds,  inhabiting  the 
equatorial  regions,  which  do  not  always  incubate  their  eggs,  trusting  to  the 
solar  heat  for  their  maturation.     It  is  said  that  the  Ostriches  of  the  inter- 
tropical  deserts  are  content  with  covering  their  eggs  with  a  thin  layer  of 
sand,  so  as  to  admit  the  action  of  the  sun  by  day,  and  to  keep  them  warm  at 
night ;  but  that  those  living  under  a  less  constantly  elevated  temperature,  sit 
upon  their  eggs, — if  not  constantly,  at  any  rate  when  the  solar  heat  is  not  suf- 
ficient.    This  statement  has  been  disputed;  but  its  truth  seems  to  be  con- 
firmed by  a  curious  observation  made  by  Mr.  Knight,  that  a  Fly-catcher, 
which  built  for  several  years  in  one  of  his  hot-houses,  sat  upon  its  eggs  when 
the  temperature  was  below  72°,  but  left  them  when  it  rose  above  that  stand- 
ard.    The  degree  of  assistance  afforded  by  the  parent  Birds  to  their  young, 
after  their  emersion  from  the  shell,  varies  much  in  different  tribes ;  in  general 
it   may  be  remarked,  however,  that   it   is   most  prolonged  in   those   which 
ultimately  attain  the  highest  development,  and  especially  in  those  whose  intel- 
ligence  is  the   greatest.     Thus  the  Chicken  and   the  Duckling,  when  just 
hatched,  are  able  to  shift  for  themselves ;  but  among  the  Raptorial  and  Inses- 
sorial  birds,  which  rank  far  higher  in  the  scale,  the  young  are  for  a  long  time 
dependent  upon  the  parent  for  food ;  and  in  the  Parrot  tribe,  which  unques- 
tionably surpasses  all  others  in  intelligence,  the  parent  not  only  supplies  its 
young  with  food  which  it  has  obtained  for  them,  but  partly  nourishes  them  by 
a  milky  secretion  from  the  interior  of  the  craw ;  impregnating  with  this  the 
aliment  which  it  swallows,  and  which  it  afterwards  disgorges  for  its  offspring. 

General  characters  of  Mammalia. 

53.  The  MAMMALIA  are  universally  regarded  as  the  highest  group  in  the 
Animal  kingdom ;  not  only  from  being  the  one  to  which  Man  belongs  (so  far, 
at  least,  as  his  bodily  structure  is  concerned),  but  also  as  possessing  the  most 
complex  organization,  adapted  to  perform  the  greatest  number  and  variety  of 
actions,  and  to  execute  these  with  the  greatest  intelligence.     The  contrast  is 
here  extremely  strong  between  the  reasoning  and  the  instinctive  powers ;  even 
when  we  put  Man  out  of  view.     When  we  compare,  for  example,  the  saga- 
city of  a  Dog,  Monkey,  or  Elephant,  and  the  great  variety  of  circumstances 


GENERAL  CHARACTERS  OF  MAMMALIA.  55 

in  which  they  will  display  an  intelligent  adaptation  of  means  to  ends,  with 
the  limited  operations  of  Insects,  over  which  the  judgment  and  will  seem  to 
have  no  control,  we  cannot  help  being  struck  with  the  difference.  The  former 
are  educable  in  the  highest  degree  next  to  Man ;  the  latter  could  not  be  made 
to  change  their,  habits,  in  any  essential  degree,  by  the  most  prolonged  course 
of  discipline ;  still  the  difference,  in  this  respect,  between  Man  and  the  most 
intelligent  of  other  Mammalia,  is  so  strongly  marked,  that  some  Naturalists 
have  proposed  to  exclude  him  altogether  from  the  classification  of  this  group, 
and  even  from  the  Animal  kingdom.  This  is,  however,  by  no  means  a  phi- 
losophical plan;  since  the  mind  of  Man  is,  in  the  present  state  of  being,  as 
closely  connected  with  its  material  tenement,  as  we  have  reason  to  believe  that 
of  brutes  to  be ;  and  since  there  is  scarcely  any  distinction  of  kind  between  their 
faculties,  which  we  have  a  right  to  assume  as  characteristic, — the  difference 
being  chiefly  in  degree  (§  72).  Man  is  like  them  actuated  by  instinctive  pro- 
pensities7, wrhich  have  an  immediate  bearing  on  his  corporeal  wants ;  an^they 
have,  like  him,  the  power  of  adapting  their  actions  to  gain  certain  feds,  of 
which  they  are  conscious.  A  Dog  or  an  Elephant  may  show  more  real  wis- 
dom, in  controlling  for  a  time  its  instinctive  propensities,  from  the  desire  to 
accomplish  some  particular  object,  than  is  displayed  by  many  Men,  wfco  give 
free  scope  to  the  exercise  of  their  sensual  passions,  although  warned  by  their 
reason  of  the  injurious  consequences  of  such  indulgence. 

54.  This  high  development  of  the  intelligence  in  Mammalia,  is  evidently 
connected  with  the  greatly  prolonged  connection  between  the  parent  and  the 
offspring,  which  we  find  to  be  a  characteristic  of  this  class.     Mammalia  are, 
like  Birds,  warm-blooded  Vertebrata,  possessing  a  complete  double  circula- 
tion ;  and  some  of  them  are  adapted  to  lead  the  life  of  Birds,  passing  a  large 
part  of  their  time  in  darting  through  the  air  on  wings,  in  pursuit  of  Insect 
prey.     But  they  differ  from  Birds  in  this  essential  particular,  that  they  are 
not  oviparous,  but  viviparous,  producing  their  young  alive, — that  is,  in  a  con- 
dition in  which  they  can  perform  spontaneous  movements,  and  can  appro- 
priate nourishment  supplied  to  them  from  without.     But  they  are  not  dis- 
tinguished from  all  other  animals  by  this  character  alone  ;  for  there  are  some 
species  among  Reptiles,  Fishes,  and  even  Insects,  which  produce  their  young 
alive, — the  egg  being  retained  within  the  oviduct  and  hatched  there.     The 
real  distinction  is  that  which  the  name  of  the  class  imports, — the  subsequent 
nourishment  of  the  young  by  suckling.     There  is  another  distinction,  which 
is  not,  however,  equally  applicable  to  the  whole  class.     In  all,  the  yolk-bag  is 
very  small  in  proportion  to  its  size  in  Birds ;  and  the  contents  of  the  ovum, 
instead  of  furnishing  (as  in  that  class)  the  materials  necessary  for  the  develop- 
ment of  the  young  animal,  up  to  the  time  when  it  can  ingest  food  for  itself, 
only  serve  for  the  earliest  set  of  changes  in  which  this  process  consists.     In 
all  the  later  stages  of  the  evolution  of  the  embryo,  it  is  supplied  with  nutri- 
ment directly  imbibed  from  its  parent.     This  is  at  first  accomplished  by  means 
oT  a  series  of  root-like  tufts,  which  are  prolonged  from  the  surface  of  the 
ovum,  and  insinuate  themselves  among  the  maternal  vessels,  without,  how- 
ever, uniting  with  them.     These  tufts  absorb,  from  the  maternal  fluid,  the 
ingredients  necessary  for  the  support  of  the  embryo ;  and  also  convey  back  to 
the  parent  its  effete  particles,  which  are  received  back  into  her  blood,  and  cast 
out  of  her  system,  by  the  processes  of  secretion,  respiration,  &c. 

55.  The  Mammalia  may  be  divided  into  two  sub-classes ;  in  one  of  which 
the  structure  just  described  is  the  greatest  advance  ever  made,  in  the  appara- 
tus by  which  the  foetus  is  nourished ;  whilst  in  the  other,  a  more  concentrated 
form  is  subsequently  assumed  by  it.     The  ovum  of  the  latter  is  delayed  for  a 
longer  period,  in  a  cavity  formed  by  the  union  of  the  two  oviducts,  termed  the 
uterus :  which  can  be  scarcely  said  to  be  developed  in  the  Marsupialia  and 


56  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

Monotremata,  the  two  orders  constituting  the  first  sub-class.  The  vascular 
tufts  proceeding  from  the  chorion  become  especially  developed  at  one  point, 
and  the  vessels  of  the  uterus  are  extremely  enlarged  in  a  corresponding  situa- 
tion ;  the  tufts  dip  down,  as  it  were,  into  a  chamber  formed  by  an  extension  of 
the  inner  lining  of  these  vessels,  and  serve  the  combined  purpose  of  the  roots 
of  plants  and  of  the  branchiae  of  aquatic  animals, — absorbing  from  the  maternal 
blood  the  materials  required  for  the  nourishment  of  the  embryo,  and  aerating 
that  of  the  foetus  by  exposing  it  to  the  influence  of  the  parents  (§  749).  The 
peculiar  organ  thus  formed  is  termed  the  placenta  ;  and  the  two  sub-classes 
of  the  Mammalia  have  thence  received  the  appellations  of  placental  and  non- 
placental.  The  animals  belonging  to  the  latter  present  many  points  of  affinity 
to  Birds,  in  the  structure  of  their  internal  organs.  That  of  the  brain  is  very 
nearly  allied  in  these  two  groups  ;  and  their  amount  of  intelligence  seems,  as 
•  far  as  can  be  determined,  to  bear  a  close  correspondence.  The  Ornithorhyn- 
cus, in  particular,  has  so  many  marks  of  alliance  to  Birds,  in  its  osteology,  as 
well  as  in  its  horny  bill,  and  in  the  spur  on  its  hind  leg  (which  resembles  that 
of  the  Cock),  that  Naturalists  have  much  debated,  whether  it  could  really  be 
termed  a  Mammiferous  animal.  No  positive  evidence  has  yet  been  obtained, 
that  its  young  are  born  alive  ;  but  on  the  other  hand,  there  is  a  strong  reason 
to  believe,  that  they  come  into  the  world  unenclosed  in  the  ovum,  although  in 
a  very  imperfect  condition.  Moreover,  it  has  been  satisfactorily  ascertained, 
that  the  young  are  nourished,  for  some  time  after  their  birth,  by  a  mammary 
secretion,  which  the  organization  of  their  mouth  at  that  period  enables  them 
to  obtain  from  the  parent.  In  the  Marsupialia,  there  is  a  remarkable  compen- 
sation for  the  abrupt  termination  of  the  period  of  uterine  gestation, — the  young 
being  received  into  a  pouch  or  marsupium,  within  which  the  nipple  is  situ- 
ated ;  this  is  extremely  prolonged,  and  the  mouth  of  the  foetus  (for  so  the 
being  must  still  be  regarded)  is  adapted  to  receive  and  hold  on  by  it ;  so  that 
the  little  creature,  which  looks  at  first  more  like  an  earth-worm  than  a  Mam- 
miferous animal,  is  thus  suspended  within  the  protective  pouch,  until  its 
development  is  so  far  advanced,  that  it  can  shift  for  itself  in  the  same  degree 
as  other  new-born  animals  can  do. 

56.  The  period  of  gestation  in  the  higher  class  of  Mammalia,  is  usually 
prolonged  until  the  foetus  is  able,  on  its  entrance  into  the  world,  to'  execute 
regular  movements ;  some  of  these  being  merely  indicative  of  its  desire  for 
food,  and  others  evidently  designed  for  the  acquirement  of  it.     In  many  species, 
the  young  animal  seems  to  be  from  the  first  in  the  full  possession  of  its  senses, 
and  has  considerable  power  of  active  locomotion ;  in  general,  however,  it  is 
very  dependent  upon  its  parent ;  only  being  able  to  obtain  food,  when  this  is 
placed  within  its  immediate  grasp.     Such  is  the  case  with  the  Human  infant, 
which  is  more  or  less  closely  dependent  upon  its  parent,  during  a  larger  pro- 
portion of  its  existence,  than  is  the  young  of  any  other  animal.     Here,  again, 
therefore,  we  perceive  the  application  of  the  general  law,  that,  the  higher  the 
grade  of  development  a  being  is  ultimately  to  assume,  the  more  does  it  require 
to  be  assisted  during  the  early  stages  of  its  progress.     In  the  case  of  Man,  the 
prolongation  of  this  period  has  a  most. important  and  evident  influence  upon  the 
social  condition  of  the  race ;  being,  in  fact,  one  of  the  chief  means,  by  which 
the  solitary  are  bound  together  in  families. 

57.  The  class  Mammalia,  taken  as  a  whole,  is  not  characterized  so  much  by 
the  possession  of  any  one  particular  faculty, — like  that  which  has  been  seen 
in  Birds, — as  by  the  perfect  combination  of  the  different  powers,  which  renders 
the  animals  belonging  to  it  susceptible  of  a  much  greater  variety  of  actions 
than  any  others  can  perform.     There  are  none  that  can  compete  with  Birds 
in  acuteness  of  sight ;  but  there  are  few  that  do  not  possess  the  senses  of  smell, 
taste,  and  touch,  in  a  more  elevated  degree.     There  are  none  which  can  rival 


CHIEF  SUB-DIVISIONS  OF  MAMMALIA. 

Birds  in  rapidity  of  locomotion ;  but  there  are  few  that  cannot  perform  several 
kinds  of  progression.  Several  of  their  movements  require  a  considerable 
amount  of  flexibility  in  the  spine;  hence  the  vertebral  column,  and  -the  bony 
framework  of  the  trunk,  are  never  so  much  consolidated  as  they  are  in  Birds. 
On  the  other  hand,  the  neck  is  much  less  movable ;  it  never  consists  of  more 
than  seven  vertebrae,  and  these  are  always  present;  so  that  they  are  sometimes 
of  great  length,  as  in  the  Giraffe,  and  sometimes  extremely  short,  as  in  the 
Whale,  which  seems  to  have  no  neck  at  all.  In  the  greatest  number  of  Mam- 
malia, the  body  is  supported  upon  all  the  four  extremities,  as  in  Reptiles; 
being  adapted  for  progression  along  the  surface  of  the  earth.  There  are  some 
species,  however,  in  which  the  typical  structure  has  undergone  a  metamor- 
phosis, by  which  it  is  made  to  resemble  that  of  a  Bird ;  whilst  in  others  it  is 
modified,  so  as  to  conform  to  the  character  of  the  Fish.  In  the  Bats,  the 
power  of  motion  is  almost  entirely  delegated  to  the  wings,  which  are  com- 
posed of  skin,  stretched  over  a  bony  framework  formed  of  the  widely  ex- 
tended hand;  and  the  sternum  has  a  projecting  keel  for  the  attachment  of 
the  pectoral  muscles,  as  in  Birds.  And  in  the  Whale  tribe,  the  power  of 
locomotion  is  almost  completely  taken  from  the  extremities,  and  given  back  to 
the  trunk,  as  in  Fishes ;  for  the  posterior  extremities  are  entirely  absent,  and 
the  anterior  serve  only  for  guidance;  there  is  this  important  difference,  how- 
ever, that  the  tail,  which  is  flattened  vertically  in  Fishes,  is  flattened  horizon- 
tally in  the  Cetacea,  which  require  the  power  of  frequently  coming  to  the 
surface  to  breathe. 

58.  The  inferior  energy  of  muscular  movement  in  the  Mammalia,  is  ac- 
companied by  an  inferior  amount  of  respiration ;  the  type  of  the  respiratory 
apparatus,  however,  is  higher  than  in  Birds,  a  large  extent  of  surface  being 
comprised  within  a  smaller  space.     The  lungs  are  confined  to  the  cavity  of 
the  thorax;  and  there  is  a  provision  for  the  regular  renewal  of  the  air  received 
into  them,  by  the  action  of  the  diaphragm,  which  here  completely  separates 
that  cavity  from  the  abdomen.     The  diminished  amount  of  respiration,  again, 
involves  the  production  of  a  lower  degree  of  animal  heat ;  so  that  the  tempera- 
ture of  this  class  seldom  rises  above  104°.     There  is,  therefore,  less  need  of 
means  for  effectually  confining  the  caloric, — especially,  too,  as  their  greater  size 
causes  their  radiating  surface  to  be  much  less,  in  proportion  to  their  bulk,  than 
is  that  of  Birds ;  and  accordingly  we  find  them  provided  only  with  a  covering 
of  hair  or  fur,  which  is  much  less  warm  than  that  of  feathers,  and  which  is 
thin  and  scanty  in  those  which  inhabit  tropical  climates.    The  chief  exception 
to  the  last  rule  is  in  the  case  of  the  Sloths  and  of  some  Monkeys,  which  inhabit 
situations  exposed  to  the  most  powerful  rays  of  the  sun,  and  which  are  covered 
with  a  long  but  thin  and  coarse  hair,  the  purpose  of  which  is  evidently  the 
protection  of  their  skin  from  the  external  heat.     The  inferior  energy  of  the 
respiration  and  circulation,  involves  a  diminished  activity  of  the  other  functions 
of  nutrition,  as  compared  with  those  of  Birds ;  and  the  demand  for  food  appears 
to  be  somewhat  less  constant.     Their  various  organs,  however,  are  developed 
upon  a  higher  plan ;  as  we  have  already  observed  in  regard  to  those  of  respi- 
ration. 

Chief  Sub-divisions  of  Mammalia. 

59.  In  sub-dividing  the  truly  Viviparous  division  of  the  class,  so  as  to  sepa- 
rate Man  from  the  tribes  with  which  he  is  associated  in  it,  we  may  be  advan- 
tageously guided,  in  the  first  place,  by  the  conformation  of  the  extremities ; 
since  upon*  the  perfection  of  the  organs  of  touch,  will  depend  much  of  the 
address  of  an  animal,  in  executing  the  actions  to  which  it  is  prompted  by  its 
intelligence.     The  degree  of  this  perfection  is  estimated,  by  the  number  and 


58  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

mobility  of  the  fingers,  and  by  the  degree  in  which  their  extremities  are  en- 
veloped, by  the  nail,  claw,  or  hoof,  that  terminates  them.  When  the  fingers 
are  partly  absent,  or  are  consolidated  together,  and  a  hoof  envelops  all  that 
portion  which  touches  the  ground,  it  is  obvious  that  the  sensibility  must  be 
blunted,  whilst  at  the  same  time  the  extremity  becomes  incapable  of  prehen- 
sion. The  opposite  extreme  is  where  (as  in  Man)  a  thin  nail  covers  only  one 
side  of  the  extremity  of  the  finger,  leaving  the  other  possessed  of  all  its  deli- 
cacy ; — where  several  such  fingers  exist,  of  which  one  can  be  opposed  to  the 
rest,  so  as  to  render  prehension  more  perfect,  and  to  perform  a  great  variety  of 
actions ; — and  where  the  plane  of  the  whole  hand  can  be  turned  in  any  posi- 
tion, by  the  nature  of  its  attachment  to  the  forearm.  Between  these,  there 
are  many  intermediate  gradations.  By  these  characters,  the  viviparous  Mam- 
malia may  be  divided  into  the  Unguiculated,  which  have  separate  fingers, 
terminated  by  distinct  nails  or  claws  ;  and  the  Ungitlated,  in  which  the  fingers 
are  more  or  less  consolidated,  and  enclosed  at  their  extremity  in  a  hard  hoof. 
Hoofed  animals  are  necessarily  Herbivorous,  inasmuch  as  the  conformation  of 
their  feet  precludes  the  possibility  of  their  seizing  a  living  prey  ;  and  they 
have  flat-crowned  grinding  teeth  for  triturating  their  food.  The  summits  of 
these  teeth  are  usually  not  covered  by  a  smooth  coat  of  enamel,  but  present  a 
.series  of  elevations  and  depressions ;  these  are  occasioned  by  the  peculiar 
structure  of  the  teeth,  which  consist  of  alternating  plates  of  enamel,  ivory  or 
dentine,  and  cementum  or  crusta  petrosa ;  these  are  of  three  different  degrees 
of  hardness ;  and,  as  the  softer  portions  will  of  course  wear  down  first,  the 
harder  remain  as  projecting  ridges.  In  order  to  give  effect  to  these,  there  is 
usually  a  considerable  power  of  lateral  motion  possessed  by  the  lower  jaw  ;  so 
that  a  regular  grinding  action  may  be  performed,  which  is  favourable  to  the 
complete  reduction  of  the  tough  vegetable  substances  that  serve  as  their  food. 
60.  Animals  with  Unguiculated  fingers  are  capable  of  more  variety  in  the 
character  of  their  food.  In  some  it  is  almost  exclusively  vegetable,  as  in  the 
Rodentia;  and  here  the  power  of  prehension  possessed  by  the  extremities  is 
small,  the  forearm  not  being  so  constructed  as  to  be  capable  of  the  motions  of 
pronation  and  supination.  In  this  order,  the  mouth  is  remarkably  adapted  for 
grinding  down  hard  vegetable  substances,— the  molar  teeth  being  furnished 
with  transverse  ridges  of  enamel,  and  the  jaws  having  a  powerful  movement 
backwards  and  forwards.*  In  others,  again,  there  is  an  almost  exclusive  adap- 
tation to  animal  food.  The  toes  are  furnished  with  long  and  sharp  claws ; 
and  the  forefoot  may  be  placed  in  a  variety  of  positions,  by  the  rotation  of  the 
two  bones  composing  the  lower  part  of  the  leg.  The  grinding  teeth  are  very 
narrow,  and  are  formed  with  sharp  points  and  edgqs,  so  as  to  be  adapted  for 
dividing  animal  flesh ;  these  are  firmly  set  in  short  strong  jaws,  which  are 
fitted  together  like  the  blades  of  a  pair  of  scissors,  having  no  action  but  a  verti- 
cal one ;  and  the  constant  friction  of  the  edges  of  the  molar  teeth  against  each 
other,  keeps  them  sharp.!  In  this  group,  too,  we  find  the  greatest  develop- 
ment of  the  canine  teeth,  which  are  commonly  absent  or  but  slightly  developed 

*  The  action  of  trituration  is  chiefly  performed  by  the  external  pteregoid  muscles. 
When  these  are  in  operation  together,  they  draw  the  whole  of  the  lower  jaw  forwards,  so 
as  to  make  the  lower  teeth  project  beyond  the  upper;  and  the  jaw  being  drawn  back 
again  by  the  digastric  muscles,  a  rapid  alternate  movement  may  be  thus  effected,  such 
as  is  seen  in  the  Rodentia.  When  only  the  muscles  of  one  side  acts,  the  condyle  of  that 
side  is  thrown  forwards;  and  by  the  alternating  operation  of  the  two,  aided  by  other 
muscles,  that  rotatory  motion  is  given  which  we  see  especially  in  Ruminating  Quad- 
rupeds. 

f  In  Carnivorous  animals,  the  muscles  which  elevate  the  lower  jaw  attain  a  very  high 
degree  of  development.  This  is  very  remarkably  seen  in  the  internal  pteregoid,  which 
in  Man  is  of  subordinate  size  and  importance,  but  which  is  a  very  powerful  muscle  in 
the  Lion,  Tiger,  &c. 


CHIEF  SUB-DIVISIONS  OF  MAMMALIA.  59 

among  herbivorous  quadrupeds ;  these  are  the  most  powerful  weapons  with 
which  Carnivorous  animals  are  furnished,  serving  both  for  the  first  attack  of 
their  prey,  and  for  subsequently  tearing  it  in  pieces.  It  is  evident  that  the 
whole  structure  of  the  body  must  undergo  modification,  in  conformity  with  the 
nature  of  the  food.  The  simple  stomach  and  intestinal  canal  of  the  carnivo- 
rous animal,  adapted  only  to  the  digestion  of  aliment  consisting  of  materials 
similar  to  those  of  its  body,  would  be  totally  useless  to  an  animal  prevented  by 
its  general  organization  from  obtaining  any  other  than  vegetable  food ;  and  on 
the  other  hand,  the  teeth  and  hoofs  of  the  herbivorous  quadruped  would  be  of 
little  assistance  to  an  animal  whose  instincts  and  general  conformation  adapted 
it  for  the  pursuit  of  animal  prey.  It  will  be  presently  seen  that,  in  regard  to 
his  organization,  Man  holds  an  intermediate  place,  between  the  purely  herbi- 
vorous and  the  purely  carnivorous  tribes ;  being  capable  of  subsisting  exclu- 
sively upon  either  kind  of  diet,  but  being  obviously  intended  by  nature  to 
employ  both  in  combination. 

61.  The  classification  of  the  Mammalia  by  Linnaeus,  although  not  strictly 
natural,  affords  us  the  readiest  means  of  separating  Man  zoologically  from  all 
other  animals.  He  arranged  under  his  order  Primates,  all  the  unguiculated 
Mammalia,  which  have  four  incisor  teeth  and  two  canines  in  each  jaw  ;  and 
thus  Man,  with  the  Monkeys  and  the  Bats,  was  distinguished  from  the 
remainder  of  those  Quadrupeds,  which  have  separate  fingers  with  distinct 
nails  or  claws.  This  group  is  now  sub-divided  into  three  orders,  correspond- 
ing with  the  Linnaean  genera,  Homo,  Simla  and  Vespertilio.  The  last  of 
these  orders,  named  Cheiroptera,  includes  the  Bat  tribe,  which  is  easily  sepa- 
rated from  all  others,  by  the  peculiar  conformation  of  the  anterior  extremities, 
from  which  its  name  is  derived.  The  second,  termed  Quadrumana,  compre- 
hends the  Apes,  Monkeys,  and  Baboons,  which  exhibit  a  regular  series, — the 
highest  approaching  Man  in  general  conformation,  and  the  lowest  having 
much  more  of  the  general  organization  of  the  inferior  carnivorous  quadrupeds. 
They  are  distinguished  from  other  viviparous  Mammalia,  by  possessing  an 
opposable  thumb  on  all  four  extremities  (whence  they  are  termed  four-handed), 
— a  character  which  is  only  found  elsewhere  in  the  Opossums.  Although 
some  of  the  higher  members  of  this  group  are  capable  of  maintaining  the 
erect  position  without  difficulty  for  some  time,  even  whilst  walking,  it  is  cer- 
tainly not  that  which  is  natural  to  them.  The  posterior  extremity, — being 
formed  on  the  plan  of  a  hand,  for  prehension  rather  than  for  direct  support, — 
is  destitute  of  the  heel  which  is  characteristic  of  Man  :  and  although  Apes  can 
climb  trees  with  facility,  they  cannot  plant  the  foot  firmly  on  the  ground,  so 
as  to  resist  attempts  to  overthrow  them ;  since  the  foot  rests  rather  upon  the 
outer  side  than  upon  its  sole,  and  the  narrowness  of  the  pelvis  is  unfavourable 
to  an  equilibrium.  There  are  many  points  of  striking  resemblance  to  Man, 
however,  in  the  details  of  the  conformation  of  the  Gtuadrumana,  especially 
among  the  most  elevated  species  ;  the  order  being  distinguished  by  the  same 
characters  from  most  others.  The  structure  of  their  alimentary  canal  differs 
extremely  little  from  his.  The  eyes  are  directed  forwards,  when  the  trunk  is 
erect ;  and  the  orbit  is  completely  separated  from  the  temporal  fossae,  by  a 
bony  partition.  The  mammae  are  situated  on  the  thorax  ;  and  the  penis  is 
pendant.  Their  coitus,  however,  is  reverse,  as  in  the  lower  Mammalia.  The 
form  of  the  brain  in  the  higher  species  corresponds  with  that  of  Man,  in  this 
remarkable  character, — that  it  is  divided  into  three  lobes,  of  which  the  pos- 
terior is  prolongea  backwards  so  as  to  cover  the  cerebellum ;  this  is  not  the 
case  in  the  hio-hest  of  the  other  Mammalia. 


60  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 


Characteristics  of  Man. 

62.  We  shall  now  review,  somewhat  in  detail,  the  distinctive  characters 
that  separate  Man  from  those  animals  which  present  the  nearest  approach  to 
him  in  general  structure  and  aspect.    These  may  be  advantageously  classified 
according  to  their  ohvious  purposes  ;  and  the  first  series  we  shall  notice,  con- 
sists of  those  by  which  Man  is  peculiarly  adapted  to  the  erect  attitude.     On 
examining  his  cranium,  we  remark  that  the  condyles,  by  which  it  is  articu- 
lated with  the  spinal  column,  are  so  placed,  that  a  "perpendicular  let  fall  from 
the  centre  of  gravity  of  the  head  would  nearly  fall  between  them,  so  as  to  be 
within  the  base  on  whi&h  it  rests.     The  foramen  magnum  is  not  placed  in  the 
centre  of  the  base  of  the  skull,  but  just  behind  it,  in  order  to  compensate  for 
the  greater  specific  gravity  of  the  posterior  part  of  the  head,  which  is  entirely 
filled  with  solid  matter,  whilst  the  anterior  part  contains  many  cavities. — 
There  is,  indeed,  a  little  over-compensation,  which  gives  a  slight  preponde- 
rance to  the  front  of  the  head ;  so  that  it  drops  forwards  and  downwards,  when 
all  the  muscles  are  relaxed.     But  the  muscles  which  are  attached  to  the  back 
of  the  head,  are  far  larger  and  more  numerous  than  those  in  front  of  the  con- 
dyles ;  so  that  they  are  evidently  intended  to  counteract  this  disposition  ;  and 
we  find,  accordingly,  that  we  can  keep  up  the  head  for  the  whole  day,  with 
so  slight  and  involuntary  an  effort,  that  no  fatigue  is  produced  by  it.     More- 
over, the  surfaces  of  the  condyles  have  a  horizontal  direction,  when  the  head 
is  upright ;  and  thus  the  weight  of  the  skull  is  laid  vertically  by  them,  upon 
the  top  of  the  vertebral  column.     If  these  arrangements  be  compared  with  the 
position  and  direction  of  the  occipital  condyles  in  other  Mammalia,  it  will  be 
found  that  these  are  placed  in  the  latter  much  nearer  to  the  back  of  the  head, 
and  that  their  plane  is  more  oblique.     Thus,  whilst  the  foramen  magnum  is 
situated,  in  Man,  just  behind  the  centre  of  the  base  of  the  skull,  it  is  found,  in 
the  Chimpanzee  and  Orang  Outan  to  occupy  the  middle  of  the  posterior  third ; 
and,  as  we  descend  through  the  scale  of  Mammalia,  we  observe  that  it  gradu- 
ally approaches  the  back  of  the  skull,  and  at  last  comes-  nearly  into  the  line  of 
its  longest  diameter,  as  we  see  in  the  Horse.     The  obliquity  of  the  condyles 
differs  in  a  similar  degree.     In  all  Mammalia  except  Man,  their  plane  is 
oblique  ;  so  that,  even  if  the  head  were  equally  balanced  upon  them,  the  force 
of  gravity  would  tend  to  carry  it  forwards  and  downwards.    In  Man,  the  angle 
which  they  make  with  the  horizontal  is  very  small ;  in  the  Orang  Outan  it  is 
as  much  as  37°  ;  and  in  the  Horse,  their  plane  is  vertical,  making  the  angle 
90°.     If,  therefore,  the  natural  posture  of  Man  were  horizontal,  he  would  in 
this  respect  be  circumstanced  like  the  Horse ;  for  the  plane  of  his  condyles, 
which  is  nearly  horizontal  in  the  erect  position,  would  then  be  vertical ;  and 
the  head,  instead  of  being  nearly  balanced  in  the  erect  position,  would  hang 
at  the  end  of  the  neck,  so  that  its  whole  weight  would  have  to  be  supported 
by  some  external  and  constantly-acting  power.     But  for  this,  there  is  neither 
in  the  skeleton,  nor  in  the  muscular  system  of  Man,  any  adequate  provision. 
In  other  Mammalia,  the  head  is  maintained  in  such  a  position,  by  a  strong 
and  thick  ligament  (the  ligamentum  nuchae),  which  passes  from  the  spines  of 
the  cervical  and  dorsal  vertebrae  to  the  most  prominent  part  of  the  occiput ; 
but  of  this  there  is  scarcely  any  trace  in  Man.     In  the  horizontal  position, 
therefore,  he  would  have  the  heaviest  head,  with  the  least  npwer  of  support- 
ing it. 

63.  The  position  of  the  face  immediately  beneath  the  brain,  so  that  its  front 
is  nearly  in  the  same  plane  as  the  forehead,  is  peculiarly  characteristic  of 
Man ;  for  the  crania  of  the  Chimpanzee  and  Orang,  which  approach  nearest 
to  that  of  Man,  are  entirely  posterior  to,  and  not  above,  the  face.     It  should  be 


CHARACTERISTICS  OF  MAN. 


61 


remarked  that,  in  the  young  Ape,  there  is  a  much  greater  resemblance  to 
Man  in  this  respect,  than  there  is  in  the  adult.  For  at  the  time  of  the  second 
dentition,  the  muzzle  of  the  Ape  undergoes  a  great  elongation,  so  that  it  pro- 
jects much  more  beyond  the  forehead ;  this  is  seen  in  Fig.  5.  The  whole 

Fig.  5. 


View  of  the  base  of  Skull  of  Man,  compared  with  that  of  the  Orang  Outan. 

cast  of  the  features  is  altered  at  the  same  time,  so  that  it  approaches  much 
more  to  that  of  the  lower  Q,uadrumana,  than  would  be  supposed  from  observa- 
tion of  the  young  animal  only.*  This  increased  projection  of  the  muzzle,  is 
an  evidence  of  want  of  perfect  adaptation  to  the  erect  posture :  whilst  the 
absence  of  it  in  Man,  shows  that  no  other  position  is  natural  to  him.  Sup- 
posing that,  with  a  head  formed  as  at  present,  he  were  to  move  on  all-fours, 
so  that  his  face  would  be  brought  into  the  same  plane  with  'the  ground, — as 
painful  an  effort  would  be  required  to  examine  with  the  eyes  an  object  placed 
in  front  of  the  body,  as  is  now  necessary  to  keep  the  eyes  fixed  on  the  zenith ; 
the  nose  would  be  unable  to  perceive  any  other  odours  than  those  which  pro- 
ceeded from  the  earth  or  from  the  body  itself;  and  the  mouth  could  not  touch 
the  ground, 'without  bringing  the  forehead  and  chin  also  into  contact  with  it. 
The  oblique  position  of  the  condyleg  in  the  Quadrumana  enables  them,  without 
much  difficulty,  to  adapt  the  inclination  of  their  heads  to  the  horizontal  or  to 
the  erect  position  of  the  body ;  but  the  Natural  position,  in  the  highest  among 
them,  is  unquestionably  one  in  which  &e  spinal  column  is  inclined,  the  body 
being  partially  thrown  forwards,  so  as  to  rest  upon  the  anterior  extremities ; 
and  in  this  position,  the  face  is  directed  forwards  without  any  effort,  owing  to 
the  mode  in  which  the  head  is  articulated  with  the  spine. 

64.  The  vertebral  column  in  Man,  though  not  absolutely  straight,  has  its 
curves  so  arranged,  that,  when  the  body  is  in  an  erect  posture,  a  vertical  line 
from  its  summit  would  fall  exactly  on  the  centre  of  its  base.  It  increases 
considerably  in  size  in  the  lumbar  region,  so  as  to  be  altogether  somewhat 
pyramidal  in  form.  The  lumbar  portion,  in  the  Chimpanzee  and  Orang,  is 
not  of  the  same  proportional  strength ;  and  contains  but  four  vertebrae  instead 
of  five.  The  processes  for  the  attachment  of  the  muscles  of  the  back  to  this 

*  None  but  young  specimens  of  the  Chimpanzee  and  Orang  Outan  have  ever  been 
brought  arlive  to  this  country  ;  and  they  have  never  survived  the  period  of  their  second 
dentition. 
6 


62 


ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 


Fig.  6 


Comparative  view  of  the  Skeleton  of  Man  and  that  of  the  Orang  Outan. 


CHARACTERISTICS  OF  MAN.  63 

part,  are  peculiarly  large  and  strong  in  Man ;  and  this  arrangement  is  obviously 
adapted  to  overcome  the  tendency,  which  the  weight  of  the  viscera  in  front  of 
the  column  would  have,  to  draw  it  forwards  and  downwards.  On  the  other 
hand,  the  spinous  processes  of  the  cervical  and  dorsal  vertebrae,  which  grfe  in 
other  Mammalia  large  and  strong,  for  the  attachment  of  the  ligamentum  nuchae 
to  support  the  head,  have  in  Man  but  little  prominence,  his  head  being  nearly 
balanced  on  the  top  of  the  column.  The  base  of  the  human  vertebral  column 
is  placed  on  a  sacrum  of  greater  proportional  breadth  than  that  of  any  other 
animal;  this  sacrum  is  fixed  between  two  widely-expanded  ilia ;  and  the  whole 
pelvis  is  thus  peculiarly  broad.  In  this  manner,  the  femoral  articulations  are 
thrown  very  far  apart,  so  as  to  give  a  wide  basis  of  support ;  and  by  the  oblique 
direction  of  the  whole  pelvis,  the  weight  of  the  body  is  transmitted  almost  ver- 
tically, from  the  top  of  the  sacrum  to  the  upper  part  of  the  thigh  bones.  The 
pelvis  of  every  other  species  of  the  class  is  very  differently  constructed ;  as 
will  be  seen  in  the  adjoining  Figure  (6),  in  which  the  skeleton  of  the  Orang 
is  placed  in  proximity  with  that  of  Man.  It  is  much  longer  and  narrower, 
having  a  far  smaller  space  between  the  iliac  bones  and  the  lowest  ribs ;  the 
sacrum  is  lengthened  and  reduced  in  width ;  the  alae  of  the  ilia  are  much  less 
expanded ;  and  the  whole  pelvis  is  brought  nearly  into  a  line  with  the  verte- 
bral column.  The  position  of  the  human  femur,  in  which  it  is  most  securely 
fixed  in  its  deep  acetabulum,  is  that  which  it  has,  when  supporting  the  body 
in  the  erect  attitude.  In  the  Chimpanzee  and  Orang,  its  analogous  position 
is  at  an  oblique  angle  to  the  long  axis  of  the  pelvis,  with  the  body  supported 
obliquely  in  front  of  it ;  in  many  Mammalia,  as  in  the  Elephant,  it  forms  nearly 
a  right  angle ;  and  in  several  others,  as  the  Horse,  Ox,  &c.,  it  forms  an  acute 
angle  with  the  axis  of  the  pelvis  and  spinal  column. 

65.  The  lower  extremities  of  Man  are  remarkable  for  their  length,  which  is 
proportionably  greater  than  that  which  we  find  in  any  other  Mammalia,  ex- 
cept the  Kangaroo  tribe.  It  is  evident  that  there  could  be  no  greater  obstacle  to 
his  progression  in  the  horizontal  posture,  than  this  length  of  what  would  then 
be  his  hind  legs.  Either  Man  would  be  obliged  to  rest  on  his  knees,  with  his 
thighs  so  bent  towards  the  trunk,  that  the  attempt  to  advance  them  would  be 
inconvenient,  his  legs  and  feet  being  entirely  useless ;  or  he  must  elevate  his 
trunk  upon  the  extremities  of  his  toes,  throwing  his  head  downwards,  and 
exerting  himself  violently  at  every  attempt  to  bring  forward  the  thighs  by  a 
rotatory  motion  at  the  hip-joint.  In  either  case,  the  only  useful  joint  would 
be  that  at  the  hip  ;  and  the  le^s  would  be  scarcely  superior  to  wooden  or  other 
rigid  supports.  The  chief  difference  in  their  proportional  length,  between 
Man  and  the  semi-erect  Apes,  is  seen  in  the  thigh  ;  and  from  the  comparative 
shortness  of  his  arms,  his  hands  only  reach  the  middle  of  the  thighs ;  whilst 
in  the  Chimpanzee  they  hang  on  a  level  with  the  knees,  and  in  the  Orang 
they  descend  to  the  ankles.  The  Human  femur  is  distinguished  by  its  form 
and  position,  as  well  as  by  its  length.  The  obliquity  and  length  of  its  neck 
still  further  increase  the  breadth  of  the  hips  ;  whilst  they  cause  the  lower  ex- 
tremities of  these  bones  to  be  somewhat  obliquely  directed  towards  each  other, 
so  that  the  knees  are  brought  more  into  the  line  of  the  axis  of  the  body.  This 
position  is  obviously  of  great  use  in  walking,  when  the  whole  weight  has  to  be 
alternately  supported  on  each  limb ;  for,  if  the  knees  had  been  further  apart, 
the  whole  body  must  have  been  swung  from  side  to  side  at  each  step,  so  as  to 
bring  the  centre  of  gravity  over  the  top  of  each  tibia ;  and,  as  a  matter  of  fact, 
it  is  noticed  that  the  walk  of  women,  in  whom  the  pelvis  is  broader  and  the 
knees  more  separated,  is  less  steady  than  that  of  man.  There  is  a  very  marked 
contrast  between  the  knee-joint  of  Man,  and  that  even  of  the  highest  Apes. 
In  the  former,  the  opposed  extremities  of  the  femur  and  the  tibia  are  expanded, 
so  as  to  present  a  very  broad  articulating  surface ;  and  the  internal  condyle  of 


64  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

the  femur  is  lengthened,  so  that  the  two  are  in  the  same  horizontal  plane,  in 
the  usual  oblique  position  of  the  femur.  In  this  manner,  the  whole  weight  of 
the  body,  in  its  erect  posture,  falls  vertically  on  the  top  of  the  tibia,  when  the 
joint  is  in  the  firmest  position  in  which  it  can  be  placed  :  and  a  comparison  of 
the  knee-joint  of  the  Orang  with  that  of  Man,  will  make  it  at  once  evident, 
that  the  former  is  not  intended  to  serve  as  more  than  a  partial  support.  The 
weight  of  the  body  is  transmitted  through  the  tibia,  to  the  upper  convex  sur- 
face of  the  astragalus,  and  thence  to  the  other  bones  of  the  foot.  The  Human 
foot  is,  in  proportion  to  the  size  of  the  whole  body,  larger,  broader,  and  stronger, 
than  that  of  any  other  Mammal,  save  the  Kangaroo.  The  sole  of  the  foot 
is  concave,  so  that  the  weight  of  the  body  falls  on  the  summit  of  an  arch,  of 
which  the  os  calcis  and  the  metatarsal  bones  form  the  two  points  of  support. 
This  arched  form  of  the  foot,  and  the  natural  contact  of  the  os  calcis  with  the 
ground,  are  peculiar  to  Man  alone.  All  the  Apes  have  the  os  calcis  small, 
straight,  and  more  or  less  raised  from  the  ground ;  which  they  touch,  when 
standing  erect,  with  the  outer  side  only  of  the  foot :  whilst  in  animals  more 
remote  from  Man,  the  os  calcis  is  brought  still  more  into  the  line  of  the  tibia ; 
and  the  foot  being  more  elongated  and  narrowed,  only  the  extremities  of-  the 
toes  come  in  contact  with  the  ground.  Hence  Man  is  the  only  species  of 
Mammalia,  which  can  stand  upon  one  leg. — If  we  look  at  the  conformation  of 
the  upper  extremity  of  Man,  we  observe  similar  proofs  that  it  is  not  intended 
as  an  organ  of  support — being  destitute  of  all  these  adaptations,  and  having  a 
conformation  obviously  designed  for  other  purposes,  which  could  not  be  possi- 
bly answered,  if  it  were  not  completely  relieved  from  the  necessity  of  bearing 
the  weight  of  the  body.  This  peculiar  conformation  will  be  subsequently 
considered. 

66.  The  other  parts  of  the  Human  body  concerned  in  locomotion,  are  ex- 
actly adapted  to  the  peculiar  construction  of  the  skeleton.  The  tibia  is  kept 
erect  upon  the  foot  by  the  very  powerful  muscles,  which  are  attached  to  the 
heel  and  which  form  the  calf  of  the  leg, — a  prominence  observed  in  no  other 
animal,  in  nearly  the  same  degree.  The  flexor  longus  pollicis  pedis,  which 
is  attached  in  the  Chimpanzee  and  Orang  to  the  three  middle  toes,  proceeds 
in  Man  exclusively  to  the  great  toe,  on  which  the  weight  of  the  body  is  often 
supported.  The  extensors  of  the  leg  upon  the  thigh  are  much  more  powerful 
than  the  flexors, — an  arrangement  seen  in  no  other  animal.  The  glutsei,  by 
which  .the  pelvis  is  kept  erect  upon  the  thigh,  are  of  far  greater  size  than  is 
elsewhere  seen.  The  superior  power  of  the  muscles  tending  to  draw  the  head 
and  spine  backwards,  has  been  already  referred  to.  In  the  general  form  of 
the  trunk,  there  is  a  considerable  difference  between  man  and  most  other  Mam- 
malia. His  chest  is  large,  but  is  flattened  in  front,  and  expanded  laterally,  so 
that  its  transverse  diameter  is  greater  than  its  antero-posterior ; — a  peculiarity 
in  which  only  the  most  Man-like  monkeys  partake.  His  sternum  ^s  short  and 
broad ;  and  there  is  a  considerable  distance  between  the  lower  ribs  and  the 
ilia,  in  consequence  of  the  small  number  of  ribs,  and  the  length  of  the  lumbar 
portion  of  the  vertebral  column.  The  viscera  in  this  space,  which  in  the  hori- 
zontal position  would  be  but  insufficiently  held  up  by  the  abdominal  muscles, 
are,  in  the  erect  attitude,  securely  supported  by  the  expanded  pelvis.  From 
all  these  facts  it  is  an  indisputable  conclusion,  that  the  erect  attitude  and  biped 
progression  are  natural  to  man ;  and  we  must  regard  as  in  great  degree  fabu- 
lous, all  those  histories  of  supposed  wild  men,  who,  it  has  been  said,  were 
found  in  woods,  dumb,  hairy,  and  crawling  on  all-fours.  The  most  elaborate 
investigation*  of  the  structure  of  the  anthropoid  Apes,  and  the  fullest  acquaint- 

*  See  especially  Mr.  Owen's  paper  on  the  Chimpanzee  and  the  Orang  Outan,  in  the 
Zoological  Transactions,  vol.  i. 


CHARACTERISTICS  OF  MAN.  65 

ance  with  their  habits,  concur  in  proving,  that  their  movements  are  not  easy 
or  agile,  unless  they  employ  all  their  limbs  for  the  support  of  their  bodies. 

(>7.  The  name  Bimana  is  the  most  appropriate  that  could  be  founcl,  for  an 
order  constituted  by  the  Human  species  only ;  since  Man  alone  is  two-handed. 
"  That,"  says  Cuvier,  "  which  constitutes  the  hand,  properly  so  called,  is  the 
faculty  of  opposing  the  thumb  to  the  other  fingers,  so  as  to  seize  the  most 
minute  objects, — a  faculty  which  is  carried  to  its  highest  degree  of  perfection 
in  Man,  in  whom  the  whole  anterior  extremity  is  free,  and  can  be  employed 
in  prehension."  Some  naturalists  refuse  the  term  hand  to  the  extremities  of 
the  Monkey  tribe,  preferring  to  call  them  graspers;  for  it  is  certainly  true, 
that,  although  usually  possessing  an  opposable  thumb,  they  are  destitute  of  the 
power  of  performing  many  of  those  actions  which  we  regard  as  most  charac- 
teristic of  the  hand.  These  actions  are  chiefly  dependent  on  the  size  and 
power  of  the  thumb ;  which  is  much  more  developed  in  Man  than  it  is  even 
in  the  highest  Apes.  The  thumb  of  the  Human  hand  can  be  brought  into 
exact  opposition  to  the  extremities  of  all  the  fingers,  whether  singly  or  in  com- 
bination ;  whilst  in  those  Quadrumana  which  most  nearly  approach  man,  the 
thumb  is  so  short  and  weak,  and  the  fingers  so  long  and  slender,  that  their 
tips  can  scarcely  be  brought  into  opposition,  and  can  never  be  opposed  in  near 
contact  with  each  other,  with  any  degree  of  force.  Hence,  although  admirably 
adapted  for  clinging  round  bodies  of  a  certain  size,  such  as  the  small  branches 
of  trees,  &c.,  the  extremities  of  the  Quadrumana  can  neither  seize  very  mi- 
nute objects  with  such  precision,  nor  support  large  ones  with  such  firmness,  as 
are  essential  to  the  dexterous  performance  of  a  variety  of  operations,  for  which 
the  hand  of  Man  is  admirably  adapted.  Hence  the  possession  of  "  four  hands" 
is  not,  as  might  be  supposed,  a  character  which  raises  the  animals  that  pos- 
sess it  above  two-handed  Man ;  for  none  of  these  four  hands  are  adapted  to 
the  same  variety  of  actions  of  prehension,  of  which  his  are  capable ;  and  all 
of  them  are  in  some  degree  required  for  support.  In  this  respect,  their  cha- 
racter approaches  much  nearer  to  that  of  the  extremities  of  the  lower  Mam- 
malia ;  and  there  are  several  among  them,  in  which  the  opposable  power  of 
the  thumb  being  deficient,  there  is  no  very  marked  distinction  between  the  so- 
called  hand,  and  the  foot  of  some  Carnivora.  There  is  much  truth,  then,  in 
Sir  C.. Bell's  remark,  that  "We  ought  to  define  the  hand  as  belonging  exclu- 
sively to  Man."  There  is  in  him,  what  we  observe  in  none  of  the  Mammalia 
that  approach  him  in  other  respects,  a  complete  distinction  in  the  functional 
character  of  the  anterior  and  posterior  extremities ;  the  former  being  adapted 
for  prehension  alone,  and  the  latter  for  support  alone.  Thus  each  function  is 
performed  with  a  much  higher  degree  of  perfection  than  it  can  be  where  two 
such  opposite  purposes  have  to  be  united.  The  arm  of  the  Ape  has  as  wide 
a  range  of  motion  as  in  Man,  so  far  as  its  articulations  are  concerned ;  but  it  is" 
only  when  the  animal  is  in  the  erect  attitude  that  its  arm  can  have  free  play. 
Thus  the  structure  of  the  whole  frame  must  conform  to  that  of  the  hand,  and 
must  act  with  reference  to  it.  But  it  cannot  be  said  with  truth  (as  some  have 
maintained),  that  Man  owes  his  superiority  to  his  hand  alone;  for  without  the 
directing  mind,  the  hand  would  be  comparatively  valueless.  His  elevated 
position  is  due  to  his  mind  and  its  instruments  conjointly;  for  if  destitute  of 
either,  mankind  would  be  speedily  extinguished  altogether,  or  reduced  to  a 
very  subordinate  grade  of  existence. 

08.  Thus,  then,  although  the  order  Bimana  cannot  be  separated  from  the 
order  duadrumana  by  any  single  obvious  structural  distinction,  like  that  which 
characterizes  the  Cetacea  or  the  Cheiroptera,  it  is  really  as  far  removed  by  the 
minuter,  but  not  less  important  modifications  which  have  been  detailed.  A 
few  other  distinctive  characters  will  now  be  noticed.  With  one  exception  (the 
fossil  genus  Anoplotherium,  which  is  allied  to  the  Tapir  tribe),  Man  is  dis- 

6* 


66  ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

tinguished  from  all  other  animals,  by  the  equality  in  the  length  of  all  his  teeth, 
and  by  the  equally  close  approximation  of  them  all  in  each  jaw.  Even  the 
anthropoid  Apes  have  the  canine  teeth  longer  than  the  others,  and  an  interval 
in  the  line  of  teeth  in  each  side  of  the  jaw,  to  receive  the  canine  teeth  of  the 
opposite  jaw.  This  is  more  evident  in  the  adult  than  in  the  young  animal. 
The  vertical  position  of  the  Human  teeth,  on  which  one  of  the  most  charac- 
teristic features  of  the  human  face — the  prominent  chin — depends,  is  also 
quite  peculiar;  and  is  intimately  connected  both  with  his  erect  attitude,  and 
with  the  perfection  of  the  hands,  by  which  the  food  is  divided  and  conveyed 
to  the  mouth.  He  has  no  occasion  for  that  protrusion  of  the  muzzle  and  lips, 
which,  in  animals  that  seize  their  food  with  the  mouth  only,  is  required  to  pre- 
vent the  face  from  coming  into  general  contact  with  it. — The  absence  of  any 
weapons  of  offence,  and  of  direct  means  of  defence,  are  remarkable  charac- 
teristics of  Man,  and  distinguish  him  from  other  animals.  On  those  to  whom 
Nature  has  denied  weapons  of  attack,  she  has  bestowed  the  means  either  of 
passive  defence,  of  concealment,  or  of  flight.  Yet  Man,  by  his  superior  rea- 
son, has  not  only  been  enabled  to  resist  the  attacks  of  other  animals,  but  even 
to  bring  them  under  subjection  to  himself.  His  intellect  can  scarcely  suggest 
the  mechanism  which  his  hands  cannot  frame ;  and  he  has  devised  and  con- 
structed arms  more  powerful  than  those  which  any  other  creature  wields,  and 
defences  so  secure  as  to  defy  the  assaults  of  all  but  his  fellow-men. — We  find, 
on  comparing  the  brain  of  Man  with  that  of  the  lower  Mammalia,  that,  as 
might  have  been  anticipated,  its  proportional  dimensions  are  much  greater,  and 
its  structure  more  complex.  The  former  part  of  this  statement  is  easily  veri- 
fied by  an  examination  of  the  cranium  alone,  comparing  tbe  size  of  its  cavity 
with  that  of  the  face.  The  amount  of  the  facial  angle,  taken  after  the  man- 
ner of  Camper,  affords  a  tolerably  correct  indication  of  the  relative  sizes  of 
these  parts.  In  Man,  the  facial  angle  is,  in  the  average  of  Europeans,  80°  ; 
in  Negroes,  it  is  about  70°.  In  the  adult  Chimpanzee  (which  approaches  in 
this  respect  nearest  to  Man),  the  facial  angle  is  only  35° ;  and  in  the  Orang,  it 
is  no  more  than  30°.  In  other  animals  it  is  still  less,  except  when  it  is  in- 
creased by  the  prominence  of  large  frontal  sinuses,  or  by  the  comparative 
shortness  of  the  jaws.  In  regard  to  the  structure  of  the  brain,  we  shall  here 
only  remark  generally,  that  the  Encephalon  of  Man  far  exceeds  that  of  the 
highest  Quadrumana,  in  the  size  of  the  cerebral  hemispheres,  in  the  com- 
plexity and  development  of  its  internal  parts,  and  in  the  depth  and  number  of 
its  convolutions. 

69.  Man  cannot  be  regarded  as  distinguished  from  other  Mammalia,  how- 
ever, either  by  acuteness  of  sensibility,  or  by  muscular  power.  His  swiftness 
in  running,  and  agility  in  leaping,  are  inferior  to  that  of  other  animals  of  his 
size, — the  full-grown  Orang,  for  example.  The  smallness  of  his  face,  compared 
with  that  of  the  cranium,  shows  that  the  portion  of  the  nervous  system  distri- 
buted to  the  organs  of  sense,  is  less  developed  in  him  than  it  is  in  most  other 
animals  ;  and  the  small  proportional  size  of  the  ganglionic  centres,  with  which 
these  organs  are  immediately  connected,  is  another  indication  of  the  same  fact. 
Accordingly,  he  is  surpassed  by  many  in  the  acuteness  of  his  sensibility  to 
light,  sound,  &c.,  but  he  stands  alone  in  the  power  of  comparing  his  sensa- 
tions, and  of  drawing  conclusions  from  them.  Moreover,  although  none  of  his 
senses  are  very  acute  in  his  natural  state,  they  are  all  moderately  so,  which  is 
not  the  case  in  other  animals  ;  and  they  are  capable  (as  is  also  his  swiftness  of 
foot)  of  being  much  improved  by  practice,  especially  when  circumstances 
strongly  call  for  their  exercise.  This  power  of  adaptation  to  varieties  in 
external  conditions,  which  makes  him  to  a  great  extent  independent  of  them, 
is  manifested  in  other  features  of  his  structure  and  economy.  He  is  capable 
of  sustaining  the  lowest  as  well  as  the  highest  extremes  of  temperature  and 


CHARACTERISTICS  OF  MAN.  67 

of  atmospheric  pressure.  In  the  former  of  these  particulars,  he  is  strikingly 
contrasted  with  the  anthropoid  Apes,  such  as  the  Chimpanzee,  which  is 
restricted  to  a  few  of  the  hottest  parts  of  Africa,  and  the  Orang  Outan,  which 
is  only  found  in  Borneo  and  Sumatra :  these  cannot  be  kept  alive  in  temperate 
climates,  without  the  assistance  of  artificial  heat ;  and  even  when  this  is 
afforded,  they  speedily  become  diseased  and  die.  His  diet  is  naturally  of  a 
mixed  kind ;  but  he  can  support  himself  in  health  and  strength,  on  either 
animal  or  vegetable  food  exclusively.  It  is  by  the  demands  which  his  peculiar 
condition  makes  upon  the  exercise  of  his  ingenuity,  that  his  mental  powers 
are  first  called  into  active  operation ;  but,  when  once  aroused,  their  develop- 
ment has  no  assignable  limit.  The  slow  growth  of  Man?  and  the  length  of 
time  during  which  he  remains  in  a  state  of  dependence  upon  his  parents,  have 
been  already  mentioned  as  peculiarities,  by  which  he  is  distinguished  from  all 
other  animals.  He  is  unable  to  seek  his  own  food,  during  at  least  the  three 
first  years  of  his  life ;  and  he  does  not  attain  to  his  full  stature  until  he  is 
more  than  twenty  years  of  age.  In  proportion  to  his  size,  too,  the  whole  sum 
of  his  life  is  greater  than  that  of  other  Mammalia.  The  greatest  age  of  the 
Horse,  for  example,  which  is  an  animal  of  much  superior  bulk,  is  between 
thirty  and  forty  years.  That  of  the  Orang,  which,  when  full  grown,  surpasses 
Man  in  stature,  is  about  the  same,  so  far  as  can  be  ascertained.  The  age  to 
which  the  life  of  Man  is  frequently  prolonged,  is  well  known  to  be  above  a 
hundred  years  ;  and  instances  of  such  longevity  are  to  be  found  in  all  nations. 
70.  Still,  however  widely  Man  may  be  distinguished  from  other  animals, 
by  these  and  other  peculiarities  of  his  structure  and  economy,  he  is  yet  more 
distinguished  by  those  mental  endowments,  and  the  habitudes  of  life  and 
action  thence  resulting,  which  must  be  regarded  as  the  essential  characteristics 
of  humanity.  In  the  highest  among  brutes,  the  mere  instinctive  propensities 
(as  already  defined  §  28,  34,)  are  the  frequent  springs  of  action ;  and  although 
the  intelligent  will  is  called  into  exercise,  to  a  'certain  extent,  the  character 
never  rises  beyond  that  of  a  child.  In  fact,  the  correspondence  between  the 
psychical  endowments  of  the  Chimpanzee,  and  those  of  the  Human  infant  of 
between  two  and  three  years  old,  is  very  close.  In  Man,  however,  the  instinctive 
propensities  only  manifest  themselves  strongly  whilst  the  intellect  is  undeve- 
loped ;  and  nearly  all  the  actions  of  adult  life  are  performed  under  the  direction 
of  the  intelligent  will.  From  the  intelligence  of  Man  results  this  improva- 
bility ;  and  his  improved  condition  impresses  itself  upon  his  organization. 
This  capability  of  improvement  in  the  bodily  as  well  as  the  mental  constitution 
of  Man,  is  the  cause  of  the  comforts  now  enjoyed  by  civilized  races,  and  of  the 
means  which  they  possess  of  still  further  elevation.  In  the  process  by  which 
these  are  attained,  we  observe  a  remarkable  difference  between  the  character 
of  Man  and  that  of  other  animals.  The  arts  of  which  these  last  are  capable 
are  limited,  and  peculiar  to  each  species ;  and  there  seems  to  be  no  general 
power  of  adapting  these  to  any  great  variety  of  purposes,  or  of  profiting  by  the 
experience  of  others.  Where  a  particular  adaptation  of  means  to  ends,  of 
actions  to  circumstances,  is  made  by  an  individual  (as  is  frequently  the  case, 
when  some  amount  of  intelligence  or  rationality  exists),  the  rest  do  not  seem 
to  profit  by  it ;  so  that  there  is  no  proof  that  any  species  or  race  among  the 
lower  animals  ever  makes  an  advance  towards  an  improvement  or  alteration 
in  its  condition.  That  modifications  in  structure  and  instincts  may  be  induced 
by  circumstances,  in  some  of  the  most  improvable  species,  such  as  the  Dog, 
has  been  shown  by  abundant  evidence ;  and  these  modifications,  if  connected 
with  the  original  habits  and  instincts  of  the  species,  may  be  hereditarily  trans- 
mitted. There  is  ample  proof  that  the  same  is  the  case,  in  regard  both  to  the 
corporeal  structure  and  psychical  endowments  of  Man.  Under  the  influence 
of  education,  physical  and  mental,  continued  through  successive  generations, 


ON  THE  PLACE  OF  MAN  IN  THE  SCALE  OF  BEING. 

the  capabilities  of  his  whole  nature,  and  especially  those  of  his  brain,  are  called 
out ;  so  that  the  general  character  of  the  race  is  greatly  improved.  On  the 
other  hand,  under  the  influence  of  a  degraded  condition,  there  is  an  equally 
certain  retrogression ;  so  that,  to  bring  up  the  New  Holland  Savage,  or  the 
African  Bushman  to  the  level  of  the  European,  would  probably  require  centu- 
ries of  civilization.  One  of  the  most  important  aids  to  the  use  and  development 
of  the  human  mind,  is  the  power  of  producing  articulate  sounds,  or  language  ; 
of  which,  as  far  as  we  know,  Man  is  the  only  animal  in  possession.  There 
is  no  doubt,  that  many  other  species  have  certain  powers  of  communication 
between  individuals ;  but  these  are  probably  very  limited,  and  of  a  kind  very 
different  from  a  veAal  language. 

71.  Although,  as  we  have  stated,  there  is  nothing  in  Man's  present  condi- 
tion which  removes  him  from  the  pale  of  the  Animal  kingdom,  and  although 
his  reasoning  powers  differ  rather  in  degree  than  in  kind  from  those  of  the 
inferior  animals,  he  seems  distinguished  by  one  innate  tendency,  to  which 
we  have  no  reason  to  suppose  that  any  thing  analogous  elsewhere  exists,  and 
which  we  might  term  an  instinct,  were  it  not  that  this  designation  is  generally 
applied  to  propensities  of  a  much  lower  character.  The  tendency  here  referred 
to,  is  that  which  seems  universal  in  Man,  to  believe  in  some  unseen  Existence. 
This  may  take  various  forms,  but  is  never  entirely  absent  from  any  race  or 
nation,  although  (like  other  innate  tendencies)  it  may  be  defective  in  indi- 
viduals. Attempts  have  been  made  by  some  travelers  to  prove  that  particular 
nations  are  destitute  of  it ;  but  such  assertions  have  been  based  only  upon  a 
limited  acquaintance  with  their  habits  of  thought,  and  with  their  outward 
observances.  For  there  are  probably  none  that  do  not  possess  the  idea  of 
some  invisible  Power  external  to  themselves ;  whose  favour  they  seek,  and 
whose  anger  they  deprecate,  by  sacrifice  and  other  religious  observances.  It 
requires  a  higher  mental  cultivation  than  is  always  to  be  met  with,  to  conceive 
of  this  Power  as  having  a  Spiritual  existence  ;  but  wherever  the  idea  of  spirit- 
uality can  be  denned,  it  seems  connected  with  it.  The  vulgar  readiness  to 
believe  in  demons,  ghosts,  &c.,  is  only  an  irregular  or  depraved  manifestation 
of  the  same  tendency.  Closely  connected  with  it,  is  the  desire  to  share  in  this 
spiritual  existence  ;  which  has  been  implanted  by  the  Creator  in  the  mind  of 
Man ;  and  which,  developed  as  it  is  by  the  mental  cultivation  that  is  almost 
necessary  for  the  formation  of  the  idea,  has  been  regarded  by  philosophers  in 
all  ages,  as  one  of  the  chief  natural  arguments  for  the  immortality  of  the  soul. 
By  this  Immortal  Soul,  the  existence  of  which  is  thus  guessed  by  Man,  but  of 
whose  presence  within  him  he  derives  the  strongest  assurance  from  Revelation, 
Man  is  connected  with  beings  of  a  higher  order,  amongst  whom  intelligence 
exists,  unrestrained  in  its  exercise  by  the  imperfections  of  that  corporeal  me- 
chanism through  which  it  here  operates;  and  to  this  state, — a  state  of  more 
intimate  communion  of  mind  with  mind,  and  of  creatures  with  their  Creator,— 
he  is  encouraged  to  aspire,  as  the  reward  of  his  improvement  of  the  talents 
here  committed  to  his  charge. 


OF  VITAL  ACTIONS,  AND  THEIR  MUTUAL  DEPENDENCE.  69 


CHAPTER  II. 


GENERAL    VIEW    OF    THE    FUNCTIONS. 

SECTION  I. — Of  Vital  Actions,  and  their  mutual  dependence. 

72.  The  idea  of  Life  or  Vital  Action  obviously  involves  that  of  change. 
We  do  not  consider  any  being  as  alive,  which  is  not  undergoing  some  continual 
alteration  perceptible  to  the  senses.     This  alteration  may  be  so  trifling  in  its 
amount,  as  not  to  be  recognized  except  by  frequent  comparison.     The  slow- 
growing  Lichen,  that  forms  the  gray  or  yellow  spots  upon  old  walls,  or  the. 
Oyster  that  is  lying  motionless  in  its  massive  bed,  may  appear  to  perform  no 
action  ;  and  yet  a  sufficiently  prolonged  knowledge  of  the  former  would  show, 
that  it  is  gradually  though  slowly  extending  itself,  and  that  it  is  multiplying 
its  race  by  a  humble  yet  effectual  process  of  fructification ;  whilst  closer  obser- 
vation of  the  latter  would  enable  us  to  perceive,  that  its  surfaces  are  covered 
with  cilia  which  are  in  continual  vibration, — that  food  is  being  regularly  taken 
into  its  stomach,  undergoes  digestion,  and  is  converted  into  materials  fit  for  the 
aliment  of  the  body, — that  a  constant  circulation  of  blood  is  maintained,  by 
the  action  of  a  powerful  heart, — that  this  circulation  is  subservient  to  the 
various  processes  of  nutrition,  secretion,  and  reproduction, — that  in  due  time  a 
number  of  young  Oysters  are  produced,  which  swim  forth  from  between  the 
valves  of  the  parent  shell,  and  locate  themselves  elsewhere, — and  lastly  that, 
apathetic  as  the  creature  seems,  it  may  be  excited  by  some  kinds  of  stimuli  to 
a  movement  which  seems  to  evince  sensation,  the  closure  of  the  shell  being 
produced  by  any  mechanical  irritation  of  the  contained  animal,  or  even,  when 
it  lies  undisturbed  in  its  native  haunts,  by  a  shadow  passing  between  it  and 
the  sun.     Thus,  then,  change  of  some  kind  is  essential  to  our  idea  of  Life. 
It  may  be  asked  what  is  the  condition  of  a  seed,  which  remains  unchanged 
during  a  period  of  many  centuries,  and  at  last  vegetates,  when  placed  in 
favourable  circumstances,  as  if  it  had  been  ripened  but  the  year  before.     The 
seed  is  not  alive,  but  it  is  possessed  of  the^property  of  vitality,  or  the  power 
of  performing  vital  actions,  when  aroused  to  them  by  the  necessary  stimuli, — 
such  as  warmth,  moisture,  oxygen,  &c.     Its  condition  is  analogous  to  that  of 
the  human  being  in  profound  sleep  ;  he  is  not  then  a  feeling  thinking  man  ; 
but  he  is  capable  of  feeling  and  thinking,  when  he  is  aroused  from  his  slum- 
ber, and  his  mind  is  put  into  activity  by  the  impressions  of  external  objects. 

73.  As  the  activity  of  a  living  being,  then,  is  dependent  upon  two  sets  of 
conditions, — the  organized  structure  which  it  possesses, — and  the  stimuli  to 
which  this  is  exposed, — we  can  scarcely  separate  from  our  notion  of  an  organ- 
ized structure,  that  of  the  peculiar  properties  with  which  it  is  endowed;  for 
we  never  see  an  organized  structure  remaining  as  such,  unless  it  possesses 
some  degree  of  vitality.     It  may  be  said  that,  when  an  Animal  or  Plant  is 
killed  by  a  strong  electric  shock,  its  organization  is  unaffected,  yet  its  vital 
properties  are  destroyed.     Yet  no  proof  of  such  an  assertion,  which  is  con- 
trary to  all  analogy,  has  ever  been  afforded.     In  no  other  circumstances  do  we 
ever  witness  the  departure  of  vitality,  without  some  change  of  structure  or  of 


70 


GENERAL  VIEW  OF  THE  FUNCTIONS. 


composition,  which  can  be  made  evident.  In  the  ordinary  death  of  an  Ani- 
mal, we  may  commonly  trace  the  action  of  the  morbific  cause  upon  some  par- 
ticular organ,  whose  function  is  thereby  either  suspended  or  perverted ;  and 
the  cessation  of  the  whole  train  of  actions  necessarily  results,  if  this  organ  be 
one  of  those  essentially  concerned  in  them.  Thus,  to  take  a  not  uncommon 
case,  a  patient  with  tubercular  deposition  nearly  filling  both  lungs,  becomes 
the  subject  of  an  ulceration,  which  suddenly  opens  a  passage  from  one  of  the 
bronchi  to  the  pleural  cavity  on  the  same  side ;  death  from  this  cause  is  fre- 
quently almost  instantaneous,  from  the  total  incapacity  of  the  other  lung  to 
maintain  by  itself  those  respiratory  actions  which  are  necessary  to  the  con- 
tinuance of  the  circulation.  Take  again,  for  example,  the  influence  of  a  nar- 
cotic poison ;  it  occasions  torpidity,  first  of  the  brain,  and  then  of  the  medulla 
oblongata.  So  long  as  its  action  is  confined  to  the  brain,  the  general  train  of 
vital  operations  is  no  more  disturbed  than  it  is  in  profound  sleep ;  but  as  soon 
as  it  affects  the  medulla  oblongata,  the  respiratory  movements  become  para- 
lyzed (from  causes  hereafter  to  be  explained),  and  the  circulation  is  soon 
brought  to  a  stand ;  and  every  organ  in  the  body  speedily  loses  its  character- 
istic properties,  by  the  commencement  of  chemical  changes  in  its  composition. 
But  if  the  respiration  be  artificially  sustained,  the  circulation  will  continue, 
and  all  the  processes  of  nutrition,  secretion,  &c.,  to  Avhich  it  is  subservient, 
will  be  performed  with  little  interruption.  Hence  the  cessation  of  the  whole 
train,  which  would  otherwise  ensue,  and  the  loss  of  vitality  of  the  general 
structure,  are  due  to  the  local  change  produced  by  the  morbific  cause ;  and 
the  same  may  be  traced,  though  not  always  so  evidently,  in  a  variety  of  other 
instances. 

74.  If  we  consider  the  actions  exhibited  by  any  living  being,  in  which  they 
are  sufficiently  complex  and  numerous  to  admit  of  being  classified,  we  shall 
perceive  that  they  may  be  associated  into  groups,  termed  Functions;  of  which 
every  one,  taken  as  a  whole,  has  some  positive  and  determinate  purpose. 
Thus,  one  of  the  most  universal  of  all  the  changes  necessary  to  the  existence 
of  a  living  being,  is  the  exposure  of  its  nutritious  fluid  to  the  air ;  by  the 
action  of  which  upon  it,  certain  alterations  are  effected.     For  the  performance 
of  this  aeration,  simple  as  the  change  appears,  many  provisions  are  required. 
In  the  first  place,  there  must  be  an  aerating  surface,  consisting  of  a  thin  mem- 
brane, permeable  to  gases ;  on  the  one  side  of  which  the  blood  may  be  spread 
out,  whilst  the  air  is  in  contact  with  the  other.     Then  there  must  be  a  provi- 
sion for  continually  renewing  the  blood,  which  is  brought  to  this  surface  ;  in 
order  that  the  whole  mass  of  fluid  may  be  equally  benefited  by  the  process. 
And,  in  like  manner,  the  stratum  of  air  must  also  be  renewed,  as  frequently  as 
its  constituents  have  undergone  any  essential  change.     We  include,  therefore, 
in  speaking  of  the  Function  of  Respiration,  not  only  the  actual  aerating  pro- 
cess, but  also  the  various  changes  which  are  necessary  to  carry  this  into°  effect, 
and  which  obviously  have  it  for  their  ultimate  purpose. 

75.  On  further  examining  and  comparing  these  Functions,  we  find  that  they 
are  themselves  capable  of  some  degree  of  classification.     Indeed,  the  distinc- 
tion between  the  groups  into  which  they  may  be  arranged,  is  one  of  essential 
importance  in  Animal  Physiology.     If  we  contemplate  the  history  of  the  Life 
of  a  Plant,  we  perceive  that  it  grows  from  a  germ  to  a  fabric  of  sometimes 
gigantic  size, — generates  a  large  quantity  of  organized  structure,  and  many 
organic  compounds,  which  form  the  products  of  secretion,  but  do  not  undergo 
organization, — multiplies  its  species,  by  the  production  of  germs  similar  to  that 
from  which  it  originated; — but  that  it  performs  all  these  complex  operations, 
without  (so  far  as  we  can  perceive)  either  feeling  or  thinking,  without  con- 
sciousness or  will.    All  the  functions  of  which  its  Life  is  composed,  are,  there- 
fore, grouped  together,  under  the  general  designation  of  Functions  of  Organic 


OF  VITAL  ACTIONS,  AND  THEIR  MUTUAL  DEPENDENCE.  71 

or  Vegetative  life  ;  and  they  are  subdivided  into  those  concerned  in  the  main- 
tenance of  the  structure  of  the  individual,  which  are  termed  functions  of  Nu- 
trition,— and  those  to  which  the  Reproduction  of  the  species  is  due.  The 
functions  of  Nutrition  in  Plants  may  be  thus  generally  described.  The  first 
step  in  the  process,  is  the  Absorption  of  nutriment  from  without.  This  is  car- 
ried by  Circulation  to  the  parts  of  the  structure  distant  from  those  at  which 
it  was  absorbed.  At  some  of  these  parts,  the  absorbed  fluid  is  brought  into 
relation  with  the  air,  by  which  certain  changes  are  effected  in  its  constitution ; 
these  may  be  included  under  the  general  term  deration,  only  a  part  of  them 
being  analogous  to  the  Respiration  of  Animals.  Having  undergone  these 
changes,  and  lost  a  considerable  part  of  its  superfluous  water  by  the  process 
of  Exhalation,  the  alimentary  fluid  is  prepared  to  be  applied  to  its  various 
purposes  in  the  system ;  and,  being  carried  through  the  fabric  by  the  Circu- 
lation, it  becomes  subservient  to  the  Nutrition  and  extension  of  the  fabric,  and 
to  the  formation  of  various  products  of  Secretion.  It  also  affords  the  means, 
to  the  organs  of  Reproduction,  of  the  performance  of  their  functions ;  since 
a  new  germ  cannot  be  formed,  any  more  than  the  parent  structure  can  be  ex- 
tended, without  organizable  materials  prepared  by  the  foregoing  processes,  and 
supplied  to  the  parts  where  active  changes  are  going  on. 

76.  On  analyzing  the  operations  which  take  place  in  the  Animal  body,  we 
find  that  a  large  number  of  them  are  essentially  the  same  in  character  with 
the  foregoing,  and  differ  only  in  the  conditions  under  which  they  are  per- 
formed; and  that  we  may,  in  fact,  readily  separate  the  Organic  functions, 
which  are  directly  concerned  in  the  riiaintenance  of  the  fabric,  from  those  of 
Animal  life,  the  chief  purpose  of  which  is  entirely  different.  In  commencing 
the  survey  of  these,  we  must  revert  to  what  has  been  already  said  in  regard 
to  the  nature  of  the  food  of  Animals,  and  the  means  by  which  it  is  prepared 
to  be  applied  to  the  wants  of  their  system  (§  14).  Not  being  received  (in 
general  at  least)  in  any  but  the  solid  form,  it  needs  to  be  reduced  to  the  fluid 
state,  before  it  can  be  introduced  by  absorption  into  the  system:  this  reduction,, 
which  is  termed  Digestion,  must  be  regarded  as  not  merely  a  process  of  me- 
chanical separation  or  solution,  but  as  one  of  chemical  change.  By  a  part  of 
the  same  process,  a  certain  degree  of  separation  is  effected,  between  that  por- 
tion of  the  reduced  aliment  which  is  fit  for  absorption  and  that  which  is  not 
adapted  to  serve  any  purpose  in  the  economy ;  and  the  latter,  together  with 
certain  products  of  secretion,  which  it  is  equally  desirable  to  get  rid  of  com- 
pletely, is  at  once  cast  out  of  the  system.  The  alimentary  fluid  is  then  taken 
up  by  Absorption,  through  the  vessels  spread  out  upon  the  walls  of  the  stom- 
ach and  intestinal  tube,  precisely  in  the  same  manner  as  it  is  received  into 
Plants  through  their  roots  distributed' in  the  soil:  hence  the  earth  has  been  not 
unaptly  designated  as  the  common  stomach  of  Plants  ;  and  Animals  have  been 
said  to  carry  their  soil  about  with  them.  The  absorbed  fluid,  having  been 
introduced  into  the  general  current  of  the  Circulation,  is  first  carried  to  the 
Respiratory  organs,  where  it  is  exposed  to  the  action  of  the  air ;  and  it  is  then 
transmitted  to  the  system,  for  the  purposes  of  Nutrition,  Secretion,  and  Repro- 
duction. So  far,  then,  the  functions  of  the  Animal  system  coincide  with  those 
of  the  Plant.  The  Organic  functions  of  the  former,  however,  have  a  purpose  or 
object  superadded  to  that  which  they  perform  in  the  latter,  Avhere  their  only 
end  seems  to  be  the  production  and  maintenance  of  the  individual  fabric,  and 
the  continuance  of  the  race.  They  are  made  subservient  in  Animals  to  those 
functions  by  which  they  are  peculiarly  characterized, — namely,  Sensation 
and  Voluntary  Motion ;  all  the  instruments  of  these  operations  being  main- 
tained, like  the  rest  of  the  organic  structure,  in  a  state  fit  for  activity,  by  the 
processes  of  Nutrition,  which  are  performed  on  the  same  plan  in  them  as  in 
other  parts. 


72  GENERAL  VIEW  OF  THE  FUNCTIONS. 

77.  Indeed  it  appears  to  be  principally  for  the  maintenance  of  these  instru- 
ments in  a  state  fit  for  activity,  that  by  far  the  largest  part  of  the  food  ingested 
by  most  Animals  is  required.  *  The  duration  of  the  existence  of  the  Muscular 
and  Nervous  tissues,  appears  to  depend  entirely  upon  the  use  that  is  made  of 
them  ;  being  less  as  their  functional  activity  is  greater.     Thus,  when  an  ani- 
mal is  very  inactive,  it  requires  but  little  nutrition ;  if  in  moderate  activity, 
there  is  a  moderate  demand  for  food ;  but  if  its  muscular  energy  be  frequently 
and  powerfully  aroused,  the  supply  must  be  increased,  in  order  to  maintain 
the  vigour  of  the  system.     There  would  seem  reason,  then,  to  believe,  that 
every  animal  movement,  requiring  the  expenditure  of  a  certain  degree  of  mus- 
cular power,  does  really  involve  the  death  and  re-formation  of  a  certain  amount 
of  muscular  tissue  ;  and  this  idea  is  confirmed  by  the  fact,  that  the  quantity  of 
waste  thrown  off  by  the   excreting  processes, — or,  at  least,  of  that  part  of  it 
which  results  from  the  disintegration  of  the  muscular  structure, — is  propor- 
tional to  the  expenditure  of  muscular  power,  increasing  (like  the  demand  for 
food  which  is  consequent  upon  it)  with  the  general  activity,  and  diminishing 
with  rest.     This  doctrine,  which  was  first  pointedly  stated  by  Liebig,  though 
propounded  in  more  general  terms  by  previous  writers,  may  probably  be  ex- 
tended from  the  Muscular  system  (in  regard  to  which  alone  it  has  been  urged 
by  Liebig)  to  the  Nervous,  as  well  as  to  the  various  organs  of  Nutrition.     Many 
circumstances  lead  to  the  belief,  that  the  Nervous  tissue,  when  in  a  state  of 
functional  activity,  undergoes  a  rapid  waste  or  disintegration,  and  a  correspond- 
ing renewal.     The  very  large  quantity  of  blood  with  which  the  nervous  cen- 
tres are  supplied,  and  the  immediate  dependence  of  nervous  power  upon  the 
maintenance  of  that  supply  (§  177),  strongly  indicate  this;  for  we  invariablj 
find,  that  parts  which  undergo  little  interstitial  change,  receive  but  a  small 
supply  of  blood.     Again,  it  is  well  known  that,  when  the  nervous  system  has 
been  in  unusual  activity,  there  is  a  marked  increase  in  the  phosphatic  depo- 
sits in  the  urine  ;  and,  as  the  quantity  of  phosphorus  in  any  others  of  the  soft 
tissues  is  very  inconsiderable,  it  is  scarcely  possible  to  attribute  this  liberation 
of  phosphorus  from  the  system  to  any  other  cause  than  the  waste  of  nervous 
matter,— that  is,  its  decomposition,  resulting  from  the  discharge  of  its  vital 
function.     Again,  the  close  chemical  relation  which  subsists  between  nervous 
and  adipose  matter  (the  substance  peculiar  to  nervous  tissue  being  a  fatty  acid, 
containing  a  very  small  proportion  of  azote,  but  united  with  a  considerable 
amount  of  phosphorus,)  corresponds  exactly  with  the  old  observation,  that  per- 
sons of  "  nervous  temperament"  are  seldom  fat ;  whilst  those  of  inert  bodily 
and  mental  habits  are  much  more  subject  to  this  deposit.     Since  nervous 
matter  is  chiefly  formed  out  of  the  same  elements  as  those  which  would  other- 
wise be  deposited  as  adipose  tissue,  it  appears  probable  that  the  demand  for 
these,  occasioned  by  the  continual  use  of  the  nervous  system,  prevents  the  de- 
posit of  fat ;  whilst  its  inactivity  allows  their  accumulation  in  another  form. 
It  may  probably  be  stated,  then,  as  a  general  ,truth,  that  every  act  of  Mind  is 
inseparably  connected,  in  our  present  state  of  being,  with  material  changes  in 
the  Nervous  System ;  a  doctrine  not  in  the  least  inconsistent  with  the  belief 
in  the  separate  immaterial  existence  of  the  Mind  itself. 

78.  The  degree  in  which  the  operations  of  the  mind  are  dependent  upon  its 
material  instruments,  is  a  question  which  cannot  be  regarded  as  conclusively 
determined  by  scientific  evidence  alone  ;  and  it  has  little  practical  bearing  on 
Physiological  research.     The  doctrine  usually  regarded  as  having  the  best 
Scriptural  basis, — that  the  mind  has  an  existence  altogether  distinct  from  that 
of  the  body, — is  attended  with  several  difficulties,  of  which  those  arising  dut  of 
the  phenomena  of  Insanity  are  perhaps  the  most  important.    On  the  other  hand, 
the  opinion  held  by  some,  that  mental  phenomena  are  the  mere  results  of  ma- 
terial changes,  appears  to  involve  difficulties  at  least  equal ;  amongst  which 

•  \ 


OF  VITAL  ACTIONS,  AND  THEIR  MUTUAL  DEPENDENCE.  73 

may  be  noticed,  the  consciousness  of  personal  identity,  preserved  throughout 
the  continual  and  rapid  changes  to  which  the  Nervous  structure  is  subject. 
The  assertion,  however,  that  psychical  operations  cannot  be  the  result  of  mate- 
rial changes,  is  based  on  the  assumption,  that  we  know  far  more  of  the  essential 
characters  of  both,  than  is  admitted  by  the  best  metaphysicians  to  be  the  case 
regarding  either.  This  is  one  of  the  questions,  which  scarcely  comes  within 
the  boundaries  of  mere  human  knowledge.  Neither  hypothesis  is  inconsistent 
with  the  Revealed  doctrine  of  the  Immortality  of  the  Soul ;  though  the  second 
could  not  be  made  to  conform  to  it,  without  the  additional  supposition  that  some 
refined  form  of  matter,  on  which  psychical  operations  essentially  depend,  has 
also  an  eternal  existence ;  and  the  upholders  of  this  doctrine  seek  a  confirma- 
tion of  it  in  the  expression  "  spiritual  body,"  used  by  an  authority  which  is  all 
but  supreme.*  The  certainty  of  a  future  existence,  in  which  all  that  is  cor- 
ruptible shall  be  done  away,  is  the  grand  practical  fact  for  the  Christian ;  on 
the  mode  of  it  the  philosopher  may  speculate ;  and,  even  though  he  may  come 
to  the  conclusion  that  "Mind  and  Matter  are  logically  distinct  existences,"  yet 
he  finds  their  operations  so  inextricably  interwoven  in  the  phenomena  of  Man's 
terrestrial  life,  that  he  cannot  pursue  either  class  by  itself  alone.  The  physi- 
ologist, therefore,  will  enter  upon  the  inquiry  with  the  best  prospect  of  success, 
if  untrammeled  by  any  preformed  opinions,  and  ready  to  form  his  deductions 
from  the  facts  presented  to  his  notice. 

79.  That  a  very  close  relation  may  be  traced  between  the  variety  and  im- 
portance of  the  psychical  phenomena  of  different  classes  of  animals,  and  the 
complexity  and  size  of  their  material  instruments,  all  must  admit ;  and  it  seems 
difficult,  on  the  supposition  of  the  completely  distinct  existence  of  Mind,  to 
separate  the  phenomena  to  which  organic  changes  are  and  must  be  essential, 
from  such  as  do  not  require  these  for  their  production.  For  example,  it  is 
universally  admitted,  that  the  mind  cannot  become  cognizant  of  any  impression 
made  by  an  object  external  to  it,  except  through  the  medium  of  a  material 
change,  commencing  in  the  orgaji  of  sense,  and  propagated  to  the  central 
sensorium ;  and  yet  of  the  absolute  nature  of  this  change  we  know  nothing. 
Now  the  Sensation  thus  produced  cannot  give  rise  (as  will.be  shown  hereafter, 
§  288,)  to  a  Perception, — the  formation  of  an  elementary  notion  of  the  nature 
of  the  object  causing  the  impression,—— without  a  series  of  changes,  in  which 
Memory,  Association,  Judgment,  &c.,  are  involved.  Memory  seems  clearly 
the  result  of  the  permanency  of  the  material  change  effected  by  the  sensation  ; 
for  it  is  peculiarly  liable  to  be  affected  by  disorders  or  injuries  of  the  brain, 
which  do  not  impair  that  power  of  Comparison,  and  perception  of  Causation, 
by  which  the  Reasoning  faculty  works  upon  the  materials  submitted  to  it.  If 
Memory  be  thus  connected  with  organic  changes,  the  power  of  mental  Concep- 
tion, which  is  dependent  upon  the  reftewal  of  the  state  immediately  produced 
by  Sensation  and  Perception,  is  scarcely  to  be  separated  from  them.  Now  it 
seems  impossible  to  draw  a  distinct  line  between  these  operations,  on  the  one 
hand,  and  the  power  of  Imagination,  which  derives  most  or  all  of  its  materials 

*  The  writer  is  most  happy  to  find  himself  supported  in  these  views,  by  so  high  a 
theological  authority  as  that  of  the  propounder  of  the  "Physical  Theory  of  Another 
Life;"  who,  after  pointing:  out  how  completely  the  question, — whether  the  human  soul  is 
ever  actually  and  entirely  separated  from  matter — is  passed  over  by  St.  Paul,  as  an  in- 
quiry altogether  irrelevant  to  religion,  thus  continues  :  "  Let  it  then  be  distinctly  kept  in 
view,  that  although  the  essential  independence  of  mind  and  matter,  or  the  abstract  possi- 
bility of  the  former  existing  apart  from  corporeal  life,  may  well  be  considered  as  tacitly 
implied  in  the  Christian  scheme,  yet  that  an  actual  incorporeal  state  of  the  human  soul, 
at  any  period  of  its  course,  is  not  necessarily  involved  in  the  principles  of  our  faith,  any 
more  than  it  is  explicitly  asserted.  This  doctrine,  concerning  what  is  called  the  immate- 
riality of  the  soul,  should  ever  be  treated  simply  as  a  philosophical  speculation,  and  as 
unimportant  to  our  Christian  profession." 


74  GENERAL  VIEW  OF  1*HE  FUNCTIONS. 

from  Conception,  and  the  Reasoning  Faculties,  which  are  still  more  closely 
dependent  upon  Impressions  made  from  without,  on  the  other.  For  the  phe- 
nomena of  Insanity  are  continually  presenting  to  us  instances  of  the  disorder 
of  these  powers,  without  any  corresponding  disorder  of  the  operations,  which 
intervene  between  them  and  the  external  world ;  and  such  disorder  is  often 
(perhaps  uniformly)  coincident  with  some  morbid  condition  of  the  brain.  In 
regard  to  the  Moral  Feelings  and  Emotions,  again,  it  would  seem  equally 
impossible  to  separate  these  by  a  distinct  line,  from  the  lower  passions  and 
instinctive  propensities,  which  are  still  more  closely  connected  with  material 
changes  ;  and  the  daily  experience,  even  of  a  person  in  ordinary  health,  reveals 
to  him  how  strongly  the  emotional  conditions  of  the  mind  are  influenced  by  the 
state  of  the  organic  functions ;  and  how  powerfully,  on  the  other  hand,  the 
latter  are  reacted  on  by  the  former.  These,  being  phenomena  which  strictly 
form  a  part  of  the  Life  of  Man,  evidently  belong  to  the  domain  of  the  Physi- 
ologist ;  and  no  speculative  views  can  (or,  at  least,  ought  to)  affect  our  reasoning 
from  facts. 

80.  The  operations  of  the  Mind  and  of  its  instruments,  taken  collectively, 
constitute  what  are  known  as  the  Functions  of  Jlnimal  Life.  Those  most  ob- 
viously connected  with  the  bodily  fabric,  are  Sensation  and  spontaneous  Motion; 
for  these  we  find  special  instruments  provided, — the  organs  of  sense  and  the 
muscular  apparatus.  Both  these,  with  the  nervous  system  itself  are  composed, 
like  other  parts  of  the  fabric,  of  organized  structure,  which  does  not  differ  essen- 
tially from  that  of  the  apparatus  of  Vegetative  life,  either  in  the  mode  of  its 
first  production,  or  in  that  in  which  its  integrity  is  maintained,  and  its  activity 
preserved.  The  conditions  requisite  for  these  objects  will  be  presently  dis- 
cussed. But,  although  the  functions  of  Animal  life  may  be  regarded  as  in 
themselves  completely  isolated  from  those  of  Organic  life, — the  latter  merely 
supplying  the  conditions  of  the  former,  by  keeping  (so  to  speak)  their  instru- 
ments in  good  order, — yet  there  are  certain  links  of  connection  between  the 
two,  which  render  the  latter  equally  dependent  on  the  former.  Thus,  in  re- 
gard to  the  acquisition  of  food,  the  Animal  has  to  make  use  of  its  senses,  its 
psychical  faculties,  and  its  power  of  locomotion,  to  obtain  that,  which  the 
Plant,  from  the  different  provision  made  for  its  support,  can  derive  without  any 
such  assistance.  Moreover,  the  propulsion  of  the  food  along  the  alimentary 
canal  is  effected  by  a  series  of  operations,  in  which  the  Nervous  and  Muscular 
systems  are  together  involved  at  the  two  extremes,  whilst  simple  Muscular 
contractility  is  alone  employed  through  the  greater  part  of  the  intestinal  canal. 
Thus,  the  change  in  the  condition  required  for  the  ingestion  of  food  by  Ani- 
mals, has  rendered  necessary  the  introduction  of  an  additional  element  in  the 
apparatus,  to  which  nothing  comparable  was  to  be  found  in  Plants.  Again, 
in  the  function  of  Respiration,  as  performed  in  the  higher  Animals,  the  Ner- 
vous and  Muscular  systems  are  alike  involved ;  for  the  movements  by  which 
the  air  in  the  lungs  is  being  continually  renewed,  are  dependent  upon  the 
action  of  both ;  and  those  by  which  the  blood  is  propelled  through  the  respi- 
ratory organs,  are  chiefly  occasioned  by  the  contractility  of  a  muscular  organ, 
—-the  heart.  But  in  regard  to  the  simple  contractility  of  muscular  fibre,  upon 
the  direct  application  of  a  stimulus  to  it,  which  is  the  agent  in  the  movements 
of  the  heart  and  of  the  alimentary  canal,  it  may  be  remarked,  that  it  does  not 
differ  in  any  essential  degree  from  that  which  is  Avitnessed  in  many  Vege- 
tables ;  and  that  it  strictly  belongs,  therefore,  to  the  functions  of  Organic  life. 
And  with  respect  to  those  concerned  in  the  act  of  Respiration,  as  well  as  those 
which  govern  the  two  orifices  of  the  alimentary  tube,  it  will  hereafter  appear 
that  they  result,  equally  with  the  former,  from  the  application  of  a  stimulus ; 
and  that  they  may  be  performed  without  any  consciousness  on  the  part  of  the 
individual  (though-  ordinarily  accompanied  by  it) : — the  difference  being,  that 


OF  VITAL  ACTIONS,  AND  THEIR  MUTUAL  DEPENDENCE.  75 

in  the  former  the  stimulus  is  applied  to  the  contractile  part  itself,  whilst  in  the 
latter  it  is  applied  to  an  organ  with  which  this  is  connected  by  nerves  only. 
Now  we  have,  even  in  Vegetables,  instances  of  the  propagation  of  an  irrita- 
tion from  one  part  to  another,  so  that  a  motion  results  in  a  part  distant  from 
that  stimulated, — as  in  the  case  of  the  Sensitive  Plant,  or  Venus's  Fly-trap. 
The  only  essential  difference,  therefore,  between  those  movements  of  Animals, 
which  are  thus  closely  connected  with  the  maintenance  of  the  organic  func- 
tions, and  those  of  Plants,  consists  in  the  medium  through  which  they  are 
performed, — this  being  in  Animals  the  Nervous  and  Muscular  apparatus, 
whilst  in  Plants  it  is  only  a  peculiar  modification  of  the  ordinary  structure. 

81.  From  what  has  been  said,  then,  it  appears  that  all  the  functions  of  the 
Animal  body  are  so  completely  bound  up  together,  that  none  can  be  suspended 
without  the  cessation  of  the  rest.  The  properties  of  all  the  tissues  and  organs 
are  dependent  upon  their  regular  Nutrition  by  a  due  supply  of  perfectly  ela- 
borated blood;  this  cannot  be  effected,  unless  the  functions  of  Circulation, 
Respiration  and  Secretion,  be  performed  with  regularity, — the  first  being 
necessary  to  convey  the  supply  of  nutritious  fluid,  and  the  twro  latter  to  sepa- 
rate it  from  its  impurities.  The  Respiration  cannot  be  maintained  without  the 
integrity  of  a  certain  part  of  the  nervous  system ;  and  the  due  action  of  this, 
again,  is  dependent  upon  its  regular  nutrition.  The  materials  necessary  for 
the  replacement  of  those,  which  are  continually  being  separated  from  the  blood, 
can  only  be  derived  by  the  Absorption  of  ingested  aliment ;  and  this  cannot 
be  accomplished,  without  the  preliminary  process  of  Digestion.  The  intro- 
duction of  food  into  the  stomach,  again,  is  dependent,  like  the  actions  of  Re- 
spiration, upon  the  operations  of  the  muscular  apparatus  and  of  a  part  of  the 
nervous  centres;  and  the  previous  acquirement  of  food  necessarily  involves 
the  purely  Animal  powers.  Now  it  will  serve  to  show  the  distinction  between 
these  powers,  and  those  which  are  merely  subservient  to  Organic  life,  if  we 
advert  to  the  case,  which  is  of  no  unfrequent  occurrence,  of  a  human  being, 
deprived  by  some  morbid  condition  of  the  brain,  of  all  the  powers  of  Animal 
life, — Sensation,  Thought,  Volition,  &c. ;  and  yet  capable  of  maintaining  a 
vegetative  existence, — all  the  organic  functions  going  on  as  usual,  the  morbid 
condition  not  having  affected  the  division  of  the  nervous  system  that  is  con- 
cerned in  the  movements  on  which  some  of  them  depend.  It  is  evident  that 
we  can  assign  no  definite  limits  to  such  a  state,  so  long  as  the  necessary  food 
is  placed  within  the  reach  of  the  grasp  of  the  muscles,  that  will  convey  it  into 
the  stomach :  as  a  matter  of  fact,  however,  it  is  seldom  of  long  continuance ; 
since  the  disordered  state  of  the  brain  is  sure  to  extend  itself,  sooner  or  later, 
to  the  rest  of  the  nervous  system.  This  condition  may  be  experimentally  imi- 
tated, however,  by  the  removal  of  the  brain,  in  many  of  the  lower  animals, 
whose  bodies  will  sustain  life  for  many  months  after  such  a  mutilation ;  but 
this  can  only  take  place,  when  that  food  is  conveyed  by  external  agency,  within 
the  pharynx,  which  they  would,  if  in  their  natural  condition,  have  obtained 
for  themselves.  A  similar  experiment  is  sometimes  made  by  Nature  for  the 
physiologist,  in  the  production  of  fo3tuses,  as  well  of  the  human  as  of  other 
species,  in  which  the  brain  is  absent ;  these  can  breathe  and  suck  and  swal- 
low, and  perform  all  their  organic  functions ;  and  there  is  no  assignable  limit 
to  their  existence,  so  long  as  they  are  duly  supplied  with  food.  Hence  we 
may  learn  the  exact  nature  of  the  dependence  of  the  Organic  functions  upon 
those  of  purely  Animal  life  ;  and  we  perceive  that,  though  less  immediate  than 
it  is  upon  the  simple  organic  operations  of  the  nervous  and  muscular  systems, 
it  is  not  less  complete.  On  the  other  hand,  the  functions  of  Animal  life  are 
even  more  closely  dependent  upon  the  Nutritive  actions  than  are  those  of  or- 
ganic life  in  general ;  for  many  tissues  will  retain  their  several  properties,  and 
their  power  of  growth  and  extension,  for  a  much  longer  period  after  a  general 


76  GENERAL  VIEW  OF  THE  FUNCTIONS. 

interruption  of  the  circulation,  than  will  the  Nervous  structure,  which  is,  in- 
deed, instantaneously  affected  by  a  cessation  of  the  due  supply  of  blood,  or  by 
the  depravation  of  its  quality. 

82.  It  is  of  little  consequence,  then,  with  which  group  of  functions  we  com- 
mence the  detailed  study  of  the  phenomena  which,  in  their  totality,  make  up 
the  life  of  Man.     In  viewing  him  merely  as  one  of  the  widely-extended  group 
of  organized  beings,  it  would  be  natural  to  commence  with  those  phenomena 
which  are  common  to  all ;  and  to  make,  therefore,  the  Organic  functions  the 
first  object  of  our  consideration.     On  the  other  hand,  regarding  Man  as  a  being 
in  some  degree  isolated  from  all  these  by  his  peculiar  characteristics,  it  seems 
right  to  inquire  into  the  latter  in  the  first  instance ;  more  especially  as,  in  a 
general  view  of  his  life,  these  occupy  the  most  prominent  place.     It  will  be 
necessary,  however,  previously  to  entering  upon  them,  to  take  a  more  detailed 
survey  than  we  have  hitherto  done,  of  the  vital  operations  performed  by  his 
several  organs,  and  of  their  connections  with  each  other.    We  shall  commence 
with  those  of  Vegetative  Life. 

Functions  of  Vegetative  Life. 

83.  It  is  one  of  the  most  peculiar  characteristics  of  organized  structure,  that 
its  elements  have  a  constant  tendency  (under  ordinary  circumstances  at  least) 
to  separate  into  more  simple  combinations  ;  and,  although  it  has  been  ordina- 
rily considered  that  their  living  state  prevents  such  a  change,  and  that  they 
have  no.  tendency  to  it  except  when  dead,  reason  will  hereafter  be  given  for 
the  belief  that  no  such  distinction  exists  (§§  645,  646).     The  maintenance  of 
the  vital  properties  of  all  organized  structure,  then,  requires  either  that  this 
structure  should  be  completely  secluded  from  air,  moisture,  warmth,  and  other 
agents  which  tend  to  its  decomposition ;  or  that  it  should  be  renewed  as  fast 
as  it  decays.     Now  the  exclusion  of  these  decomposing  agents  would  prevent 
any  vital  actions  from  being  called  into  operation ;  since  they  are  the  ordinary 
stimuli,  which  are  necessary  to  them.     For  instance,  a  seed  which  is  buried 
so  deep  in  the  soil  as  to  be  excluded  from  the  contact  of  air,  and  from  the 
warmth  of  the  sun,  will  not  vegetate,  although  it  may  retain  its  power  of  germi- 
nating when  placed  in  more  favourable  circumstances ;  and  it  will  not  decay, 
because  secluded  from  the  air  and  warmth  which  are  necessary  to  its  decom- 
position.    But  as  a  certain  decomposition  appears  to  be  a  necessary  condition 
of  its  vital  activity,  it  is  obviously  necessary  that  a  provision  should  be  made, 
for  removing  from  the  organism  all  those  particles,  which  are  manifesting  an 
incipient  tendency  to  decay,  and  are  thus  losing  their  vital  properties ;  and  for 
replacing  these  by  newly-combined  particles,  which  in  their  turn  undergo  the 
same  process.     Thus  we  find  that,  in  the  softest  parts  of  the  Animal  frame- 
work, as  in  those  of  the  Plant,  there  is  much  less  permanency  than  there  is 
in  those  harder  and  more  solid  portions,  which  often  seem  altogether  to  defy 
the  lapse  of  time.     Now  it  is  in  the  former  that  the  most  active  vital  changes 
take  place, — those  of  the  nervous  system,  for  example  ;  whilst  of  the  latter,  the 
function  is  chiefly,  if  not  entirely,  that  of  giving  mechanical  support  to  the 
structure.    The  fact,  which  is  easily  proved,  that  the  former  organs  are  renewed 
many  times,  whilst  the  fabric  of  the  latter  is  not  once  completely  changed, 
shows  a  very  interesting  correspondence  between  the  degree  in  which  the 
action  of  any  organized  structure  is  removed  from,  or  is  similar  to,  that  of  a 
mere  inorganic  substance,  and  the  amount  of  tendency  to  decomposition  which 
that  structure  exhibits ;  since  this  constant  renewal  can  scarcely  serve  any 
other  purpose  than  that  of  making  up  for  the  effects  of  decay. 

84.  One  of  the  most  important  purposes  of  the  supply  of  aliment,  therefore, 
which  all  living  beings  continually  require,  is  the  replacement  of  the  portions 


FUNCTIONS  OF  VEGETATIVE  LIFE.  77 

of  the  fabric  that  are  thus  lost.  The  effects  of  the  process  of  decay,  when 
uncompensated  by  that  of  renovation,  are  remarkably  seen  in  cases  of  starva- 
tion ;  for  it  is  a  very  constant  indication  of  this  condition,  that  the  body  exhales 
a  putrescent  odour,  even  before  death,  and  that  it  subsequently  passes  very 
rapidly  into  decomposition.  This,  it  may  be  considered,  is  the  reason  why  a 
constant  supply  of  aliment  is  still  required  for  the  maintenance  of  every  organic 
structure,  though  it  may  have  arrived  at  its  full  growth  ;  and  it  also  affords 
one  source  of  explanation  of  the  fact,  that  old  people  require  less  food  than 
adults,  since  their  tissues  are  more  consolidated,  and  thus  become  at  the  same 
time  unable  to  perform  their  usual  actions  with  their  pristine  energy,  whilst 
their  tendency  to  decomposition  is  less.  In  the  growing  state,  however,  an 
additional  important  source  of  demand  for  food  obviously  exists,  in  the  extension 
which  the  tissues  themselves  are  constantly  receiving ;  yet  this,  perhaps,  does 
not  make  so  great  a  difference  as  it  appears  to  do  in  the  supply  which  is 
requisite.  For  if  the  addition  which  is  made  by  growth  to  the  body  in  any 
given  time,  be  compared  with  the  amount  of  exchange  which  has  taken  place 
in  the  same  time, — the  latter  being  judged  of  by  the  quantity  of  matter  excreted 
from  the  lungs,  liver,  kidneys,  skin,  &c., — it  will  be  found  to  bear  but  a  very 
small  proportion  to  it,  except  during  fetal  life,  when  the  growth  is  very  rapid, 
and  a  large  proportion  of  the  effete  particles  are  brought  to  the  maternal  blood, 
to  be  excreted  from  it.  The  real  cause  of  the  increased  demand  for  nutriment 
during  the  early  part  of  life  is  rather  this, — that  the  tissues  are  far  from  having 
acquired  that  firmness  and  consolidation  which  they  gain  at  adult  age  ;  and 
that  they  are,  therefore,  more  prone  to  decomposition,  at  the  same  time  that 
their  vital  activity  is  greater,  as  is  well  known  to  be  the  case.  The  feeling 
of  hunger  or  desire  for  food  originates,  we  shall  hereafter  find  reason  to  believe 
(§§  430,  437),  not  so  much  in  the  stomach  itself,  as  in  the  system  at  large  ;  of 
whose  condition,  in  regard  to  the  requirement  of  an  increased  supply  of  ali- 
ment, it  may,  during  the  state  of  health,  be  considered  as  a  pretty  faithful  index. 
The  same  may  be  said  of  thirst.  The  feeling  of  hunger,  then,  is  the  stimulus 
to  the  mental  operations  which  have  for  their  object  the  acquisition  qf  food, 
whether  these  be  of  a  voluntary  or  of  a  purely  instinctive  kind ;  in  Man  they 
are  obviously  the  former,  during  all  but  infant  life.* 

85.  The  food  received  into  the  mouth,  and  prepared  there  by  the  acts  of 
mastication  and  insalivation  (the  movements  concerned  in  which  are  dependent 
upon  the  brain,  and  can  only  be  performed  when  it  is  in  a  condition  of  some 
activity),  is  brought  by  them  within  reach  of  the  pharyngeal  muscles,  whose 
contraction  cannot  be  effected  by  the  will,  but  is  purely  instinctive,— resulting 
merely  from  the  impression  made  upon  the  fauces  by  the  contact  of  the  sub- 
stance swallowed,  which  impression  is  conveyed  to  the  medulla  oblongata  and 
reflected  back  to  the  muscle  (§  191).  By  these  it  is  propelled  down  the  oeso- 
phagus ;  and,  after  their  action  has  ceased,  it  is  taken  up  (as  it  were)  by  the 
muscular  coat  of  the  oesophagus  itself,  and  conveyed  into  the  stomach.  How 
far  the  movements  of  the  lower  parts  of  the  oesophagus  and  of  the  stomach  are 
in  Man  dependent  upon  reflex  action,  is  uncertain;  the  facts  which  have  been 
ascertained  on  this  point,  by  experiment  on  animals,  will  be  detailed  in  their 
proper  place  (§  194).  In  the  stomach,  the  food  is  subjected  to  the  gastric 
secretion ;  the  chemical  action  of  which,  aided  by  the  constantly  elevated  tem- 
perature of  the  interior  of  the  body,  and  by  the  continual  agitation  effected  by 
the  contractions  of  the  parietes  of  the  organ,  effects  a  more  or  less  complete 
solution  of  it.  Reason  will  hereafter  appear  for  the  belief  that,  up  to  this  point, 
no  action  peculiarly  vital  is  immediately  concerned  in  the  reduction  of  the 
food ;  and  that,  if  the  physical  conditions  of  the  process  could  be  exactly  imi- 
tated out  of  the  body,  the  result  would  be  precisely  the  same.  The  mixture 
of  the  biliary  and  pancreatic  secretions  with  the  chyme  thus  produced,  occa- 

7* 


78  GENERAL  VIEW  OF  THE  FUNCTIONS. 

sions  a  separation  of  its  elements  into  those  adapted  for  nutrition,  and  those  of 
which  the  character  is  excrementitious ;  and  this  separation  can  scarcely  be 
regarded  in  any  other  light  than  as  a  chemical  precipitation.  The  nutritious 
portion  is  then  taken  up  by  the  Absorbent  vessels,  or  Lacteals,  which  are  dis- 
tributed on  the  walls  of  the  alimentary  canal ;  whilst  the  remainder  is  propelled 
along  the  intestinal  tube  by  the  simple  contractility  of  its  walls,  undergoing  at 
the  same  time  some  further  change,  by  which  the  nutritive  materials  are  still 
more  completely  extracted  from  it.  And  at  last,  the  excrementitious  matter, — 
consisting  not  only  of  a  portion  of  the  food  taken  into  the  stomach,  but  also  of 
part  of  the  secretion  of  the  liver,  and  of  that  of  the  mucous  surface  of  the 
intestines, — is  voided  from  the  opposite  extremity  of  the  canal,  by  a  muscular 
exertion,  which  is  partly  reflex,  like  that  of  deglutition,  but  is  partly  voluntary, 
especially  (as  it  would  appear)  in  Man. 

86.  There  seems  no  doubt  that  fluid,  containing  saline  or  other  soluble 
matters,  may  be  absorbed  by  the  blood-vessels,  with  which  the  mucous  mem- 
brane of  the  alimentary  canal  is  so  copiously  supplied ;  and  this  simple  process 
of  Imbibition  probably  takes  place,  according  to  the  physical  laws  of  Endos- 
mose.     But  the  Selection  and  Absorption  of  the  nutritious  fluid  appear  to  be 
performed,  not  by  vessels,  but  by  cells  ;  which  are  developed  at  the  extremities 
of  the  villi,  from  germs  previously  existing  there ;   and  which,  after  having 
filled  themselves  with  the  ingredients  drawn  from  the  cavity  of  the  intestinal 
canal,  deliver  these  to  the  lacteal  absorbents,  either  by  bursting,  or  by  dissolv- 
ftig  away, — their  own  term  of  life  being  expired.     The  absorbed  fluid,  which 
now  receives  the  name  of  Chyle,  is  propelled  through  the  Lacteals  by  the 
contractility  of  their  walls  ;  aided  in  part,  perhaps,  by  a  vis  a  tergo  derived 
from  the  force  of  the  absorption  itself.     With  the  reception  of  the  nutritious 
fluid  into  the  absorbent  vessels,  commences  its  real  preparation  for  organiza- 
tion.    Up  to  that  period,  it  cannot  be  said  to  be  in  any  degree  vitalized  ;  the 
changes  which  it  has  undergone  being  only  of  a  chemical  and  physical  nature, 
and  such  as  merely  prepare  it  for  subsequent  assimilation.     But  in  its  passage 
through  the  long  and  tortuous  system  of  absorbent  vessels  and  glands,  it  un- 
dergoes changes  which,  Avith  little  chemical  difference,  manifest  themselves 
by  a  decided  alteration  in  its  properties  ;  so  that  the  chyle  of  the  thoracic  duct  is 
evidently  a  very  different  fluid  from  the  chyle  of  the  lacteals,  approaching  much 
nearer  to  blood  in  its  general  characters.     These  characters  are  such  as  indi- 
cate that  the  process  of  organization  and  vitalization  has  commenced ;  as  may 
be  known  alike  from  the  microscopic  appearance  of  the  fluid,  and  from  the 
actions  it  performs  when  removed  from  the  body.     There  is  reason  to  believe 
that  the  changes,  which  the  Chyle  undergoes  in  its  progress  through  the  lac- 
teals, are  due  to  the  action  of  certain  cells  which  are  seen  to  be  diffused  through 
the  liquid  ;  these,  by  their  own  independent  powers  of  growth,  are  continually 
absorbing  into  themselves  the  fluid  in  which  they  float ;  whilst,  by  bursting  or 
liquefying,  as  soon  as  their  term  of  life  is  completed,  they  give  this  back  in  an 
altered  state.     The  Chyle  thus  modified  is  conveyed  into  the  Sanguiferous 
system  of  vessels,  and  flows  directly  to  the  heart ;  by  which  it  is  transmitted, 
with  the  mass  of  the  blood,  to  the  lungs.     It  there  has  the  opportunity  of  ex- 
creting its  superfluous  carbonic  acid,  and  of  absorbing  oxygen  ;   and  probably 
acquires  gradually  the  properties  by  which  the  blood  previously  formed  is 
distinguished, — thus  becoming  the  pabulum  vitas  for  the  whole  system. 

87.  The  Circulation  of  the  Blood  through  the  tissues  and  organs  which  it 
is  destined  to  support,  is  a  process  evidently  necessary  for  the  conveyance  to 
them  of  the  nutritious  materials,  which  are  provided  for  the  repair  of  their 
waste  ;  and  for  the  removal  of  those  elements  of  their  fabric,  which  are  in  a 
state  of  incipient  decomposition.     In  the  lowest  classes  of  organized  beings, 
every  portion  of  the  structure  is  in  direct  relation  with  its  nutritive  materials ; 


FUNCTIONS  OF  VEGETATIVE  LIFE.  79 

it  can  absorb  for  itself  that  which  is  required,  and  it  can  readily  part  with  that 
of  which  it  is  desirable  to  get  rid.  Hence  in  such,  no  general  circulation  is 
necessary.  In  Man,  on  the  other  hand,  the  digestive  cavity  occupies  so  small 
a  portion  of  the  body,  that  the  organs  at  a  distance  from  it  have  no  other 
means,  than  their  vascular  communication  affords,  of  participating  in  the 
results  of  its  operations ;  and  it  is,  moreover,  necessary,  that  they  should  be 
continually  furnished  with  the  organizable  materials,  of  which  the  occasional 
operation  of  the  digestive  process  would  otherwise  afford  only  an  intermitting 
supply.  This  is  especially  the  case,  as  already  mentioned,  with  the  nervous 
system,  which  is  so  predominant  a  feature  in  the  constitution  of  Man ;  and  we 
accordingly  find  both  objects  provided  for,  in  the  formation  of  a  large  quantity 
of  a  semi-organized  product,  which  contains  within  itself  the  materials  of  all 
the  tissues,  and  is  constantly  being  carried  into  relation  with  them.  Blood 
has  been  not  unaptly  termed  chair  coulante,  or  liquid  flesh ;  and  although  it 
has  been  heretofore  much  questioned,  whether  it  could  be  regarded  as  either 
organized  or  endowed  with  vital  properties,  there  now  appears  to  be  sufficient 
reason  for  admitting  that  this  is  the  case  to  a  very  considerable  extent.  The 
propulsion  of  the  blood  through  the  large  trunks,  which  subsequently  divide 
into  capillary  vessels,  is  due  to  the  contractions  of  a  hollow  muscular  organ, 
the  Heart ;  but  these,  like  the  peristaltic  movements  of  the  alimentary  canal, 
are  quite  independent  of  (though  frequently  influenced  by)  the  agency  of  the 
nervous  system ;  and  are  therefore  to  be  referred  to  the  class  of  organic  move^ 
ments,  such  as  occur  in  Vegetables. 

88.  Upon  the  circulation  of  the  blood  through  all  parts  of  the  fabric,  depends 
in  the  first  place  the  Nutrition  of  the  tissues.  Upon  this  subject,  formerly 
involved  in  the  greatest  obscurity,  much  light  has  recently  been  thrown.  In 
the  lowest  classes  of  Plants  and  Animals,  the  whole  or  the  greatest  part  of  the 
fabric  is  composed  of  vesicles  or  cells  aggregated  together,  each  of  which  has 
a  certain  degree  of  independent  vitality,  and  can  live  to  a  great  extent  by  itself 
alone,  if  duly  supplied  with  nutriment.  These  cells  differ  but  little  from  each 
other  in  structure  and  endowment ;  and  the  whole  mass  approaches  far  more 
nearly,  therefore,  to  the  homogeneous  character  of  inorganic  bodies  than  does 
the  fabric  of  beings  more  elevated  in  the  scale.  This  is  precisely  the  condi- 
tion of  the  embryonic  structure  of  the  highest  Animals,  at  an  early  period  of 
their  existence.  Now  in  such  fabrics,  there  is  no  distinct  vascular  system. 
Every  cell  absorbs, — either  from  the  surrounding  nutritious  materials  with 
which  it  may  be  itself  in  contact,  or  from  other  cells  in  nearer  proximity  to 
these, — the  aliment  it  requires  for  its  own  growth  and  reproduction ;  and  per- 
forms all  its  vital  processes,  with  little  direct  influence  from  any  general  con- 
trolling power.  The  extension  of  the  individual  structure  is  partly  effected  by 
the  enlargement  of  its  original  vesicles ;  but  principally  by  the  generation  of 
new  ones  within  these  ;  and  the  latter,  in  their  turn,  go  through  the  same  pro- 
cesses. In  the  higher  Plants,  however,  we  find  a  greater  variety  of  tissues ; 
but  these  all  take  their  origin  in  cells.  The  straight  tubes,  for  instance,  which 
convey  the  sap  from  the  roots  to  the  leaves,  were  evidently  at  first  a  line  of 
large  cells,  laid  end  to  end,  the  partitions  between  which  have  broken  down, 
so  that  their  cavities  coalesce  ;  and  the  network  of  anastomozing  vessels,  by 
which  the  descending  or  nutritious  sap  is  conveyed  through  the  tissues,  may 
be  traced  to  a  corresponding  origin.  The  circulation  of  the  sap  which  thus 
regularly  takes  place,  causes  these  Plants  to  receive  the  name  of  Vascular, 
whilst  the  others  are  designated  as  Cellular  ;  but  still  it  is  to  be  remembered, 
that  the  great  bulk  of  the  structure  in  the  former,  like  the  whole  of  the  latter, 
is  composed  of  cellular  tissue  ;  and  that  the  central  part  of  the  islands,  so  to 
speak,  which  are  composed  of  this,  in  the  interstices  of  the  vascular  network, 
cannot  be  nourished  in  any  other  way  than  by  absorption  from  the  cells  which 


80  GENERAL  VIEW  OF  THE  FUNCTIONS. 

surround  them.  In  the  higher  Animals,  the  variety  of  tissues  which  present 
themselves  in  the  adult  structure,  all  formed  by  a  metamorphosis  from  the 
original  vesicles  of  the  embryo,  is  very  great ;  but  these  are  all  nourished,  in  a 
more  or  less  energetic  manner,  by  the  blood  conveyed  to  them  in  the  network 
of  minute  vessels  which  traverses  them.  Still  between  the  reticulations  of 
these  vessels,  there  must  necessarily  be  islands  of  solid  tissue  (as  seen  in  Fig. 
90),  of  no  inconsiderable  size  ;  and  the  central  portions  of  these  must  derive 
their  nourishment  from  the  surrounding  cells,  exactly  as  in  the  humblest  Cel- 
lular Plants.  Moreover  there  are  some  tissues  in  which,  in  the  healthy  state 
at  least,  no  very  minute  distribution  of  blood-vessels  can  be  ascertained  to 
exist ;  and  in  these  the  cellular  nutrition  must  go  on  to  a  considerable  extent. 
The  decay  and  renewal  of  such  tissues,  however,  are  by  no  means  rapid  ;  and 
it  is  only  in  such  as  require  little  change  from  time  to  time,  and  whose  actions 
are  of  a  physical  rather  than  of  a  vital  character  (such,  for  instance,  as  Car- 
tilage), that  this  mode  of  nutrition  is  sufficient. 

89.  In  the  nutrition  of  the  tissues  which  are  already  completely  formed,  it 
seems  probable  that  the  fluid  portion  of  the  blood  performs  the  chief  part.     It 
will  be  shown  hereafter,  that  the  particles  of  this  substance, — probably  in  virtue 
of  the  preparation  it  has  undergone  by  the  agency  of  the  cells  just  described 
(§  86),  which  exist  in  blood  as  well  as  in  chyle,  and  are  known  under  the 
name  of  colourless  corpuscles, — have  the  power  of  so  arranging  themselves  as 
to  form  a  regular  fibrous  tissue.     These  are  the  only  corpuscles  existing  in  the 
circulating  fluid  of  Invertebrated  animals ;  but  in  the  blood  of  Vertebrata  there 
are  others,  which  contain  a  colouring  fluid,  and  give  to  the  whole  mass  its  red 
or  purple  hue.  *  These  red  corpuscles  appear  to  serve  the  important  purpose 
of  conveying  oxygen  from  the  lungs  into  the  interior  of  the  system,  and  of 
carrying  away  carbonic  acid  from  the  tissues  ;  since  it  is  evidently  in  them, 
that  the  chief  chemical  changes  effected  by  Respiration  are  produced  ;  and  the 
heat  regularly  maintained  in  any  class  of  animals,  bears  a  very  close  proportion 
to  the  quantity  of  red  particles  in  their  blood. 

90.  The  history  of  the  changes  by  which  one  group  of  cells  is  transformed 
into  bone,  another  into  cartilage,  another  into  nerve,  another  into  muscle, — and 
so  on, — is  extremely  interesting,  and  will  be  given  hereafter  in  as  much  de- 
tail as  the  limits  of  this  work  permit.     Of  the  reason  why  this  variety  of  pro- 
ducts should  spring  up,  when  the  cells  in  which  they  all  originate  appear  to 
be  so  exactly  alike,  and  have  themselves  a  common  origin,  no  account  can 
be  given ;  and  this  is  one  of  the  most  cufious  problems  that  at  present  offers 
itself  for  investigation.     The  important^  discoveries,  which  are  here  briefly 
summed  up,  are  not  confined  to  healthy  structures  ;  for  it  has  been  ascertained 
that  diseased  growths  have  a  similar  origin  and  mode  of  extension ;  and  that 
the  malignant  character,  assigned  to  Cancer,  Fungus  Hcmnatodes,  and  other 
such  productions,  is  to  be  traced  to  the  fact,  that  they  are  composed  of  cells 
which  undergo  little  metamorphosis,  and  retain  their  reproductive  power  ;~-so 
that  from  a  single  cell,  as  from  that  of  a  Vegetable  Fungus,  a  large  structure 
may  rapidly  spring  up,  the  removal  of  which  is  by  no  means  attended  with 
any  certainty  that  it  will  not  speedily  re-appear,  from  some  germs  left  in  the 
system. 

91.  The  independent  character  of  the  cells  in  which  all  organized  tissues 
originate,  might  be  of  itself  a  satisfactory  proof  that,  in  Animals,  as  in  Plants, 
the  actions  of  Nutrition  are  performed  by  the  powers  with  which  they  are 
individually  endowed ;  and  that,  whatever  influence  the  nervous  system  may 
have  upon   them,  they  are  not  in  any  way  essentially  dependent  upon  it. 
Moreover,  there  is  an  evident  improbability  in  the  idea,  "that  any  one  of 
the  solid  textures  of  the  living  body  should  have  for  its  office,  to  give  to  any 
other  the  power  of  taking  on  any  vital  actions  ;"  and  the  improbability  becomes 


FUNCTIONS  OF  VEGETATIVE  LIFE.  81 

an  impossibility,  when  the  fact  is  made  known,  that  no  formation  of  nervous 
matter  takes  place  in  the  embryonic  structure,  until  the  processes  of  organic 
life  have  been  for  some  time  in  active  operation.  The  influence  which  the 
Nervous  System  is  known  to  have  upon  the  Function  of  Nutrition,  is  probably 
exerted,  rather  through  the  medium  of  its  power  of  regulating  the  diameter  of 
the  arteries  and  capillaries,  by  which  it  controls  in  some  degree  the  afflux  of 
blood,  and  of  affecting  those  preliminary  actions  on  which  the  quantity  and 
quality  of  the  nutritious  fluid  depend,  than  in  any  more  direct  manner.  At 
any  rate,  it  may  be  safely  asserted,  that  no  such  proof  of  its  more  direct  influ- 
ence, as  is  required  to  counterbalance  the  manifest  improbability  which  has 
been  shown  to  attend  it,  has  yet  been  given, — all  the  facts  which  have  been 
adduced  in  support  of  this  hypothesis  being  equally  explicable  on  the  other, 
which,  being  in  itself  more  probable,  ought  to  be  preferred. 

92.  The  renewal  which  the  various  tissues  of  the  body  are  continually 
undergoing,  has  for  its  chief  object  the  counteraction  of  the  decay,  into  which 
they  would  otherwise  speedily  pass ;  and  it  is  obviously  required  that  a  means 
should  be  provided  for  conveying  away  the  waste,  as  well  as  for  supplying 
the  new  material.  This  is  partly  effected  by  the  venous  circulation,  which 
takes  up  a  large  part  of  the  products  of  incipient  decomposition,  and  conveys 
them  to  organs  where  they  may  be  separated  and  cast  forth  from  the  body. 
The  first  product  of  the  decay  of  all  organized  structures,  is  carbonic  acid ; 
and  this  is  the  one  which  is  most  constantly  and  rapidly  accumulating  in  the 
system,  and  the  retention  of  which,  therefore,  within  the  body,  is  the  most  in- 
jurious. Accordingly  we  find  two  large  organs — the  Lungs  and  the  Liver — 
adapted  to  remove  it;  and  to  both  these  Venous  blood  passes, before  it  is  again 
sent  through  the  system.  The  function  of  the  Lungs  is  so  important  in  warm- 
blooded animals,  that  a  special  heart  is  provided  for  propelling  the  blood 
through  them,  in  addition  to  the  one  possessed  by  most  of  the  lower  animals, 
the  function  of  which  is  the  propulsion  of  the  blood  through  the  system.  In 
these  organs,  the  blood  is  subjected  to  the  influence  of  the  atmosphere,  by 
which  the  carbonic  acid  with  which  it  was  charged,  is  removed  and  replaced 
by  oxygen ;  and  this  change  takes  place,  through  the  delicate  membrane  that 
lines  the  air-cells  of  the  lungs,  according  to  the  physical  law  of  the  mutual 
diffusion  of  gases.  The  introduction  of  oxygen  into  the  blood  seems  necessary 
alike  to  maintain  its  general  vivifying  powers,  and  to  remove  the  carbon  set 
free  in  the  tissues,  by  converting  it  into  carbonic  acid;  which  corresponds 
with  the  general  fact,  that  carbonic  *acid  cannot  be  formed  by  decomposition, 
at  least  to  any  large  amount,  except  when  the  decaying  substance  has  oxygen 
within  its  reach.  The  continual  formation  of  carbonic  acid  in  the  tissues,  ap- 
pears to  have  a  most  important  purpose  in  the  vital  economy, — that  of  keeping 
up  its  temperature  to  a  fixed  standard  ;  for  the  union  of  carbon  and  oxygen  in 
this  situation  may  be  compared  to  a  process  of  slow  combustion ;  and  it  is  well 
known  that  the  more  energetic  this  is  the  higher  is  the  'temperature.  Thus 
in  Birds,  whose  nutrition  is  so  active,  and  whose  respiration  is  so  energetic, 
the  temperature  is  constantly  maintained  at  a  point  higher  than  that  which 
other  animals  ever  attain,  in  the  healthy  state  at  least ;  whilst  in  Reptiles,  which 
present  a  condition  exactly  the  reverse  of  this,  the  temperature  is  scarcely 
above  that  of  the  surrounding  medium.  The  function  of  the  Liver  is,  like 
that  of  the  lungs,  two-fold  : — it  separates  from  the  blood  a  large  quantity  of  the 
superfluous  carbon  which  it  acquires  by  circulating  through  the  tissues  ; — and 
it  combines  that  carbon  with  other  elements,  into  a  secretion,  which,  as  we 
have  seen,  is  of  great  importance  in  the  digestive  process.  The  hepatic 
circulation,  however,  is  not  kept  up  by  a  distinct  impelling  organ ;  but  the 
venous  blood  from  ;the  abdominal  viscera  (and,  in  the  lower  Vertebrata,  that 


82  GENERAL  VIEW  OF  f HE  FUNCTIONS. 

from  the  posterior  part  of  the  body)  passes  through  the  Liver  on  its  return  to 
the  heart. 

93.  All  animal  substances  have  a  tendency,  during  their  decomposition,  to 
throw  off  nitrogen,  as  well  as  carbonic  acid  ;  and  this  nitrogen  may  take  either 
the  form  of  cyanogen,  by  going  off  in  combination  with  carbon,  or  of  ammonia, 
by  uniting  at  the  time  of  its  liberation  with  hydrogen.     The  chief  function  of 
the  Kidneys  is  evidently  to  separate  the  azotized  products  of  decay  from  the 
circulating  fluid ;   for  the  secretion  which  is  characteristic  of  them, — namely, 
urea, — contains  a  larger  proportion  of  nitrogen  than  is  found  in  any  other  or- 
ganic compound ;  it  is  identical  in  its  chemical  nature  with  cyanide  of  ammonia, 
and  may  be  considered  as  the  result  of  the  union  of  these  two  products  of  ani- 
mal decomposition.     The  action  of  the  kidneys  is  equally  essential  to  the  con- 
tinued performance  of  the  other  vital  functions,  with  that  of  the  lungs  and 
liver  ;  since  death  invariably  follows  its  suspension,  unless  some  other  means 
be   provided  by  Nature  (as  occasionally  happens),  for  the  separation  of  its 
characteristic  excretion  from  the  circulating  blood.     But  death  does  not  so 
speedily  ensue,  when  the  functional  action  of  the  liver  and  the  kidneys  is 
suspended,  as  when  that  of  the  lungs  is  checked  ;  and  for  this  obvious  reason, 
—that  only  apart  of  the  whole  current  of  blood  flows  through  the  former  organs, 
and  that,  although  a  disturbance  of  the  usual  course  of  the  circulation  must 
ensue  from  a  stagnation  of  the  flow  through  them,  it  is  not  from  this  cause 
brought  to  a  stand;   whilst,  in  the  case  of  the  lungs,  the  fact  that  the  whole  of 
the  blood  is  sent  to  them,  before  it  can  be  again  impelled  through  the  body, 
necessitates  the  immediate  cessation  of  the  systemic  circulation,  when  the  pul- 
monary has  been  checked.     In  the  class  of  Reptiles,  the  lungs  are  on  some- 
what of  the  same  footing  writh  the  liver  and  kidneys  in  warm-blooded  Verte- 
brata, — that  is,  only  a  part  of  the  blood  which  has  returned  from  the  system 
is  transmitted  through  them,  before  being  again  propelled  through  the  body ; 
and,  accordingly,  the  interruption  of  the  pulmonary  circulation  does  not  in 
them  involve  immediate  death.     Indeed,  in  the  naked-skinned  Batrachia,  the 
cutaneous  surface  has  enough  respiratory  power,  to  effect  that  degree  of  aljra- 
tion  of  the  blood  which  is  necessary,  whilst  the  temperature  is  low,  and  the 
vital  actions  thereby  diminished  in  energy. 

94.  There  seems  reason  to  believe,  however,  that,  of  the  products  of  decom- 
position which  are  set  free  in  the  various  tissues  and  organs  of  the  body,  only 
a  part  is  destined  to  be  immediately  excreted ;  and  that  it  is  this  part  which 
is  taken  up  by  the  Veins,  and  conveyed,  by  the  general  vascular  apparatus, 
to  the  several   glands  which  are  to  separate  it.     The  remainder,  consisting  of 
substances  which  are  fit  to  be  re-assimilated,  appears  to  be  taken  up  by  a  dis- 
tinct system  of  vessels,  termed  Lymphatics  ;  which  may  be  considered  as  an 
extension  of  the  Lacteal  system  through  the  fabric  at  large.     There  is   good 
reason  to  believe,  that  the  special  functions  of  the  Lymphatics  is,  like  that  of 
the  Lacteals,  to  minister  to  Nutritive  absorption,  (although  other  substances 
may  find  their  way  into  them,  by  the  mere  physical  process  of  imbibition) ; 
the  latter  being  especially  destined  to  take  up  assimilable  matter  from  the  di- 
gestive cavity,  whilst  the  former  absorb  the  products  of  the  secondary  digestion 
which  is  continually  going  on  in  every  part  of  the  body.     (See  §§  404 — 467.) 
Of  these,  however,  a  portion  may  still  be  destined  to  immediate  excretion. 

95.  The  various  Secretions  which  have  not  already  been  adverted  to,  appear 
for  the  most  part  to  have  for  their  object  the   performance  of  some  special 
function  in  the  system,  rather  than  the  conveyance  out  of  it  of  any  substances 
which  it  would  be  injurious  to  retain.     This  is  the  case,  for  example,  in  regard 
to  the  secretion  of  the  Lachrymal,  Salivary,  and  Mammary  Glands,  as  well  as 
with  that  of  the  Mucous  and  Serous  Membranes.     The  Excretion  of  fluid  from 
the  cutaneous  surface,  however,  appears  to  answer  two  important  purposes, — 


FUNCTIONS  OF  VEGETATIVE  LIFE.  83 

the  removal  from  the  body  of  a  portion  of  its  superfluous  fluid, — and  the  regu- 
lation of  its  temperature.  Just  as,  by  the  action  of  the  Lungs,  the  conditions 
are  supplied,  by  which  the  temperature  of  the  body  is  kept  up  to  a  certain 
standard,  so,  by  that  of  the  Skin,  it  is  prevented  from  rising  too  high;  for  by 
the  continual  excretion  from  its  surface,  of  fluid  which  has  to  be  carried  off  by 
evaporation,  a  degree  of  cold  is  generated,  which  keeps  the  calorifip  processes 
in  check;  and  this  excretion  is  augmented,  in  proportion  to  the  elevation  of 
the  external  temperature,  which  seems,  in  fact,  the  direct  stimulus  to  the  pro- 
cess. In  all  forms  of  true  Secretion,  the  selection  of  the  materials  to  be  sepa- 
rated from  the  blood,  is  accomplished,  like  selective  Absorption,  by  the  agency 
of  cells.  These  are  developed  in  the  interior  of  the  secreting  organ ;  and  when 
they  are  distended  with  the  fluid  they  have  imbibed,  their  term  of  life,  appears 
to  have  expired, — so  that  they  burst  or  liquefy,  yielding  their  contents  to  the 
ducts,  by  which  the  secreted  product  is  conveyed  away.  In  the  case  of  Adi- 
pose tissue,  we  have  an  instance  in  which  the  secreted  product  (separated 
from  the  blood  by  the  cells  of  which  this  tissue  essentially  consists)  is  not 
carried  out  of  the  body,  but  remains  to  form  a  constituent  part  of  it.  The 
regulation  of  the  amount  of  fluid  in  the  vessels,  is  provided  in  a  kind  of  safety- 
valve  structure,  which  has  been  lately  shown  to  exist  in  the  Ipdneys.  This 
readily  permits  the  escape  of  aqueous  fluid  from  the  capillary  vessels,  into  the 
urinary  canals,  by  a  process  altogether  distinct  from  the  secretion  of  the  solid 
matter,  which  it  is  the  office  of  the  kidneys  to  separate  from  the  circulating 
fluid.  Hence,  if  the  excretion  of  fluid  from  the  skin  be  checked  by  cold,  so 
that  an  accumulation  would  take  place  in  the  vessels,  the  increased  pressure 
within  them  causes  an  increased  escape  of  water  through  the  kidneys.  The 
relation  between  the  true  process  of  Secretion,  which  is  performed  by  the 
selective  power  of  cells,  and  that  of  simple  Transudation,  is  the  same  as  that 
which  has  been  already  pointed  out  between  Selective  Absorption,  and  simple 
Imbibition  (§  86). 

96.  There  is  no  sufficient  reason  to  believe,  that  the  Nervous  System  has 
any  more  direct  influence  on  the  process  of  Secretion  than  it  has  been  stated 
to  have  on  that  of  Nutrition.    That  almost  every  secretion  in  the  body  is  affected 
by  states  of  mind,  which  must  operate  through  the  nerves,  daily  experience 
teaches ;  but  the  very  remarkable  degree  of  control  which  the  nervous  system 
possesses  over  the  circulation,  appears  sufficient  to  explain  any  of  these  effects, 
whether  they  be  local  or  general.     The  flow  of  the  secreted  fluids  through 
their  efferent  ducts  seems  to  be  principally  caused  by  the  proper  contractility 
of  these,  which  (like  that  of  the  heart  and  alimentary  canal)  is  directly  stimu- 
lated by  the  contact  of  their  contents ;  but  there  is  also  evidence  that  this  con- 
tractility may  be  affected  (as  it  is  in  those  two  instances)  by  the  nervous  system; 
and  thus  we  have  an  additional  means  of  influence,  by  which  the  nervous 
system  can  operate  on  these  processes,  since  its  power  is  probably  not  confined 
to  the  large  ducts,  but  extends  to  their  ultimate  ramifications.     Where,  as 
happens  in  the  case  of  the  urinary  excretion,  there  is  a  reservoir -into  which  it 
is  received  as  fast  as  it  is  formed,  for  the  purpose  of  preventing  the  incon- 
venience which  its  constant  passages  from  the  body  would  otherwise  occasion, 
— the  power  of  emptying  this  reservoir  is  usually  placed  in  some  degree  under 
the   dominion  of  the  will,  although  chiefly  governed  by  reflex  action.     It  is 
obvious  that  such  a  provision  is  by  no  means  essential  to  the  function  ;  and  that 
it  has  for  its  object  the  adaptation,  merely,  of  that  function,  to  the  conditions  of 
.Animal  existence. 

97.  Thus  we  see  that,  when  we  enter,  as  it  were,  into  the  penetralia  of  the 
Animal  system,  and  study  those  processes  of  which  the  Life  of  the  material 
fabric  essentially  consists,  we  find  them  performed  under  conditions  essentially 
the  same  as  those  which  obtain  in  Plants ;  and  we  observe  that  the  operations 


84  GENERAL  VIEW  OF  THE  FUNCTIONS. 

of  the  Nervous  System  have  none  but  an  indirect  influence  or  control  over 
them.  '  It  is,  therefore,  quite  philosophical  to  distinguish  these  Organic  Func- 
tions, or  phenomena  of  Vegetative  Life,  from  those  concerned  in  the  Life  of 
Relation,  or  Animal  Life.  The  distinction  is,  indeed,  of  great  practical  im- 
portance, and  lies  at  the  foundation  of  all  Physiological  Science ;  yet  it  is  seldom 
accurately  made,  and  a  very  confused  notion  on  the  subject  is  generally  pre- 
valent. It  is  commonly  said,  for  example,  that  the  function  of  Respiration  is 
the  connecting  link  between  the  two :— the  fact  being,  however,  that  the  true 
process  of  Respiration  is  no  more  a  function  of  Animal  life  than  is  any  ordi- 
nary process  of  secretion;  but  that,  in  order  to  secure  that  constant  interchange 
of  air,  which  is  necessary  to  its  performance,  the  assistance  of  the  nervous  and 
muscular  systems  is  called  in,  though  not  in  a  manner  which  necessarily  in- 
volves either  consciousness  or  will. 

98.  The  process  of  Reproduction,  like  that  of  Nutrition,  has  been  until  re- 
cently involved  in  great  obscurity ;  and  although  it  cannot  be  said  to  be  yet 
fully  elucidated,  it  has  been  brought,  by  late  investigations,  far  more  within 
our  comprehension  than  was  formerly  deemed  possible.    The  close  connection 
between  the  Reproductive  and  Nutritive  operations,  both  as  regards  their  re- 
spective characters,  and  their  dependence  upon  one  another,  has  long  been 
recognized ;  and  it  is  now  rendered  still  more  evident.     Nutrition  has  been 
not  unaptly  designated  "a  perpetual  reproduction;"  and  the  expression  is 
strictly  correct.     In  the  fully-formed  organism,  the  supply  of  alimentary  ma- 
terial to  every  part  of  the  fabric  enables  it  to  produce  a  tissue  resembling  itself; 
thus  we  only  find  true  bone  produced  in  continuity  with  bone,  nerve  with  nerve, 
muscle  with  muscle,  and  so  on.     Hence  it  would  appear  that,  when  a  group 
of  cells  has  once  taken  on  a  particular  kind  of  development,  it  continues  to 
reproduce  itself  on  the   same  plan.     But  in  the  Reproductive  process  it  is 
different.     A  single  cell  is  generated  by  certain  preliminary  actions, — from 
which  single  cell,  all  those  which  subsequently  compose  the  embryonic  struc- 
tures, take  their  origin ;  and  it  is  not  until  a  later  period,  that  any  distinction 
of  parts  can  be  traced,  in  the  mass  of  vesicles  which  spring  from  it.     Hence 
the  essential  character  of  the  process  of  Reproduction  consists  in  the  formation 
of  a  cell,  which  can  give  origin  to  others,  from  which  again  others  spring ; — 
and  in  the  capability  of  these  last  to  undergo  several  kinds  of  transformation, 
so  as  ultimately  to  produce  a  fabric,  in  which  the  number  of  different  parts  is 
equal  to  that  of  the  functions  to  be  performed,  every  separate  part  having  a 
purpose  distinct  from  that  of  the  rest.     Such  a  fabric  is  considered  as  a  very 
heterogeneous  one;  and  is  eminently  distinguished  from  those  homogeneous 
organisms,  in  which  every  part  is  but  a  repetition  of  the  rest.    Of  all  Animals, 
Man  possesses,  as  already  shown,  the  greatest  variety  of  endowments, — the 
greatest  number  of  distinct  organs ;  and  yet  Man,  in  common  with  the  simplest 
Animal  or  Plant,  takes  his  origin  in  a  single  cell.     It  is  in  the  almost  homo- 
geneous fabrics  of  the  Cellular  Plants,  that  we  find  the  closest  connection  be- 
tween the  function  of  Nutrition  and  that  of  Reproduction ;  for  every  one  of  the 
vesicles  which  compose  their  fabric,  is  endowed  with  the  power  of  generating 
others  similar  to  itself;  and  these  may  either  extend  the  parent  structure,  or 
separate  into  new  and  distinct  organisms.     Hence  it  is  scarcely  possible  to 
draw  a  line,  in  these  cases,  between  the  Nutrition  of  the  individual,  and  the 
Reproduction  of  the  species. 

99.  But,  it  will  be  inquired,  how  and  where  in  the  Human  body  (and  in  the 
higher  Animals  in  general)  is  this  embryonic  vesicle  produced,  and  what  are 
the  relative  offices  of  the  two  sexes  in  its  formation?     This  is  a  question 
which  must  still  be  answered  with  some  degree  of  doubt ;  and  yet  observed 
phenomena,  if  explained  by  the  aid  of  analogy,  seem  to  lead  to  a  very  direct 
conclusion.     The  embryonic  vesicle  itself,  like  other  cells,  must  arise  from  a 


FUNCTIONS  OF  ANIMAL  LIFE.  85 

germ ;  and  reasons  will  be  hereafter  given  for  the  belief,  that  the  germ  is  sup- 
plied by  the  male  parent,  and  that  the  female  supplies  only  the  materials  for 
its  development.  Here,  as  in  the  Nutritive  processes,  we  find  that  the  opera- 
tions immediately  concerned  in  this  function, — namely,  the  act  of  fecundation, 
and  the  development  of  the  ovum, — are  not  directly  influenced  in  any  way  by 
the  nervous  system ;  and  that  the  functions  of  Animal  Life  are  called  into 
play  only  in  the  preliminary  and  concluding  steps  of  the  process.  In  many 
of  the  lower  Animals,  there  is  no  sexual  congress,  even  where  the  concurrence 
of  two  sets  of  organs  (as  in  the  Phanerogamic  Plants)  is  necessary  for  the  pro- 
cess ;  the  ova  are  liberated  by  one,  and  the  spermatozoa  by  the  other;  and  the 
accidental  meeting  of  the  two  produces  the  desired  result.  In  many  Animals 
higher  in  the  scale,  the  impulse  which  brings  the  sexes  together  is  of  a  purely 
instinctive  kind.  But  in  Man,  it  is  of  a  very  compound  nature.  The  instinc- 
tive propensity,  unless  unduly  strong,  is  controlled  and  guided  by  the  will,  and 
serves  (like  the  feelings  of  hunger  and  thirst)  as  a  stimulus  to  the  reasoning 
processes,  by  which  the  means  of  gratifying  it  are  obtained ;  and  a  moral  sen- 
timent or  affection  of  a  much  higher  kind  is  closely  connected  with  it,  which 
acts  as  an  additional  incitement.  Those  movements,  however,  which  are  most 
closely  connected  with  the  essential  part  of  the  process,  are,  like  those  of  deglu- 
tition, respiration,  &c.,  simply  reflex  and  involuntary  in  their  character;  and 
thus  we  have  another  proof  of  the  constancy  of  the  principle,  that,  where  the 
action  of  the  apparatus  of  Animal  Life  is  brought  into  near  connection  with 
the  Organic  functions,  it  is  not  such  as  requires  the  operation  of  the  purely 
animal  powers, — sensation  and  volition.  Thus,  then,  as  it  has  been  lucidly 
remarked,  "  the  Nervous  System  lives  and  grows  within  an  Animal,  as  a  para- 
sitic Plant  does  in  a  Vegetable ;  with  its  life  and  growth,  certain  sensations 
and  mental  acts,  varying  in  the  different  classes  of  Animals,  are  connected  by 
nature  in  a  manner  altogether  inscrutable  to  man;  but  the  objects  of  the 
existence  of  Animals  require,  that  these  mental  acts  should  exert  a  powerful 
controlling  influence  over  all  the  textures  and  organs  of  which  they  are  com- 
posed." 

Functions  of  Animal  Life. 

100.  The  existence  of  consciousness,  by  which  the  individual  (le  moi,  in  the 
language  of  French  physiologists)  becomes  sensible  of  impressions  made  upon 
its  bodily  structure, — and  the  power  of  spontaneously  exciting  contractions  in 
its  tissues,  by  which  evident  motions  are  produced, — have  been  already  stated 
to  be  the  peculiar  attributes  of  the  beings  composing  the  Animal  kingdom.  The 
evident  motions  exhibited  by  some  Plants,  cannot  be  regarded  as  indicating  the 
existence  of  any  psychical  endowments  in  the  beings  included  in  the  Vege- 
table kingdom ;  for  they  are  usually  to  be  referred  without  difficulty  to  the 
action,  either  direct  or  indirect,  of  an  external  stimulus,  upon  a  contractile 
tissue ;  and  even  where  no  such  action  evidently  takes  place,  there  is  good 
reason  to  suppose  its  existence.     To  refer,  therefore,  the  movements  of  Vege- 
tables to  a  nervous  system,  of  which  no  traces  can  be  found, — still  more  to 
suppose  them  endowed  with  consciousness  and  will,  as  some  have  done,— is 
to  violate  most  grossly  a  well-known  rule  in  philosophy,  which  cannot  be  too 
steadily  kept  in  view  in  prosecuting  physiological  inquiries — nonfingere  hy- 
potheses. 

101.  There  are  in  Animals,  however,  many  movements  which  are  equally 
dependent  upon  direct  stimuli  for  their  production.     Such  are  (as  we  have 
seen),  even  in  the  highest,  the  actions  of  the  heart  and  of  the  alimentary  canal. 
These,  in  the  lowest  tribes,  probably  bear  a  much  greater  proportion  to  the 

8 


86  GENERAL  VIEW  OF  THE  FUNCTIONS. 

whole  amount  of  those  exhibited  by  the  beings,  than  they  do  in  the  higher; 
whilst  those  which  we  may  regard  as  specially  dependent  on  a  nervous  sys- 
tem, appear  to  constitute  but  a  small  part  of  their  general  vital  actions.  The 
life  of  such  beings,  therefore,  bears  a  much  closer  resemblance  to  that  of  the 
Vegetable  than  to  that  of  the  higher  Animal.  Their  organic  functions  are 
performed  with  scarcely  more  of  sensible  movement  than  is  seen  in  plants ; 
and  of  the  motions  which  they  do  exhibit  (nearly  all  of  them  immediately 
concerned  in  the  maintenance  of  the  organic  functions),  it  is  probable  that 
many  are  the  result  of  the  simple  contractility  of  their  tissues,  called  into  ac- 
tion by  the.  stimuli  directly  applied  to  them.  It  is  scarcely  possible  to  imagine 
that  such  beings  can  enjoy  any  of  those  higher  mental  powers,  which  Man 
recognizes  by  observation  on  himself,  and  of  which  he  discerns  the  manifes- 
tations in  those  tribes,  which,  from  their  nearer  relation  to  himself,  he  regards 
as  more  elevated  in  the  scale  of  existence.  If  we  direct  our  attention,  on  the 
other  hand,  to  the  psychical*  operations  of  Man,  as  forming  part  of  his  gene- 
ral vital  actions,  we  perceive  that  the  proportion  is  completely  reversed.  So 
far  from  his  organic  life  exhibiting  a  predominance,  it  appears  entirely  subor- 
dinate to  his  animal  functions,  and  seems  destined  only  to  afford  the  conditions 
for  their  performance.  If  we  could  imagine  his  nervous  and  muscular  systems 
to  be  isolated  from  the  remainder  of  his  corporeal  structure,  and  endowed  in 
themselves  with  the  power  of  retaining  their  integrity  and  activity,  we  should 
have  all  that  is  essential  to  our  idea  of  Man.  But,  as  at  present  constituted, 
these  organs  are  dependent,  for  the  maintenance  of  their  integrity  and  func- 
tional activity,  upon  the  nutritive  apparatus ;  and  the  whole  object  of  the  latter 
appears  to  be  the  supply  of  those  conditions  which  are  necessary  to  the  exer- 
cise of  the  peculiarly  animal  functions.  That  his  mental  activity  should  be 
thus  made  dependent  upon  the  due  supply  of  his  bodily  wants,  is  a  part  of  the 
general  scheme  of  his  probationary  existence  ;  and  the  first  excitement  of  his 
intellectual  powers  is  in  a  great  degree  dependent  upon  this  arrangement. 

102.  The  most  simple  or  elementary  function  of  the  Nervous  System  is,  as 
already  observed,  the  establishment  of  a  communication  between  a  part  which 
is  susceptible  of  impressions,  and  another  which  can  perform  contractile  move- 
ments ;  so  that  a  stimulus  applied  to  one  may  immediately  excite  a  respondent 
action  in  the  other,  however  great  may  be  its  distance.  Hence  it  may  be  said 
to  have  an  internuncial  function  ;  but  this,  so  far  as  it  is  performed  without 
the  necessary  participation  of  the  consciousness  or  will  of  the  individual,  is 
not  essentially  higher  in  character  than  the  corresponding  function  in  Plants, 
although  the  latter  is  effected  by  a  different  apparatus.  The  ministration  of 
the  nervous  system  to  purely  Animal  life,  obviously  consists  in  its  rendering 
the  mind  cognizant  of  that  which  is  taking  place  around,  and  in  enabling  it  to 
act  upon  the  material  world,  by  the  instruments  with  which  the  body  is  pro- 
vided for  the  purpose.  It  is  curious  to  observe  that  every  method  at  present 
known,  by  which  mind  can  act  upon  mind,  requires  muscular  contraction  as 
its  medium,  and  sensation  as  its  recipient.  This  is  the  case,  for  example,  not 
only  in  that  communication  which  takes  place  by  language,  whether  written 
or  spoken ;  but  in  that  less  evident  but  not  less  eloquent  converse,  by  which 
two  minds  "attuned  to  nature's  sweetest  harmony,"  can  read  each  other's 
thoughts.  The  look,  the  touch,  the  gesture,  which  are  so  frequently  more 
expressive  than  any  words  can  be,  are  all  the  result  of  muscular  contractions 
excited  in  the  nervous  centres ;  and  thus  we  trace  the  limitation  which,  even 
in  communication  that  appears  so  far  removed  from  the  material  world,  con- 

*  Here  and  elsewhere  this  term  will  be  employed  in  its  most  extended  sense,  to  desig- 
nate all  the  mental  operations, — whether  intellectual,  emotional,  or  instinctive, — of  which 
Man's  nervous  system  is  the  instrument. 


FUNCTIONS  OF  ANIMAL  LIFE. 

stantly  bounds  the  operations  of  the  most  powerful  intellect,  and  the  highest 
flights  of  the  imagination.  That  in  a  future  state  of  heing  the  communion  of 
mind  with  mind  will  be  more  intimate,  and  that  Man  will  be  admitted  into  more 
immediate  converse  with  his  Maker,  appear  to  be  alike  the  teachings  of  the 
most  comprehensive  philosophical  inquiries,  and  of  the  most  direct  Revelation 
of  the  Divinity. 

103.  The  Organs  of  Sense  are  instruments  which  are  adapted  to  enable 
particular  nerves  to  receive  impressions  from  without ;  of  a  kind,  and  in  a 
degree,  of  which  they  would  not  otherwise  be  sensible.  Thus,  although  the 
simple  contact  of  a  hard  body  with  the  nerve  may  be  readily  conceived  to  pro- 
duce a  material  change  in  it,  of  such  a  kind  as  would  be  easily  propagated  to 
the  central  sensorium,  it  is  evident  that  a  nerve  must  be  peculiarly  modified 
to  receive  and  conduct  sonorouS  impressions  from  the  undulations  of  the  air ; 
still  more-^-to  be  susceptible  of  the  impressions  produced  by  the  undulations 
of  that  ethereal  medium,  to  the  vibrations  of  which  most  Natural  Philosophers 
now  attribute  the  transmission  of  light.  And,  even  when  this  difficulty  has 
been  provided  for  by  some  modification  in  the  structure  of  the  nerve  itself, 
there  is  evidently  another  still  remaining, — that  of  understanding  how  distinct 
images  of  the  form,  colour,  &c.,  of  external  objects  can  be  communicated  to 
the  nerve  of  sight, — or  ideas  of  the  direction,  pitch,  quality,  &c.,  of  sono- 
rous undulations,  can  be  obtained  through  the  auditory  nerve.  There  is  reason 
to  believe  that  many  among  the  lower  Animals,  which  do  not  see  objects  around 
them,  are  conscious  of  the  influence  of  light ;  and  thus  the  distinction  between 
the  mere  reception  of  the  impression,  and  the  communication  of  the  optical 
image,  becomes  evident.  The  former  may  take  place  through  the  intervention 
of  nerves,  whose  sensory  extremities  offer  no  peculiarities  :  the  latter  can  only 
be  received  through  the  medium  of  an  instrumenf/which  shall,  from  the  mix- 
ture of  rays  falling  equally  upon  every  part  of  a  surface,  produce  an  optical 
image,  and  then  impress  it  upon  the  expanded  surface  of  the  nerve ;  so  that 
each  fibril  may  receive  a  distinct  impression,  the  image  presented  to  the  mind 
being  formed  by  the  combination  of  the  whole.  That  this  is,  in  fact,  the  share 
which  the  organs  of  special  sense  bear  in  the  general  endowments  of  the  whole 
apparatus,  may  be  inferred  especially  from  the  conformation  of  the  Eye,  which 
is  in  every  respect  a  merely  optical  instrument  of  the  greatest  beauty  and  per- 
fection, adapted  to  present  to  the  nerve,  in  the  most  advantageous  manner,  the 
images  of  surrounding  objects  in  all  their  variations;  and  we  might  conceive 
that,  if  it  were  possible  for  the  interior  of  the  living  eye  to  be  replaced  by  one 
constructed  of  inorganic  materials  by  the  hand  of  man,  and  for  the  retina  to 
preserve  its  functional  activity,  the  powrer  of  sight  would  be  but  little  impaired, 
—except  through  the  incapability,  on  the  part  of  any  piece  of  human  mecha- 
nism, to  imitate  those  wondrous  contrivances  of  Infinite  Skill,  which  have  for 
their  object  the  adaptation  of  the  instrument  to  varieties  of  distance,  of  intensity 
of  light,  &?c.  There  can  be  little  doubt  that  the  structure  of  the  Ear  is  arranged 
to  do  the  same  for  the  sonorous  vibrations  which  the  eye  does  for  the  rays  of 
light;  that  is,  through  its  means,  the  undulations  which  strike  upon  the 
external  surface  of  the  organ  are  separated  and  distinguished,  those  of  a  like 
kind  being  brought  together  upon  one  division  of  the  nerve,  and  those  of 
another  order  upon  a  different  set  of  fibres;  so  that  the  different  kinds  of  sound, 
and  the  peculiar  quality  and  direction  of  each,  may  be  discriminated ;  whilst, 
by  the  concentration  of  all  the  impressions  of  the  same  character,  a  higher 
amount  of  force  is  given  to  them.  Of  the  sense  of  Smell,  no  similar  account 
can  be  given;  since  the  medium  by  which  odours  are  propagated  is  not  known. 
If,  as  is  generally  believed,  this  is  accomplished  by  the  diffusion  through  space 
of  minute  particles  of  the  odoriferous  body  itself  (which  supposition  seems  to 
derive  support  from  the  general  fact,  that  the  most  volatile  substances  are 


88  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

usually  most  odoriferous*),  smell  may  be  regarded, — as  taste  also  is  probably 
to  be  considered, — in  the  light  of  a  refined  kind  of  touch. 

104.  Thus,  the  general  rule  holds  good,  here  as  elsewhere,  that  the  pro- 
cesses by  which  the  organism  is  immediately  brought  into  relation  with  the 
external  world,  are  performed  in  obedience  to  physical  laws  ;  the  living  struc- 
ture only  affording  certain  peculiar  conditions  which  may  be  imitated  in  a 
great  degree  by  other  means.     This  is  the  case,  for  example,  with  regard  to 
Digestion,  which  is  in  itself  a  simply  Chemical  process,  that  will-  take  place 
out  of  the  body  as  well  as  in  it,  if  the  materials  and  the  necessary  solvent  be 
submitted  to  the  same  circumstances,  as  those  to  which  they  are  exposed  in 
the  stomach ;  and  in  regard  also  to  the  act  of  Respiration,  which  depends  upon 
the  Physical  tendency  to  mutual  diffusion,  inseparable  from  the  existence  of 
gases ;  and  we  notice  the  prevalence  of  the  same  general  fact  in  the  Animal 
as  in  the  Organic  life.     We  cannot  become  cognizant  of  the  changes,  or  even 
of  the  existence,  of  the  external  world,  unless  some  material  effect  be  produced 
by  it  on  our  organs  of  sense  ;  nor  can  we  produce  any  alteration  in  its  condi- 
tion, except  by  powers  which  act  according  to  purely  mechanical  principles. 

105.  In  regard  to  the  Muscular  System,  it  has  already  been  sufficiently  ex- 
plained that  it  forms  a  part  of  the  apparatus  of  Animal  life  no  otherwise  than 
as  the  instrument  by  which  nervous  energy  operates  upon  external  objects. 
The  contractility  which  it  manifests  on  the  application  of  a  stimulus,  is  an 
endowment  which  it  derives  from  its  own  structure,  and  not  from  the  nervous 
system ;  for  it  will  be  clearly  proved  in  its  appropriate  place,  that  the  presence 
of  this  contractility  is  connected  with  the  healthy  nutrition  of  the  tissue,  and 
its  due  supply  of  arterial  blood ;  and  that  the  complete  separation  of  any  mus- 
cular part  from  all  its  nervdpB  connections,  has  none  but  an  indirect  influence 
on  its  properties. 


CHAPTER    III. 

FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

I.  General  Summary. 

106.  ALL  our  positive  knowledge  of  the  functions  of  the  Nervous  System, 
is  derived  from  observation  of  the  movements  exhibited  by  animals,  and  from 
our  own  consciousness  of  what  passes  within  ourselves.  Except  through  the 
movements  consequent  upon  them,  we  have  no  means  of  ascertaining  whether 
or  not  particular  changes  in  the  nervous  system  are  attended  with  sensation. 
The  cries  and  struggles  of  the  animal  made  the  subject  of  experiment,  are 
ordinarily  considered  as  indications  of  sensations ;  but  it  is  not  right  so  to  re- 
gard them  in  every  instance;  nor  are  we  justified  in  asserting  that  conscious- 
ness results  from  any  external  irritation,  merely  because  movements  evidently 
tending  to  get  rid  of  this  are  performed  in  respondence  to  it.  We  know  that 
the  contractions  of  the  heart  and  alimentary  tube  are  ordinarily  excited  by  a 
stimulus,  without  any  sensation  being  involved ;  and  these  movements,  like 

*  Some  of  the  most  strongly  odoriferous  substances,  however,  are  solid; — for  instance, 
musk:  and  it  has  been  experimentally  proved,  that  the  loss  of  weight,  which  follows  the 
free  exposure  of  a  minute  quantity  of  this  perfume  to  an  atmosphere  constantly  renewed 
during  several  years,  is  not  appreciable  by  the  finest  balance. 


GENERAL  SUMMARY.  89 

all  that  are  concerned  in  the  maintenance  of  the  organic  functions,  have  an 
obvious  design,  when  considered  either  in  their  immediate  effects,  or  in  their 
more  remote  consequences.  The  character  of  adaptiveness,  then,  in  muscular 
movements  excited  by  external  stimuli,  is  no  proof  that  they  are  performed 
in  obedience  to  sensation ;  much  less,  that  they  have  a  voluntary  character. 
In  no  case  is  this  adaptiveness  more  remarkable  than  in  some  of  those  purely 
instinctive  actions  which  are  not  only  performed  without  any  effort  of  the  will, 
but  which  the  will  cannot  imitate.  This  is  the  case,  for  example,  with  the  act 
of  deglutition ;  the  muscles  concerned  in  which  cannot  be  thrown  into  contrac- 
tion by  a  voluntary  impulse,  being  stimulated  only  by  impressions  conveyed 
from  the  mucous  surface  of  the  fauces  to  the  medulla  oblongata,  and  thence 
reflected  along  the  motor  nerves.  No  one  can  swallow,  without  producing  an 
impression  of  some  kind  upon  this  surface,  to  which  the  muscular  movements 
will  immediately  respond.  Now  it  is  impossible  to  conceive  any  movements 
more  perfectly  adapted  to  a  given  purpose  than  those  of  the  parts  in  ques- 
tion ;  and  yet  they  are  not  only  independent  of  volition,  but  of  sensation, — being 
still  performed  in  cases  in  which  consciousness  is  completely  suspended,  or 
entirely  absent. 

107.  There  is  much  difficulty,  then,  in  ascertaining  the  really  elementary 
functions  of  the  Nervous  system,  by  experiments  upon  animals ;  and  it  is  only 
when  their  results  are  corrected  and  explained  by  pathological  observation  on 
Man, — the  sole  case  in  which  we  can  obtain  satisfactory  evidence  of  the  pre- 
sence or  absence  of  sensation, — that  they  have  much  value  to  the  physiological 
inquirer.     From  these  combined  sources,  however,  a  vast  amount  of  know- 
ledge of  the  functions  of  the  nervous  system  has  recently  been  gained ;  and 
the  general  purposes  to  which  it  is  subservient  may  be  advantageously  stated 
in  a  systematic  form,  before  we  enter  upon  any  detailed  examination  of  them. 

I.  The  Nervous  System  receives  impressions,  which,  being  conveyed  by 
its  afferent  fibres  to  the  sensorium,  are  there  communicated  to  the  conscious 
mind.     It  is  subservient  in  some  way  to  the  acts  of  that  mind ;  and,  as  the 
result  of  these  acts,  a  motor  impulse  is  transmitted  along  the  efferent  trunks 
to   particular  muscles,  exciting  them  to  contraction.      This  motor   impulse, 
however,  may  be  either  of  an  emotional  or  a  voluntary  character.     We  shall 
hereafter  see  reason  to  believe  that,  to  these  functions,  the  Encephalon,  and 
the  nerves  proceeding  from  it,  are  subservient. 

II.  Certain  parts  of  the  Nervous  System  receive  impressions  which  are 
propagated  along  afferent  fibres,  that  terminate  in  ganglionic  centres  distinct 
from  the  sensorium;    and  in  these  a  reflex  motor  impulse  is  thus  excited, 
which,  being  conveyed   along  the  efferent   trunks   proceeding   from  them, 
excites  muscular  contraction,  without  any  necessary  intervention  of  sensation 
or  volition.     Of  this  function  (called  by  Dr.  Hall,  to  whom  the  discovery  of  it 
is  in  great  part  due,  the  reflex  function),  we  shall  find  that  the  portion  of  the 
Spinal,  Cord  of  Vertebrata,  which  is  not  continuous  with  the  fibrous  structure 
of  the  brain,  together  with  the  portion  of  the  nervous  trunks  which  are  con- 
nected with  it  alone,  is  the  instrument. 

III.  Another  division  of  the  Nervous  System  appears  to  have  for  its  object, 
to  combine  and  harmonize  the  muscular  movements  immediately  connected 
with  the  maintenance  of  organic  life,  and  to  bring  these  into  relation  with 
certain  conditions  of  the  mind.    There  is  reason  to  believe  (though  this  is  less 
certain)  that  it  also  influences,  and  brings  into  connection  with  each  other,  the 
processes  of  nutrition,  secretion,  &c. ;  though  these,  like  the  muscular  move- 
ments just  mentioned,  are  essentially  independent  of  it. 

108.  Now,  in  reference  to  the  first  class  of  operations,  it  is  well  to  explain 
that,  though  the  physiologist  speaks  of  the  intellectual  powers,  moral  feelings, 
&c.,  as  functions  of  the  Nervous  System,  they  are  not  so  in  the  sense  in  which 

8* 


90  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  term  is  employed  in  regard  to  other  operations  of  the  hodily  frame,  tn 
general,  by  the  function  of  an  organ,  we  understand  some  change  which  may 
be  made  evident  to  the  senses,  as  well  in  our  own  system  as  in  the  body  of 
another.  Sensation,  Thought,  Emotion  and  Volition,  however,  are  changes  im- 
perceptible to  our  senses,  by  any  means  of  observation  we  at  present  possess. 
We  are  cognizant  of  them  in  ourselves,  without  the  intervention  of  those  pro- 
cesses by  which  we  observe  material  changes  external  to  our  minds  ;  but  we 
judge  of  them  in  others,  only  by  inferences  founded  on  the  actions  to  which 
they  give  rise,  when  compared  with  our  own.  When  we  speak  of  sensation, 
thought,  emotion,  or  volition,  therefore,  as  functions  of  the  Nervous  System, 
we  mean  only  that  this  system  furnishes  the  conditions  under  which  they 
take  place  in  the  living  body;  and  we  leave  the  question  entirely  open, 
whether  the  tyxn  nas  or  nas  not  an  existence  independent  of  that  of  the  mate- 
rial organism,  by  which  it  operates  in  Man  as  he  is  at  present  constituted. 

109.  In  regard  to  the  second  class  of  actions,  it  may  be  remarked,  that  they 
are  nearly  all  connected,  more  or  less  closely,  with  the  organic  functions,  or 
with  the  protection  of  the  body  from  danger.     Thus  the  movements  of  the 
pharynx  supply  to  the  stomach  the  alimentary  materials  it  prepares  for  the 
nutrition  of  the  body;  those  of  the  muscles  of  the  thorax,  &c.,  maintain  that 
constant  interchange  of  air  in  the  lungs,  which  is  necessary  for  the  aeration 
of  the  blood ;  whilst  those  by  which  a  limb  is  involuntarily  retracted  from  any 
cause  of  pain  or  irritation,  are  obviously  adapted  to  the  latter  of  these  two  ends. 

II.  Elementary  Structure  of  the  Nervous  System. 

110.  Wherever  a  distinct  Nervous  System  can  be  observed,  it  is  found  to 
consist  of  two  kinds  of  structure ;  the  presence  of  both  of  which,  therefore, 
may  be  regarded  as  essential  to  our  idea  of  it  as  a  whole.     One  of  these  is 
that  which  is  designated  the  white  or  fibrous  matter.     This  constitutes  (with 
the  neurilema  or  nerve-sheath,  and  the  areolar  tissue  which  it  encloses),  the 
whole  of  the  nervous  trunks,  wherever  they  occur ;  and  forms  a  large  part  of 
the  central  masses  with  which  they  are  connected.     It  consists  of  tubes  of 
great  minuteness,  which  are  composed  of  an  interlacement  of  extremely  deli- 
cate fibres ;  some  of  these  passing  in  a  longitudinal,  and  some  in  a  transverse 
or  spiral  direction.     When  these  tubes  are  examined  immediately  after  death, 
their  contents  appear  pellucid  and  homogeneous,  and  of  a  fluid  consistence  ; 
so  that  each  tube  or  fibre  'looks  like  a  cylinder  of  clear  glass,  with  simple, 
well-defined,  dark  edges.     But  a  kind  of  coagulation  soon  takes  place  in  the 
contained  substance,  which  makes  it  easily  distinguishable  from  the  tube 
itself;  for  the  latter  is  then  marked  by  a  double  line,  as  shown  in  Fig.  7. 
This  last  state  of  the  nervous  fibre  has  been  regarded  by  Remak  and  others 
(but  probably  erroneously)  as  the  natural  one  ;  and  the  substance  contained 
within  the  tube  has  been  described  as  a  band  or  axis,  composed  of  several 
distinct  filaments.      It  has   even  been   asserted   that,  at  the   extremities  of 
these  nerves,  the  filaments  diverge  from  one  another,  and  form  loops, — the 
tubular  envelop  being  lost ;  but  this  is  probably  erroneous.     The  walls  of  the 
tube  are  not  unfrequently  seen  to  contain  the  nuclei  of  the  cells,  by  the  coa- 
lescence of  which  it  was  originally  formed.     The  diameter  of  the  cylindrical 
tubuli  of  the  nerve-trunks  is  estimated  to  vary  from  about  the  l-2000th  to  the 
1 -3000th  of  an  inch.     The  fibres  gradually  decrease  in  size,  however,  as  they 
approach  the  brain,  either  directly,  or  through  the  medium  of  the  spinal  cord ; 
and  in  the  brain  itself  they  continue  to  grow  less  as  they  pass  through  the 
medullary  to  the   cortical  part ;    so  that  in  the  former  they  measure   from 
1 -7000th  to  l-8000th  of  an  inch,  and  in  the  latter  not  more  than  l-14000th  of 
an  inch.     The  fibres  of  the  olfactory  and  optic,  and,  in  a  less  degree,  those  of 


ELEMENTARY  STRUCTURE  OF  NERVOUS  SYSTEM. 


91 


the  auditory  nerves,  are  equally  small  in  every  part  of  their  course  ;  and  thus 
resemble,  in  size  as  well  as  in  structure,  those  portions  of  the  other  nervous 
fibres  which  are  continued  into  the  nervous  centres. — A  different  structure 
has  been  described  by  Ehrenberg,  as  composing  the  bulk  of  the  medullary 
substance  of  the  brain,  under  the  name  of  varicose  tubes ;  and  he  states  that 
these  are  also  found  largely  in  the  spinal  cord,  and  less  abundantly  in  the 
nerves  of  special  sense ;  but  that  they  are  seldom  to  be  met  with  in  the  other 
trunks.  These  tubes  were  so  named,  from  their  not  being  cylindrical,  but 
presenting  dilatations  at  intervals,  so  as  to  resemble  a  string  of  beads ;  and  the 
appearance  of  these  dilatations  has  given  rise  to  the  opinion,  that  the  brain  is 
composed  of  globules.  It  is  now,  however,  satisfactorily  shown  that  they  are 
the  result  of  the  pressure  and  other  manipulations,  to  which  the  objects  are 
subjected  in  preparation  for  the  microscope ;  and  that,  if  the  nervous  fibres  of 
the  brain  and  other  parts  are  examined  in  a  recent  state,  they  are  cylindrical, 
like  those  of  the  nervous  trunks  in  general.  Still  there  must  be  some  differ- 
ence in  their  structure,  since  they  exhibit  this  tendency  to  become  varicose, 
which, is  elsewhere  wanting ;  this  difference  appears  chiefly  to  consist  in  the 
greater  thinness  and  delicacy  of  the  walls  of  the  tube  itself,  rendering  it  more 
liable  to  be  distended  at  certain  points,  by  the  accumulation  of  the  contained 
substance  in  little  masses,  when  coagulating. — Besides  these  tubular  fibres, 
which  constitute  the  white  portions  of  the  nervous  matter,  there  are  other  fila- 
ments of  a  yellowish-gray  colour,  and  of  about  half  the  usual  diameter,  with- 
out distinct  cavities,  which  exist  especially  in  the  sympathetic  nerves,  but 
which  may  also  be  detected  in  others.  These  fibres  may  be  termed  organic; 
those  existing  in  the  sympathetic  system  of  nerves  may  be  traced  to  its  gan- 
glipnic  centres ;  whilst  those  which  are  found  in  the  cerebro-spinal  nerves,  are 
connected  with  the  ganglia  upon  their  posterior  roots.* 

Fig.  7. 


Structure  of  nerve-tubes,  magnified  350  Diam.  A,  cylindrical  tubuli  from  nerve.  B,  varicose  tubuli 
from  brain,  c,  nerve-tubes,  of  which  one  exhibits  the  remains  of  nuclei  in  its  walls.  (After  Wagner.) 

111.  The  other  elementary  form  of  Nervous  structure  is  termed  the  dneri- 
tious  or  gray  matter.  It  seems  to  consist  principally  of  a  plexus  of  blood-ves- 
sels, into  which  the  fibres  of  the  former  may  be  traced ;  and  amongst  these  lie 
a  number  of  nucleated  globules,  which  do  not  seem  to  have  any  definite  ar- 
rangement. This  substance  is  usually  disposed  in  the  interior  of  the  larger 

*  The  distinctness  of  the  sympathetic  fibres  from  the  cerebro-spinal,  which  has  been 
denied  by  some  Microscopists,  appears  to  have  been  fully  established  by  the  recent 
laborious  inquiries  of  Volkmann  and  Bidder. 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Fig.  8. 


Primitive  fibres  and  ganglionic  globules.  A,  from  sympathetic  ganglion ;  *  a  separate  vesicle,  showing 
its  pellucid  nucleus  and  nucleolus.  B,  from  gray  substance  of  human  cerebellum ;  a,  6,  plexus  of  primitive 
fibres;  c,  nucleated  globules:  *  a  separate  globule  from  human  Gasserian  ganglion.  350  Diam.  (After 
Wagner.) 

masses,  with  which  the  nervous  trunks  are  connected.  It  forms  the  centre  of 
the  ganglia,  which  are  the  centres  of  the  nervous  system  in  the  Invertebrata : 
it  occupies  part  of  the  interior  of  the  spinal  cord  of  Vertebrate d  animals,  which 
may  be  regarded  as  a  chain  of  similar  ganglia;  and  in  the  distinct  ganglia 
which  occur  among  the  latter,  it  holds  the  same  relative  position.  In  the  brain 
of  Vertebrata,  however,  it  is  disposed  externally,  and  forms  a  sort  of  coating  to 
the  mass  beneath,  which  almost  entirely  consists  of  fibrous  structure  ;  hence  it 
has  been  called  the  cortical  substance,  whilst  the  fibrous  portion  has  been 
termed  medullary  matter. — The  ganglion-globules  (Figs.  8  and  9)  are  usually 
from  l-300th  to  l-1250th  of  an  inch  in  diameter ;  possessing  a  spherical  or 
oval  form,  more  or  less  flattened ;  and  having  a  reddish  colour,  to  which  the 
characteristic  hue  of  the  ganglionic  substance  (whence  it  has  received  the  ap- 
pellation cineritious)  is  chiefly  owing.  Each  contains  one  or  more  nuclei  with 
subordinate  nucleoli;  and  is  enclosed  in  a  very  fine  filamentous  investment,  in 


Primitive  fibres  and  ganglionic  globules  of  human  brain,  after  Purkinje.  A,  gangl'onic  globules  lying, 
amongst  varicose  nerve-tubes,  and  blood-vessels,  in  substance  of  optic  thalamus;  a,  globule  more  enlarged; 
6,  vascular  trunk.  B,  B,  globules  with  variously-formed  peduncles,  from  dark  portion  of  crus  cerebri.  350 
Diara.  (After  Wagner.) 


ELEMENTARY  FUNCTIONS  OF  NERVOUS  STRUCTURE.  93 

which  it  is  commonly  found  to  be  somewhat  loosely  suspended.  The  sheaths 
of  the  several  globules  are  connected  with  each  other  by  prolonged  filaments 
or  peduncles,  as  seen  at  BB,  Fig.  9 ;  and  these  form  a  kind  of  network,  which 
occupies  the  interstices  of  the  fine  vascular  plexus,  by  which  every  part  of  the 
gray  matter  is  traversed.  On  the  surface  of  the  cortical  substance  of  the  brain, 
another  kind  of  structure  is  present,  which  is  found,  however,  in  smaller 
quantity  in  other  parts  of  the  gray  matter:  this  is  a  finely  granular  substance, 
containing  spherical  or  oval  vesicles,  with  one  or  two  dark  granules  in  them. 
In  a  rather  deeper  layer,  these  vesicles,  instead  of  being  irregularly  scattered 
through  the  granular  substance,  seem  to  have  appropriated — each  to  itself — a 
portion  of  the  latter  for  an  independent  covering;  and  from  this  condition  there 
seems  to  be  a  regular  gradation,  till,  in  the  yet  depeer  layers  of  the  cortical 
substance,  the  vesicles  with  their  granular  coverings,  are  replaced  by  perfect 
ganglion-like  globules  with  their  filamentous  sheaths.  Hence  it  may  be 
surmised,  that  this  substance  is  an  incipient  state  of  the  true  ganglionic  matter. 
11*2.  It  appears  uncertain,  from  the  results  of  the  most  recent  microscopic 
inquiries,  whether  the  nervous  fibres  can  be  said  to  have  any  distinct  termina- 
tions, either  in  the  ganglionic  centres,  or  in  the  organs  to  which  they  are 
distributed.  In  the  gray  matter  of  the  brain  of  Vertebrata,  they  seem  to  form 
a  kind  of  plexus  of  loops,  like  that  represented  in  Fig.  8,  B  ;  but  the  ultimate 
fibres  never  anastomoze.  It  Avould  appear  that,  in  the  spinal  cord  of  Verte- 
brata, and  in  the  ganglionic  cord  of  the  Articulata,  the  fibres  pass  through  the 
ganglionic  substance,  without  any  interruption ;  but  Mr.  Newport  has  remarked 
that  they  evidently  become  softer,  and  that  their  diameter  increases,  whilst 
they  are  traversing  it.  (See  §  143  and  Fig.  12.) — The  following  appears  to 
be  the  mode  in  which  the  nervous  fibres  are  distributed  to  the  peripheral 
organs.  The  trunks  subdivide  into  small  fasciculi,  each  of  which  consists  of 
from  two  to  six  fibres ;  and  these  form  plexuses,  whose  arrangement  bears  a 
general  resemblance  to  that  of  the  elements  of  the  tissue  in  which  they  are 
placed.  The  primitive  fibres  then  separate;  and  each,  after  passing  over 
several  elementary  parts  of  the  containing  tissue  (as  in  the  case  of  muscular 
fibre),  or  after  forming  a  single  narrow  loop  (as  in  the  sensory  papillae),  returns 
to  the  same  or  to  an  adjoining  plexus,  and  pursues*  its  way  back  to  the  nervous 
centre  from  which  it  set  out.  In  other  words,  each  fibre  becomes  continuous 
with  another  arising  from  the  same  or  a  neighbouring  fasciculus.  There  is 
thus,  strictly  speaking,  no  more  termination  of  nerves,  than  there  is  of  blood- 
vessels; for  both  form  circles.  The  characters  of  the  fibres  are  scarcely  altered 
in  the  substance  of  the  organs  receiving  them ;  their  sheaths  become  finer,  but 
they  are  npt  lost;  and  there  is  no  fusion  of  the  nervous  into  the  adjacent  sub- 
stance. The  loops  of  the  sensory  nerves  are  surrounded,  when  they  enter  the 
papillae,  by  a  plexus  of  blood-vessels,  including  globules,  which  bear  a  close 
resemblance  to  those  of  the  ganglionic  substance ;  and  each  of  these  papilla 
may  probably  be  considered — like  the  larger  ganglia — as  a  distinct  originator 
of  nervous  power  (§  116). 

III.  Elementary  Functions  of  Nervous  Structure. 

113.  There  can  be  little  doubt  that  the  functions  of  these  two  divisions  of 
the  nervous  system  are  different.  »  That  of  the  fibrous  structure,  as  it  exists  in 
the  nervous  trunks,  is  unquestionably  to  conduct  or  convey  the  influence  of 
changes,  which  have  taken  place  elsewhere.  And  in  accordance  with  what 
has  previously  been  stated,  of  the  mode  in  which  the  mind  is  brought  into 
relation  with  the  external  world,  through  this  nervous  apparatus,  we  find  that 
there  are  (in  the  higher  tribes  of  Animals,  at  least,  if  not  in  all)  two  sets  of 
fibres :  one  of  which  has  for  its  office  to  convey  external  impressions  towards 


FUNCTIONS  OR  THE  NERVOUS  SYSTEM. 

the  nervous  centres ;  whilst  the  other  conveys  the  influence  of  these  central 
organs  to  the  structure  at  large,  and  especially  to  the  muscular  system.  Hence 
it  will  be  convenient  to  denominate  the  first  afferent  fibres,  and  the  second  effe- 
rent. These  are  to  be  regarded  as  general  terms,  expressing  only  the  direc- 
tion in  which  they  propagate  the  changes  to  which  they  are  subservient.  The 
nature  of  these  changes  will  be  a  subject  of  future  inquiry.  Although,  as  just 
stated,  the  fibres  can  no  where  be  said  to  have  free  extremities,  yet  the  afferent 
fibres,  which  convey  to  the  central  organs  the  influence  of  changes  taking 
place  at  the  periphery,  may  be  said  to  originate  in  the  ganglionic  matter  dif- 
fused through  the  latter,  and  to  terminate  in  the  central  ganglia:  whilst  the 
efferent  fibres,  which  convey  to  the  muscles  the  motor  influence  generated  in 
these  last  organs,  may  be  said  to  originate  in  the  central  ganglia,  and  to  termi- 
nate in  the  muscular  tissue. 

114.  Every  fibre,  there  is  reason  to  believe,  runs  a  distinct  course,  between 
the  central  organ,  in  which  it  loses  itself  at  one  extremity,  and  the  muscle  or 
organ  of  sense  in  which  it  terminates  at  the  other.     Each  Nervous  Trunk  is 
made  up  of  several  fasciculi  of  these  fibres ;  and  each  fasciculus  is  composed 
of  a  large  number  of  the  ultimate  fibres  themselves.  Although  the  fasciculi  occa- 
sionally intermix  and  exchange  fibres  with  one  another,  (as  occurs  in  what  is 
termed  a  plexus,)  the  fibres  themselves  never  inosculate.     Each  fibre  would 
seem,  therefore,  to  have  its  appropriate  office,  which  it  cannot  share  with  ano- 
ther.    The  objects  of  a  plexus  are  twofold.     In  some  instances  it  serves  to 
intermix  fibres,  which  have  endowments  fundamentally  different:  for  example, 
the  spinal  accessory  nerve,  at  its  origin,  appears  to  be  exclusively  motor,  and 
the  roots  of  the  par  vagum  are  as  exclusively  sensory ;  but  by  the  early  admix- 
ture of  these,  a  large  number  of  motor  fibres  are  imparted  to  the  par  vagum, 
and  are  distributed,  in  variable  proportion,  with  its  different  branches ;  whilst 
few  of  its  sensory  filaments  seem  to  enter  the  spinal  accessory.     In  other  in- 
stances the  object  of  a  plexus  appears  to  be,  to  give  a  more  advantageous  dis- 
tribution to  fibres,  which  all  possess  corresponding  endowments.     Thus  the 
brachial  plexus  mixes  together  the  fibres  arising  from  five  segments  of  the 
spinal  cord,  and  sends  off  five  principal  trunks  to  supply  the  arm.     Now  if 
each  of  these  trunks  had  arisen  by  itself,  from  a  distinct  segment  of  the  spinal 
cord,  so  that  the  parts  on  which  it  is  distributed  had  only  a  single  connection 
with  the  nervous  centres,  they  would  have  been  much  more  liable  to  paralysis 
than  at  present.     By  means  of  the  plexus,  every  part  is  supplied  with  fibres 
arising  from  each  segment  of  the  spinal  cord ;  and  the  functions  of  the  whole 
must  therefore  be  suspended,  before  complete  paralysis  of  any  part  can  occur, 
from  a  cause  which  operates  above  the  plexus.     Such  a  view  is  borne  out  by 
direct  experiment ;  for  it  has  been  ascertained  by  Fanizza  that,  in  Frogs,  whose 
crural  plexus  is  much  less  complicated  than  that  of  Mammalia,  section  of  the 
roots  of  one  of  the  three  nerves  which  enter  into  it,  produces  little  effect  on  the 
general  movements  of  the  limb ;  and  that,  even  when  two  are  divided,  there  is 
no  paralysis  of  any  of  its  actions,  all  being  weakened  in  a  nearly  similar 
degree. 

115.  It  is  not  unlikely  also  that,  by  this  arrangement,  a  consent  aneousness 
of  action  is  in  some  degree  favoured,  as  is  supposed  by  Sir  C.  Bell;  for  com- 
parative anatomy  shows  that  something  resembling  it  may  be  traced,  wherever 
a  similar  purpose  has  to  be  attained.   "Thus,  in  the  Hymenoptera,  there  is  a 
similar  interlacement  between  the  nerves  of  the  anterior  and  posterior  pairs  of 
wings,  which  act  very  powerfully  together ;  whilst  in  the  Coleoptera,  in  which 
the  anterior  wings  are  converted  into  elytra,  and  are  motionless  during  flight, 
the  nerves  supplying  each  pair  run  their  course  distinctly.     In  the  Octopus, 
or  Poulp,  again,  the  trunks  which  radiate  from  the  cephalic  mass  to  the  eight 
large  anus  surrounding  the  head,  are  connected  by  a  circular  band ;  forming  a 


ELEMENTARY  FUNCTIONS  OF  THE  NERVOUS  STRUCTURE.          95 

kind  of  plexus,  which  evidently  contributes  to  the  very  powerful  and  harmo- 
nious movements  of  the  arms  of  this  Cephalopoda — It  is  considered  by  Dr.  Ali- 
son, that  the  origin  of  the  trunks  which  supply  the  various  muscles  of  the  ex- 
tremities from  several  segments  of  the  spinal  cord,  instead  of  one,  has  the  further 
use  of  enabling  the  mind  to  vary,  in  greater  degree  than  would  otherwise  be 
possible,  the  power  with  which  the  muscle  shall  be  called  into  action;  and  this 
idea  is  certainly  supported  by  the  curious  fact,  that  it  is  in  the  nerves  of  the 
extremities  only  that  this  plexiform  arrangement  prevails ;  and  that  the  nerves 
of  the  eyeball,  in  whose  action  there  is  an  equal  degree  of  consentaneousness, 
but  far  less  variety  of  power,  arise  from  single  points  of  the  cerebro-spinal 
axis.  It  is  further  considered  by  Dr.  A.,  that  the  plexiform  arrangement  may 
enable  the  sensations  proceeding  from  the  muscles  (which  are  important  guides 
in  their  movement),  to  be  more  distinct,  and  consequently  more  easily  discrimi- 
nated from  one  another,  than  they  would  otherwise  be  ;  and  there  does  not 
seem  any  reason  why  the  same  view  should  not  be  extended  to  the  sensory 
impressions  communicated  from  the  general  surface  of  the  extremities. 

116.  There  is  no  valid  reason  to  believe  that  the  nervous  fibres  undergo 
any  change  of  function  along  their  whole  course ;  and  we  may,  probably,  com- 
pare them,  by  way  of  analogy  only,  to  the  conducting  wires  of  a  galvanic 
apparatus.     But  it  is  evident  that  the  special  structure  into  which  they  pass, — 
the  plexus  of  blood-vessels  and  ganglionic  globules,— must  have  some  particu- 
lar function ;  and  there  seems  no  reasonable  ground  for  doubt,  that  in  this  struc- 
ture, those  changes  originate  which  are  conducted  by  the  fibres  to  distant 
points.     Following  out  the  same  analogy,  then,  we  might  compare  this  struc- 
ture with  the  galvanic  combination,  by  which  the  electric  influence  is  gene- 
rated, that  is  conveyed  to  some  distant  point  by  the  connecting  wires  and 
there  produces  a  decomposition  or  other  similar  change;  and  there  seems 
to  be  as  much  reason  for  thus  assigning  the  functions  of  the  production  and 
conduction  of  nervous  power  to  the  gray  and  white  portions  of  the  nervous 
system  respectively,  as  there  is  for  attributing  the  production  of  electric  power 
to  the  galvanic  trough,  and  its  conduction  to  the  connecting  wires.     Wherever 
we  have  reason  to  believe  that  new  power  is  generated,  there  do  we  find  gray 
matter ;  and,  on  the  other  hand,  there  are  few,  if  any,  instances  in  which  gray 
matter  is  present,  without  our  being  able  to  assign  to  it  some  obvious  purpose 
of  this  kind. 

117.  The  belief  that  all  changes  in  the  nervous  system,  whether  they  take 
place  at  the  centre  or  at  the  periphery,  originate  at  the  points  in  which  the 
fibres  come  into  relation  with  the  vascular  plexus,  derives  confirmation  from 
the  well-known  dependence  of  these  changes  upon  the  activity  of  the  circu- 
lation through  the  part  at  which  they  occur.     Thus,  if  the  circulation  of  blood 
through  the  brain  be  suspended  for  an  instant,  insensibility  supervenes.     If 
the  cause  of  suspension  be  local  only,  the  remdnder  of  the  nervous  system 
may  still  be  excited  to  action.     This  was  the  case  in  experiments  made  by  Sir 
A.  Cooper.     After  having  tied  both  carotid  arteries  in  a  dog,  he  compressed 
the  vertebral  trunks,  and  immediate  insensibility  resulted,  proving  the  inactive 
condition  of  the  brain ;    whilst  convulsions  also  occurred,  showing  that  the 
functions  of  the  spinal  cord  were  not  suspended,  but  only  deranged.     But  if, 
as  in  syncope,  the  circulation  through  the  spinal  cord  also  be  weakened,  its 
power  of  producing  motions  in  respondence  to  impressions  is  diminished  in 
like  proportion.     In  the  same  manner  the  production  of  impressions  on  the 
peripheral  origins  of  the  afferent  nerves,  appears  equally  dependent  upon  the 
active  influence  of  the  vascular  system.     Every  one  knows  that  cold,  which 
retards  the  circulation  of  blood  through,  the  skin,  diminishes  also  its  sensi- 
bility ;  and  obstruction  to  the  circulation  by  any  other  cause,  such  as  pressure 
on  the  arterial  trunks,  produces  the  same   effect.     Moreover,  it  is  always 


96  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

found,  that  an  increase  in  local  circulation  is  accompanied  by  an  exaltation  of 
the  sensibility  of  the  part.  This  may  be  especially  noticed  in  the  genital 
organs  of  animals  during  the  period  of  heat ;  and  in  those  of  man  when  in  a 
state  of  venereal  excitement.  It  may  be  remarked,  also,  in  those  affections  so 
closely  bordering  upon  inflammation,  to  which  the  term  active  congestion,  or 
determination  of  blood,  has  been  applied.  The  pain  which  usually  accom- 
panies inflammation  may  be  partly  referred  to  this  source ;  but  it  seems  prin- 
cipally dependent  upon  other  causes. 

118.  It  may  be  argued  against  this  view  of  the  respective  functions  of  the 
granular  and  fibrous  structures,  that  sensation  may  be  produced  by  pinching 
an  afferent  trunk  in  its  course,  and  that  motion  may  be  excited  by  irritating 
an  efferent  nerve ;  so  that  the  changes  which  have  been  spoken  of  as  occurring 
at  their  points  of  origin  in  the  vascular  plexus,  are  not  to  be  regarded  as  the 
means  by  which  such  influences  are  produced.     But  this  argument  will  have 
little  weight,  when  it  is  recollected  that  on  the  same  ground,  we  might  infer 
that  neither  the  organs  of  sensation  on  the  one  hand,  nor  any  part  of  the  brain, 
or  spinal  cord,  on  the  other,  are  the  sources  of  the  changes  in  question.     The 
effects  are  obviously  due  to  the  fact  that  the  artificial  stimulus  imitates  the 
natural  one ;  and  thus  it  is  that  if  a  sensory  nerve  be  compressed,  the  sensa- 
tion produced  is  referred  to  the  part  of  the  surface,  to  which  its  branches  are 
distributed. 

119.  Our  simplest  idea,  then,  of  a  nervous  system,  includes  a  Central  organ, 
of  which  the  gray  matter, — formed  by  the  intermixture  of  nervous  fibres,  blood- 
vessels, and  ganglionic  globules, — is  the  essential  part ;  and  an  afferent  and 
efferent  set  of  fibres  connected  with  it, — one  conveying  to  it  the  impressions 
produced  by  external  changes  upon  the  periphery  (where  also  the  nervous 
structure  comes  into  peculiar  relation  with  the  vascular  system), — and  the  other 
conducting  from  it  the  motor  stimulus,  originating  in  itself,  to  the  contractile 
tissue.     This  is  precisely  what  we  find  in  the  lowest  of  those  animals  in  which 
a  nervous  apparatus  can  be  distinguished,  as  will  be  hereafter  explained.    At 
present  it  will  be  desirable  to  consider  some  other  questions,  which  early  pre- 
sent themselves  in  the  study  of  Neurology. 

IV.  Mode  of  determining  the  Functions  of  Nerves. 

120.  Various  methods  of  determining  the  functions  of  particular  nerves 
present  themselves  to  the  physiological  inquirer.     One  source  of  evidence  is 
drawn  from  their  anatomical  distribution.     For  example,  if  a  nervous  trunk  is 
found  to  lose  itself  entirely  in  the  substance  of  muscles,  it  may  be  inferred  to  be 
chiefly,  if  not  entirely,  motor  or  efferent.   In  this  manner,  Willis  long  ago  deter- 
mined that  the  third,  fourth,  sixth,  portio  dura  of  the  seventh  and  ninth  cranial 
nerves,  are  almost  entirely  subservient  to  muscular  movement ;  and  the  same 
had  been  observed  of  the  fibres  proceeding  from  the  small  root  of  the  fifth  pair, 
before   Sir  C.  Bell  experimentally  determined  the   double  function  of  that 
division  of  the  nerve,  into  which  alone  it  enters.     Again,  where  a  nerve 
passes  through  the  muscles,  with  little'  or  no  ramification  among  them,  and 
proceeds  to  a  cutaneous  or  mucous  surface,  on  which  its  branches  are  minutely 
distributed,  there  is  equal  reason  to  believe  that  it  is  of  a  sensory,  or  rather  of 
an  afferent,  character.     In  this  manner  Willis  came  to  the  conclusion,  that  the 
ijfth  pair  of  cranial  nerves  differs  from  those  previously  mentioned,  in  being 
partly  sensory.     Further,  where  a  nerve  is  entirely  distributed  upon  a  surface 
adapted  to  receive  impressions  of  a  special  kind,  as  that  of  the  Schneiderian 
membrane,  the  retina,  or  the  membrane  lining  the  internal  ear,  it  may  be 
inferred  that  it  is  not  capable  of  transmitting  any  other  kind  of  impressions ; 
for  experiment  has  shown  that  the  special  sensory  nerves,  do  not  possess  com- 


MODE  OF  DETERMINING  THE  FUNCTIONS  OF  NERVES.  97 

mon  sensibility.  The  case  is  different,  however,  in  regard  to  the  sense  of 
taste,  which  originates  in  impressions  not  far  removed  from  those  of  ordinary 
touch;  and  it  is  probable  that  the  same  nerves  minister  to  both.  Anatomical 
evidence  of  this  kind  is  valuable  also,  not  only  in  reference  to  the  functions  of 
a  principal  trunk,  but  even  as  to  those  of  its  several  branches,  which,  in  some 
instances,  differ  considerably.  Thus,  some  of  the  branches  of  the  par  vagum 
are  especially  motor,  and  others  almost  exclusively  afferent;  and  anatomical 
examination,  carefully  prosecuted,  not  only  assigns  the  reasons  for  these  func- 
tions, when  ascertained,  but  is  in  itself  nearly  sufficient  to  determine  them. 
Thus  the  superior  laryngeal  nerve  is  distributed  almost  entirely  upon  the 
mucous  surface  of  the  larynx,  the  only  muscle  it  supplies  being  the  crico- 
thyroid ;  whilst  the  inferior  laryngeal  or  recurrent  is  almost  exclusively  dis- 
tributed to  the  muscles.  From  this  we  should  infer  that  the  former  is  an 
afferent,  and  the  latter  a  motor  nerve ;  and  experimental  inquiries  (hereafter 
to  be  detailed)  fully  confirm  this  view.  In  like  manner  it  may  be  shown, 
that  the  glosso-pharyngeal  is  chiefly  an  afferent  nerve,  since  it  is  distributed 
to  the  surface  of  the  tongue  and  *pharynx,  and  scarcely  at  all  to  the  muscles 
of  those  parts ;  whilst  the  pharyngeal  branches  of  the  par  vagum  are  chiefly, 
if  not  entirely,  motor.  Lower  down,  however,  the  branches  of  the  glosso- 
pharyngeal  cease,  and  the  oesophageal  branches  of  the  par  vagum  are  dis- 
tributed both  to  the  mucous  surface  and  to  the  muscles ;  from  which  it  may 
be  inferred  that  they  are  both  afferent  and  motor — a  deduction  which  experi- 
ment confirms. 

121.  We  perceive,  therefore,  that  much  knowledge  of  the  function  of  a 
nerve  may  be  obtained  from  the  attentive  study  of  its  ultimate  distribution : 
but  it  is  necessary  that  this  should  be  very  carefully  ascertained,  before  it  is 
made  to  serve  as  the  foundation  for  physiological  inferences.     As  an  example 
of  former  errors  in  this  respect,  may  be  mentioned  the  description  of  the 
pprtio  dura  of  the  seventh,  at  first  given  by  Sir  C.  Bell :  he  stated  it  to  be 
distributed  to  the  skin  as  well  as  to  the  muscles  of  the  face,  and  evidently 
regarded  it  as  in  part  an  afferent  nerve,  subservient  to  respiratory  impressions 
as  well  as  to  motions.     In  the  same  manner,  from  inaccurate  observation  of 
the  ultimate  distribution  of  the  superior  laryngeal  nerve,  it  was  long  regarded 
as  that  which  stimulated  to  action  the  constrictors  of  the  glottis.     But  the 
knowledge  obtained  by  such  anatomical  examinations  alone  is  of  a  very  gene- 
ral kind;  and  requires  to  be  made  particular, — to  be  corrected  and  modified, 
— by  other  sources  of  information.     One  of  these  relates  to  the  connection  of 
the  trunks  with  the  central  organs.     The  evidence  derived  from  this  source, 
however,  is  seldom  of  a  very  definite  character  ;  and,  in  fact,  the  functions  of 
particular  divisions  of  the  nervous  centres  have  been  hitherto  rather  judged  of 
by  those  of  the  nerves  with  which  they  are  connected,  than  affording  aid  in  the 
determination  of  the  latter.     Still,  this  kind  of  examination  is  not  without  its 
use,  when  there  is  reason  to  believe  that  a  particular  tract  of  fibrous  structure 
has  a  certain  function,  and  when  the  office  of  a  nerve  whose  roots  terminate 
in  it  is  doubtful.     Here,  again,  however,  very  minute  and  accurate  examina- 
tion is  necessary,  before  any  sound  physiological  inferences  can  be  drawn  from 
facts  of  this  description ;  and  many  instances  might  be  adduced  to  show,  that 
the  real  connections  of  nerves  and  nervous  centres  are  often  very  different 
from  their  apparent  ones. 

122.  Experimental  inquiries  into  the  functions  of  particular  nerves  are  also 
liable  to  give  fallacious  results,  unless  they  are  prosecuted  with  a  full  know- 
ledge of  all  the  precautions  necessary  to  insure  success.     Some  of  these  will 
be  here  explained.     Suppose  that,  upon  irritating  the  trunk  of  a  nerve,  whilst 
still  in  connection  with  its  centre,  muscular  movements  are  excited ;  it  must 
not  be  hence  concluded  that  the  nerve  is  an  efferent  one,  for  it  may  have  no 

9 


98  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

directly  motor  powers.  The  next  step  would  be  to  divide  the  trunk,  and  to 
irritate  each  of  the  cut  extremities.  If,  upon  irritating  the  end  separated  from 
the  centre,  muscular  contractions  are  produced,  it  may  be  safely  inferred  that 
the  nerve  is,  in  part  at  least,  of  an  efferent  character.  Should  no  such  result  fol- 
low, this  would  be  doubtful.  If,  on  the  other  hand,  muscular  movement  should 
be  produced  by  irritating  the  extremity  in  connection  with  the  centre,  it  will 
then  be  evident,  that  it  is  occasioned  by  an  impression  conveyed  towards  the 
centre  by  this  trunk,  and  propagated  to  the  muscles  by  some  other;  in  other 
words,  to  use  the  language  of  Dr.  M.  Hall,  this  nerve  is  an  exciter  of  motion, 
not  a  direct  motor  nerve.  The  glosso-pharyngeal  nerve  has  been  satisfactorily 
determined  to  be  chiefly,  if  not  entirely,  an  efferent  nerve;  by  experiments 
of  this  kind,  performed  by  Dr.  J.  Reid. 

123.  It  has  been  from  the  want  of  a  proper  mode  of  experimenting,  that  the 
functions  of  the  posterior  roots  of  the  spinal  nerves  have  been  regarded  as  in 
any  degree  motor.     If  they  be  irritated,  without  division  of  either  root,  motions 
are  often  excited ;  but  if  they  be  divided,  and  their  separated  trunks  be  then 
irritated,  no  motions  ensue  ;  nor  are  any  movements  produced  by  irritation  of 
the  roots  in  connection  with  the  spinal  cord,  if  the  anterior  roots  have  been 
divided.  Hence  it  appears  that  the  motor  powers  of  these  fibres  are  not  direct, 
but  that  they  convey  an  impression  to  the  centre,  which  is  reflected  to  the 
muscles  through  the  anterior  roots.     Another  source  of  fallacy  is  to  be  guarded 
against,  arising  from  the  communication  to  a  nerve,  in  its  course,  of  properties 
it  did  not  possess  at  its  root,  by  inosculation  with  another  nerve.     Of  this 
many  instances  will  hereafter  present  themselves. 

124.  The  same  difficulties  do  not  attend  the  determination  of  the  sensory 
properties  of  nerves.     If,  when  the  trunk  of  a  nerve  be  pricked  or  pinched, 
the  animal  exhibits  signs  of  pain,  it  may  be  concluded  that  the  nerve  is  sensi- 
ble to  ordinary  impressions  at  its  peripheral  extremity,     feut  not  unfrequently 
this  sensibility  is  derived  by  inosculation  with  another  nerve ;  as  is  the  case 
with  the  portio  dura,  which  is  sensory  after  it  has  passed  through  the  parotid 
gland,  having  received  there  a  twig  from  the  fifth  pair.     A  similar  inoscula- 
tion explains  the  apparent  sensibility  of  the  anterior  roots  of  the  spinal  nerves. 
If  these  be  irritated,  the  animal  usually  gives  signs  of  uneasiness ;  but  if  they 
be  divided,  and  the  cut  ends  nearest  the  centre  be  irritated,  none  such  are  ex- 
hibited; whilst  they  are  still  shown,  when  the  farther  ends  are  irritated,  but 
not  if  the  posterior  roots  are  divided.     This  seems  to  indicate  that,  from  the 
point  of  junction  of  the  two  roots,  sensory  fibres  derived  from  the  posterior 
root  pass  backwards  (or  towards  the  centre)  in  the  anterior ;  and  thus  its  ap- 
parent sensory  endowments  are  entirely  dependent  upon  its  connection  with 
the  posterior  column  of  the  spinal  cord,  through  the  posterior  roots. 

125.  The  fallacies  to  which  all  experiments  upon  the  nerves  are  subject, 
arising  from  the  partial  loss  of  their  powers  of  receiving  and  conveying  im- 
pressions, and  of  exciting  the  muscles  to  action,  after  death,  are  too  obvious  to 
require  particular  mention  here  ;  yet  they  are  frequently  overlooked.     Of  a 
similar  description  are  those  arising  from  severe  disturbance  of  the  system, 
in  consequence  of  operations ;  which  also  have  not  been  enough  regarded  by 
experimenters. 

f" 
V.  Nature  of  the  Changes  in  the  Nervous  System. 

126.  Of  the  actual  nature  of  the  changes,  by  which  impressions  are  received 
upon  the  peripheral  origins  of  the  afferent  nerves,  or  are  communicated  to  the 
central  origins  of  the  motor,  and  are  conducted  along  each  to  their  opposite 
extremities,  physiologists  have  no  certain  knowledge.     That  they  are  electri- 
cal has  been,  and  still  continues  to  be,  a  favourite  theory  with  some ;  and  that 


NATURE  OF  THE  CHANGES  IN  THE  NERVOUS  SYSTEM.  99 

there  is  a  great  analogy  between  the  propagation  of  nervous  and  that  of  elec- 
trical influence,  cannot  be  denied.  But  the  reasons  in  favour  of  their  identity 
are  not  greater  than  those  which  might  be  adduced  to  prove  that  nervous  in- 
fluence is  identical  with  other  physical  forces ;  since  mechanical  and  chemical 
stimulation  will,  equally  with  electricity,  imitate,  to  a  certain  extent,  the  natural 
changes  in  this  system.  On  the  other  hand,  there  are  many  valid  reasons 
against  such  a  supposition ;  of  which  one  of  the  most  cogent  is,  that  by  putting 
a  ligature  round  a  trunk,  its  functions  as  a  conductor  of  nervous  influence  are 
paralyzed,  whilst  it  is  still  capable  of  conveying  electricity.  The  various  fibrils, 
too,  are  not  as  completely  insulated  from  each  other  in  regard  to  the  passage  of 
electricity,  as  we  know  them  to  be  in  respect  to  nervous  agency.  To  the 
influence  (whatever  its  nature  may  be)  which  the  nerves  convey,  the  term  vis 
nervosa  has  been  provisionally  applied. ;  and  it  is  convenient  to  employ  a  term 
of  this  nature,  when  the  laws  according  to  which  it  operates  are  being  speci- 
fied. It  must  be  remembered,  however,  that  nothing  is  really  gained  by  the 
use  of  such  a  term,  which  resembles  one  of  the  unknown  quadpies  in  algebra. 
It  is  quite  possible  that  the  changes  in  the  afferent  nerves  may  differ  from  those 
that  take  place  in  the  efferent ;  and  that  the  changes  which  convey  some  kinds 
of  impressions  through  the  former,  may  differ  from  those  concerned  in  others. 
No  real  progress  is  made,  therefore,  by  attributing  any  phenomena  of  the  ner- 
vous system  to  the  vis  nervosa ;  any  more  than  by  referring  the  various  mate- 
rial changes  in  the  organism  to  the  operation  of  the  vital  principle.  The 
laws  according  to  which  these  changes  take  place  are,  however,  legitimate 
subjects  for  physiological  investigation.  Those  regulating  the  propagation  of 
nervous  agency  may  be  briefly  stated  as  follows.  They  evidently  result  from 
the  facts  already  mentioned,  respecting  the  isolated  character  of  each  fibril, 
and  the  identity  of  its  endowments  through  its  whole  course.  They  are  here 
stated,  with  some  modification,  in  the  language  of  Mil  Her. 

I.  When  the  whole  trunk  of  a  sensory  nerve  is  irritated,  a  sensation  is  pro- 
duced, which  is  referred  by  the  mind  to  the  parts  to  which  its  branches  are 
ultimately  distributed ;  and  if  only  part  of  the  trunk  be  irritated,  the  sensation 
will  be  referred  to  those  parts  only  which  are  supplied  by  the  fibrils  it  con- 
tains.    This  is  evidently  caused  by  the  production  of  a  change  in  the  senso- 
rium,  corresponding  with  that  which  would  have  been  transmitted  from  the 
peripheral  origins  of  the  nerves,  had  the  impression  been  made  upon  them. 
Such  a  change  only  requires  the  integrity  of  the  afferent  trunk  between  the 
point  irritated  and  the  sensorium ;  and  is  not  at  all  dependent  upon  the  state 
of  the  extremity  to  which  the  sensations  are  referred.     This  may  have  been 
paralyzed  by  the  division  of  the  nerve ;  or  altogether  separated,  as  in  ampu- 
tation ;  or  the  relative  position  of  its  parts  may  have  been  changed.     It  results 
from  the  foregoing,  that,  when  different  parts  of  the  thickness  of  the  same 
trunk  are  separately  subjected  to  irritation,  the  sensations  are  successively 
referred  to  the  several  parts  supplied  by  these  divisions.     This  may  be  easily 
shown  by  compressing  the  ulnar  nerve,  in  different  directions,  where  it  passes 
at  the  inner  side  of  the  elbow-joint. 

II.  The  sensation  produced  by  irritation  of  a  branch  of  the  nerve,  is  con- 
fined to  the  parts  to  which  that  branch  is  distributed,  and  does  not  affect  the 
branches  which  come  off  from  the  nerve  higher  up.     The  rationale  of  this 
law  is  at  once  understood :  but  it  should  be  mentioned  that  there  are  certain 
conditions,  in  which  the  irritation  of  a  single  nerve  will  give  rise  to  sensations 
over  a  great  extent  of  the  body.     This  is  due,  however,  to  a  particular  state 
of  the  central  organs,  and  not  to  any  direct  communication  among  the  sensory 
fibres.  •  X  '    ,*     ,»,*••<     ,^ 

III..  The  motor  influent is?prcpagate<  ohiy  inte  ceftf-riftig^Mirection,  never 
in  a  retrograde  course.    Jtjnay  originate  in  a  spoiltaneeu^  change  in  the  cen- 


10U  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

tral  organs  :  or  it  may  be  excited  by  an  impression  conveyed  to  them  through 
afferent  nerves;  but  in  both  cases  its  law  is  the  same. 

IV.  When  the  whole  trunk  of  a  motor  nerve  is  irritated,  all  the  muscles 
which  it  supplies  are  caused  to  contract ;  but  when  only  a  part  of  the  trunk  or 
a  branch  is  irritated,  the  contraction  is  confined  to  the  muscles  which  receive 
their  nervous  fibres  from  it.  This  contraction  evidently  results  from  the  simi- 
larity between  the  effect  of  an  artificial  stimulus  applied  to  the  trunk  in  its 
course,  and  that  of  the  change  in  the  central  organs  by  which  the  vis  nervosa 
is  ordinarily  propagated.  In  this  instance,  as  in  the  other,  there  is  no  lateral 
communication  between  the  fibrils. 

VI.   Comparative  Anatomy  and  Physiology  of  the  Nervous  System. 

127.  Although  the  structure  and  distribution  of  the  Nervous  System  in  the 
different  classes  of  Animals  have  been,  until  recently,  but  little  appealed  to  in 
the  determi^^Hp-  of  its  functions,  they  are  capable  of  supplying  evidence 
regarding  some  of  these,  not  less  important  in  its  character  than  that  which 
Comparative  Anatomy  affords  to  other   departments  of  Physiology.     Some 
of  the  principal  of  these  contributions  will  now  be  pointed  out 

128.  In  the  lowest  tribes  of  the  RADIATED  division  of  the  animal  kingdom, 
no  nervous  system  has  yet  been  discovered.     These  have,  therefore,  been 
separated  by  some  naturalists  into  a  new  primary  group,  to  which  the  desig- 
nation of  Jlcrita  has  been  given,  on  account  of  the  (supposed)  "  indistinct, 
diffused,  or  molecular  character  of  their  nervous  system."     This  idea  of  a 
"  diffused  nervous  system"  seems  to  be  regarded  l>y  many — physiologists  as 
well  as  naturalists — as  the  necessary  alternative,  resulting  from  the  want  of 
any  definite  indications  of  its  presence.     It  may  be  said,  however,  to  be  based 
on  very  erroneous  notions,  as  to  the  true  offices  of  the  nervous  apparatus.    Its 
influence  is  not  required  to  endow  the  tissues  with  contractility ;  a  property 
possessed  in  a  high  degree  by  the  structures  of  many  Plants,  to  which  these 
beings  present  a  much  greater  general  resemblance  than  they  bear  to  the 
higher  Animals;  and,  even  in  the  latter  (as  will  be  shown  hereafter),  this  pro- 
perty is  independent  of  "nervous  agency,"  although  generally  called  into  ex- 
ercise by  it.  That  a  nervous  system  is  not  required  by  them  for  the  performance 
of  the  functions  of  Nutrition  and  Reproduction,  otherwise  than  to  supply,  by 
its  locomotive  actions,  the  conditions  of  those  functions,  would  also  appear  from 
its  absence  in  Plants.     It  is  on  the  sensible  movements  of  these  beings  that 
our  belief  in  their  possession  of  a  nervous  system  must  be  founded,  when  we 
cannot  render  it  cognizable  by  our  senses.   But  we  must  be  careful  not  to  draw 
hasty  inferences  from  such  phenomena.     Sensible  movements  are,  as  we  have 
seen,  performed  by  the  Dionsea  and  Sensitive  plant,  in  respondence  to  external 
stimuli  acting  on  distant  organs;  and  here  the  channel  of  communication  is 
probably  the  vascular  system.    We  observe,  however,  that  even  in  Polypes,  an 
impression  made  upon  one  part  (one  of  the  tentacula,  for  example),  is  propa- 
gated to  distant  parts,  and  excites  respondent  movements  in  them,  more  rapid- 
ly than  we  could  imagine  to  occur,  without  such  a  channel  of  communication 
as  a  nervous  system  only  is  known  to  afford.     Moreover,  some  of  their  actions 
appear  to  show  a  certain  degree  of  voluntary  power,  and,  therefore,  of  con- 
sciousness ;  being  independent,  so  far  as  can  be  ascertained,  of  the  operation 
of  external  stimuli.     These  phenomena,  then,  would  lead  us  to  suspect  the 
existence  of  a  nervous  system  in  the  beings  which  exhibit  them ;  not,  how- 
ever, in  a  "  diffused"  condition,  but  in  the  form* of  connected  filaments.     For, 
what  consentanepusness  of-actio»  can  he  jb&l£e«£  fpr*in  a  being  whose  nervous 
matter  is  incorporated -lii  th<>  state  •pf,"  isolated  gltfbules  with  its  tissues  ?     How 
should  an  impression  tnatle'  on  one  part  be  propagated  by  these  to  a  distance  ? 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY. 

And  how  can  that  consciousness  and  will,  which  are  one  in  each  individual, 
exist  in  so  many  unconnected  particles  ?  If,  then,  we  allow  any  sensibility, 
consciousness,  and  voluntary  power,  to  the  beings  of  this  group  of  Acrita — to 
deny  which  would  be  in  effect  to  exclude  them  from  the  Animal  Kingdom — 
we  must  regard  these  faculties  as  associated  with  nervous  filaments,  of  such 
delicacy  as  to  elude  our  means  of  research.  When  the  general  softness  of 
the  textures,  and  the  laxity  of  structure  that  characterize  the  nervous  fibres, 
in  the  lowest  animals  in  which  they  can  be  traced,  are  kept  in  view,  little  dif- 
ficulty need  be  felt  in  accounting  for  their  apparent  absence.  The  case  is  very 
different  from  that  of  Vegetable  structure,  the  greater  consistency  of  which 
enables  us  to  place  much  more  reliance  upon  the  negative  evidence  afforded 
by  anatomical  research. 

129.  The  correctness  of  this  view  (which  has  been  here  dwelt  on  the  longer, 
because  it  involves  a  fundamental  question  in  Nervous  Physiology),  is  borne 
out  by  the  fact,  that,  in  those  members  of  the  group  whose  size  and  consistency 
allow  their  structures  to  be  sufficiently  examined,  a  definite  nervous  system 
has  been  detected,  in  the  position  which  it  might,  a  priori,  be  expected  to 
occupy,  according  to  the  type  of  the  individual.  Thus,  in  the  large  fleshy 
isolated  polype,  commonly  known  as  the  Sea-Anemone  (Jlctinia),  a  nervous 
ring  has  been  discovered,  surrounding  the  mouth  as  in  other  Radiata,  and 
sending  off  branches  to  the  tentacula,  with  a  minute  ganglionic  enlargement 
at  the  base  of  each.  In  the  higher  Radiata,  as  the  Star-Fish,  the  nervous 
system  has  the  same  regular  form  as  that  which  prevails  through  the  other 
organs.  The  mouth  is  surrounded  by  a  filamentous  ring,  which  presents  a 
regular  series  of  gangliohic  enlargements,  one  of  them  corresponding  with 
each  segment  of  the  body.  From  every  one  of  these,  a  branch  is  transmitted 
to  the  corresponding  ray ;  and  two  smaller  ones  proceed  to  the  viscera  in- 
cluded in  the  central  disk. 

180.  The  Polypiftra  being  the  lowest  of  the  Radiated  classes  in  wrhich 
there  is  a  regularly-organized  digestive  apparatus,  and  which  perform  move- 
ments of  a  character  ascribable  only  to  a  nervous  system,  it  will  be  desirable 
to  inquire  a  little  more  particularly  into  the  phenomena  they  exhibit,  and  the 
degree  in  which  these  necessarily  involve  the  possession  of  the  higher  mental 
endowments.  In  this  inquiry  we  shall  refer  principally  to  the  little  Hydra, 
or  fresh-water  Polype,  the  habits  of  which  are  better  known  than  those  of  any 
other  species.  Although  no  nervous  filaments  have  been  detected  in  this,  we 
have  a  right  to  infer  their  presence  for  the  reasons  already  given ;  and  they 
probably  form  a  ring  around  the  mouth,  as  in  the  Actinia,  sending  filaments  to 
the  tentacula.  This  interesting  little  being  may  be  regarded  as  essentially  a 
stomach;  and  the  orifice  of  this  is  provided  with  tentacula,  which  contract 
when  irritated  by  the  touch  of  any  adjacent  body,  and  endeavour  to  draw  it 
towards  the  entrance.  Now,  the  action  in  the  Human  body,  to  which  this  is 
most  allied,  is  evidently  that  of  the  muscles  of  Deglutition ;  which  lay  hold,  as 
it  were,  of  the  food  that  has  been  conveyed  to  the  fauces,  and  carry  it  into  the 
stomach.  These  muscles  are  called  into  action,  not  by  an  effort  of  the  will, 
but  by  the  contact  of  the  food  with  the  lining  membrane  of  the  pharynx.  This 
impression  is  propagated  by  the  glosso-pharyngeal  nerve  to  the  medulla 
oblongata,  where  a  respondent  motor  impulse  is  excited,  which  is  transmitted 
through  the  pharyngeal  branches  of  the  par  vagum  to  the  muscles  of  degluti- 
tion, and  causes  their  contraction.  This  phenomenon  will  be  more  fully  ex- 
amined hereafter ;  it  is  here  adduced  simply  as  an  instance  of  the  important 
class  of  reflex  movements  which  are  independent  of  the  brain  (though,  to  a 
certain  extent,  controlled  by  it),  which  are  altogether  involuntary,  and  which 
do  not  necessarily  involve  the  production  of  sensation.  There  would  appear 
to  be  little  difference,  in  the  character  of  this  movement,  between  the  simple 

9* 


102  FUNCTIONS  OF  THE  NERVOUS  SYSTEJVI. 

Hydra  and  the  most  perfect  Vertebrated  animal.  In  the  latter,  however,  an- 
other set  of  muscles  are  superadded  to  these,  for  the  purpose  of  preparing  the 
aliment  by  mastication  for  the  operation  of  the  stomach,  and  of  bringing  it 
within  reach  of  the  pharyngeal  constriction.  But,  it  has  been  urged,  the  inac- 
tivity of  the  tentacula  when  the  Hydra  is  gorged  with  food,  proves  that  they 
are  excited  to  action  by  the  will  of  the  animal.  This  inference,  however,  may 
be  easily  disproved.  The  muscles  of  deglutition  in  Man  are  not  called  into 
action  with  nearly  the  same  readiness  and  energy,  wThen  the  stomach  is  dis- 
tended, as  when  it  is  empty ;  a  fact  of  which  any  one  may  convince  himself, 
by  observing  the  relative  facility  of  swallowing  at  the  commencement  and  the 
termination  of  a  full  meal.  No  one  will  assert  that  this  variation  is  an  effect 
of  the  will ;  indeed,  it  is  often  opposed  to  it ;  being  one  of  those  beautiful 
adaptations,  by  which  the  welfare  of  the  economy  is  provided  for,  but  which 
the  indulgence  of  the  sensual  appetites  opposes.  Most  of  the  movements  of 
this  animal,  and  of  others  of  the  class,  appear  to  be  equally  the  result  of  ex- 
ternal stimuli  with  that  already  described  ;  and  it  is  only  in  a  few  instances, 
principally  those  of  absolute  locomotion  or  change  of  place,  that  any  evidence 
of  voluntary  action  can  be  discerned.  It  may  be  occasionally  remarked,  how- 
ever, that  one  or  more  of  the  tentacula  are  retracted  or  extended,  without  the 
slightest  appreciable  change  in  any  of  those  external  circumstances  which 
seem  ordinarily  to  affect  the  motions  of  the  animal ;  and  this  action  we  can 
scarcely  regard  as  otherwise  than  voluntary. 

131.  Thus  in  the  Nervous  System  of  Radiated  Animals,  we  have  an  instance 
of  that  community  of  function  which  is  so  remarkable  in  the  organism  of  the 
lower  tribes,  when  contrasted  with  the  separation  which  is  perceptible  in  those 
at  the  opposite  extremity  of  the  scale.     The  visceral  nerves  of  the  Asterias  are 
not  isolated  at  their  central  terminations  from  those  which  are  connected  with 
the  sensorial  and  locomotive  functions :  nor  are  those  which  minister  to  the 
instinctive  actions  separable  from  those  which  convey  the  influence  of  the 
will.     Every  segment  of  the  body  appears  equal  in  its  character  and  endow- 
ments to  the  remainder ;  each  has  a  ganglion  appropriated  to  it ;  and,  as  the 
ganglia,  like  the  segments,  are  all  alike,  neither  of  them  can  be  regarded  as 
having  any  presiding  character. 

132.  From  the  Radiated  we  now  pass  to  the  MOLLUSCOUS  glasses,  the  gene- 
ral character  of  which,  as  a  natural  group,  is  the  remarkable  predominance  of 
the  Nutritive  system  over  that  of  Animal  life.     In  fact,  although  the  organs 
which  minister  to  their  vegetative  functions  attain  a  very  high  degree  of  deve- 
lopment, the  animal  powers  of  sensation  and  locomotion  are,  in  general,  so 
feebly  manifested,  as  to  show  that  they  are  entirely  subservient  to  the  exercise 
of  tMe  former.     There  is  not  in  the  Mollusca,  as  in  theRadiata,  any  repetition 
of  parts  around  a  common  centre  ;  and  we  do  not,  therefore,  meet  in  them  with 
a  number  of  ganglia  nearly  or  altogether  alike  in  endowments.     In  some  of 
the  higher  species,  there  is  a  conformity  between  the  two  sides  of  the  body, 
or  a  lateral  symmetry :  which  involves  a  subdivision  of  some  of  the  ganglia, 
that  are  single  in  the  inferior  tribes,  into  two  masses,  which  always  remain  in 
connection  with  each  other.     With  this  exception,  it  may  be  observed,  that  all 
the  ganglia,  to  the  number  of  four  or  five,  which  we  meet  with  in  the  higher 
Mollusca,  appear  to  have  distinct  functions  ;  as  may  be  determined  by  tracing 
the  .distribution  of  their  nerves.     Thus  we  find  a  pair  of  cephalic  ganglia, 
situated  above  the  oesophagus,  connected  with  the  organs  of  special  sensation, 
and  sending  motor  nerves  (as  we  shall  see  reason  to  believe)  to  all  parts  of  the 
body.     This  is  obviously  analogous  to  the  brain  of  Vertebrata.     Below  the 
oesophagus  there  is  generally  a  small  ganglion,  connected  with  the  apparatus 
of  deglutition,  which  may  be  called  the  stomato-gastric  ganglion.     In  connec- 
tion with  the  gills  we  have  always  one  ganglion,  sometimes  a  pair,  which  may 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  103 

be  termed  the  branchial  ganglion.  Another  is  found  at  the  base  of  the  foot, 
which  may  be  called  the  pedal  ganglion.  And  there  is  sometimes  another, 
which  especially  supplies  the  mantle  with  nerves ;  and  this  may  be  called  the 
pallcal  ganglion.  The  distribution  of  their  nerves  to  the  different  organs 
would  alone  indicate  their  respective  functions  ;  but  these  are  placed  beyond 
doubt  by  that  very  great  variety  in  the  disposition  of  these  organs  which  is 
characteristic  of  the  Mollusca.  The  development  of  the  sensory  organs,  the 
situation  of  the  gills,  the  structure  and  position  of  the  foot,  the  conformation 
and  uses  of  the  mantle,  are  well  known  to  differ,  in  the  most  obvious  manner, 
in  genera  which  are  closely  allied  to  each  other.  Hence  the  anatomist  is  able, 
by  the  discovery  of  corresponding  changes  in  the  nervous  system,  to  satisfy 
himself  of  the  particular  functions  of  its  different  centres.* 

133.  It  is  only  in  the  higher  tribes,  however,  that  this  separation  of  function 
is  evident ;  and  it  may  be  especially  noticed  in  the  class  GASTEROPODA  ;  which 
is  so  named  from  the  presence  of  a  kind  of  foot,  or  locomotive  organ,  on  the 
under  side  of  the  body, — this  being  formed  by  a  thickening  of  the  muscular 
part  of  the  mantle  in  that  situation.  Of  the  animals  belonging  to  this  class, 
some  form  univalve  shells,  whilst  others  are  entirely  shell-less. — They  are  much 
superior  in  general  organization  to  the  animals  inhabiting  bivalve  shells,  which 
are  included  in  the  class  Conchifera;  and  this  superiority  manifests  itself 
strongly  in  the  development  of  the  powers  of  locomotion  and  sensation.  The 
Conchifera  belong  to  the  group  of  bicephalous,  or  headless  Mollusca ;  the 
mouth  not  being  placed  upon  a  prominent  part  of  the  body,  nor  guarded  with 
organs  of  special  sensation.  The  lowest  form  of  this  group  consists  of  the 
class  Tunicata  ;  composed  of  animals  in  which  the  whole  body  is  enclosed  in 
a  tunic  or  bag,  having  but  two  orifices,  through  one  of  which  the  water  is 
drawn  in  by  ciliary  action,  whilst  through  the  other  it  is  expelled.  This  bag 
forms  a  large  chamber,  the  lining  of  which  is  devoted  to  the  respiratory 
function ;  and  at  the  bottom  of  it  lies  the  mass  of  the  viscera,  on  which  is  the 
true  mouth  or  entrance  to  the  stomach.  A  part  of  the  water  which  is  taken 
into  the  respiratory  chamber  flows  into  this,  and  passes  through  the  in- 
testinal canal ;  being  discharged  along  with  that  which  has  only  served  the 
purpose  of  aerating  the  blood.  These  animals  have  no  power  of  motion, 
but  such  as  is  effected  by  the  general  contraction  of  the  respiratory  sac ;  that 
is  effected  by  a  single  ganglion  placed  between  its  orifices,  wrhich  is  there- 
fore chiefly  a  branchial  ganglion,  and  is  the  only  nervous  centre  they  possess. 
Although  none  of  the  GASTEROPODA  are  able  to  execute  very  active  move- 
ments, few  are  entirely  fixed;  all  are  more  or  less  dependent  upon  the  exer- 
cise of  these  powers  for  their  supply  of  food ;  and  the  higher  tribes  employ 
them  also  in  the  perpetuation  of  the  race,  since  the  connection  of  two 
individuals  is  in  them  an  essential  part  of  this  function.  Although  the  foot 
is  the  chief  instrument  of  locomotion,  some  of  the  naked  aquatic  species  have 
other  means  of  propelling  themselves.  These  move  through  the  water  by  the 
undulations  of  their  whole  bodies,  like  the  leech,  or  the  vermiform  fishes :  and 
a  few  appear  materially  assisted  by  an  expansion  of  the  mantle  on  the  ante- 
rior part  of  the  body,  which  contains  muscular  fibres,  and  seems  to  act  as  a 
fin.  In  every  division  of  the  Animal  Kingdom,  we  find  the  development  of 
special  sensory  organs  to  bear  a  close  relation  with  that  of  the  locomotive  appa- 
ratus. In  the  present  instance,  we  observe  an  evident  example  of  this  general 
rule.  The  organs  of  vision,  which,  when  existing  at  all  among  the  Conchi- 
fera, were  very  imperfect,  are  here  almost  constant  and  more  highly  deve- 
loped; rudimentary  organs  of  hearing  maybe  detected;  the  tentacula  are  more 

*  See  Mr.  Garner  on  the  Nervous  System  of  the  Mollusca,  in  the  Linnasan  Transac- 
tions, vol.  xvii. 


104  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

sensitive,  and  are  sometimes  increased  in  number  to  six  or  eight ;  and  there  is 
reason  to  believe  that  some  of  them  occasionally  minister  to  the  sense  of  smell. 
These  senses,  as  well  as  the  locomotive  powers  of  the  animals,  have  an  obvious 
relation  with  the  supply  of  the  digestive  system ;  which  is  not  here,  as  in  the 
inferior  classes,  dependent  upon  the  miscellaneous  aliment  conveyed  to  the 
mouth  by  the  movement  of  the  surrounding  fluid  medium,  but  is  more  limited 
as  to  the  character  of  the  food  to  which  it  is  adapted  ;  so  that  the  animal  re- 
quires the  means  of  becoming  acquainted  with  the  proximity  of  what  it  can 
digest. 

134.  It  is  not  a  little  curious,  however,  that,  although  the  general  surface 
appears  highly  susceptible  of  impressions  which  excite  responsive  movements 
adapted  to  fulfil  some  important  office  in  the  economy,  it  does  not  seem  to  be 
susceptible  of  painful  impressions,  in  any  thing  like  the  same  degree.     This, 
which  cannot  but  be  regarded  as  a  beneficent  provision  for  the  happiness  of 
animals  so  incapable  of  offering  any  active  resistance  to  injury,  would  appear 
from  the  observations  of  various  experimenters,  and  especially  from  the  testi- 
mony of  M.  Ferussac,  who  says,  "I  have  seen  the  terrestrial  Gasteropods 
allow  their  skin  to  be  eaten  by  others,  and,  in  spite  of  large  wounds  thus  pro- 
duced, show  no  pain."     This  fact  has  an  important  bearing  on  our  general 
views  of  the  operations  of  the  nervous  system ;  since  it  would  seem  to  confirm 
an  opinion  founded  upon  other  phenomena,  that  the  impressions  which  pro- 
duce reflex  actions  through  the  nervous  system  do  not  always  involve  the 
production  of  sensation.     (§  173 — 182.) 

135.  The  nervous  system  of  the  Gasteropoda  consists  of  at  least  three  dis- 
tinct centres ;  the  relative  position  of  which  varies  with  that  of  the  organs 
they  supply.    The  anterior  or  cephalic  ganglia  are  larger,  in  proportion  to  the 
rest,  than  in  the  Conchifera ;  and  they  exhibit  a  tendency  to  gain  a  position 
anterior  to  the  oesophagus,  and  to  approximate  towards  each  other,  so  as  to 
meet  and  form  a  single  ganglionic  mass  on  the  median  line.     The  branchial 
ganglion  is  constantly  to  be  met  with,  but  its  position  is  extremely  variable. 
This  centre,  however,  always  bears  a  close  relation  with  the  gills,  both  in  situa- 
tion and  in  degree  of  development;  and  even  where  conjoined,  as  it  frequently 
is,  with  the  pedal  ganglion,  it  may  be  distinguished  from  it  by  the  distribution 
of  its  nerves,  as  well  as  by  its  separate  connection  with  the  cephalic  ganglia, 
which  is  always  noticed  in  such  cases.     This  may  be  observed  in  the  Patella 
(limpet)  and  Limax  (slug).     Sometimes  the  functions  of  this  ganglion  are 
subdivided  .between  two;  of  which  one  is  still  appropriated  to  the  branchiae; 
whilst  the  other  is  connected  with  the  general  surface  of  the  mantle,  and  with 
the  respiratory  passages  which  are  prolongations  of  it,  and  hence  may  be 
called  the  palleal  ganglion.     The  position  of  the  pedal  ganglion  (which  is 
generally  double  in  the  Gasteropoda,  though  the  foot  is  single)  also  varies,  but 
in  a  less  degree,  since  it  is  generally  in  the  neighbourhood  of  the  head. — 
Besides  these  nervous  centres,  we  find,  in  many  of  the  Gasteropoda,  a  sepa- 
rate system  connected  with  a  very  important  set  of  organs,  the  gustatory  and 
manducatory,  which  are  but  slightly  shadowed  out  among  the  Conchifera.    In 
these  higher  tribes,  the  oesophagus  is  dilated  at  its  commencement  into  a  mus- 
cular cavity,  containing  a  curious  rasp-like  tongue,  often  supported  upon  car- 
tilages, which  serves  to  reduce  the  food ;  and  sometimes  furnished  with  horny 
maxillae.     The  nerves  which  supply  these  do  not  proceed  directly  from  the 
cephalic  ganglia,  but  from  a  distinct  centre ;  from  which  ramifications  proceed 
along  the  oesophagus  and  stomach,  and  these  are  occasionally  connected  with 
the  other  nerves  by  inosculating  filaments.     This  set  of  ganglia  and  nerves, 
which  is  even  more  important  from  its  relative  development  in  some  other 
classes,  and  into  the  analogies  of  which,  in  the  nervous  system  of  Vertebrata, 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  105 

we  shall  hereafter  inquire,  may  be  called,  from  its  distribution,  the  stomato- 
g  as  trie  system. 

130.  The  ganglia  just  described  may  be  regarded  as  corresponding  with 
those  parts  of  the  nervous  centres  in  the  Vertebrata,  the  distribution  of  whose 
ntrves  is  analogous.  Thus  the  branchial  ganglion  obviously  corresponds  with 
that  portion  of  the  Medulla  Oblongata  which  is  the  centre  of  the  respiratory 
actions  in  Vertebrata.  The  pedal  ganglion  is  analogous  to  that  division  of  the 
Spinal  Cord,  from  which  the  nerves  of  the  anterior  or  posterior  extremities 
pass  off.  It  is  well  known  that  such  portions  of  the  spinal  cord  may  be  com- 
pletely isolated,  without  destroying  the  functions  to  which  they  minister. 
Thus,  the  brain  and  lower  part  of  the  spinal  cord  may  be  removed, — that 
portion  only  of  the  cerebro-spinal  axis  being  left  which  connects  the  principal 
respiratory  nerves,  in  fact  the  respiratory  ganglion, — and  yet  the  animal 
may  continue  to  exist  for  some  time.  It  is  then  reduced  to  a  condition  similar 
to  that  of  the  Tunicata,  whose  single  ganglion,  though  combining,  in  some 
degree,  the  functions  of  those  which  exist  separately  in  the  higher  tribes,  has 
evidently  the  regulation  of  the  respiratory  movements  for  its  chief  object.  In 
the  same  manner,  the  integrity  of  the  segment  of  the  cord,  with  which  the 
nerves  of  the  extremities  are  connected,  will  enable  them  to  execute  those 
movements  of  a  reflex  character  which  depend  upon  its  power  as  their  centre, 
even  though  it  is  isolated  from  every  other  part  of  the  nervous  apparatus.  The 
cephalic  ganglia  must  be  regarded  as  analogous,  not  to  any  single  portion  of 
the  Encephalon  in  Vertebrata,  but  in  some  degree  to  the  whole.  We  find 
nerves  of  special  sensation  proceeding  from  them,  certainly  to  eyes  and  an 
auditory  apparatus,  perhaps  also  to  olfactive  organs,  as  well  as  others  of  com- 
mon sensation,  supplying  the  tentacula  and  mouth.  Hence  we  must  admit 
that  they  perform  the  functions  of  the  optic  ganglia  of  Vertebrata,. and  perhaps 
also  of  the  olfactory  lobes,  as  well  as  of  the  portion  of  the  medulla  oblongata 
in  which  the  sensory  portion  of  the  fifth  pair  terminates.  Moreover,  they 
certainly  give  origin  also  to  motor  nerves,  and  must  thus  perform  the  functions 
of  the  Medulla  Oblongata,  from  which  the  corresponding  nerves  arise  in  Ver- 
tebrata, as  well  as,  perhaps,  of  the  Cerebellum.  And  if  we  regard  these 
animals  as  enjoying  the  perceptive,  reasoning  and  volitional  faculties,  in  how- 
ever low  a  degree,  we  must  attribute  to  their  cephalic  ganglia  some  portion  of 
the  attributes  of  the  cerebral  hemispheres  in  the  highest  classes.  This  com- 
bination of  function  will  not  appear  so  extraordinary,  when  it  is  recollected 
that  all  the  central  operations  of  the  nervous  system  are  performed  in  the 
Tunicata  by  one  ganglion,  and  in  the  Radiata  by  a  series,  of  which  each  is 
but  a  repetition  of  the  rest ;  and  it  is  quite  conformable  to  the  general  principle 
of  the  gradual  specialization  of  function  which  may  be  observed  in  ascending 
the  scale  of  organization. 

137.  It  is  obvious  that  the  portion  of  the  Nervous  system  of  the  Gasteropod 
Mollusca,  into  the  analogies  of  which  we  have  thus  inquired,  cannot  in  the 
least  be  compared  as  a  whole  with  the  Sympathetic  system  of  the  Vertebrata, 
which  it  was  formerly  imagined  to  resemble.     The  distribution  of  some  of  its 
nerves  to  the  viscera,  however,  may  indicate  that  it  partly  performs  the  func- 
tions of  that  system;  with  which  it  is  structurally  intermixed,  even  in  Verte- 
brata,— as  the  late  inquiries  of  Miiller,  Volkmann,  and  others  (of  which  the 
results  will  hereafter  be  stated),  have  shown.     But  the  stomato-gastric  system 
may,  perhaps,  with  more  probability  be  considered  as  executing  its  offices. 
Into  the  peculiar  character  of  that  system  we  shall  be  more   competent  to 
inquire,  when  we  have  traced  it  through  other  classes  of  Invertebrata. 

138.  Having  thus  separately  considered  the  nervous  centres  of  the  Gastero- 
poda, and  determined  their  special  functions  by  their  structural  relations,  we 
shall  inquire  into  the  mode  in  which  these  functions  are  combined,  so  as  to 


108 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  10. 


Nervous  system  of  Aplysia.  The  most  anterior 
ganglion  is  the  pharyngeal;  and  below  this  is  seen 
the  cephalic.  The  cephalic  is  connected,  by  three 
distinct  cords  on  each  side,  with  the  lateral  masses, 
which  combine  the  functions  of  pedal  and  palleal 
ganglia;  these  are  united  with  each  other  by  two 
transverse  bands,  between  which  the  aorta  passes. 
From  the  lateral  ganglia,  a  connecting  cord  passes 
backwards  on  each  side  to  the  branchial  ganglion ; 
this  cord  is  continuous  \vith  one  of  the  three  pro- 
ceeding from  the  cephalic  ganglion. 


enable  them  to  act  in  harmony.  This 
is  an  inquiry  of  much  interest,  in  re- 
ference to  the  determination  of  the 
offices  of  the  different  parts  of  the 
nervous  centres  in  Vertebrated  a^i- 
mals.  If  we  examine  the  mode  in 
which  the  different  ganglia  are  united 
by  connecting  trunks,  we  are  led  to 
perceive  the  important  fact  that,  while 
they  have  little  or  no  communication 
with  each  other,  they  are  all  directly 
connected  with  the  cephalic  ganglia ; 
which  seem  thus  to  harmonize  and 
control  their  individual  actions.  Fre- 
quently a  communication  with  one 
another  appears  to  exist,  where  there 
is  really  none.  Thus,  in  the  Aplysia, 
a  cord  passes  from  the  branchial  gan- 
glion, which  is  situated  in  the  pos- 
terior part  of  the  body,  to  the  pedal 
ganglion.  Where  such  is  the  case, 
the  trunk  is  not  united  with  that  pro- 
ceeding from  the  ganglion  through 
which  it  passes ;  but  the  two  remain 
distinct,  though  running  in  the  same 
direction.  Moreover,  the  double  func- 
tion of  a  ganglion  may  be  sometimes 
recognized,  by  its  being  connected 
with  the  cephalic  mass  by  a  double 
trunk.  Thus,  in  the  Aplysia,  that 
which  has  been  termed  the  pedal 
ganglion  is  really  made  up  of  a  pedal 
and  palleal  ganglion,  as  it  is  proved 
by  the  distribution  of  its  branches; 
and  in  conformity  with  this  double 
function,  we  find  it  communicating 
with  the  cephalic  mass  by  two  cords, 
besides  the  one  which  has  been  just 
mentioned  as  passing  through  it,  and 
which  appears  as  a  third.  In  the 
BulldRa,  whose  nervous  system  is  dis- 
posed on  the  same  general  plan,  the 
pedal  and  palleal  ganglia  are  sepa- 


rately connected  with  the  cephalic; 
the  cord  from  the  branchial  ganglion  passing  through  the  palleal. 

139.  Further,  a  careful  examination  of  these  ganglia,  and  of  their  connecting 
cords,  discloses  this  important  fact,  which  is  peculiarly  evident  in  the  case  of 
the  pedal  ganglia — that  the  cord  does  not  lose  itself  in  the  gray  matter  of  the 
ganglion,  but  divides  itself  into  filaments,  which  mix  with  those  proceeding 
from  it,  to  form  the  nervous  trunks  which  it  distributes.  We  can  scarcely, 
then,  fail  to  infer  that  the  pedal  ganglion,  with  the  nervous  fibrils  proceeding 
from  itself,  is  the  source  of  the  reflex  actions  of  this  organ ;  whilst  the  filaments 
which  are  continuous  with  those  of  the  connecting  trunk,  and  which  are  thus 
connected  with  the  nucleus  of  the  cephalic  ganglia,  are  the  channels  of  sensory 
impressions,  and  of  the  motor  impulses  of  volition  or  instinct.  This  is  well 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  107 

illustrated  in  the  curious  disposition  of  parts  which  we  find  in  the  arms  of  the 
Cuttle-fish.  These  are  provided,  it  is  well  known,  with  a  series  of  suckers, 
which  are  to  the  animal  important  instruments  of  locomotion  and  prehension. 
It  has  been  observed  by  Dr.  Sharpey,  that  the  nerves  which  supply  these  arms 
are  furnished  with  ganglionic  enlargements,  of  which  one  corresponds  with 
each  sucker:  and  that  each  trunk  consists  of  two  tracts,  in  one  of  which  the 
ganglionic  enlargements  exist ;  whilst  the  other  passes  continuously  over  these, 
but  sends  off  nervous  filaments,  which  help  to  form  the  branch  going  to  each 
sucker.  It  has  been  supposed  that  the  white  or  fibrous  tract  is  the  motor  por- 
tion, and  the  ganglionic  the  sensory ;  but  this  is  inconsistent  with  the  facts 
known,  regarding  the  influence  of  the  nerves  upon  the  movements  of  the 
suckers.  When  the  animal  wishes  to  embrace  any  object  firmly  with  its  arm, 
it  brings  all  the  suckers  simultaneously  to  bear  upon  it.  There  can  be  little 
doubt  that  this  action  is  occasioned  by  a  motor  impulse,  propagated  from  the 
cephalic  masses  by  the  non-ganglionic  portion  of  the  cord,  which  supplies  all 
the  suckers  alike.  On  the  other  hand,  any  individual  sucker  may  be  made 
to  attach  itself,  by  placing  a  substance  in  contact  with  it  alone ;  this  action  is 
independent  of  the  cephalic  ganglia,  as  is  evident  from  the  fact  that  it  will 
take  place  when  the  arm  is  severed  from  the  body,  or  even  in  a  small  piece  of 
the  arm,  if  recently  separated ;  and  it  can  scarcely  be  doubted,  that  it  is  due 
to  the  reflection  of  the  impression  made  upon  the  sucker,  through  the  small 
ganglion  in  its  neighbourhood,  where  it  excites  a  motor  impulse.  The  operation 
of  these  independent  centres  appears,  in  the  entire  living  animal,  to  be  con- 
trolled, directed  and  combined,  by  the  cephalic  ganglia,  through  the  medium 
of  the  fibrous  band  which  passes  over  them,  and  which  mixes  its  branches  with 
theirs.  A  very  similar  arrangement  will  be  presently  shown  to  exist  in  the 
double  nervous  column  of  the  Articulata. 

140.  Upon  reviewing  all  the  anatomical  facts  hitherto  stated,  it  will  be  per- 
ceived that  ganglionic  masses,  characterized  by  nuclei,  of  gray  matter,  or  of 
something  equivalent  to  it,  seem  to  exist,  wherever  it  is  desirable  that  impres- 
sions made  upon  the  afferent  nerves  should  excite  motions ;  and  that,  as  we 
rise  in  the  scale,  there  is  an  increase  in  the  number  of  centres  possessing  a 
diversity  of  functions.  We  have  seen  that  sometimes  these  centres  are,  for 
the  sake  of  convenient  disposition,  united  into  one  mass ;  whilst,  on  the  other 
hand,  when  the  organs  are  multiplied,  they  also  are  repeated  to  a  like  extent ; 
especially  when  it  is  desirable  that  they  should  be  able  to  act  independently 
of  one  another,  as  in  the  case  of  the  suckers  of  the  Cuttle-fish.  It  may  further 
be  remarked,  that,  wherever  the  presence  of  special  sensory  organs,  confined 
to  one  part  of  the  body,  gives  to  that  part  a  predominance  over  the  remainder 
(the  entrance  to  the  alimentary  canal  being  always  in  this  neighbourhood),  we 
find  the  ganglia  with  which  they  are  connected  possessing  a  special  relation 
with  all  the  rest,  which  these  do  not  possess  with  each  other.  It  is  obvious 
that,  where  visual  organs  are  developed,  the  impressions  made  upon  these  will 
determine  the  movements  of  the  animal  more  than  those  of  any  other  kind; 
and  it  would  seem  to  be  chiefly  owing  to  the  information  they  communicate, 
that  the  cephalic  ganglion  has  such  an  evident  presiding  influence  over  the 
rest,  even  when  smaller  than  any  of  .them.  This  is,  however,  more  the  case 
in  animals  whose  movements  are  rapid,  and  in  which,  therefore,  the  perception 
of  distant  objects  is  more  important — as  in  the  Insect  tribes.  Except  in  the 
Cephalopoda,  the  subservience  of  the  nervous  system  to  the  nutritive  functions 
of  the  Mollusca  is  so  great,  that  it  might  almost  be  regarded  as  an  appendage 
to  the  digestive  organs,  destined  for  the  selection  and  prehension  of  aliment. 
But  in  the  more  active  members  of  that  class,  it  derives  a  more  elevated  cha- 
racter, from  the  development  of  organs  of  special  sensation  and  of  active  loco- 
motion. 


108 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  11. 


Nervous  System  of  Larva  of  SPHINX  LIGUS- 
TRI,  after  Newport;  A,  cephalic  ganglia;  1-11, 
ganglia  of  the  trunk,  disposed  at  nearly  equal 
distances;  the  last  is  formed  by  the  consolida- 
tion of  the  llth  and  !S2th. 


141 .  The  animals  composing  the  group 
ARTICULATA,  all  present,  in  a  more  or  less 
evident  degree,  a  division  into  segments, 
which  have  an  obvious  tendency  to  re- 
semble one  another,  as  in  the  Radiata. 
In  those  in  which  these  segments  differ 
but  little  (as  in  the  Centipede,  or  the  Ca- 
terpillar of  the  Insect),  the  nervous  system 
is  a  repetition  of  similar  parts ;  disposed, 
not  in  a  circle,  as  in  the  Radiata,  but  in  a 
continuous  line.    The  most  interior  of  the 
ganglia,  however,  has   an    evident   pre- 
dominating  influence  over  the  rest,  for 
the  reason  just  specified;  and  this  influ- 
ence will  be  found,  by  comparison  in  other 
classes,  to  diminish  with  the  loss,  and  to 
increase  with   the    development,  of  the 
faculties  of  special  sensation,  which  have 
their  seat  there.     The  locomotive  powers 
are  just  as  predominant  in  the  Articulated 
series,  as  are  the  nutritive  functions  among 
the  Mollusca.     Accordingly,  we  find  the 
development  of  the  Nervous  System  to 
bear  a  special  reference  to  them ;  and  the 
sen sori -motor  divisions  of  it  can  be  more 
distinctly  separated  than  in  the  Mollusca, 
from  the  portion  which  ministers  to  the 
organic  functions. 

142.  The  general  arrangement  of  the 
Nervous  System  differs  so  little,  except  as 
to  the  degree  of  concentration  of  the  gan- 
glia, in  the  different  classes  of  this  sub- 
kingdom,  that  it  is  of  little  consequence 
what  example  we  select.     It  will  be  con- 
venient to  take  for  illustration  that  of  the 
Larva  of  the  Sphinx  Ligustri,  or  Privet 
Hawk-Moth,  which   has  been  minutely 
described  by  Mr.  Newport.     Here  we  ob- 
serve a  chain  of  ganglia  running  from  one 
extremity  of  the  body  to  the  other,  along 
the  ventral  surface,  and  in  the  median 
line.     These   ganglia  are  connected  by 
trunks,  which,  on  close  examination,  are 
seen  to  consist  of  two  cords  closely  united. 
The  cephalic  ganglion  is  bilobed;    evi- 
dently consisting  of  two   masses,  which 
are  united  on  the  median  line.    These  re- 
ceive the  nerves  of  the  eyes  and  antennae ; 
but  they  are  still  of  small  size,  in  accord- 
ance with  the  low  development  of  the  sen- 
sory organs.     The  ganglia  of  the  longi- 
tudinal cord  are  nearly  equal,  from  one 
extremity  of  the  body  to  the  other.    Each 
sends  off  nerves  to  its  respective  segments ; 
and  the  branches  proceeding  from   the 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  109 

different  ganglia  have  little  communication  with  each  other.  The  highest  of 
them,  situated  just  beneath  the  oesophagus,  is  connected  with  the  cephalic 
masses  by  two  cords,  between  which  that  canal  passes,  encircled,  as  it  were, 
in  a  ring. 

143.  The  most  detailed  account  of  the  conformation  of  the  Nervous  Centres 
in  the  Articulata,  is  that  recently  given  by  Mr.  Newport,  in  regard  to  the 
Julus,  and  other  animals  of  the  class  MYRIAPODA.*     Their  general  arrange- 
ment corresponds  with  that  which  has  been  just  described  in  the  larva  of  the 
Sphinx  Liguslri;  but  the  number  of  ganglia   is  much    greater.     In  each 
lateral  half  of  the  cord,  two  distinct  tracts  or  layers  of  fibres  can  be  detected  ; 
of  these,  one — known  as  the  fibrous  tract— is  continuous  with  the  brain,  and 
contains  no  gray  matter ;  whilst  the  other — known  as  the  ganglionic  tract — 
has  gray  matter  deposited  at  intervals  amongst  its  fibres,  some  of  which  are 
continuous  with  the  brain,  whilst  others  do  not  reach  it.     (Fig.  13,  A.)  Every 
nerve  that  is  given  off  from  this  ventral  column,  is  connected  writh  both  tracts ; 
and  thus  it  has  two  sets  of  roots,  one  proceeding  to  the  brain,  the  other  e^ter- 
ing  the   ganglion  near  which  it  arises.     Of 

this  last  division,  a  part  crosses  to  the  oppo-  Fig.  12. 

site  side,  forming  the  commissural  fibres  which 
unite  together  the  lateral  halves  of  the  cord ; 
whilst  another  bundle  of  fibres  runs  along  the 
side  of  the  ganglionic  tract,  for  a  greater  or 
less  proportion  of  its  length,  and  then  emerges 
again,  forming  part  of  another  nervous  trunk. 
In  Fig.  12  is  seen  Mr.  N.'s  representation  of 
one  of  the  ventral  ganglia,  and  part  of  the 
cord,  of  Polydesmus  maculalus  ;  showing  the 
longitudinal  and  commissural  fibres,  together 
with  those  to  which  he  has  given  the  name  of 
fibres  of  reinforcement.  These  lateral  fibres,  *r 

which  do  not  pass  on  to  the  brain,  but  issue  Portion  of  the  ganglionic  tract  of  Pf>. 
again  from  the  ventral  cord  at  a  point  a  little  lydesmus  macuiatus;  6,  imer-gangiionic 

distant  from  their  entrance,  Seem  tO  be  more  cord;  c,  anterior  nerves;  d,  posterior 
numerous  in  the  hinder  part  Of  the  bdldy  of  nerves;  /,  k,  fibres  of  reinforcement; 

the  Centipede  tribe,  than  in  its  front  portion  :     f- /J'  cora™ssu;al  fi,bres;  ''  lo»shudi"al 

,     ,          i     .        ,  1  11-  c     i  i       fibres,   softened   and    enlarged,   as  they 

and  thus  it  is,  that  the  whole  size  of  the  cord     pass  lhrough  ganglionic  matter. 
remains  nearly  the  same  along  its  entire  length; 

whilst  that  of  the  portion  which  passes  backwards  from  the  brain,  must  be  con- 
tinually diminishing,  as  it  gives  off  fibres  to  the  nerves. 

144.  After  what  has  been  said  of  the  offices  which  the  ganglia  perform  in 
the  Mollusca,  and  of  the  relation  which  they  bear  to  the  cephalic  mass,  we 
shall  have  little  difficulty  in  understanding  the  character  of  the  nervous  appa- 
ratus in  the  Articulata,  if  our  minds  be  unoccupied  by  any  preconceived  notion. 
When  we  examine  into  the  actions  of  the  ventral  cord,  we  perceive  that  those 
of  all  its  ganglia  are  similar  to  each  other ;  being  related  only  to  the  move- 
ments of  their  respective  segments,  and  of  the  members  which  belong  to  them. 
In  fact,  these  ganglia  may  be  regarded  as  so  many  repetitions  of  the  pedal  or 
locomotive  ganglion  of  the  Mollusca.     It  is  easily  proved,  that  the  movements 
of  each  pair  of  feet  may  be  produced  by  that  ganglion  alone  with  which  it  is 
connected  ;  since  a  single  segment,  isolated  from  the   rest,  will  continue  to 
perform  these  movements  for  some  time,  under  favourable  circumstances.     If 
an  Earth\vorm  be  cut  in  two,  whilst  crawling,  each  portion  will  continue  to 
advance,  though  the  anterior  one  only  will  permanently  preserve  its  vitality. 

*  Philosophical  Transactions,  1843. 
10 


1 10  FUNCTIONS  OF  THE  NERVOUS  SYSTEM 

If  a  Centipede  be  divided  into  several  portions  under  the  same  circumstances, 
each  will  execute  motions  of  progression  for  some  time.  But  it  is  evident  that 
these  must  be  placed,  in  the  living  animal,  under  some  general  control ;  by 
which  the  consentaneousness  of  action,  that  is  essential  to  regular  locomotion, 
may  be  produced.  This  is  easily  proved  by  experiment.  If  in  a  Mantis,  for 
example,  the  nervous  cord  be  divided  between  the  first  and  second  thoracic 
ganglia,  so  as  to  isolate  the  ganglionic  centres  of  the  posterior  legs,  the  limbs 
will  continue  to  move  energetically,  but  not  with  a  combined  object,  and  no 
progression  will  take  place.  We  can  scarcely  account  for  the  exercise  of  this 
general  control,  otherwise  than  by  attributing  it  to  the  fibrous  portion  of  the 
cord,*  which  connects  each  of  the  nervous  trunks  immediately  with  the  cepha- 
lic ganglia,  as  in  the  Mollusca ;  and  this  must,  therefore,  conduct  to  the  sen- 
sorium  (whose  seat  is  probably  in  the  latter)  the  impressions  which  there  pro- 
duce sensations,  and  must  convey  downwards  the  locomotive  impulse  ;  whilst 
the  ganglion  of  each  segment,  with  the  filaments  connected  with  its  nucleus, 
will  form  the  circle  necessary  for  the  simply  reflex  actions  of  its  members. 
The  independence  of  the  segments  of  the  Articulata,  as  far  as  their  reflex 
actions  are  concerned,  and  their  common  subordination  to  one  presiding  centre 
of  the  will,  are  fully  explained  on  this  supposition.  It  is  also  quite  conform- 
able to  the  analogy  both  of  the  Mollusca  and  of  Vertebrata. 

145.  The  number  and  variety  of  the  reflex  actions  which  take  place  in  the 
Articulata  after  decapitation,  is  very  remarkable ;  and  they  seem  to  have  a 
consentaneousness,  proportioned  to  the  closeness  of  the  relation  between  the 
nervous  centres  in  the  respective  species.  Thus,  in  the  Centipede,  we  find 
the  ganglia  of  the  several  segments  distinct,  but  connected  by  a  commissural 
trunk.  Here  an  impression  made  equally  upon  the  afferent  nerves  of  aU  the 
ganglia,  will  produce  a  consentaneous  action.  Thus,  if  the  respiratory  orifices 
on  one  side  of  a  decapitated  Centipede  be  exposed  to  an  irritating  vapour,  the 
body  will  be  immediately  flexed  in  the  opposite  direction ;  and  if  the  stigmata 
of  the  other  side  be  then  similarly  irritated,  a  contrary  movement  will  occur. 
But  different  actions  may  be  excited  in  different  parts  of  the  cord,  by  the  pro- 
per disposition  of  the  irritating  cause.  In  the  higher  classes,  however,  where 
the  ganglia  of  the  locomotive  organs  are  much  concentrated,  the  same  irritation 
will  produce  consentaneous  motions  mseveral  members,  similar  to  those  which 
the  unmutilated  animal  performs.  In  the  Mantis  religiosa,  for  example, — 
which  ordinarily  places  itself  in  a  very  curious  position,  especially  when 
threatened  or  attacked,  resting  upon  its  two  posterior  pair  of  legs,  and  elevat- 
ing its  thorax  and  the  anterior  pair,  which  are  armed  with  powerful  claws,—- 
if  the  anterior  segment  of  the  thorax,  with  its  attached  members,  be  removed, 
the  posterior  part  of  the  body  will  still  remain  balanced  upon  the  four  legs 
which  belong  to  it,  resisting  any  attempts  to  overthrow  it,  recovering  its  posi- 
tion when  disturbed,  and  performing  the  same  agitated  movements  of  the  wings 
and  elytra,  as  when  the  unmutilated  animal  is  irritated :  on  the  other  hand,  the 
detached  portion  of  the  thorax,  which  contains  a  'ganglion,  will,  when  sepa- 
rated from  the  head,  set  in  motion  its  long  arms,  and  impress  their  hooks  on 
the  fingers  which  hold  it.  These  facts  prove  unequivocally,  that  the  automa- 

*  It  is  believed  by  Mr.  Newport,  that  the  fibrous  portion  of  the  ganglionic  trad,  which 
lies  nearest  the  surface  of  the  body,  may  be  the  channel  by  which  sensory  impressions 
are  conveyed  to  the  brain;  whilst  the  fibrous  tract  itself  may  convey  downwards  the 
motor  impulses  which  originate  in  the  cephalic  ganglia.  The  chief  reason  for  this  sup- 
position, is  the  correspondence  in  position, — relatively  to  each  other,  and  to  the  rest  of 
the  body, — between  the  fibrous  and  ganglionic  columns  in  Articulata,  and  the  portions  of 
the  Spinal  Cord  of  Vertebrata,  from  which  the  anterior  or  motor  roots,  and  the  posterior 
or  sensory,  respectively  arise.  But  the  fibres  which  are  peculiar  to  the  ganglionic  tract, 
obviously  form  a  distinct  system. 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  Ill 

tic  movements  of  these  parts,  which  are  performed  in  direct  respondence  to 
external  impressions,  are  only  dependent  for  their  stimulation  upon  that  gan- 
glionic  centre  with  which  the  nerves  that  excite  them  are  immediately  con- 
nected. Another  instance,  related  by  Burmeister,  is  still  more  satisfactory  in 
regard  to  the  manner  in  which  these  movements  are  excited.  A  specimen  of 
the  Dytiscus  sulcatus,  from  which  the  cephalic  ganglia  had  been  removed, 
and  which  remained  in  a  motionless  condition  whilst  lying  with  its  abdomen 
on  a  dry  hard  surface,  executed  the  usual  swimming  motions,  when  cast  into 
water,  with  great  energy  and  rapidity,  striking  all  its  comrades  to  one  side  by 
its  violence,  and  persisting  in  this  for  half  an  hour. 

146.  These  conclusions  are  also  fully  confirmed  by  the  experiments  of  Mr. 
Newport,  upon  various  Insects  and  Myriapoda ;  the  results  of  which  have 
been  recently  made  public.*  The  following,  upon  the  Julus  terrestris,  is 
particularly  interesting.  "  The  cord  was  divided  in  the  fourteenth  and  also 
the  twentieth  segment ;  and  the  intervening  portion  was  destroyed  by  break- 
ing it  down  with  a  needle.  The  animal  exhibited,  in  the  anterior  part  of  its 
body,  all  the  evidences  of  perfect  volition.  It  moved  actively  along,  turning 
itself  back  on  either  side  repeatedly,  as  if  to  examine  the  anterior  wounded 
portion,  which  it  felt  again  and  again  with  its  antennae  ;  and  when  attempting 
to  escape,  frequently  turned  back  as  if  in  pain  and  aware  of  some  hindrance 
to  its  movements ;  but  it  seemed  perfectly  unconscious  of  the  existence  of  the 
posterior  part  of  its  body,  behind  the  first  incision.  In  those  segments  in 
which  the  cord  was  destroyed,  the  legs  were  motionless  ;  while  those  of  the 
posterior  division,  behind  the  second  incision,  were  in  constant  but  involuntary 
motion,  the  movements  being  similar  to  those  of  walking  or  running,  uniformly 
continued,  but  without  any  consentaneous  action  with  those  of  the  anterior 
part,  by  which  locomotion  was  performed,  dragging  the  posterior  divisions  of 
the  body  after  them.  When  the  animal  was  held  by  the  posterior  segments, 
reflex  actions  were  excited  in  the  legs,  and  powerful  contractions  and  gyra- 
tions of  the  whole  animal  were  performed  in  those  segments  ;  but  these  move- 
ments appeared  to  be  entirely  the  result  of  reflex  actions  of  the  muscles,  since 
exactly  similar  ones  took  place  in  the  whole  body  of  decapitated  specimens. 
At  the  expiration  of  twelve  hours,  the  most  perfectly  voluntary  acts  were  per- 
formed by  the  head  and  anterior  division  of  the  body,  such  as  locomotion  for- 
wards or  to  either  side,  avoidance  of  any  obstacle,  touching  it  with  the  anten- 
nas, (which  were  in  rapid  action,  as  in  an  uninjured  animal,)  and  attempting 
to  reach  and  to  climb  up  an  object  presented  to  it,  but  not  in  immediate  con- 
tact with  it.  But  reflex  movements  alone  existed  in  the  posterior  division,  in 
which  the  legs  were  very  slowly  moved,  even  when  the  animal  was  not  pro- 
gressing. Brisk  actions  were  now  more  easily  excited  in  them  than  at  first, 
either  by  contact  with  the  segments,  by  irritation  of  one  or  two  of  the  legs 
themselves,  or  by  a  sudden  current  of  air.  By  these  means,  when  the  animal 
was  lying  still,  actions  were  immediately  excited  in  all  the  legs  of  the  poste- 
rior parts  of  the  body,  anterior  and  posterior  to  those  which  were  irritated ;  and 
these  actions  were  induced  in  those  of  both  sides  of  the  body,  but  appeared  to 
commence  on  the  opposite  side,  in  the  legs  corresponding  to  those  which  were 
first  irritated.  In  eighteen  hours,  the  anterior  part  of  the  body  was  quite 
dead,  so  that  no  motions  whatever  could  be  excited  in  it,  either  voluntary  or 
reflex ;  but  reflex  actions  were  then  readily  excited  in  the  posterior,  and  also 
slightly  so  by  mechanical  irritation,  even  at  twenty-four  hours."  It  would 
appear,  then,  that  we  may  obtain  more  decided  proof,  in  the  Articulated  series, 
of  the  real  character  of  reflex  actions,  and  of  their  dependence  upon  a  distinct 
system  of  nerves,  than  we  can  draw  from  any  other  class  of  animals.  In  the 
Vertebrata,  it  is  easy  to  distinguish  the  sensory  from  the  motor, — the  afferent 

*  Philos.  Trans.,  1843,  p.  267. 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

from  the  efferent — fibres ;  but  the  distinctness  of  the  excito-motor  system  from 
the  sensori-volitional,  is  not  so  clearly  made  out.  Here,  however,  the  afferent 
and  efferent  fibres  cannot  be  readily  distinguished ;  but  it  is  obvious  that  the 
reflex  actions,  which  manifest  themselves  when  the  communication  with  the 
cephalic  ganglia  is  cut  off,  are  to  be  attributed  to  those  fibres  which  enter  the 
cord  under  the  afferent  character, — pass  into  the  edge  of  the  ganglion  as  the 
fibres  of  reinforce?nent,  or  cross  it  as  commissural  fibres, — and  then  emerge 
again  as  efferent  fibres,  either  in  the  nerves  of  the  same  segment,  or  in  those 
of  another  more  or  less  distant.  By  traversing  the  cord  along  a  part  of  its 
length,  and  thus  placing  the  several  segments  in  communication  with  each 
other,  the  fibres  of  reinforcement  thus  constitute  a  part  of  the  longitudinal 
filaments  of  the  cord, — the  remainder  consisting  of  the  fibres  continuous  with 
the  cephalic  ganglia. 

147.  Without  describing -in  minute  detail  the  forms  which  the  nervous 
system  presents  in  the  higher  classes  of  Articulata,  or  tracing  that  interesting 
series  of  changes  which  it  undergoes  during  the  metamorphosis  of  Insects,  a 
few  particulars  may  be  stated  on  these  subjects  as  having  an  immediate  bear- 
ing on  our  present  object.  The  nervous  system  of  the  Larva,  like  that  of  the 
Annelida,  or  Myriapoda,  presents  an  obvious  relation  to  the  means  and  extent 
of  locomotion  possessed  by  the  animal.  Each  segment  is  equally  concerned 
in  locomotion;  and  with  each  is  associated  a  pedal  ganglion.  None  of  the 
movements  of  the  animal  are  very  energetic;  simple  and  slow  progression  is 
all  for  which  its  structure  is  adapted ;  and  the  uniformity  in  the  actions  of  its 
legs  would  render  it  easy  to  combine  them  at  the  will  of  the  animal,  even 
though  their  respective  centres  remain  much  isolated  from  one  another.  But, 
in  the  perfect  Insect,  the  whole  locomotive  apparatus  is  concentrated  in  the 
thorax.  The  six  legs  (which  are  now  all  that  remain),  and  the  single  or 
double  pairs  of  wings,  are  all  developed  from  its  three  segments;  and  a  much 
greater  variety  of  action  is  required,  as  well  as  more  complete  consentaneous- 
ness,  on  account  of  the  increased  number  and  velocity  of  the  movements  of  the 
animal.  We  accordingly  find  that  the  ganglionic  matter  of  the  ventral  cord  of 
perfect  Insects,  is  more  or  legs  concentrated  in  the  thoracic  region  ;  whilst  the 
ganglia  of  the  abdomen  are  usually  few  and  small ;  the  nerves  to  its  segments, 
however,  being  given  off  as  before  at  regular  intervals.  In  some  of  the  Cole- 
optera  and  Hemiptera,  the  concentration  of  the  thoracic  ganglia  takes  place  to 
such  an  extent,  that  they  seem  to  form  but  one  mass ;  and  this  is  the  case  also 
among  some  of  the  Crustacea,  the  different  forms  of  whose  nervous  system  are 
exactly  parallel  to  those  of  their  congeners  among  the  inhabitants  of  the  air 
and  land.  The  nerves  which  supply  the  wings  of  Insects  are  found,  in  all 
stages  of  the  development  of  these  organs,  to  have  a  double  origin.  One  root 
arises  from  the  fibrous  tract  alone  ;  whilst  the  other  takes  its  origin  from  both 
tracts  at  the  point  of  enlargement.  When  the  ganglionic  centres  which  sup- 
ply the  anterior  and  posterior  pairs  of  wings  remain  distinct,  there  is  a  curious 
plexiform  arrangement  of  their  nerves  ;  more  or  less  intricate,  according  as 
the  wings  are  destined  to  act  with  greater  or  less  consentaneous  energy ;  and 
absent  when  the  anterior  pair  serve  only  as  elytra,  and  do  not  assist  in  flight.* 
This  would  remind  us  of  the  circular  filament,  which  connects  the  nerves  of 
the  arms  in  the  naked  Cephalopoda.  Besides  these  nerves,  the  wings  are 
supplied  from  the  respiratory  system  next  to  be  described,  from  which  scarcely 
any  branches  go  to  the  legs.  This  will  be  readily  understood,  when  it  is  con- 
sidered that  the  wings  are  developed,  as  it  were,  out  of  an  extension  of  the 
respiratory  apparatus,!  and  that  their  movements  are  closely  connected  with 
its  actions. 

*  Newport,  in  Phil.  Trans.,  1834,  p.  394,  5. 

•j-  See  Principles  of  General  and  Comparative  Physiology,  2J  ed.  §  465. 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY. 


113 


148.  Hitherto  we  have  spoken  only  of  that  division  of  the  nervous  system 
of  the  Articulata,  which  may  be  regarded  as  corresponding  with  the  sensory 
and  locomotive  ganglia  of  the  Mollusca ;  namely,  the  cephalic,  the  pedal,  and 
(in  some  instances)  the  palleal.  We  have  next  to  inquire  what  we  find  corre- 
sponding with  the  branchial  ganglion.  It  is  to  be  recollected  that  the  respira- 
tory apparatus  of  Insects  is  diffused  throughout  the  whole  body,  so  that  its 
presiding  system  of  nerves  must  be  proportionally  extended ;  and  we  are, 
therefore,  prepared  to  find  the  branchial  ganglion  of  the  Mollusca  repeated, 
like  the  pedal,  in  each  segment.  Besides  the  nervous  trunks  proceeding  from 
the  ventral  cord  at  its  ganglionic  enlargement,  we  find,  in  most  of  the  Articu- 
lated classes,  a  series  of  smaller  nerves,  given  off  at  intermediate  points,  with- 
out any  apparent  swelling  at  the  points  of  divergence.  The  connections  of 
these  are  most  distinctly  seen  in  the  thoracic  region,  just  as  the  Larva  is  pass- 
ing into  the  Pupa  state  ;  for  the  cords  of  the  ventral  column  then  diverge,  so 
that  an  additional  tract  may  be  seen,  which  occupies  the  central  line.  By  a 
close  scrutiny,  this  tract  may  be  found  in  the  perfect  Insect,  on  the  superior  or 
visceral  aspect  of  the  cord ;  and  its  nerves  are  given  off  from  minute  gangli- 
onic enlargements  upon  it.  It  seems  to  be  quite  unconnected  along  its  whole 
course  with  the  column  upon  which  it  lies.  Its  nerves,  however,  communi- 
cate with  those  of  the  sensori-motor  system ;  but  they  have  a  separate  distri- 
bution, being  transmitted  especially  to  the  trachea,  on  the  parietes  of  which 

Fig.  13. 


Parts  of  Nervous  System  of  Articulata,  after  Newport.  A,  single  ganglion  of  Centipede,  much  enlarged, 
showing  the  distinctness  of  the  purely  fibrous  tract,  fc,  from  the  ganglionic  column,  a.  B,  portion  of  the 
double  cord  from  thorax  of  Pupa  of  Sphinx  ligustri,  showing  the  respiratory  ganglia  and  nerves  between 
the  separated  cords  of  the  symmetrical  system,  c,  view  of  two  systems  combined,  showing  their  arrange- 
ment in  the  Larva;  a,  ganglion  of  ventral  column;  6,  fibrous  tract  passing  over  it;  cc,  respiratory  system 
of  nerves  distinct  from  both. 

10* 


114 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  14. 


they  ramif}?-  minutely,  and  also  to  the  muscles  concerned  in  the  respiratory 
movements.  (The  latter,  however,  being  a  part  of  the  general  locomotive 
apparatus,  are  also  supplied  from  the  principal  ganglionic  column.)  These 
nerves,  then,  which  are  evidently  analogous  to  those  of  the  gills  and  siphonic 
apparatus  in  the  Mollusca,  may  be  regarded  as  corresponding  with  the  pneu- 
monic portion  of  the  par  vagum  in  Vertebrata  (which  is  in  like  manner  distri- 
buted on  the  air-passages),  and  with  its  associated  motor  nerves. 

149.  In  comparing  the  nervous  system  of  Insects  with  that  of  the  higher 
Mollusca,  it  will  be  seen  that  they  differ  more  in  the  arrangement  and  in  the 
relative  proportions  of  their  parts  than  in  their  essential  character.  In  both 
there  is  a  cephalic  division  of  the  ganglionic  centres,  in  which  sensibility  and 
psychical  power  appear  to  reside  more  particularly,  if  not  entirely.  In  both 
there  is  a  division  specially  appropriated  to  the  locomotive  apparatus,  differing 
only  in  the  multiplication  of  the  centres  in  Insects,  conformably  with  the 
arrangement  of  the  members  they  supply;  and  sometimes  consolidated  to 
nearly  the  same  degree.  In  both,  also,  we  find  a  division  appropriated  to  the 
respiratory  apparatus,  in  which  there  is  a  corresponding  multiplicity  of  cen- 
tres in  the  Articulata,  in  harmony  with  the  universal 
distribution  of  their  tracheal  system.  And  in  both,  as 
Ave  shall  now  see,  there  is  a  separate  system  of  nerves, 
distributed  to  the  alimentary  apparatus,  and  supplying 
the  organs  of  mastication  (with  the  salivary  glands),  of 
deglutition,  and  of  digestion. 

150.  Of  the  stomato-gastric  system,  some  traces 
may  be  found  in  nearly  all  the  Articulated  classes. 
Thus,  in  the  Leech,  we  find  a  minute  ganglion  existing 
at  the  base  of  each  of  the  three  teeth  which  form  the 
mouth;  these  ganglia  are  connected  together,  and,  to 
the  cephalic,  by  slender  filaments  ;  and  they  seem  also 
to  be  in  connection  with  other  filaments,  which  may 
be  traced  on  the  alimentary  canal.  As  a  specimen  of 
its  highly-developed  form,  we  shall  describe  that  of 
the  Gryllotalpa  vulgaris  (common  Mole-Cricket). 
Here  we  find  it  consisting  of  two  divisions  ;  one  placed 
on  the  median  line,  which  may  hence  be  called  the 
median  system;  the  other  running  on  each  side  at 
some  little  distance,  and  heflce  called  the  lateral  sys- 
tem. The  Median  system  appears  to  originate  in  a 
small  ganglion,  situated  anteriorly  and  inferiorly  to 
the  cephalic  mass,  with  which  it  communicates  by  a 
connecting  branch  on  each  side.  From  this  ganglion, 
nerves  proceed  to  the  walls  of  the  buccal  cavity,  the 
mandibles,  &c.  Its  principal  trunk,  however,  (the  re- 
current of  authors,)  is  sent  backwards  beneath  the 
pharynx.  The  ramifications  of  this  are  distributed 
along  the  resophageal  tube  and  dorsal  vessel  ;  whilst 
the  trunk  passes  downwards  to  the  stomach,  where  its 
branches  inosculate  with  those  supplied  by  the  lateral 
system,  and  seem  to  assist  in  forming  a  pair  of  small 
ganglia,  from  which  most  of  the  visceral  nerves  radi- 
ate.  The  ganglia  of  the  Lateral  system  are  two  on 
each  side,  lying  behind  and  beneath  the  cephalic 
masses.  The  anteri0r  pair  are  the  largest,  and  meet  on 


Stomato-gastric  system  of 
GRYLLOTALPA  VULGABIS;  A  A, 
cephalic  ganglia;  a,  anterior 


gangiia. 


with  which  they  communicate.     Posteriorly  to  these 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  115 

lie  the  second  pair,  which  are  in  connection  with  them.  Two  cords  pass 
backwards  on  each  side,  one  derived  from  the  anterior,  the  other  from  the 
posterior,  of  these  ganglia.  They  run  along  the  sides  of  the  oesophagus  and 
dorsal  vessel;  and,  after  inosculating  with  the  branches  of  the  central  system, 
enter  the  two  coeliac  ganglia,  from  which  branches  radiate  to  the  abdominal 
viscera. 

151.  This  system  of  ganglia  and  nerves  has  an  evident  affinity  with  the 
Sympathetic  system  of  Vertebrata,  as  well  as  with  some  parts  of  the  Cerebro- 
spinal  system,  more  especially  with  the  Par  Vagum.     It  is  to  be  remembered, 
that  the  Pneumogastric  nerve  of  Vertebrata  is  distributed  to  three  separate 
systems — the  respiratory,  the  circulating,  and  the  digestive.  As  we  know  that 
the  ultimate  fibrils  of  nerves  never  anastomoze,  there  can  be  no  doubt  that  these 
branches  might  be  separately  traced  backwards  into  their  ganglionic  centres ; 
and  they  may  thus  be  regarded  as  functionally  three  distinct  nerves,  though 
bound  up  in  a  single  trunk.     There  is  no  difficulty,  then,  in  understanding 
that  the  respiratory  system  of  Insects  and  other  Invertebrata  may  be  analogous 
with  the  pneumonic  portion  of  the  Par  Vagum ;  although  it  bears  no  relation 
with  the  cardiac  and  gastric  divisions  of  the  nerve.     To  the  latter  divisions 
the  analogy  of  the  recurrent  nerve  becomes  sufficiently  plain,  when  we  look 
at  its  distribution  upon  the  dorsal  vessel,  oesophagus,  and  stomach  ;*  but  its 
commencement  in  the  anterior  ganglion,  which  also  supplies  the  mouth  and 
pharynx,  might  seem  to  place  it  on  a  different  footing,  until  we  have  deter- 
mined the  true  analogy  of  this  last  centre.     It  may  be  inferred  from  its  situa- 
tion, and  from  the  distribution  of  its  nerves,  that  this  anterior  ganglion  is 
analogous  both  to  the  labial  and  pharyngeal  ganglia  of  the  higher  Mollusca. 
These  appear  to  form  a  division  of  the  nervous  system,  by  which  the  actions 
immediately  concerned  in  the  prehension  of  food  are  performed ;  and  these 
seem  almost  as  independent  of  the  cephalic  ganglia  as  are  those  of  respira- 
tion.    There  is  evidently,  however,  a  greater  tendency  towards  the  union  of 
these  centres  with  the  cesophageal  collar  than  of  those  presiding  over  the 
respiratory  function,  which  is  more  independent  of  the  will. 

152.  The  division  of  the  nervous  system  of  Vertebrata  with  which  this 
Stomato-Gastric  system  corresponds,  is  a  question  of  more  apparent  difficulty ; 
but  if  we  bring  into  comparison  not  only  the  highest  but  the  lowest  forms  of 
the  cerebro-spinal  apparatus,  the  chief  difficulties  will  be  removed.     The  ana- 
logies drawn  from  the  distribution  of  the  nervous  branches  would  lead  us  to 
infer,  that  the  third  division  of  the  Fifth  pair  (including  its  sensory  and  motor 
origins),  the  Glosso-Pharyngeal,  and  the  gastric  portion  of  the  Par  Vagum, 
would  most  nearly  represent  it.     Now,  when  the  fifth  pair  is  traced  back  to  its 
true  origin,  it  is  found  to  be  not  a  cerebral  but  a  spinal  nerve  ;  and  it  is  then 
seen  to  arise  from  the  medulla  oblongata,  in  such  close  approximation  with  the 
Par  Vagum  and  Glosso-Pharyngeal,  as  to  show,  that  if  this  portion  of  the  ner- 
vous centres  were  isolated  from  the  rest,  the  nerves  which  proceed  from  it 
would  form,  anatomically,  as  well  as  functionally,  a  natural  group.     The  fifth 
pair,  like  other  spinal  nerves,  may  act  in  a  simply  reflex  character;  although, 
in  Man,  it  is  usually  under  the  dominion  of  the  will.     In  the  lower  animals 
we  find  these  reflex  actions  bearing  a  much  larger  proportion  to  the  voluntary 
than  in  Man ;  and  even  in  him  we  not  unfrequently  meet  with  cases  in  which 
the  functions  of  the  cerebral  hemispheres  seem  suspended,  whilst  those  of  the 
spinal  cord  are  unimpaired ;  so  that  the  prehension  of  food  by  the  lips  may 
take  place  without  any  effort  of  the  will.     This  has  been  observed  in  anen- 
cephalous  foetuses,  in  puppies  from  which  the  brain  has  been  removed,  and 
in  profound  apoplexy.     Further,  the  connection  between  the  Fifth  pair  and 

*  See  Newport,  in  Phil.  Trans.,  1832,  p.  386. 


116  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Par  Vagum  is  very  intimate  in  Fishes,  the  class  which  approaches  nearest  in 
the  character  of  its  nervous  system  to  the  Invertebrata.  We  may  reasonably 
infer,  then,  that  the  anterior  ganglion  is  the  principal  centre  of  the  reflex  actions 
of  the  nerves  which  correspond  to  the  third  branch  of  the  fifth  pair,  to  the 
glosso-pharyngeal,  and  to  the  gastric  portion  of  the  Par  Vagum,  in  Vertebrata ; 
whilst  the  branches  which  connect  them  with  the  cephalic  ganglia,  bring  these 
nerves  more  or  less  under  the  influence  of  the  latter. 

153.  The  lateral  ganglia  seem  more  analogous  to  the  centres  of  the  Sympa- 
thetic system  in  Vertebrata;   especially  in  the  connection  of  their  branches 
with  all  the  other  systems  of  nerves;  and  in  the  share  which  they  have  in  the 
formation  of  the  coeliac  ganglia.     This  view  of  the  relative  functions  of  these 
two  divisions  of  the  stomato-gastric  system,  is  strengthened  by  the  fact,  that 
the  connection  between  the  Sympathetic  system  of  Fishes  and  the  Par  Vagum 
is  much  more  intimate  than  in  the  higher  Vertebrata;  although,  even  in  the 
latter,  as  will  be  shown  hereafter,  it  is  by  no  means  so  slight  as  it  appears.* 

154.  Upon  taking  a  general  review  of  the  facts  which  have  been  stated, 
and  of  the  inferences  which  have  been  erected  upon  them,  we  perceive  that 
between  the  strictly  sensorial  functions  of  the  nervous  system  and  those  ope- 
rations in  which  its  internuncial  character  only  is  employed,  a  tolerably  distinct 
line  of  demarkation  may  generally  be  drawn.     We  have  hitherto  viewed  this 
apparatus  under  two  aspects:—!.  As  the  instrument  of  the  mind,  by  which  it 
acquires  a  knowledge  of  the  external  world  through  the  medium  of  sensation, 
and  operates  upon  it  by  an  exercise  of  volition.     2.  As  the  means  by  which 
various  movements  are  excited  in  the  bodily  structure,  that  are  immediately 
necessary  to  the  performance  of  the  organic  functions,  and  to  its  protection 
from  injury;  these  motions  take  place  in  direct  respondence  to  external  im- 
pressions, without  the  intervention  of  the  will,  without  any  designed  adapta- 
tion to  purpose  on  the  part  of  the  animal,  and  often  without  its  consciousness 
being  necessarily  affected . — The  first  of  these  objects  appears  to  be  answered, 
chiefly  if  not  entirely,  by  the  cephalic  ganglia  and  the  nerves  proceeding  from 
them.     The  second  is  carried  into  effect  by  the  ganglia  connected  with  each 
organ,  or  series  of  organs,  whose  movements  are  thus  excited.    We  have  seen, 
that,  however  small  is  the  bulk  of  the  cephalic  ganglia  compared  with  the 
sum  of  the  other  masses,  they  send  nerves  to  every  part  of  the  body  supplied 
by  the  latter;  for  the  purpose,  it  would  seem,  of  controlling,  harmonizing,  or 
antagonizing  their  actions.    These  nerves  proceed  as  connecting  trunks  from 
the  cephalic  ganglia  to  the  other  centres ;  and  then  divide  into  filaments,  which 
unite  with  those  proceeding  from  them  to  the  several  organs.     Each  organ, 
therefore,  receives  four  sets  of  fibres; — an  afferent  and  efferent  set,  which  con- 
nect it  with  the  cephalic  ganglia,  and  are  the  channels  of  sensation,  and  of  the 
influence  of  the  will; — and  an  afferent  and  efferent  set,  which  connect  it  with 
its  own  peculiar  ganglion,  as  well  as  with  other  similar  ganglia ;  and  which 
serve  to  convey  the  stimulus  of  impressions  that  produce  motions  by  reflected 
influence.     In  proportion  as  the  special  sensory  organs  are  developed,  and  the 
actions  of  the  animal  are  less  completely  of  a  simply  reflex  character,  we  find 
the  cephalic  ganglia  and  system  of  nerves  more  predominant. 

155.  We  observe  among  the  Articulata  the  greatest  perfection  of  instinctive 
movements  any  where  exhibited.    In  these  movements  there  is  a  most  remark- 

*  The  view  given  above  of  the  comparative  structure  and  offices  of  the  Nervous  Sys- 
tem in  the  Invertebrated  animals,  is  chiefly  abridged  from  the  Author's  Prize  Thesis  on 
this  subject,  in  which  additional  details  will  be  found,  as  well  as  many  other  illustrative 
figures  and  references  to  authorities.  He  has  there,  also,  discussed  the  physiological 
explanation  which  had  been  previously  given  of  the  double  nervous  cord  of  the  Arti- 
culata; and  having  shown  that  it  is  neither  consistent  with  itself,  nor  capable  of  being 
applied  to  the  other  Invertebrata,  he  has  deemed  it  unnecessary  to  complicate  the  pre- 
sent sketch  by  introducing  it. 


COMPARATIVE  ANATOMY  AND  PHYSIOLOGY.  117 

able  adaptation  of  means  to  ends;  as  in  the  construction  of  habitations  by 
various  Insects,  and  especially  by  the  social  Hymenoptera.  But  few  persons 
will  maintain  that  this  adaptation  is  performed  by  the  mind  of  the  animal ; 
since,  on  this  supposition,  every  Bee  solves  a  problem  which  has  afforded 
scope  for  the  laborious  inquiries  of  the  acutest  human  mathematician.*  The 
adaptation  is  in  the  original  construction  of  a  nervous  system,  which  should 
occasion  particular  movements  to  be  performed  under  particular  external  condi- 
tions ;  and  the  constancy  with  which  these  are  performed  by  different  indi- 
viduals of  the  same  species,  when  placed  in  the  same  conditions,  leads  at  once 
to  the  belief,  that  they  must  be  independent  of  any  operations  so  variable  as 
those  of  judgment  and  voluntary  exertion.  On  the  other  hand,  in  the  Verte- 
brata,  we  find  the  purely  instinctive  movements  forming  a  smaller  proportion 
of  the  whole  actions,  and  brought  under  a  more  complete  subjection  to  the 
sensori-volitional  system.  This  is  evident  from  the  greater  variety  which  the 
actions  exhibit ;  from  the  mode  in  which  they  are  adapted  to  peculiar  circum- 
stances; from  the  degree  in  which  they  may  be  modified  by  education;  and 
from  various  other  indications  of  a  superior  kind  of  Intelligence.  At  last,  in 
Man,  those  instinctive  movements  which  are  not  immediately  requisite  (like « 
those  of  respiration)  for  the  maintenance  of  the  organic  functions,  are  placed 
under  the  control  of  the  will.  This  is  especially  true  of  the  locomotive  organs, 
whose  reflex  actions  are  entirely  guided  by  the  will ;  being  only  distinguish- 
able, when,  from  peculiar  states  of  the  system,  the  immediate  influence  of  the 
brain  upon  them  is  suspended. 

156.  There  is  a  third  aspect,  however,  under  which  we  are  to  consider  the 
Nervous  System ;  and  this  becomes  more  important  in  the  highest  division  of 
the  Animal  kingdom,  on  which  we  are  now  about  to  dwell.  We  have  hitherto 
spoken  only  of  its  influence  on  the  contractile  properties  of  the  tissues,  to 
which  it  is  distributed.  It  has,  however,  an  important  and  direct  connection 
with  the  purely  organic  functions  of  Nutrition  and  Secretion ;  and  we  shall 
see  reason  to  regard  it  as  the  means,  not  only  of  placing  the  animal  in  relation 
with  the  external  world,  but  of  harmonizing  and  controlling  the  organic  changes 
taking  place  in  its  own  structure,  and  of  bringing  these  under  the  influence  of 
particular  mental  conditions.  The  opinion  is  entertained  by  many,  that  all 
the  organic  functions  are  dependent  upon  the  innervation  supplied  to  them  by 
the  system  of  nerves,  which  has  been  termed  Sympathetic  or  vsiceral.  It  is 
incumbent,  however,  on  those  who  uphold  the  necessity  of  this  nervous  power, 

*  The  hexagonal  form  of  the  cell  is  the  one  in  which  the  greatest  strength,  and  the 
nearest  approach  to  the  cylindrical  cavity  required  for  containing  the  larva,  are  attained, 
with  the  least  expenditure  of  material.  But  the  instinct  which  directs  the  Bees  in  the 
construction  of  the  partition  that  forms  the  bottom  or  end  of  the  cell,  is  of  a  nature 
still  more  wonderful  than  that  which  governs  its  general  shape.  The  bottom  of  each  cell 
rests  upon  three  partitions  of  cells  upon  the  opposite  side  of  the  comb;  so  that  it  is 
rendered  much  stronger  than  if  it  merely  divided  the  cavities  of  two  cells  opposed  to  one 
another.  The  partition  is  not  a  single  plane  surface  ;  but  is  formed  by  the  union  of  three 
rhomboidal  planes,  uniting  in  the  centre  of  each  cell.  The  angles  formed  by  the  sides 
of  these  rhombs,  were  determined  by  the  measurements  of  Maraldi  to  be  109°  28'  and 
70°  32';  and  these  have  been  shown  by  mathematical  calculation  to  be  precisely  the 
angles  at  which  the  greatest  strength  and  capacity  can  be  attained  with  the  least  expen- 
diture of  wax.  The  solution  of  the  problem  was  first  attempted  by  Koenig,  a  pupil  of 
the  celebrated  Bernoulli;  and  as  his  result  proved  to  differ  from  the  observed  angle  by 
only  two  minutes  of  a  degree,  it  was  presumed  that  the  discrepancy  was  due  to  an  error 
of  observation,  which  it  was  easy  to  account  for  by  the  smallness  of  the  surfaces  whose 
inclination  had  to  be  measured.  The  question  has  been  since  taken  up,  however,  by 
Lord  Brougham,  (Appendix  to  his  Illustrated  edition  of  Paley's  Natural  Theology),  who 
has  worked  it  out  afresh,  and  has  shown  that,  when  certain  small  quantities,  neglected 
by  Krenig,  are  properly  introduced  into  the  calculation,  the  result  is  exactly  accordant 
with  observation, — the  Bees  being  thus  proved  to  be  right,  and  the  Mathematician  wrong. 


118  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

to  prove  it  definitely ;  since  all  analogy  leads  to  an  opposite  conclusion.  We 
may  regard  the  capability  of  separating  a  particular'  secretion  from  the  blood, 
as  a  peculiar  property  inherent  in  the  glandular  membrane,  just  as  contractility 
is  the  inherent  property  of  muscular  fibre.  As  the  peculiar  arrangement  of 
the  excitable  and  contractile  tissues  in  Animals  requires  a  nervous  system  to 
act  as  a  conductor  between  them,  and  to  blend  their  actions,  so  may  the  com- 
plicated organic  functions  of  Animals  require  to  be  harmonized  and  kept  in 
sympathy  with  each  other,  by  some  mode  of  communication  more  direct  and 
certain  than  that  afforded  by  the  circulating  system,  which  is  their  bond  of 
union  in  Plants.  We  have  seen,  in  the  foregoing  sketch,  that  the  visceral 
system  does  not  exist  in  a  distinct  form  in  the  lower  classes  of  Invertebrated 
animals ;  and  also  that  the  nervous  system  of  these  classes  cannot,  as  a  whole, 
be  compared  with  it,  although  it  may  be  regarded  as  containing  some  rudi- 
ments of  it.  As  the  divisions  of  this  system  become  more  evident,  however, 
and  the  organic  functions  more  complicated,  some  appearance  of  a  separate 
Sympathetic  system  presents  itself;  but  this  is  never  so  distinct  as  in  Verte- 
brata.  Hence  it  may  fairly  be  inferred  that, — as  the  Sympathetic  system  is 
not  developed  in  proportion  to  the  predominant  activity  of  the  functions  of 
organic  life  (which  is  so  remarkable  in  the  Mollusca  when  contrasted  with  the 
Articulata),  but  in  proportion  to  the  development  of  the  higher  divisions  of  the 
nervous  system, — its  office  is  not  to  contribute  to  these  functions  any  thing 
essential  to  tljeir  performance ;  but  rather  to  exercise  that  general  control  over 
them,  which  becomes  the  more  necessary  as  they  become  more  independent  of 
one  another;  and  to  bring  them  into  relation  with  the  system  of  Animal  life. 

VII.  Nervous  System  of  Vertebrata. 

157.  When  we  direct  our  attention  to  the  Nervous  system  of  the  Verte- 
brated  classes,  we  are  immediately  struck  by  two  remarkable  differences  which 
its  condition  presents,  from  that  under  which  we  have  seen  it  to  exist  in  the 
Invertebrata.     In  the  latter  it  has  seemed  but  a  mere  appendage  to  the  rest  of 
the  organism, — a  mechanism  superadded  for  the  purpose  of  bringing  its  various 
parts  into  more  advantageous  relation.     On  the  other  hand,  in  the  Vertebrata 
the  whole  structure  appears  subservient  to  it,  and  designed  but  to  carry  its 
purposes  into  operation.    Again,  in  the  Invertebrata,  we  do  not  find  any  special 
adaptation  of  the  organs  of  support,  for  the  protection  of  the  Nervous  System. 
It  is  either  enclosed,  with  the  other  soft  parts  of  the  body,  in  one  general  hard 
tegumentary  envelop,  as  in  the  Echinodermata  and  Articulata,  or  it  receives 
a  still  more  imperfect  protection,  as  in  the  Mollusca.     In  the  latter,  the  naked 
species  are  destitute  of  any  means  of  passive  resistance,  and  the  Nervous  Sys- 
tem shares  the  general  exposed  condition  of  the  whole  body ;  and  it  is  not  a 
little  remarkable  that,  in  the  testaceous  kinds,  the  portion  of  the  body  contain- 
ing the  nervous  centres  should  be  protruded  beyond  the  shell,  whilst  the  prin- 
cipal viscera  are  retained  within  it.    Now,  in  the  Vertebrata,  we  find  a  special 
and  complex  bony  apparatus,  adapted  in  the  most  perfect  manner  for  the  pro- 
tection of  the  Nervous  system ;  and  it  is,  in  fact,  the  possession  of  a  jointed 
spinal  column,  and  of  its  cranial  expansion,  which  best  characterizes  the  group. 

158.  When  we  look  more  particularly  at  the  Nervous  Centres  themselves, 
we  perceive  that  they  combine  the  general  characters  of  those  of  the  Articu- 
lata with  those  of  the  Mollusca.    In  the  former,  the  power  of  active  locomotion 
seems  the  chief  object  to  be  attained ;  and  the  predominant  part  of  the  appa- 
ratus is  evidently  the  series  of  ganglia  connected  with  the  locomotive  organs'. 
The  sensory  ganglia  appear   subservient  to  these  both  in  size    and  func- 
tion.    On  the  other  hand,  in  the  Mollusca,  the  sensory  ganglia  predominate  ; 
and  under  their  function,  which  is  to  direct  these  walking  stomachs  to  their 


NERVOUS  SYSTEM  OF  VERTEBRATA.  119 

food,  the  control  of  the  locomotive  apparatus  seems  to  be  placed.  Now,  in  the 
Vertebrata  we  have  the  locomotive  powers  of  the  Articulata  (comparatively 
reduced,  however,  in  activity"),  united  with  the  complex  nutritive  system  of 
the  Molmsca ;  and  we  find  this  combination  manifested,  not  only  in  the  organs 
themselves,  but  in  the  Nervous  System,  which  stands  in  so  close  a  relation 
with  them.  The  Spinal  Cord  of  Vertebrata  is  evidently  the  analogue  of  the 
ventral  columns  of  Articulata.  It  is  a  continuous  ganglion,  containing  two  por- 
tions as  distinct  as  the  two  tracts  in  the  Articulata; — a  fibrous  structure,  which 
is  continuous  between  the  Brain  and  the  spinal  nerves,  and  thus  resembles  the 
white  tract  in  Insects; — and  a  ganglionic  portion,  principally  composed  of 
gray  matter.  Into  this  gray  matter,  as  in  the  ventral  ganglia  of  Insects,  a  part 
of  the  roots  of  the  spinal  nerves  may  be  traced ;  whilst  others  pass  on  continu- 
ously to  the  brain.  At  the  upper  extremity  of  the  Spinal  Cord  (commonly 
termed  the  Medulla  Oblongafa),  we  find  the  ganglia  and  nerves  of  special 
sensation ;  and  the  organs  which  these  supply  are  placed  in  immediate  proxi- 
mity with  the  entrance  to  the  alimentary  canal,  holding  the  same  relation  to 
it  as  in  the  Mollusca.  But  in  addition  to  these,  we  find  two  ganglionic  masses 
in  all  Vertebrata,  to  which  we  have  no  distinct  analogue  in  the  lower  classes — 
the  Cerebral  Hemispheres,  and  the  Cerebellum.  With  the  development  of  the 
former  of  these,  the  perfection  of  the  reasoning  powers  appears  to  hold  a  close 
relation ;  that  of  the  latter  seems  connected  with  the  necessity  which  exists 
for  the  adjustment  and  combination  of  the  locomotive  powers,  when  the  variety 
of  movements  performed  by  the  animal  is  great,  and  the  harmony  required 
among  them  is  more  perfect.  Upon  these  points,  however,  we  shall  hereafter 
dwell. 

159.  The  Visceral  system  of  nerves  now  assumes  a  more  distinct  form. 
It  does  not  share  the  protection  of  the  Spinal  column ;  but  its  ganglia  lie  for 
the  most  part  in  the  general  cavity  of  the  trunk.  The  connections  of  the 
Cerebro-Spinal  and  Sympathetic  systems  may  be  best  studied  in  the  trunk ; 
since  the  regularity  of  the  distribution  of  the  spinal  nerves  prevents  the  exist- 
ence of  that  doubt  regarding  the  nature  of  the  communication  which  obscures 
the  relation  of  the  cranial  nerves  with  the  sympathetic.  The  great  visceral 
ganglia — the  cardiac  and  semilunar, — may  probably  be  regarded  as  the  true 
centres  of  the  Nervous  system  of  Organic  life ;  whilst  the  chain  of  ganglia, 
which  lie  along  the  spine,  are  intermediate  between  these  and  the  cerebro- 
spinal  system.  When  the  filaments  connecting  these  ganglia  with  the  roots 
of  the  spinal  nerves  are  closely  examined,  they  are  found  to  contain  both  kinds 
of  fibres ;  and  they  can  no  more,  therefore,  be  regarded  as  the  roots  by  which 
the  sympathetic  system  arises  from  the  cerebro-spinal  (as  they  were  formerly 
considered),  than  as  the  roots  by  which  the  latter  originates  from  the  former. 
The  white  tubular  fibres  which  these  filaments  contain,  are  found,  upon  close 
examination,  to  be  derived  from  both  roots  of  the  spinal  nerves,  and  not  from 
the  posterior  only,  as  some  have  supposed.  The  quantity  of  white  fibres  in 
the  nerves  proceeding  from  this  lateral  chain  of  ganglia,  is  much  greater  than 
that  contained  in  the  nerves  of  the  solar  plexus ;  and  it  is  confirmatory  of  the 
idea  just  stated  (that  the  visceral  ganglia  are  the  true  centres  of  the  sympa- 
thetic system),  to  find  that  the  nerves  proceeding  from  them  are  almost  entirely 
composed  of  the  fibres  characteristic  of  this  system  (§  110).  A  few  visceral 
fibres  may  be  found  in  almost  all  the  Cerebro-spinal  nerves;  they  are  particu- 
larly abundant,  however,  in  the  first  division  of  the  Fifth  pair.  It  would  seem 
that  only  a  part  of  these  are  derived  immediately  from  the  sympathetic  nerve ; 
and  that  the  remainder  may  be  traced  into  the  gray  matter  of  the  ganglia, 
formed  on  the  posterior  roots  of  the  spinal  nerves,  and  on  the  larger  root  of  the 
fifth  pair.  As  this  gray  matter  consists  of  nucleated  globules,  like  those  which 
are  found  in  the  centres  of  the  Sympathetic  system,  it  may  be  surmised  that 


120 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  15. 


this  series  of  ganglia  also  may  be 
regarded  as  belonging  to  that  sys- 
tem ;  and  as  bearing  the  same  re- 
lation to  the  gray  fibres '  contained 
in  the  cerebro-spinal  nerves,  as 
that  which  the  semilunar  ganglia 
have  to  the  nerves  of  the  solar 
plexus, — in  other  words,  acting  as 
their  centres  of  power. 

160.  The  branches  proceeding 
from  the  Semilunar  ganglia  are 
distributed  upon  the  abdominal 
viscera  ;  and  those  of  the  Cardiac 
ganglia  upon  the  heart  and  the 
vessels  proceeding  from  it.  The 
latter  seem  to  accompany  the  arte- 
rial trunks  through  their  whole 
course,  ramifying  minutely  upon 
their  surface ;  and  can  scarcely  be 
doubted,  that  they  exercise  an  im- 
portant influence  over  their  func- 
tions. What  the  nature  of  that 
influence  is,  however,  will  be  a 
subject  for  future  inquiry.  It  is 
so  evidently  connected  with  the 
operations  of  nutrition,  secretion, 
&c.,  that  the  designation  of  "nerv- 
ous system  of  organic  life,"  as  ap- 
plied to  this  system,  does  not  seem 
objectionable,  provided  that  we  do 
not  understand  it  as  denoting  the 
dependence  of  these  functions  upon 
it.  Even  in  Vertebrata,  however, 
we  do  not  always  find  the  visceral 
system  distinct  from  the  cerebro- 
spinal.  In  the  Cyclostome  Fishes, 
the  par  vagum  supplies  the  intes- 
tinal canal  along  its  whole  length, 
as  well  as  the  heart ;  and  no  ap- 
pearance of  a  distinct  sympathetic 
can  be  discovered.  In  Serpents, 
again,  the  lower  part  of  the  ali- 
mentary canal  is  supplied  from 
the  Spinal  Cord,  and  the  upper 

A  view  of  the  Great  Sympathetic  Nerve.— 1,  the  plexus  on  the  carotid  artery  in  the  carotid  foramen; 
2,  sixth  nerve  (motor  externus) ;  3.  first  branch  of  the  fifth  or  ophthalmic  nerve;  4.  a  branch  on  the  sep- 
lum  narium  going  to  the  incisive  foramen;  5,  the  recurrent  branch  or  vidian  nerve  dividing  into  the  caro- 
tid and  petrosal  branches;  6, posterior  palatine  branches:  7,  the  lingual  nerve  joined  by  the  corda  tympani; 
e.  the  portio  dura  of  the  seventh  pair  or  the  facial  nerve;  9.  the  superior  cervical  ganglion;  10.  the  mid- 
dle cervical  ganglion;  11,  the  inferior  cervical  ganglion;  12,  the  roots  of  the  great  splanchnic  nerve 
arising  from  the  dorsal  ganglia;  13,  the  lesser  splanchnic  nerve;  14,  the  renal  plexus;  15,  the  solar 
plexus;  16,  the  mesenteric  plexus;  17,  the  lumbar  ganglia:  18,  the  sacral  ganglia;  19,  the  vesical  plexus; 
20.  the  rectal  plexus;  21,  the  lumbar  plexus  (cerebro-spinal) ;  22,  the  rectum:  23.  the  bladder;  24,  ihe  pubis ; 
2o.:  the  csest  of  the  ileum;  26,  the  kidney;  27,  the  aorta;  23,  the  diaphragm;  29,  the  heart;  30,  the  larynx; 
31  the  sub-maxillary  gland;  32,  the  incisor  teeth;  33,  nasal  septum;  34,  globe  of  the  eye ;  35,  36,  cavity  of 
the  cranium. 


24 


NERVOUS  SYSTEM  OF  VERTEBRATA.  121 

part  by  the  par  vagum ;  and  though  the  lateral  cords  of  the  sympathetic  may 
be  traced,  they  are  almost  destitute  of  ganglia.  Even  in  the  highest  Verte- 
brata,  some  of  the  glands,  of  which  the  secretion  is  most  directly  influenced 
by  the  condition  of  the  mind,  are  supplied  with  most  of  their  nerves  from  the 
cerebro-spinal  system  ;  thus,  the  lachrymal  and  sublingual  glands  receive  large 
branches  from  the  fifth  pair,  and  the  mammary  glands  from  the  intercostal 
nerves.  It  may  therefore  be  regarded  as  not  improbable,  that  the  organic 
fibres  contained  in  these  nerves,  and  principally  derived  from  the  ganglia  at 
their  roots,  are  the  most  direct  channels  through  which  the  processes  of  nutri- 
tion and  secretion  are  influenced  by  mental  emotions ;  and  that  the  office  of 
the  distinct  visceral  system,  is  rather  to  bring  these  functional  changes  into  har- 
mony with  each  other  than  to  supply  any  condition  necessary  for  the  separate 
operations  themselves. 

161.  The    Spinal   Cord,  with   its   encephalic   continuation — the   Medulla 
Oblongata, — may  be  regarded  as  constituting  the  essential  part  of  the  nervous 
system  of  Vertebrata.     Although  the  Cerebral  Hemispheres  in  Man  bear  so 
large  a  proportion  to  it  in  size,  that  the  Spinal  Cord  seems  but  a  mere  append- 
age to  them,  the  case   is  reversed  when  we  look  at  the  other  extremity  of  the 
scale  ; — the  Cerebral  Hemispheres  jn  many  Fishes  being  but  ganglionic  pro- 
tuberances from  the  Medulla  Oblongata.     Moreover,  the  fact  that  animals  are 
capable  of  living  without  the  brain,  whilst  they  at  once  die  if  deprived  of  the 
spinal   cord,   sufficiently  demonstrates   this.     The   spinal  cord,  then,  when 
viewed  in  relation  to  the  nervous  system  of  the  Invertebrata,  may  be  regarded 
as  including  their  respiratory,  stomato-gastric,  and  pedal  ganglia.     That  these 
should    be  associated   together,  can  scarcely  be  considered  remarkable.     It 
is  obviously  convenient  that  they  should  all  be  enclosed  in  the  bony  sheath 
provided  for  their  protection;  and  their  closer  relation  favours  that  sympathy 
of  action,  which  is  so  important  in  animals  of  such  complex  structure  and 
mutually  dependent  functions  as  the  higher  Vertebrata.     An  animal,  either 
congenitally  or  experimentally  deprived  of  its  cerebral  hemispheres,  is  very 
much  in  the  condition  of  one  of  the  Acephalous  Mollusca.     It  can  perform 
those  respiratory  movements  on  which  depend  the  maintenance  of  its  circula- 
tion, and  consequently  its  whole  organic  life ;  it  can  swallow  food  brought 
within  its  reach,  and  it  can,  in  some  degree,  exert  its  locomotive  powers  to 
obtain  it ;  but   it  is  unconscious  of  the  direction  in  which  these  can  be  best 
employed,  and  is  dependent  upon  the  supplies  of  food  that  come  within  its 
grasp.     The  Acephalous  Mollusca  are  so  organized,  that  they  find  support 
from  the  particles  brought  in  by  their  respiratory  current ;  but  the  more  highly- 
organized  Vertebrata  are  not  capable  of  so  existing,  and  they  must  have  the*ir 
food  provided  for  them  by  an  exertion  of  the  mental  powers.     So  long  as  an 
encephalous  Vertebrate  animal  is  duly  supplied  with  its  requisite  food,  so  long 
may  it  continue  to  exist ;  and  thus  it  is  seen  that  the  operations  of  the  brain 
are  rather  connected  with  the  intelligence  than  with  the  blind,  undesigning 
instinct  of  the  animal. 

162.  It  is  only  in  the  Vertebrata,  that  the  difference  between  the  afferent 
and  efferent  fibres  of  the  nerves  has  been  satisfactorily  determined.     The 
merit  of  this, discovery  is  almost  entirely  due  to  Sir  C.  Bell.     He  was  led  to 
it  by  a  chain  of  reasoning  of  a  highly  philosophical  character;  and  though 
his  first  experiments  on  the  spinal  nerves  were  not  satisfactory,  he  virtually 
determined  the  respective  functions  of  their  two  roots,  by  experiments  and 
pathological  observations  upon  the  cranial  nerves,  before  any  other  physio- 
logist came  into  the  field.*     Subsequently  his  general  views  were  confirmed 
by  the  very  decided  experiments  of  Mtiller;  but,  until  very  recently,  some  ob- 

*  See  British  and  Foreign  Medical  Review,  vol.  ix.  p.  140,  &c. 


122  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

scurity  hung1  over  a  portion  of  the  phenomena.  It  was  from  the  first  maintained 
by  Magendie,  and  has  been  subsequently  asserted  by  other  physiologists,  that 
Jhe  anterior  and  posterior  roots  of  the  nerves  were  both  concerned  in  the 
"reception  of  sensations  and  in  the  production  of  motions;  for  that,  when  the 
anterior  roots  were  touched,  the  animal  gave  signs  of  pain,  at  the  same  time 
that  convulsive  movements  were  performed;  and  that,  on  touching  the  poste- 
rior roots,  not  only  the  sensibility  of  the  animal  seemed  to  be  affected,  but  mus- 
cular motions  were  excited.  These  physiologists  were  not  willing,  therefore, 
to  admit  more  than  that  the  anterior  roots  were  especially  motor,  and  the  pos- 
terior especially  sensory.  But  the  recently  attained  knowledge  of  the  reflex 
function  of  the  spinal  cord,  enables  the  latter  portion  of  these  phenomena  to 
be  easily  explained.  The  motions  excited  by  irritating  the  posterior  root  are 
entirely  dependent  upon  its  connection  with  the  spinal  cord,  arid  upon  the 
integrity  of  the  anterior  roots  and  of  the  trunks  into  which  they  enter ;  whilst 
they  are  not  checked  by  the  separation  of  the  posterior  roots  from  the  peri- 
pheral portion  of  the  trunk.  It  is  evident,  therefore,  that  excitation  of  the 
posterior  root  does  not  act  immediately  upon  the  muscles  through  the  trunk  of 
the  nerve,  which  they  contribute  to  form,  but  that  it  excites  a  motor  impulse 
in  the  Spinal  Cord,  which  is  propagated  through  the  anterior  roots  to  the  peri- 
phery of  the  system.  The  converse  phenomenon,  the  apparent  sensibility  of 
the  anterior  roots,  has  been  still  more  recently  explained  by  the  experiments 
of  Dr.  Kronenberg  ;*  who  has  satisfactorily  proved  that  it  is  dependent  upon 
a  branch  of  the  posterior  root  passing  into  the  anterior  root  at  their  point  of 
inosculation,  and  then  directing  itself  towards  the  cord  (§  124). 

163.  On  the  other  hand,  the  distinctness  of  the  system  of  nerves  concerned 
in  the  simply  reflex  actions,  from  those  which  minister  to  sensation  and  voli- 
tion by  their  connection  with  the  brain,  is  by  no  means  so  obvious  as  in  the 
Invertebrated  classes.     When  first  pointed  out  by  Dr.  Marshall  Hall,  who  had 
grounded  his  opinion  more  upon  physiological  phenomena  than  upon  anato- 
mical facts,  the  statement  did  not  command  general  assent ;   since,  while  the 
phenomena  were  admitted,  the  inferences  which  he  drew  from  them  by  him 
were  not  regarded  as  necessary  results.     When,  however,  the  anatomy  of  the 
nervous  centres  in  Vertebrata  was  more  closely  inquired  into  (by  Mr.  Grain- 
ger, who  had  been  partly  anticipated  by  Bellingeri),  it  was  found  to  present 
certain  phenomena  which  might  be  regarded  as  supporting  Dr.  M.  Hall's 
views ;  and  when  the  inquiry  was  extended  to  the  Invertebrated  classes,  the 
confirmation  was  found  to  be  still  more  decisive.   In  our  previous  sketch  these 
doctrines  have  been  treated  as  established ;  since  they  have  been  found  not 
only  to  correspond  with  the  facts  disclosed  by  anatomical  research,  but  to  be 
required  by  them.     We  shall  now  apply  them  to  the  nervous  apparatus  of  the 
Vertebrata. 

164.  The  Spinal  Cord  consists  of  two  lateral  halves;  these  are  partially 
separated  in  the  higher  classes,  by  the  superficial  anterior  and  posterior  fis- 
sures;  and  in  Fishes  by  an  internal  canal,  which  is  continuous  with  the  fourth 
ventricle.!     This  canal  is  evidently  the  indication  of  that  complete  separation 
of  the  two  columns,  which  exists  in  the  lower  Articulata;  and  the  fourth  ven- 
tricle, which  in  many  fishes  remains  unclosed  (the  cerebellum  ngt  being  suffi- 
ciently developed  to  overlap  it,)  corresponds  with  the  passage  between  the 
cords  uniting  the  cephalic  ganglia  with  the  first  subcesophageal,  through  which 
the  oesophagus  passed  in  all  the  Invertebrata.     The  two  lateral  halves  have 
little  connection  with  each  other  in  Fishes,  and  the  pyramidal  bodies  at  their 

*  Mailer's  Archiv.  1839,  Heft  v.;  and  Brit,  and  For.  Med.  Rev.,  vol.  ix.  p.  547. 

1  his  canal  may  be  traced  in  the  Spinal  Cord  of  Man  and  other  Mammalia;  but  it  is 
nearly  obliterated. 


NERVOUS  SYSTEM  OF  VERTEBRATA. 


123 


1 B 


apex  scarcely  decussate ;  but,  in  ascending  towards 
the  higher  classes,  the  communication  between  the 
two  sides  is  more  intimate,  and  a  larger  proportion 
of  the  pyramidal  fibres  crosses  to  the  opposite  sides. 
In  all  the  Vertebrata,  the  true  Spinal  Cord  contains 
gray  substance,  or  something  equivalent  to  it;  thus 
possessing  the  character  of  a  continuous  ganglion. 
The  proportion  of  the  vertebral  column  which  this 
ganglionic  portion  occupies,  is,  however,  extremely 
variable ;  depending  principally  on  the  position  of 
the  chief  organs  of  locomotion.  Thus,  in  the  Eel, 
and  other  Vermiform  Fishes,  it  is  continued  through 
the  whole  spinal  canal;  whilst  in  the  Lophius  and 
Tetraodon,  whose  body  is  less  prolonged,  and  more 
dependent  for  its  movements  upon  the  anterior  extre- 
mities, the  true  Spinal  Cord  scarcely  passes  out  of 
the  cranium.  The  quantity  of  gray  matter  is  nearly 
uniform  in  every  part  of  the  cord,  where  there  is  no 
great  diversity  in  the  functions  of  the  nerves  which 
originate  from  each  portion.  In  most  Fishes,  for 
example,  the  body  is  propelled  through  the  water 
more  by  the  lateral  action  of  the  flattened  trunk 
(whose  surface  is  extended  by  the  dorsal  and  caudal 
fins  erected  upon  prolongations  of  its  vertebras),  than 
by  the  movements  of  its  extremities,  which  serve  prin- 
cipally  to  guide  it.  Hence  we  usually  find  the  amount 
of  gray  matter  varying  but  little  in  different  parts  of 
the  cord.  But  in  the  Flying-fish,  and  others  whose  pectoral  fins  are  unusually 
powerful,  a  distinct  ganglionic  enlargement  of  the  cord  takes  place  where  the 
nerves  are  given  off.  In  Serpents,  again,  the  spinal  cord  is  nearly  uniform 
throughout  its  entire  length ;  whilst  in  Amphibia  it  is  so  during  the  Tadpole 
condition,  but  presents  enlargements  corresponding  to  the  anterior  and  poste- 
rior extremities,  when  these  are  developed ;  at  the  same  time  becoming  much 
shortened,  as  the  tail  is  less  important  to  locomotion,  or  is  altogether  atrophied. 
In  Birds,  the  ganglionic  en- 


Nervous Centres  in  Frog; 
A,  olfactive  ganglia;  B,  cere- 
bral hemispheres ;  c,  optic 
ganglia;  D,  cerebellum,  so 
small  as  not  to  cover  the  4th 
ventricle,  or  cavity  left  by  the 
of  the  columns  of 


largements  are  generally  very 
perceptible;  and  bear  a  close 
relation  in  size,  with  the  de- 
velopment of  the  locomotive 
organs  with  which  they  are 
connected.  Thus,  in  Birds  of 
active  flight,  and  short  power- 
less legs,,  the  anterior  enlarge- 
ment is  the  principal ;  but  in 
those  which  are  more  adapted 
to  run  on  land  than  to  wing 
their  way  through  the  air,  such 
as  the  whole  tribe  of  Struthi- 
ous  birds,  the  size  of  the  pos- 
terior enlargement  is  very  re- 
markable. Hence  we  have 
a  right  to  infer,  that  the  in- 
crease in  the  quantity  of  gray 
matter  in  the  cord  has  some 
connection  with  the  amount  of 


Fig.  17. 


Transverse  sections  of  human  Spinal  Cord  at  different 
po;nts.  showing  proportional  quantity  and  arrangement  of 
gray  and  white  mailer  at  each;  after  Solly:  1,  opposite  11  ih 
dorsal  vertebra;  2,  opposite  10th  dorsal;  3,  opposite  Sth  dor- 
sal; 4,  opposite  5th  dorsal;  5,  opposite  7th  cervical;  G,  oppo- 
site 4th  cervical ;  7.  opposite  3d  cervical ;  8,  section  of  medulla 
pbloiigata  through  centre  of  corpus  olivare. 


124  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

power  to  be  supplied ;  and  this  exactly  corresponds  with  what  has  been 
observed  in  the  Articulated  classes,  and  especially  in  watching  tlje  metamor- 
phosis of  Insects.  In  Birds  and  Mammalia,  however,  the  whole  amount  of  the 
gray  matter  in  the  spinal  cord  does  not  bear  so  large  a  proportion  to  the  bulk 
of  the  nerves  proceeding  from  it,  as  in  the  lower  Vertebrata ;  and  the  reason 
of  this  seems  obvious.  The  actions  of  the  locomotive  organs  are  less  and  less 
of  a  reflex  character,  and  are  more  directly  excited  by  the  will,  and  conse- 
quently by  the  brain,  than  in  the  inferior  tribes;  and  just  in  proportion,  there- 
fore, to  the  development  of  the  Brain,  will  it  become  the  centre  of  all  the  actions 
performed  by  the  animal,  and  the  Spinal  Cord  a  mere  appendage  to  it.  Still, 
in  all  the  Mammalia,  even  in  Man,  do  we  find  these  ganglionic  enlargements 
of  the  spinal  cord ;  and  in  Man  it  is  the  posterior  (or  rather  the  inferior)  one 
which  contains  the  largest  quantity  of  gray  matter.  In  the  cord  of  this  class, 
too,  the  lateral  halves  are  much  more  intimately  united  than  in  the  classes 
below ;  for  not  only  is  the  central  canal  for  the  most  part  absent,  but  the  two 
crescent-shaped  plates  of  gray  matter  are  united  by  a  transverse  lamella,  which 
connects  their  centres  like  a  commissure. 

165.  The  Cord  is  traversed,  not  only  by  the  anterior  and  posterior  fissures, 
but  by  two  furrows  on  each  side,  marking  out  three  columns  upon  it.  We 
have,  therefore,  on  each  half  of  the  cord,  an  anterior,  middle  or  lateral,  and 
posterior  column.  The  points  of  the  crescentic  lamellce  of  gray  matter  ap- 
proach these  furrows  pretty  closely ;  but  elsewhere  the  gray  matter  is  covered 
deeply  by  the  fibrous  columns.  Each  spinal  nerve  arises  from  two  sets  of 

roots.  The  anterior  roots  join  the  spinal 

Fig.  IS.  cord  near  the  anterior  furrow;  and  the 

posterior  near  the  posterior  furrow. 
Respecting  their  intimate  connection 
with  the  principal  divisions  of  the  cord, 
a  considerable  diversity  has  existed 
among  the  statements  of  anatomists  ; 
but  it  seems  to  be  now  satisfactorily 
ascertained,  that,  as  in  the  Articulata, 

A  transverse  section  of  the  Spinal  Marrow.-  a  part  Qf  each  rQot  enters  the  mat. 

1,1.  the  two  halves  of  the  spinal  marrow;  2   the  /•       •  •  r    i 

anterior  middle  fissure;  3,  the  posterior  middle  I-  ^.P1  S^gllOHW   portion   of  the    COrd, 

sure;  4,  the  position  of  the  cineritious  matter  to  each  whl/st    a   P^rt     IS    COlltmUOUS     With     its 

half  of  the  spinal  marrow;  5,  the  origin  of  orfe  of  Whit*  OY  ftbrOUS  Columns.      The  COUrSC 

the  anterior  roots  of  a  spinal  nerve ;  6,  the  origin  of  of    tile     fibres     which     enter    the     gray 

one  of  the  posterior  roots.  matter,  has  been  lately  displayed,  in 

part,  at  least,  by  the  researches  of  Dr. 

Stilling.*  It  appears  that  of  the  fibres  of  the  posterior  roots,  some  form  loops 
in  the  gray  matter,  and  become  continuous  with  those  of  the  anterior  roots  of 
the  same  side,  as  seen  at  A,  fig.  19.  Others  cross  the  gray  matter,  and  become 
continuous  with  those  of  the  anterior  roots  of  the  opposite  side,  as  seen  at  B.  It 
can  scarcely  be  doubted  that  these  fibres,  being  unconnected  with  the  brain, 
constitute  the  system  to  which  reflex  actions  are  due.  Although  Dr.  Stillinp-'s 
inquiries  have  not  proved  the  fact,t  yet  it  may  be  inferred  from  physiological 
phenomena,  as  well  as  from  the  facts  recently  shown  by  Mr.  Newport  (§  143), 
that  there  are  other  fibres,  which  pass  from  the  posterior  roots  into  the  anterior 
roots  of  other  nerves  above  and  below,  both  on  the  same  and  on  the  opposite 
>f  the  portions  of  the  roots  which  are  continuous  with  the -fibrous 
columns,  it  is  stated  by  Sir  C.  Bell  that  the  anterior  fasciculi  pass  to  the  an- 

*  Ueber  die  Textur  und  Function  der  Medulla  Oblongata. 

-  It  may  be  thought  that  the  mode  of  examination  which  he  adopted,— that  of  making 
very  thin  transverse  sections  of  the  Spinal  Cord,-is  not  well  fitted  to  display  the  con- 
nections  of  the  roots  with  longitudinal  fibres. 


NERVOUS  SYSTEM  OF  VERTEBRATA. 


Structure  of  the  Spinal  Cord,  ac- 
cordingto  Stilling;  A,  posterior  fibres 
continuous  with  the  anterior  of  the 
same  side,  through  the  nucleus  of 
the  cord;  B,  posterior  fibres  continu- 
ous with  the  anterior  of  the  opposite 
side. 


terior  columns  only,  and  that  the  posterior  are  Fig.  19. 

restricted  to  the  lateral  columns.     On  the  other 

hand,  Mr.  Grainger  and  Mr.  Swan  maintain  that 

both  sets  are  connected  with  the  lateral  cclumns 

only  ;    the  anterior  and  posterior  lateral  fissures 

definitely  limiting  the  two  roots.     Perhaps  both 

these  statements  are  rather  too  exclusive.     The 

anterior  roots  would  seem  to  have  a  connection 

with  both  the  anterior  and  lateral  columns ;  and 

the  posterior  cannot  be  said  to  be  restricted  to  the 

lateral  column,  some  of  their  fibres  entering  the 

posterior  division  of  the  cord. 

166.  As  the  white  or  fibrous  portion  of  the 
Spinal  Cord  Jkcontinuous  with  the  medullary 
matter  of  theJBln,the  roots  of  the  nerves  which 
enter  it  are  "flfcity  thus  brought  into  connec- 
tion with  the  Cerebral  Hemispheres  and  Cere- 
bellum ;  and  the  posterior  division  of  these  may, 
therefore,  be  regarded  as  conducting  to  the  brain 
those  impressions  which  there  become  sensa- 
tions ;  whilst  the  anterior  roots  convey  the  motive 
influence,  which  has  been  propagated,  by  a  volun- 
tary or  emotional  impulse,  down  the  tract  of  the 
Spinal  Cord  with  which  they  are  continuous. 
On  the  other  hand,  the  passage  of  one  portion 
of  each  set  of  roots  through  the  gray  matter 
of  the  Cord,  completes  the  nervous  circle  re- 
quired for  the  performance  of  reflex  actions ;  and  by  this  they  would  seem 
to  take  place  in  Vertebrated  animals,  just  as  through  the  distinct  system  of 
excito-motor  fibres  in  the  Articulata  (§  143).  The  fibres  which  pass  continu- 
ously from  the  posterior  to  the  anterior  roots  of  the  nerves  on  the  same  side, 
probably  constitute  the  channel  of  those  reflex  actions,  which  can  be  excited 
in  a  part  supplied  by  any  compound  nerve,  by  stimulating  its  afferent  fibres, 
and  thus  causing  a  motor  impulse  to  be  transmitted  from  the  Spinal  Cord  along 
its  efferent  portion.  The  fibres  which  cross  to  the  opposite  side,  will  produce 
similar  movements  in  its  corresponding  parts.  And  the  fibres,  if  such  there 
be,  that  pass  from  the  posterior  (afferent)  roots  of  each  nerve,  into  the  anterior 
(motor)  roots  of  distant  nerves,  would  convey  to  a  great  variety  of  muscles,  the 
influence  of  a  stimulus  applied  to  a  single  afferent  nerve.  It  follows,  then,  on 
this  view  of  the  character  of  the  Spinal  Cord,  that  the  continuity  of  the  fibrous 
tracts  is  all  that  is  required  to  convey  the  influence  of  the  brain  to  the  parts 
below ;  whilst  the  completeness  of  the  nervous  circle  is  all  that  is  necessary 
for  the  performance  of  reflex  actions  excited  through  it.  This  is  found  to  be 
strictly  true ;  the  former  having  been  observed  in  cases  of  disease,  and  the 
latter  having  been  proved  by  experiment.  As  far  as  simple  reflex  actions 
are  concerned,  there  is  as  much  segmental  independence  in  Vertebrata,  as  in 
the  Articulata ;  but  these  actions  seldom  have  so  completely  the  character  of 
adaptation,  and  are  of  a  more  irregular  and  convulsive  nature.  Still,  however, 
there  is  an  essential  correspondence  between  them ;  and  we  may,  therefore, 
regard  the  distinction  between  the  reflex  and  voluntary  movements  as  tte  same 
in  each  group  ; .  the  former  predominating  in  Articulata,  the  latter  in  Verte- 
brata. On  this  view,  then,  each  spinal  nerve  contains  at  least  four  sets  of 
fibres. 

I.  A  sensory  bundle  passing  upwards  to  the  brain. 

11* 


126  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

II.  A  motor  set,  conveying  the  influence  of  volition  and  emotion  downwards 
from  the  brain. 

III.  A  set  of  excitor  or  centripetal  fibres,  terminating  in  the  true  spinal  cord 
or  ganglion,  and  conveying  impressions  to  it. 

I V.  A  motor  or  centrifugal  set,  arising  from  the  same  ganglionic  centre,  and 
conveying  the  motor  impulse  reflected/rom  it  to  the  muscles. 

Of  these,  the  first  and  third  are  united  in  the  posterior  or  afferent  roots  ;  the 
second  and  fourth  in  the  anterior  or  efferent  roots. 

167.  It  is  difficult  to  trace  the  course  of  the  fibres  within  the  Spinal  Cord; 
and  some  recent  experiments  by  Valentin,  appear  to  prove,  that  Sir  C.  Bell 
was  not  altogether  correct  in  his  idea  that  the  functions  of  the  columns  of 
the  cord  are  respectively  similar  to  those  of  the  roots  connected  with  them. 
Cases,  indeed,  are  of  no  unfrequent  occurrence,  in  which  a  portion  of  one  of 
the  columns  has  been  almost  entirely  destroyed  by  injury  ojjjlsease,  without 
any  corresponding  loss  of  the  function  attributed  to  it.     Such  cases  have  kept 
alive,  in  the  minds  of  many  eminent  practical  men,  a  considerable  distrust  of 
the  accuracy  of  Sir  C.  Bell's  conclusions.     We  have  seen  that,  in  regard  to 
the  roots  of  the  nerves,  his  first  statements  have  been  confirmed,  and  rendered 
more  precise,  by  subsequent  researches  ;  but  it  is  not  so  in  regard  to  the  func- 
tions of  the  anterior  and  posterior  divisions  of  the  Spinal  Cord.     Bellingeri 
was  led,  by  experiments  on  the  spinal  cord,  to  the  conclusion,  that  the  anterior 
roots  of  the  nerves  were  for  the  flexion  of  the  various  articulations,  and  the 
posterior  for  their  extension.     He  also  was  wrong,  in  extending  an  inference, 
founded  on  experiments  on  the  Cord,  to  the  roots  of  the  nerves.     The  recent 
experiments  of  Valentin,  whilst  they  fully  confirm  Sir  C.  Bell's  determination 
of  the  functions  of  the  roots  of  the  nerves,  coincide,  to  no  small  degree,  writh 
Bellingeri's  opinion  in  regard  to  the  offices  of  the  anterior  and  posterior  divi- 
sions of  the  Cord.     He  obtained  reason  to  believe  that,  in  the  Frog,  neither 
the  superior  nor  inferior  strand  of  the  cord  (posterior  and  anterior  columns  in 
Man)  solely  possess  motor  functions ;  but  he  found  that,  when  the  former  were 
irritated,  sensations  predominated ;  and  when  the  latter,  motions  were  chiefly 
excited.     He  further  states  that,  if  the  superior  strand  (posterior  column)  be 
irritated  at  the  point  at  which  the  nerves  of  either  extremity  are  given  off,  that 
extremity  is  extended;  and  that  if  the  inferior  strand  (anterior  column)  be 
irritated,  the  extremity  is  flexed.     At  their  entrance  into  the  spinal  cord,  there- 
fore, it  would  appear  that  the  rrjotor  fibres  of  the  extensors  pass  towards  the 
superior  stratum  (posterior  column  in  Man),  whilst  those  of  the  flexors  are 
continuous  with  the  inferior  stratum  (anterior  column) ;  their  course  being 
more  altered,  however,  when  they  are  examined  far  from  the  point  of  issue. 
This  doctrine  was  confirmed  by  experiments  on  Mammalia ;  and  is  borne  out 
(according  to  Valentin)  by  pathological  phenomena  observed  in  Man.    Accord- 
ing to  this  eminent  physiologist,  also,  relaxation  of  the  sphincters  is  analogous 
to  the  extended  state  of  the  extremities ;  and  he  has  noticed  a  manifest  relaxa- 
tion of  the  sphincter  ani  in  the  frog,  when  the  superior  part  of  the  spinal  cord 
was  irritated  so  as  to  produce  extension  of  the  limbs.     These  statements  are 
entitled  to  considerable  weight,  on  account  of  the  quarter  from  which  they 
come  ;  but  they  are  not,  perhaps,  to  be  received  altogether  without  hesitation, 
until  confirmed  by  other  physiologists,  especially  whilst  the  phenomena  of 
reflex  action  are  still  so  imperfectly  known.     For  it  is  quite  possible  that, 
whilst  stimulation  of  the  anterior  part  of  the  cord  may  excite  direct  motions  of 
flexion,  in  preference  to  those  of  extension,  the  movements  of  extension  pro- 
duced by  stimulating  the  posterior  column  may  be  of  a  reflex  character. 

168.  There  is  no  reason  to  believe,  that  the  functions  of  the  Spinal  Cord 
are  essentially  different  along  its  whole  length.     Everywhere  it  appears  to 
consist  of  a  ganglionic  centre,  supplying  nerves  to  its  particular  segment ;  and 


NERVOUS  SYSTEM  OF  VERTEBRATA. 


127 


of  con.  ibres,  by  which  the  nerves  proceeding  from  anyone  division 

are  brought  into  relation  with  distant  portions  of  the  organ,  and  with  the  large 
ganglionic  masses  at  its  anterior  extremity.  In  this  respect,  then,  it  corre- 
sponds precisely  with  the  doable  nervous  cord  of  the  Articulata;  the  only 
prominent  difference  between  the  two  being,  that  in  the  former  the  ganglionic 
matter  is  continuous  from  one  extremity  of  the  organ  to  the  other,  whilst  in 
the  latter  it  is  interrupted  at  intervals ;  and  in  the  Mollusca,  the  centres  are 
still  further  separated  from  each  other.  The  connection  of  the  Spinal  Cord 
with  the  large  ganglia  contained  within  the  cavity  of  the  cranium,  is  effected 
by  means  of  processes  from  its  superior  extremity,  the  arrangement  of  which 
is  somewhat  complex.  This  portion  of  the  cord,  which  also  lies  within  the 
cavity  of  the  cranium,  has  been  termed  the  Medulla  Oblongaia.  It  has 


Fig.  20. 


Fig.  21. 


A  posterior  superior  view  of  the  Pons  Varolii,  the 
Cerebellum,  and  the  Medulla  Oblongata  and  Spinalis. 
1, 1,  the  crura  cerebri ;  2,  the  pens  varolii  or  tuber-aii- 
nularis;  3,  its  middle  fossa;  4,  an  oblique  band  of  me- 
dullary matter  seen  passing  from  its  side ;  5,  the  external 
surface  of  the  cms  cerebelli  in  its  natural  state  ;  G,  the 
same  portion  deprived  of  outer  layer;  7,  the  "nervous 
matter  which  united  it  to  4;  8,  the  trigeminus  or  fifth 
pair  of  nerves;  9,  portion  of  the  auditory  nerve — the 
white  neurine  is  seen  passing  from  the  oblique  band 
which  comes  from  the  corpus  .restiforme  to  the  trige- 
minus nerve  in  front,  and  the  auditory  nerve  behind  ; 
10,  11,  the  superior  portion  of  the  hemispheres  of  the 
cerebellum;  12,  lobulus  amygdaloides ;  13,  corpus  oli- 
vare;  14.  corpus  pyramidale  ;  15,  medulla  spinalis. 


A  posterior  view  of  the  Medulla  Ob- 
lonsrata,  as  split  open  vertically  on  the 
middle  line— At  the  bottom  of  the  fis- 
sure is  a  succession  of  fasciculi  which 
interlock  and  cross  from  right  to  left. 
The  cerebellum  has  also  been  cut  off 
from  its  crura  with  great  care,  so  as  to 
show  plainly  the  three  principal  ele- 
ments in  its  composition.  1.  the  thalami 
nervi  optici  slightly  separated;  2,  the 
corpora  geniculata;  3,  the  tubercula 
quadrigemina;  4,  the  pineal  gland  di- 
vided in  the  middle;  5,  the  aqueduct  of 
Sylvius  laid  open;  6,  the  fasciculated 
portion  of  the  crura  cerebelli;  7,  8,  9,  the 
internal,  middle  and  external  fasciculi 
of  the  crura  cerebelli ;  10,  rootoWne  au- 
ditory nerve ;  11,  corpus  restiforme  ;  12, 
posterior  portion  of  the  corpus  pyra- 
midale ;  13,  posterior  middle  fissure  of 
the  spinal  marrow;  14,  point  of  the  cala- 
mus scriptorius;  15.  15,  between  th«6e 
figures  is  seen  the  interlocking  of  the 
two  halves  of  the  me"dulla  oblongata. 


128 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  22. 


the  anterior  columns  of  the 
spinal  marrow ;  7,  the  lateral 
columns. 


been  supposed  to  be  the  peculiar  seat  of  vitality  ;  but 
the  only  real  foundation  of  this  idea  is,  that  it  is  the 
great  centre  of  the  Respiratory  actions,  on  the  con- 
tinuance of  which  all  the  other  functions  are  depend- 
ent. The  Brain  may  be  removed  from  above,  and 
nearly  the  whole  Spinal  Cord  from  below,  without  an 
immediate  check  being  put  upon  all  the  phenomena 
of  life.  In  this  Medulla  Oblongata,/owr  different  parts 
maybe  distinguished  on  each  side  ; — 1,  The  Anterior 
Pyramids,  or  Corpora  Pyramidalia  ;  2,  The  Olivary 
bodies,  or  Corpora  Olivaria  ;  3,  The  Restiform  bodies, 
or  Corpora  Restiformia,  otherwise  called  Processus 
a  Cerebello  ad  Medullam  Oblongatam;  4,  The  Pos- 
terior Pyramids,  or  Corpora  Pyramidalia  Posteriora. 
The  connections  of  these  with  the  Brain  above,  and 
with  the  Spinal  Cord  below,  will  be  now  traced.* 

An  anterior  view  of  the  Me-         169.  As  our   object,  however,  is  rather  Physiolo- 

duiia  Obiongata  and  of  the  ter-       -^  tjian  pure}y  Anatomical,  we  shall  commence  with 

a  description  of  the  motor  and  sensory  tracts,  which 

Mitischelh.— 1.  the  pons  va-  r  J       .         ' 

roiii;  2,  the  emminentia  oiiva-  may,  according  to  Sir  C.  Bell,t  be  very  distinctly  sepa- 
ria;  3,  the  corpus pyramkiaie ;  rated  in  the  Pons  Varolii.  The  Pons  has  been  correctly 
4,  the  corpus  restiforme ;  5,  the  designated  as  the  great  Commissure  of  the  Cerebel- 
decussation  of  Mitischeiii;  6,  jum?  enclosing  the  Crura  Cerebri ;  and  its  transverse 
fibres  not  only  surround  the  longitudinal  bands  which 
connect  the  Cerebrum  with  the  Spinal  Cord,  but  pass 
through  them,  so  as  in  some  degree  to  isolate  the  two 
lateral  halves  from  one  another,  and  to  form  a  complete  septum  between  the 
anterior  and  posterior  portions  of  each.  The  Motor  tract  is  brought  into  view, 
by  simply  raising  the  superficial  layer  of  the  Pons,  and  tracing  upwards  and 
downwards  the  longitudinal  fibres  which  then  present  themselves.  It  is  then 
found,  that  these  fibres  may  be  traced  upwards,  chiefly  into  the  Corpora  Striata, 
whence  they  radiate  to  the  Hemispheres ;  and  downwards,  chiefly  into  the  An- 
terior Pyramids.  From  this  tract  arise  all  the  Motor  nerves  usually  reckoned 
as  Cerebral ;  as  will  be  seen  in  the  accompanying  Figure. — The  Sensory 
tract  is  displayed,  by  opening  the  Medulla  Obiongata  on  its  posterior  aspect ; 
and  then  separating  and  turning  aside  the  Restiform  Columns,  so  as  to  bring 
into  view  the  Posterior  Pyramids  which  lie  on  the  outside  of  the  calamus 
scriptorius.  On  tracing  their  fibres  upwards,  it  is  found  that  they  form  a  part 
of  the  posterior  layer  of  the  Crura  Cerebri,  ultimately  passing  on  to  the  Thalami 
nervorum  opticorum,  whence  they  radiate  to  the  Hemispheres.  From  this 
tract,  no  motor  nerves  arise ;  but  on  tracing  it  downwards  into  the  Spinal 
Cord,  it  is  found  that  the  sensory  root  of  the  fifth  pair  terminates  in  it,  and 
that  the  posterior  roots  of  the  spinal  nerves  are  evidently  connected  with  its 

*  Great  diversities  will  b,e  found  in  the  accounts  given  of  these  connections  by  differ- 
ent authors ;  some  of  which  are  attributable  to  a  variation  in  the  use  of  terms,  which 
must  not  pass  unnoticed.  By  the  majority  of  Anatomists,  the  name  of  Corpora  Reslifor- 
mia  is  given  to  the  Cere.bellar  Columns;  and  this  designation,  therefore,  it  seems  advisa- 
ble to  retain.  Some,  however,  and  amongst  them  Dr.  J.  Reid,  in  his  late  very  excellent 
desertion  of  the  Anatomy  of  the  Medulla  Obiongata,  (Edinb.  Med.  &  Surg.  Journal, 
Jan.  1841,)  give  the  name  to  the  columns  that  pass  up  from  the  posterior  division  of  the 
spinal  cord  into  the  crus  cerebri, — which  are  here  called  (after  Sir  C.  Bell)  the  posterior 
pyramids;  and  apply  the  term  Posterior  Pyramids  to  the  Cerebellar  column.  The  truth 
is  that,  as  Sir  C.  Bell  has  justly  observed,  all  the  tracts  of  fibrous  matter  connecting  the 
Brain  with  the  Spinal  Cord  have  a  somewhat  pyramidal  form;  and  it  might  be  added 
that  all  have  something  of  a  restiform  or  cord-like  aspect. 

•j-  Philosophical  Transactions,  1835. 


NERVOUS  SYSTEM  OF  VERTEBRATA. 
Fig.  23. 


129 


Course  of  the  Motor  tract  after  Sir  C.  Bell.  A,  A,  fibres  of  the  hemispheres,  converging  to  form  the  ante- 
rior portion  of  the  cms  cerebri;  B,  the  same  tract  where  passing  the  eras  cerebri;  c,  the  right  pyramidal 
body,  a  little  above  the  point  of  decussation;  D,  the  remaining  part  of  thepons  varolii.  a  portion  having  been 
dissected  off  to  expose  B. — 1,  olfactory  nerve,  in  outline ;  2,  union  of  optic  nerves;  3,  3,  motor  oculi ;  4,  4, 
patheticus  ;  5,  5,  trigeminus ;  6,  6,  its  muscular  division ;  7,  7,  its  sensory  root ;  8,  origin  of  sensory  root  from 
the  posterior  part  of  the  medulla  oblongata ;  9,  abducens  oculi;  10,  auditory  nerve;  11,  facial  nerve;  12, 
eighth  pair;  13,  hypoglossal ;  14,  spinal  nerves;  1.5, spinal  accessory  of  right  side,  separated  from  par  vagum 
and  glosso-pharyngeal. 

continuation.  Also  forming  part  of  the  posterior  division  of  the  crus  cerebri, 
and  separated  from  the  anterior  by  the  transverse  septum,  is  a  layer  of  fibres 
which  ascends  from  the  Olivary  bodies,  some  of  which  terminate  in  the  Cor- 
pora Quadrigemina. 


130 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 
Fig.  24. 


Course  of  the  Sensory  tract  after  Sir  C.  Bell.  A,  pons  varolii ;  B.  B,  sensory  tract  separated ;  c,  union  and 
decussaiion  of  posterior  columns ;  D,  D,  posterior  roots  of  spinal  nerves ;  E,  sensory  roots  of  fifth  pair. 

170.  On  tracing  upwards  the  four  divisions  of  the  Medulla  Oblongata,  the 
following  are  found  to  be  their  chief  connections  with  the  brain.     The  fibres 
of  the  Anterior  Pyramids  for  the  most  part  enter  the  Crura  Cerebri,  passing 
through  the  Pons  Varolii,  and  traversing,  the  Optic  Thalami  (which,  it  must 
be  carefully  borne  in  mind  by  the  student,  have  no  real  connection  with  the 
Optic  Nerves  or  with  the  sense  of  sight) ;  after  which  they  diverge  and  be- 
come intermingled  with  gray  matter,  thus  forming  the  Corpora  Striata,  and 
finally  radiate  to  the  convolutions  of  the  Cerebrum.     The  fibres  of  the  Olivary 
body  also  pass  into  the  Pons  Varolii,  and  there  divide  into  twro  bands,  of  which 
one  proceeds  upwards  and  forwards  to  join  the  Crus  Cerebri,  whilst  the  other 
passes  upwards  and  backwards  into  the  Corpora  Gluadrigemina.     Of  the  true 
Restifdrm  bodies,  the  fibres  pass  entirely  into  the  Cerebellum.    Finally,  of  the 
Posterior  Pyramids,  the  fibres  pass  directly  onwards  through  the  Crura  Cerebri 
into  the  Thalami,  whence  they  radiate  to  the  convolutions. 

171.  The  downward  course  of  these  fibres  into  the  Spinal  Cord  now  re- 
mains to  be  traced;  and  their  arrangement  is  by  no  means  a  simple  one.    The 
anterior  Pyramids  decussate,  as  is  well  known,  at  their  lower  extremity ;  the 
principal  part  (but  not  the  whole)  of  the  fibres  on  each  side,  passing  over  to 
the  other.    The  decussating  fibres  pass  backwards  as  well  as  downwards,  and 
enter,  not  the  anterior  column  of  the  spinal  cord  (as  commonly  stated),  but 
the  middle  column.*     The  smaller  bundle  of  fibres,  which  do  not  decussate, 
passes  downwards,  along  with  those  of  the  olivary  bodies,  to  form  the  anterior 
column.     The  fibres  descending  from  the  Olivary  bodies  converge,  as  those  of 
the  pyramids  pass  backwards  from  between  them,  until  they  meet  on  the 
median  line,  forming  the  greater  part  of  the  anterior  column.     The  fibres  of 

*  See  Dr.  J.  Reid,  in  Edinb.  Med.  and  Surg.  Journal,  Jan.,  1841. 


NERVOUS  SYSTEM  OF  VERTEBRATA. 

Fig.  25.  Fig.  26. 


131 


A  lateral  view  of  the  Spinal  Marrow.  &c..  of 
a  new-born  infant,  to  show  the  lateral  fascicu- 
lus, which  is  then  more  apparent.  1,  crura 
cerebri ;  2,  3,  4,  one  of  the  hemispheres  of  the 
cerebellum;  5,  external  fasciculus  of  the  crus 
cerebelli;  6,  lobulus  amygdaloicles  and  nervi 
pneumogastrici :  7,  point  where  the  lateral 
column  of  the  spinal  marrow  enters  the  cere- 
bellum; 8,  pons  varolii;  9,  10, 11,  continuation 
of  7,  or  of  the  lateral  fasciculus  all  the  way 
down  the  spinal  marrow — in  the  new-born  in- 
fant it  is  very  nearly  white,  whilst  the  matter 
around  is  of  a  light  gray ;  12.  emminentia  oli- 
varia;  13.  corpora  pyramidal: a;  14.  corpus  res- 
ti  forme. 


A  posterior  view  of  the  medulla  spinalis.  with  tin- 
fasciculi  of  the  corpora  restiformia  cut  off  from  each 
side  of  the  calamus  scriptorius.  From  the  top  of  this 
section  as  far  as  the  lumbar  portion  of  the  medulla  spin- 
alis these  posterior  fasciculi  have  been  dissected  out 
down  to  the  axis  of  the  medulla.  1,  the  pineal  gland ; 
2,  the  tubercula  quadrigemina:  3,  origin  of  the  4th  pair 
of  nerves ;  4,  the  valve  of  the  vieussens  turned  up  a 
little;  5.  posterior  portion  of  the  crus  cerebri ;  6.  section 
of  the  crus  cerebelli;  7,  anterior  portion  of  the  crus 
cerebri;  8,  section  of  the  corpus  restiforme  on  one  side  ; 
9,  the  corpus  restiforme  untouched  on  the  other  side  ;  10. 
a  prominent  lateral  fasciculus  on  the  floor  of  the  calamus 
scriptorius;  11.  point  of  the  calamus— from  its  point  to 
the  end  of  the  medulla  spinalis  are  seen  the  junctions 
of  the  fasciculi  of  each  side,  which  make  the  axis  of  the 
medulla  spinalis ;  12,  the  lateral  fasciculus ;  13,  the  en- 
largement for  the  axillary  nerves;  14, 
for  the  lumbar  nerves. 


132  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  Posterior  Pyramids  are  stated  by  Sir  C.  Bell  to  decussate^  like  those  of  the 
anterior ;  they  pass  down  chiefly  into  the  posterior  part  of  the  middle  column, 
forming  part  also  of  the  posterior.  The  fibres  of  the  Restiform,  or  Cerebellar 
columns,  which,  like  those  of  the  Olivary  columns,  do  not  decussate,  mostly 
pass  downwards  into  the  posterior  columns  ;  but  a  band,  (which  has  been 
termed,  from  its  curved  aspect,  the  arciform  layer)  passes  forwards  into  the 
anterior  columns. 

172.  The  following  tabular  view  may  assist,  better  than  any  delineations 
could  do,  in  the  comprehension  of  this  very  intricate  piece  of  Anatomy  ;  the 
knowledge  of  which  can  be  already  applied  to  the  explanation  o/  many  curious 
pathological  phenomena,  and  cannot  but  assist  in.  the  elucidation  of  others 
whose  rationale  is  as  yet  obscure. 

SPIXAL  CORD.  MEDULLA  OBLOXGATA.  BIIAIX. 

I  Arciform  fibres  of  Cerebellar  Columns       ?  Cerebellum 

Anterior  Column    <  Olivary  Columns        -        ...        5  Corpora  Quadrigemina 
f  Non-decussating  portion  of  Ant.  Pyramids  7  p, 
>  Decussating  portion  of  Ant.  Pyramids         J  CorPora  Stnata 


Middle  Column 


Post.  Pyramidal  Columns  (decussating)     t 

5-> 


S  Portion    of  Post.  Pyramids   (non-decus-  >  Thalami  Optici 
sating?)  ) 

Restiform  Columns  Cerebellum 


VIII.     Functions  of  the  Spinal  Cord. 

173.  The  functions  of  the  Nervous  System  in  Vertebrated  Animals  are  so 
complex  in  their  nature,  and  our  means  of  analyzing  them  are  so  imperfect, 
that  the  inquiry  is  confessedly  one  of  the  greatest  difficulty,  and  needs  all  the 
light  which  can  be  thrown  upon  it  from  any  source.  The  great  accession  to 
our  knowledge  of  them,  which  has  been  made  within  the  last  few  years, 
chiefly  by  the  labours  of  Sir  C.  Bell  and  Dr.  M.  Hall,  has  so  far  changed  the 
aspect  of  this  department  of  Physiological  Science,  as  to  render  it  necessary 
for  those  who  had  previously  studied  it,  to  begin  de  novo.  This  is  especially 
the  case  in  regard  to  the  actions  dependent  on  the  Spinal  Cord  ;  which  it 
seems  desirable  to  consider  in  the  first  instance,  in  order  that  it  may  be  clearly 
defined  what  the  Brain  does  not  do.  By  many,  even  in  recent  times,  the 
Spinal  Cord  has  been  considered  as  a  mere  appendage  to  the  Brain ;  but  the 
phenomena  of  its  independent  action  render  such  an  idea  quite  inadmissible. 
These  phenomena  have  been  especially  pointed  out  by  Dr.  M.  Hall;  and  it 
is  mainly  owing  to  his  arguments,  that  Physiologists  are  now  for  the  most 
part  agreed  in  the  general  fact, — that  the  Spinal  Cord  constitutes  a  distinct 
centre,  or  rather  a  collection  of  centres,  of  nervous  influence,  and  that  its  ope- 
rations are  carried  on  through  the  nervous  trunks  with  which  it  is  connected. 
It  is  further  generally  admitted  that  its  functions  are  independent  of  the  will ; 
and  that  they  are  in  effect  frequently  opposed  to  those  of  the  brain,  which 
operates  on  the  muscles  either  by  a  volitional  or  by  an  emotional  impulse. 
And,  lastly,  its  actions  are-always  (except  when  excited  by  a  physical  irrita- 
tion directly  applied  to  itself)  entirely  of  a  reflex  character:  that  is  to  say, 
the  motor  impulses  which  originate  in  it  are  not  spontaneous,  but  result  from 
the  stimulus  of  impressions,  conveyed  to  it  by  the  afferent  trunks,  and  ope- 
rating upon  it,  to  use  the  expression  of  Prochaska,  according  to  certain  "pecu- 
liar laws  written,  as  it  were,  by  nature  on  its  medullary  pulp."  It  is  not, 
however,  universally  admitted  that  these  actions  are  independent  of  sensation; 
and  some  eminent  physiologists,  among  whom  may  be  named  Dr.  Alison,  still 
hold  that  the  intervention  of  sensation  is  necessary, — in  the  case  at  least,  of 
the  ordinary  associated  movements,  which  have  definite  ends  in  view,  and 


FUNCTIONS  OF  THE  SPINAL  CORD.  133 

folloAv  one  another  in  regular  succession,  as  those  of  Respiration, — for  an  im- 
pression to  give  rise  to  that  organic  change  in  the  Spinal  Cord  which  shall 
terminate  in  a  muscular  motion.*  It  will  be  desirable,  therefore,  to  consider 
the  evidence  upon  which  the  statement  rests,  that  reflex  actions  are  independ- 
ent of  sensation,  though  ordinarily  accompanied  by  it. 

174.  In  the  first  place,  then,  it  has  long  been  well  known  that,  in  the  Hu- 
man Jbeing,  the  Spinal  Cord  does  not  by  itself  possess,  in  the  remotest  degree, 
the  power  of  communicating  sensory  impressions  to  the  mind ;  since,  when 
its  lower  portion  has  been  severed  from  the  brain  by  injury  or  disease,  there 
is  complete  anaesthesia  of  all  the  parts  of  the  body  which  derive  their  nerves 
exclusively  from  it.     Hence^it  might  be  inferred,  that,  throughout  the  Verte- 
brated  classes,  the  spinal  cord  is  equally  destitute  of  sensibility;  and  that  any 
movements  produced  by  stimuli  acting  through  it,  are  the  results  of  a  physical, 
and  not  of  a  sensorial  change.     This  inference,  however,  has  been  disputed ; 
and,  if  unsupported  by  other  evidence,  it  would  not,  perhaps,  be  entitled  to 
rank  as  an  ascertained  truth.     The  very  performance,  by  decapitated  animals 
of  inferior  tribes,  of  actions  which  had  not  been  witnessed  in  Man  under  similar 
circumstances,  has  been  held  to  indicate,  that  the  spinal  cord  in  them  has  an 
endowment  which  his  does  not  possess.     The  possibility  of  such  an  explana- 
tion— however  unconformable  to  that  analogy  throughout  organized  nature, 
which,  the  more  it  is  studied,  the  more  invariably  is  found  to  guide  to  truth — 
could  not  be  disproved.     Whatever  •experiments  on  decapitated  animals  were 
appealed  to,  in  support  of  the  doctrine  that  the  brain  is  the  only  seat  of  sensi- 
bility, could  be  met  by  a  simple  denial  that  the  spinal  cord  is  everywhere  as 
destitute  of  that  endowment  as  it  appears  to  be  in  Man.     The  cases  of  pro- 
found sleep  and  apoplexy  might  be  cited,  as  examples  of  reflex  action  without 
consciousness ;  and  these  might  be  met  by  the  assertion,  that  in  such  condi- 
tions sensations  are /<?//,  though  they  are  not  remembered.    It  is  difficult,  how- 
ever, to  apply  such  an  explanation  to  the  case  of  anencephalous  human  infants 
(in  which  all  the  ordinary  reflex  actions  have  been  exhibited,  with  an  entire 
absence  of  brain),  without  supposing  that  the  Medulla  Oblongata  is  the  seat  of 
a  sensibility,  which  we  know  that  the  lower  part  of  the  Spinal  Cord  does  not 
possess  ;  and  of  this  there  is  no  evidence  whatever. 

175.  Experiments  on  the  lower  animals,  then,  and  observation  of  the  phe- 
nomena manifested  by  apoplectic  patients  and  anencephalous  infants,  might 
lead  to  the  conclusion,  that  the  Spinal  Cord  does  not  possess  sensibility,  and 
that  its  reflex  actions  are  independent  of  sensation.     At  this  conclusion,  Pro- 
chaska,  Sir  G.  Blane,  Flourens,  and  other  physiologists,  had  arrived.;  but  it 
was  not  until  special  attention  was  directed  to  the  subject  by  Dr.  M.  Hall,  that 
facts  were  obtained,  by  which  a  positive  statement  of  it  could  be  supported. 
For  the  question  might  have  been  continually  asked — If  the  spinal  cord  in  Man 
is  precisely  analogous  in  function  to  that  of  the  lower  Vertebrata,  why  are  not 
its  reflex  phenomena  manifested,  when  a  portion  of  it  is  severed  from  the  rest 
by  disease  or  injury?     The  answer  to  this  question  is  twofold.     In  the  first 
place,  simple  division  of  the  cord  with  a  sharp  instrument  leaves  the  separated 
portion  in  a  state  of  much  more  complete  integrity,  and  therefore  in  a  state 
much  more  fit  for  the  performance  of  its  peculiar  functions,  than  it  ordinarily 
is  after  disease  or  violent  injury ;  and  as  the  former  method  of  division  is  one, 
with  which  the  Physiologist  is  not  likely  to  meet  in  Man  as  a  result  of  acci- 
dent, and  which  he  cannot  experimentally  put  in  practice,  the  cases  in  which 
reflex  actions  are  manifested,  are  likely  to  be  comparatively  few.    But,  secondly, 

*  See  Outlines  of  Physiology,  3d  edit.,  p.  211.  By  many  of  the  German  Physiologists, 
also,  it  is  maintained  that  Sensation  is  a  necessary  link  in  the  chain  of  reflex  actions; 
but  as  they  employ  the  term  sensation  in  a  sense  which  does  not  involve  consciousness,  it 
is  obvious  that  their  dissent  from  Dr.  Hall's  views  is  chiefly  verbal. 


134  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

a  number  of  such  instances  have  now  been  accumulated,  sufficient  to  prove  that 
the  occurrence  is  by  no  means  so  rare  as  might  have  been  supposed  ;  and  that 
nothing  is  required  but  patient-  observation,  to  throw  great  light  on  this  inte- 
resting question,  from  the  phenomena  of  disease.  A  most  valuable,  collection 
of  such  cases,  occurring  within  his  own  experience,  has  been  published  by 
Dr.  W.  Budd;*  and  the  leading  facts  observed  by  him  \vill  be  now  enumerated. 

176.  In  the  first  case,  paraplegia  was  the  result  of  angular  distortion  of  the 
spine  in  the  dorsal  region.     The  sensibility  of  the  lower  extremities  was  ex- 
tremely feeble,  and  the  power  of  voluntary  motion  was  almost  entirely  lost. 
"  When,  however,  any  part  of  skin  is  pinched  or  pricked,  the  limb  that  is  thus 
acted  on  jumps  with  great  vivacity ;  the  toes  are  retracted  towards  the  instep, 
the  foot  is  raised  on  the  heel,  and  the  knee  so  flexed  as  to  raise  it  off  the  bed ; 
the  limb  is  maintained  in  this  state  of  tension  for  several  seconds  after  the  with- 
drawal of  the  stimulus,  and  then  becomes  suddenly  relaxed."     "In  general, 
while  one  leg  was  convulsed,  its  fellow  remained  quiet,  unless  stimulus  was 
applied  to  both  at  once."     "In  these  instances,  the  pricking  and  pinching 
was  perceived  by  the  patient ;  but  much  more  violent  contractions  are  excited 
by  a  stimulus,  of  whose  presence  he  is  unconscious.    When  a  feather  is  passed 
lightly  over  the  skin,  in  the  hollow  of  the  instep,  as  if  to  tickle,  convulsions 
occur  in  the  corresponding  limb,  much  more  vigorous  than  those  induced  by 
pinching  or  pricking ;  they  succeed  one  another  in  a  rapid  series  of  jerks, 
which  are  repeated  as  long  as  the  stimulus  is  maintained."     "When  any' 
other  part  of  the  limb  is  irritated  in  the  same  way,  the  convulsions  which 
ensue  are  very  feeble,  and  much  less  powerful  than  those  induced  by  pricking 
or  pinching."     "  Convulsions,  identical  with  those  already  described,  are  at 
all  times  excited  by  the  acts  of  defecation  and  micturition.     At  these  times, 
the  convulsions  are  much  more  vigorous  than  under  any  other  circumstances, 
insomuch  that  the  patient  has  been  obliged  to  resort  to  mechanical  means  to 
secure  his  person  while  engaged  in  these  acts.     During  the  act  of  expulsion, 
the  convulsions  succeed  one  another  rapidly,  the  urine  is  discharged  in  inter- 
rupted jets,  and  the  passage  of  the  fasces  suffers  a  like  interruption."     The 
convulsions  are  more  vigorous,  the  greater  the  accumulation  of  urine ;  and 
involuntary  contractions  occur  whenever  the  bladder  is  distended,  and  also 
when  the  desire  to  relieve  the  rectum  is  manifested.     "In  all  these  circum- 
stances, the  convulsions  are  perfectly  involuntary ;  and  he  is  unable  by  any 
effort  of  the  will,  to  control  or  moderate  them.     The  patient  subsequently 
regained,  in  a  gradual  manner,  both  the  sensibility  of  the  lower  extremities, 
and  voluntary  power  over  them;  and  as  voluntary  power  increased,  the  sus- 
ceptibility to  involuntary  movements,  and  the  extent  and  power  of  these,  dimi- 
nished. 

177.  This  case,  then,  exhibits  an   increased  tendency  to  perform  reflex 
actions,  when  the  control  of  the  brain  was  removed ;  and  it  also  shows  that  a 
slight  impression  upon  the  surface,  of  which  the  patient  was  not  conscious, 
was  more  efficacious  in  exciting  reflex  movements  than  were  others  that  more 
powerfully  affected  the  sensory  organs.     This  is  constantly  observed  in  expe- 
riments upon  the  lower  animals ;  and  it  harmonizes,  also,  with  the  important 
fact,  that  when  the  trunk  of  an  afferent  nerve  is  pinched,  pricked,  or  other- 
wise irritated,  the  reflex  function  will  not  be  nearly  so  strongly  excited  as 
when  a  gentler  impression  is  made  on  a  surface  supplied  by  the' branches  of 
this  nerve.     The  former  produces  pain,  whilst  the  latter  does  not ;  the  amount 
of  sensation,  therefore,  does  not  at  all  correspond  with  the  intensity  of  reflex 
Action,  but  rather  bears  a  converse  relation  to  it.     Mr.  Grainger  found,  that  he 
could  remove  the  entire  hind  leg  of  a  Salamander  with  the  scissors,  without 

*  Medico-Chirurgical  Transactions,  vol.  xxii. 


FUNCTIONS  OF  THE  SPINAL  CORD.  135 

the  creature  moving,  or  giving  any  expression  of  suffering,  if  the  spinal  cord 
had  been  divided ;  yet  that,  by  irritation  of  the  foot,  especially  by  heat,  in  an 
animal  similarly  circumstanced,  violent  convulsive  actions  in  the  leg  and  tail 
were  excited. — It  should  be  added  that,  in  the  foregoing  case,  the  nutrition  of 
the  lower  extremities  was  not  impaired,  as  in  most  cases  of  paraplegia.  The 
rationale  of  this  phenomenon,  which  is  to  be  constantly  observed  when  the 
reflex  actions  of  the  part  remain  entire,  will  be  hereafter  noticed  (§  381). 

178.  In  another  case,  the  paralysis  was  more  extensive,  having  been  pro- 
duced by  an  injury  (resulting  from  a  fall  into  the  hold  of  a  vessel)  at  the  lower 
part  of  the  neck.  There  was  at  first  total  loss  of  voluntary  power  over  the 
lower  extremities,  trunk  and  hands ;  slight  remaining  voluntary  power  in  the 
wrists,  rather  more  in  the  elbows,  and  still  more  in  the  shoulders.  The  inter- 
costal muscles  did  not  participate  in  the  movements  of  respiration.  The  sen- 
sibility of  the  hands  and  feet  was  greatly  impaired.  There  were  retention  of 
urine,  and  involuntary  evacuation  of  the  faeces.  Recovery  took  place  very 
gradually;  and  during  its  progress,  several  remarkable  phenomena  of  reflex 
action  were  observed.  At  first,  tickling  one  sole  excited  to  movement  that  limb 
only  which  was  acted  upon;  afterwards,  tickling  either  sole  excited  both  legs, 
and,  on  the  26th  day,  not  only  the  lower  extremities,  but  the  trunk  and  upper 
extremities  also.  Irritating  the  soles,  by  tickling  or  otherwise,  was  at  first  the 
only  method,  and  always  the  most  efficient  one,  by  which  convulsions  could  be 
excited.  From  the  26th  to  the  69th  day,  involuntary  movements  in  all  the 
palsied  parts  continued  powerful  and  extensive,  and  were  excited  by  the  fol- 
lowing causes : — In  the  lower  extremities  only,  by  the  passage  of  flatus  from 
the  bowels,  or  by  the  contact  of  a  cold  urinal  with  the  penis ;  convulsions  in 
the  upper  extremities  and  trunk,  attended  with  sighing,  by  plucking  the  hair 
of  the  pubes.  On  the  41st  day,  a  hot  plate  of  metal  was  applied  to  the  soles, 
and  found  a  more  powerful  exciter  of  movement  than  any  before  tried.  The 
movements  continued  as  long  as  the  hot  plate  was  kept  applied.;  but  the  same 
plate,  at  the  common  temperature,  excited  no  movements  after  the  first  contact. 
The  contact  was  distinctly  felt  by  the  patitent ;  but  no  sensation  of  heat  was 
perceived  by  him,  although  the  plate  was  applied  hot  enough  to  cause  vesica- 
tion.  At  three  different  intervals,  the  patient  took  one-eighth  of  a  grain  of 
strychnia  three  times  a  day.  Great  increase  of  susceptibility  to  involuntary 
movements  immediately  followed,  and  they  were  excited  by  the  slightest 
causes.  No  convulsions  of  the  upper  extremities  could  ever  be  produced, 
however,  by  irritating  their  integument ;  though,  under  the  influence  of 
strychnia,  pulling  the  hair  of  the  head,  or  tickling  the  chin,  would  occasion 
violent  spasmodic  actions  in  them.  Spontaneous  convulsions  of  the  palsied 
parts,  which  occurred  at  other  times,  were  more  frequent  and  more  powerful 
after  the  use  of  strychnia.  On  the  first  return  of  voluntary  power,  the  patient 
was  enabled  to  restrain,  in  some  measure,  the  excited  movements;  but  this  re- 
quired a  distinct  effort  of  the  will;  and  the  first  attempts  to  walk  were  curiously 
affected,  by  the  persistence  of  the  susceptibility  to  excited  involuntary  move- 
ments. When  he  first  attempted  to  stand,  the  knees  immediately  became 
forcibly  bent  under  him,  this  action  of  the  legs  being  excited  by  contact  of  the 
soles  with  the  ground.  On  the  95th  day  this  effect  did  not  take  place,  until 
the  patient  had  made  a  few  steps;  the  legs  then  had  a  tendency  to  bend  up,  a 
movement  which  he  counteracted  by  rubbing  the  surface  of  the  belly:  this 
rubbing  excited  the  extensors  to  action,  and  the  legs  became  extended  with  a 
jerk.  A  few  more  steps  were  then  made;  the  manoeuvre  repeated,  and  so  on. 
This  susceptibility  to  involuntary  movements  from  impressions  on  .the  soles, 
gradually  diminished;  and  on  the  141st  day,  the  patient  was  able  to  walk 
about,  supporting  himself  on  the  back  of  a  chair  which  he  pushed  before  him ; 
but  his  gait  was  unsteady,  and  niuch  resembled  that  of  chorea.  Sensation  im- 


136  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

proved  very  slowly :  it  was  on  the  53d  day  that  he  first  slightly  perceived  the 
heat  of  the  metal  plate. 

179.  This  important  case  suggests  many  interesting  reflections.  Common 
sensation  was  not  so  completely  abolished  as  in  the  former  instance ;  but  of 
the  peculiar  kind  of  impression,  which  was  found  most  efficacious  in  exciting 
reflex  movements,  no  consciousness  whatever  was  experienced.  Not  less 
interesting  was  the  circumstance,  that  convulsions  could  be  readily  excited  by 
impressions  on  surfaces  above  the  seat  of  injury ;  as,  by  pulling  the  hair  of 
the  scalp,  a  sudden  noise,  and  so  on.  This  proves  two  important  points :  first, 
that  a  lesion  of  the  cord  may  be  such  as  to  intercept  the  transmission  of  volun- 
tary influence,  and  yet  may  allow  the  transmission  of  that  reflected  from  inci- 
dent nerves.  Secondly,  that  all  influences  from  impressions  on  incident 
nerves  are  diffused  through  the  cord ;  for,  in  the  instance  adduced,  the  reflect- 
ed influence  was  undoubtedly  not  made  to  deviate  into  the  cord  by  the  morbid 
condition  of  that  organ,  but  followed  its  natural  course  of  diffusion,  being  ren- 
dered manifest  in  this  case  by  the  convulsions  which  were  excited,  in  conse- 
quence of  increased  activity  of  the  motor  function  of  the  cord.  It  is  further 
interesting  to  remark,  that  in  the  foregoing  case,  the  reflex  actions  were  very 
feeble  during  the  first  seven  days,  in  comparison  with  their  subsequent  en- 
ergy, being  limited  to  slight  movements  of  the  feet,  which  could  not  always 
be  excited  by  tickling  the  soles.  In  another  case  of  very  similar  character,  it 
was  three  days  after  the  accident,  before  any  reflex  actions  could  be  produced. 
It  is  evident,  then,  that  the  spinal  cord  must  have  been  in  a  state  of  concus- 
sion, which  prevented  the  manifestation  of  its  peculiar  functions,  so  long  as  this 
effect  lasted ;  and  it  is  easy,  therefore,  to  perceive  that  a  still  more  severe 
shock  might  permanently  destroy  its  power,  so  as  to  prevent  the  exhibition  of 
any  of  the  phenomena  of  reflex  action. 

180.  It  seems  well  established,  then,  by  such  cases,  that  the  Spinal  Cord, 
or  small  segments  of  it,  may  serve  in  Man  as  the  centre  of  very  energetic 
reflex  actions,  when  the  voluntary  power  exercised  through  the  Brain,  over 
the  muscular  system,  is  suspended^  or  destroyed.  And  it  is  further  evident, 
that  these  movements  are  produced  by  a  mere  physical  change  in  the  nervous 
centres;  the  consciousness  of  the  individual  not  being  affected  in  their  per- 
formance, and  sensation  having,  therefore,  no  necessary  participation  in  them. 
As  the  movements  witnessed  in  the  lower  animals,  under  the  same  circum- 
stances, are  altogether  of  a  similar  character,  there  seems  no  good  reason  to 
attribute  to  their  Spinal  Cord  an  attribute,  of  which  it  is  certainly  destitute  in 
Man.  There  is  no  essential  difference,  either  in  structure,  or  in  the  nature 
of  the  actions  performed  by  them,  between  the  Spinal  Cord  and  the  Medulla 
Oblongata,  which  can  warrant  us  in  assigning  to  the  latter  a  function  that  the 
former  does  not  possess  :  and  if  the  reflexions  of  the  Spinal  Cord  do  not  involve 
sensation,  there  is  good  reason  for  concluding,  that  this  change  is  not  a  neces- 
sary element  in  those  of  the  Medulla  Oblongata.  It  is  perfectly  true,  that  it 
usually  accompanies  in  us  the  greater  number  of  actions,  to  which  that  division 
of  the  centre  is  subservient ;  for  example,  those  of  respiration  and  degluti- 
tion :  and  it  is  scarcely  possible  for  such  an  accident  to  occur  in  the  Human 
being,  as  the  separation  of  the  Medulla  Oblongata  from  the  brain,  without  the 
destruction  of  the  independent  functions  of  both.  It  is  not  likely  that  we  can 
ever  have  the  power  of  ascertaining,  by  the  testimony  of  a  patient  so  affected, 
that  the  respiratory  movements  are  performed  without  the  necessary  interven- 
tion of  sensation;  as  we  have  been  able  to  do  in  regard  to  other  reflex  move- 
ments. But  as  the  general  fact  is,  that  there  is  no  positive  ground  whatever 
for  regarding  any  part  of  the  spinal  cord  as  a  sensorlum  independent  of  the 
brain,  and  that  the  respiratory  movements  certainly  correspond  in  all  their 
conditions  with  the  actions  denominated  reflex,—there  would  seem  no  good 


FUNCTIONS  OF  THE  SPINAL  CORD.  137 

reason  for  maintaining  that  sensation  is  an  element  in  their  production,  whilst 
it  is  admitted  to  be  not  essential  in  the  case  of  the  less  regular  convulsive 
actions  already  described.  The  character  of  adaptiveness  to  a  designed  end, 
in  regard  to  their  combination  and  succession,  which  the  movements  of  respira- 
tion and  deglutition  exhibit,  is  clearly  no  proof  of  their  dependence  on  sensa- 
tion ;  since  an  equally  perfect  adaptiveness  is  witnessed  in  the  actions  of 
the  heart,  alimentary  canal,  &c.,  which  are  still  further  removed  from  the 
control  of  the  will.  And,  further,  it  does  not  appear  by  any  means  evident, 
what  end  or  purpose  could  be  answered  by  the  production  of  sensation,  as  a 
part  of  the  chain  of  phenomena  of  reflex  action.  The  question  is,  are  these 
movements  guided  in  any  way  by  the  mind  ;  or  do  they  necessarily  result 
from  certain  physical  conditions  of  the  nervous  system  ?  If  their  adaptive- 
ness  is  the  result  of  mental  guidance,  then  not  only  sensation,  but  an  operation 
either  of  instinct  or  of  intelligent  will  must  necessarily  be  involved ;  since  it 
is  impossible  that  sensation  can  guide  to  the  choice  of  one  out  of  many  modes  of 
action,  without  the  exercise  of  these  faculties.  On  the  other  hand,  if  it  be 
said  that  certain  movements  are  from  t'he  first  necessarily  associated  with  cer- 
tain sensations,  it  is  difficult  to  see  why  they  should  not  be  equally  associated 
with  the  impressions  by  which  the  sensations  are  produced.  Sensation  is  a 
psychical  phenomenon.  It  is  the  communication  to  the  mind,  of  a  certain 
organic  change  in  the  nervous  system.  It  is  the  first  step  in  the  train  of 
purely  mental  operations;  and  these  terminate  in  the  formation  of  an  instinc- 
tive or  volitional  impulse,  which  reacts  on  the  body.  But  we  have  no  reason 
to  believe  that  sensation  can  itself  react  on  the  body ;  or  that,  if  it  could,  it 
would  be  a  better  guide  than  the  impression  which  produced  it.  Thus — 

Impression  a  produces 

Sensation  A,  with  which  is  associated 

Motion  a ; 
and  in  like  manner, 

Impression  b  produces 

Sensation  B,  with  which  is  associated 

Motion  )3. 

There  seems  no  valid  reason,  then,  to  assert  that  a  motign  may  not  have  an 
equally  close  connection  with  the  impression,  as  it  is  asserted  to  have  with 
the  sensation  resulting  from  it. 

181.  The  question  has  been  often  put  to  those  who  advocate  this  view — 
why  the  sensation  should  be  so  constantly  associated  with  these  changes,  if 
not  essential  to  produce  the  motion?  An  objection  might  fairly  be  made  to 
any  reasoning  from  final  causes,  in  a  question  of  facts ;  but  the  inquiry  may 
be  easily  answered.  In  many  instances  the  production  of  sensations  is  the 
stimulus  necessary  for  the  excitement  of  other  actions,  which  are  required  for 
the  continued  maintenance  of  those  in  question.  This  may  be  rendered  more 
comprehensible  by  a  simple  illustration.  A  cistern  filled  with  water  may  be 
speedily  emptied  by  a  cock  occasionally  opened  at  the  bottom  ;  but,  if  it  com- 
municate with  a  reservoir,  by  means  of  a  valve  opened  by  a  ball  floating  on 
the  surface  of  the  water  it  contains,  it  may  be  kept  constantly  full.  The  lower 
cock  is  opened,  and  the  water  flows  out ;  and,  in  consequence  of  the  lowering 
of  the  surface  thus  produced,  the  floating  valve  above  is  opened,  and  the  cistern 
is  refilled  from  the  reservoir.  Now  here  the  action  of  the  ball-cock  at  the  top  is 
not  essential  to  the  flow  of  water  at  the  bottom,  but  is  rather  consecutive  upon 
it.  Just  so  it  is  with  regard  to  those  movements  of  Animals,  which  are  con- 
cerned in  the  ingestion  of  their  food.  The  muscular  contractions  required  to 
propel  it  along  the  alimentary  canal,  from  the  stomach  downwards,  are  pro- 
vided for,  without  even  the  intervention  of  the  nervous  system.  To  bring  it 

12* 


138  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

within  reach  of  these,  a  muscular  apparatus  is  provided,  by  which  any  thing 
that  comes  within  its  grasp  is  conveyed  downwards,  through  a  reflex  opera- 
tion, originating  in  the  impression  made  upon  the  surface  of  the  pharynx. 
Now  this  action,  in  the  ordinary  condition,  may  be  considered  as  attended  with 
sensation,  in  order  that  the  Animal  may  be  called  upon  to  execute  those  other 
movements  which  will  bring  food  within  the  reach  of  the  apparatus  of  deglu- 
tition. The  Polype  is  dependent  for  its  supplies  of  aliment  upon  what  the 
currents  in  the  surrounding  fluid,  or  other  chances,  bring  into  its  neighbour- 
hood ;  but  any  thing  which  touches  its  tentacula  is  entrapped  and  conveyed 
into  its  stomach.  The  anencephalous  Infant,  again,  can  swallow,  and  even 
suck ;  but  it  can  execute  no  other  movements  adapted  to  obtain  the  supply  of 
food  continually  necessary  for  maintenance,  because  it  has  not  a  mind  which 
sensations  could  awake  into  activity. 

182.  The  sensation  connected  with  reflex  actions  has  not  only  this  important 
end,  but  it  frequently  contributes  to  enjoyment,  as  in  suction  and  ejaculatio 
seminis.     Now  there  is  evidence  that  the  latter  of  these  processes,  involving 
though  it  does  the  combined  action  of  a  number  of  muscles,  and  dependent  as 
it  seems  upon  sensation  of  a  very  peculiar  kind,  may  take  place  without  con- 
sciousness on  the  part  of  the  individual.    Brachet  mentions  a  case  of  this  kind 
in  the  Human  subject,  in  which  the  patient's  own  testimony  could  be  adduced ; 
and  he  ascertained  that  emission  could  be  produced  in  dogs,  in  which  the 
spinal  cord  had  been  divided  in  the  back,  and  in  which,  therefore,  it  can 
scarcely  be  doubted  that  the  sensibility  of  the  genital  organs  was  destroyed. 
Such  cases,  it  might  be  thought,  are  sufficient  to  prove  that  the  Reflex  power, 
operating  independently  of  sensation,  is  not  confined  to  such  irregular  con- 
vulsive movements  as  are  seen  in  Man  after  disease  or  injury ;  but  is  exer- 
cised in  producing  the  regular  combined  actions  which  are  necessary  for  the 
maintenance  of  the  organic  functions.     The  sensation  accompanying  these 
actions,  moreover,  frequently  affords  premonition  of  danger,  or  gives  excite- 
ment to  supplementary  actions  destined  to  remove  it,  as  in  the  case  of  respira- 
tion ;  for  where  any  thing  interferes  with  the  due  discharge  of  the  function, 
the  uneasy  sensation  that  ensues  occasions  unwonted  movements,  which  are 
more  or  less  adapted  to  remove  the  impediment,  in  proportion  as  they  are 
guided  by  judgment  as  well  as  by  consciousness.     Again,  sensation  often 
gives  warning  against  inconvenience,  as  in  the  excretory  functions ;  and  here 
it  is  very  evident,  that  its  object  is  not  only  (if  it  be  at  all)  to  excite  the  asso- 
ciated muscles  necessary  for  the  excretion,  but  actually  to  make  the  will  set 
up  the  antagonizing  action  of  the  sphincters,  as  will  be  hereafter  explained 
(§  202).     There  is  one  unequivocal  case,  in  the  ordinary  condition  of  the 
human  body,  of  reflex  action  without  sensation ;  this  is  the  muscular  contrac- 
tion, by  which  the  food  is  propelled  from  the  bottom  of  the  pharynx  to  the 
stomach.     Unless  the  morsel  be  very  bulky,  so  as  to  press  on  the  surrounding 
parts,  or  be  very  different  in  temperature  from  the  surface  it  touches,  or  have 
any  peculiar  irritating  quality,  we  are  not  more  conscious  of  its  presence, 
whilst  it  is  passing  down  the  lower  part  of  the  ossophagus,  than  when  it  is 
being  propelled  along  the  intestinal  tube ;   and  yet,  as  Dr.  J.  Reid's  experi- 
ments* have  shown,  this  contraction  is  of  a  reflex  character,  not  being  stimu- 
lated by  direct  contact,  but  requiring  the  completeness  of  the  nervous  circle 
for  its  performance. 

183.  We  shall  now  separately  consider  the  chief  operations,  in  which  the 
Spinal  Cord  and  its  system  of  nerves  are  usually  concerned,  in  the  ordinary 
course  of  the  vital  actions  of  the  Human  body.    Upon  taking  a  general  survey 
of  these,  it  will  be  found  that  their  ordinary  function  is,  to  supply  the  condi- 

*  Edinb.  Med.  and  Surg.  Journ,  vol.  xlix. 


RESPIRATORY  MOVEMENTS.  139 

tions  requisite  for  the  maintenance  of  the  various  Organic  processes.  Thus, 
the  aeration  of  the  blood,  which  takes  place  whenever  that  fluid  is  pieced  in 
relation  with  the  atmosphere,  can  only  be  carried  on,  by  the  regular  exchange 
of  the  small  quantity  of  the  gas  contained  in  the  lungs ;  if  this  cease,  the  cir- 
culation is  soon  brought  to  a  stand,  and  loss  of  vitality  of  the  whole  system 
speedily  results.  Hence  this  is  the  most  constantly  necessary  of  all  the  actions 
of  the  Spinal  Cord;  and  wre  find  its  maintenance,  in  spite  of  accident  or  disease 
of  the  spine,  remarkably  provided  for,  in  the  location  of  the  centre  of  the  respira- 
tory movements,  which  occupies  a  position  where  it  receives  the  greatest 
possible  amount  of  protection.  The  supply  of  the  digestive  apparatus,  again, 
is  immediately  dependent  upon  the  Spinal  system ;  and  this,  being  another 
essential  function,  has  its  centre  equally  protected.  The  outlets  of  the  cavities 
are  also  controlled  by  the  Spinal  system  ;  but  this  function,  although  essential 
to  the  comfort  of  life,  is  less  necessary  to  its  maintenance  ;  and  we  find  it 
dependent  upon  a  portion  of  the  Cord,  which  is  more  liable  to  lose  its  powers 
by  disease  or  injury.  It  is  possible,  as  will  hereafter  be  shown,  that  several 
actions,  which  are  at  first  voluntary,  may  be  effected,  when  so  frequently  per- 
formed as  to  become  habitual,  through  the  medium  of  the  Spinal  system :  of 
this  kind  seem  to  be  the  movements  of  locomotion,  which  are  continued  invo- 
luntary, when  the  whole  attention  of  the  mind  is  given  to  other  objects,  but 
which  the  Will  can  check  at  any  time.  We  shall  commence  our  particular 
survey  of  the  Reflex  movements  in  Man,  with  the  consideration  of  those  of 
Respiration,  which  are  well  adapted  for  illustrating  their  general  character. 

*!       IX.  Respiratory  Movements. 

184.  The  centre  of  the  Respiratory  movements  is  the  upper  part  of  the 
Medulla  Oblongata;  into  this  may  be  traced  the  excitor  nerves,  that  convey 
the  stimulus  on  which  the  movements  are  dependent;  and  from  it  proceed, 
either  directly  or  indirectly,  the  motor  nerves  by  which  they  are  carried  into 
effect.  The  chief  Excitor  of  the  respiratory  movements  is  unquestionably  the 
Par  Vagum.  When  this  is  divided  on  both  sides,  according  to  the  experi- 
ments of  Dr.  Reid,*  the  number  of  respiratory  movements  is  considerably 
diminished,  usually  about  one-half.  Now  if  this  nerve  excites  the  motions  of 
respiration  by  its  powerful  action  in  producing  sensation,  we  should  expect 
to  find  its  trunk  endowed  with  considerable  sensibility,  which  is  not  the  case  ; 
for  all  experimenters  agree  in  stating  that,  when  its  trunk  is  pinched  or 
pricked,  the  animal  does  not  exhibit  signs  of  pain  nearly  so  acute  as  when 
the  trunks  of  the  ordinary  spinal  nerves,  or  of  the  fifth  pair,  are  subjected  to 
similar  treatment.  It  cannot  be  questioned,  however,  that  its  power  as  an 
exciter  of  respiration  is  very  great;  since,  besides  the  fact  of  the, diminution  in 
the  number  of  inspirations  which  occurs  immediately  on  section  of  it,  irrita- 
tion of  its  trunk,  in  the  neck  is  instantly  followed  by  an  act  of  inspiration.  It 
is  evident  that  this  power  must  arise  from  impressions  made  upon  its  peri- 
pheral extremities.  The  impression  is  probably  due  to  the  presence  of  venous 
blood  in  the  capillaries  of  the  lungs ;  or,  as  Dr.  M.  Hall  thinks,  to  the  pre- 
sence of  carbonic  acid  in  the  air-cells.  Either  or  both  may  be  true. — The 
Pneifmogastric  nerve,  however,  is  not  the  only  exciter  of  the  respiratory 
movements,  since,  when  the  nerve  is  cut  on  each  side,  they  still  continue. 
Dr.  Reid  has  satisfactorily  shown  the  statement  of  many  experimenters,  that 
the  inspirations  are  increased  in  frequency  after  this  operation,  to  be  erro- 
neous ;  this  idea  having  originated  in  their  very  prolonged  and  laborious  cha- 
racter. The  removal  of  the  Encephalon,  also,  diminishes  the  frequency  of 

*  Edinb.  Med.  and  Surg.  Journ,  vol.  li. 


140  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  respiratory  movements,  whether  it  be  performed  before  or  after  the  section 
of  the  Vagi.  Dr.  Reid  found  that,  in  a  kitten  of  a  day  old,  in  which  the  inspira- 
tions were  100  per  minute,  they  fell  to  40  when  the  Encephalon  was  removed ; 
and  on  subsequently  cutting  the  Pneumogastrics,  the  number  of  inspirations 
instantly  fell  to  between  3  and  4  in  the  minute,  and  continued  so  for  some 
time.  Hence  it  appears  that  the  respiratory  movements  are  partly  dependent 
upon  cerebral  agency  or  volition ;  and  this  may  also  be  learned  from  the  pro- 
longed and  laborious  character  of  the  inspirations  during  sleep  or  profound 
attention,  when  the  influence  of  the  Cerebrum  is  more  or  less  suspended. 

185.  But  why  (it  may  be  asked)  do  the  movements  continue,  when  the 
Pneumogastrics  have  been  divided,  and  the  Encephalon  has  been  removed? 
It  is  evident  that  there  must  be  other  exciters  to  the  action  of  the  respiratory 
muscles.  Amongst  these,  the  nerves  distributed  to  the  general  surface,  and 
particularly  to  the  face,  probably  perform  an  important  part ;  and  in  exciting 
the  first  inspiration,  the  Fifth  pair  seems  the  principal  agent.  It  has  long  been 
a  well-known  fact,  that  the  first  inspiratory  effort  of  the  new-born  infant  is 
most  vigorously  performed,  when  the  cool  external  air  comes  into  contact  with 
the  face ;  and  that  impressions  on  the  general  surface,  such  as  a  slap  of  the 
hand  on  the  nates,  are  often  effectual  in  exciting  the  first  inspiratory  move- 
ments, when  they  would  not  otherwise  commence.  Dr.  M.  Hall  relates  an 
interesting  case,  in  which  the  first  inspiration  was  delayed,  simply  because  the 
face  was  protected  by  the  bed-clothes  from  the  atmosphere ;  and,  on  lifting  up 
these,  the  infant  immediately  breathed.  Dr.  M.  Hall  has  recently  mentioned 
the  important  fact,  that  if  the  cerebrum  be  removed  and  the  pneumogastrics 
be  divided  in  a  young  kitten,  the  number  of  acts  of  respiration  will  be  reduced 
to  four  in  a  minute ;  but  by  directing  a  stream  of  air  on  the  animal,  or  by  irri- 
tating various  parts  of  the  general  surface,  we  may  excite  twenty  or  thirty  acts 
of  respiration  within  the  same  space  of  time.  He  further  remarks,  that  in  the 
very  young  warm-blooded  animal,  as  in  the  cold-blooded  animal,  the  pheno- 
mena of  the  excito-motor  power  are  far  more  vividly  manifested  than  in  the 
older  and  the  warm-blooded.  In  the  very  young  kitten,  even  when  asphyxi- 
ated to  insensibility,  •  every  touch,  contact,  or  slight  blow, — every  jar  of  the 
table,  any  sudden  impression  of  the  external  air,  or  that  of  a  few  drops  of  cold 
water,  induces  at  once  energetic  reflex  movements,  and  acts  of  inspiration. 
This  may  be  looked  upon  as  Nature's  provision  for  the  first  establishment  of 
the  acts  of  inspiration  in  the  new-born  animal.  But  the  influence  of  the  nerves 
of  the  general  system  is  by  no  means  wanting  in  the  adult ;  as  the  following 
experiment  of  Dr.  J.  Reid's  demonstrates.  After  dividing  the  pneumogastrics, 
and  removing  the  cerebrum  and  cerebellum,  he  divided  the  spinal  cord  high 
up  in  the  neck,  so  as  to  cut  off  the  communication  between  the  spinal  nerves 
and  the  Medulla  Oblongata ;  and  he  found  that  the  frequency  of  the  respira- 
tory movements  was  still  further  diminished,  although  they  were  not  even 
then  entirely  suspended.  Every  one  knows  the  fact,  that  the  first  plunge  into 
cold  water,  the  first  descent  of  the  streams  of  the  shower-bath,  or  even  dashing 
a  glass  of  cold  water  in  the  face,  will  produce  inspiratory  efforts  ;  and  this  fact 
has  many  important  practical  applications.  Thus,  in  the  treatment  of  Asphyxia, 
whether  congenital  or  the  result  of  narcotic  poisoning,  drowning,  &c.,  the 
alternate  application  of  cold  and  heat  is  found  to  be  one  of  the  most  effica- 
cious means  of  restoring  the  respiratory  movements;  and  a  paroxysm  of  hys- 
teric laughter  may  be  cut  short  by  dashing  a  glass  of  cold  water  in  the  face. 
It  may  be  surmised  that  the  Sympathetic  nerve,  which  derives  many  filaments 
from  the  Cerebro-Spinal  system,  and  which  especially  communicates  with  the 
Pneumogastric  nerves,  is  one  of  the  exciters  to  this  function;  and  this,  per- 
haps, not  only  through  its  ramifications  in  the  lungs,  which  are  considerable, 
but  also  by  its  distribution  on  the  systemic  vessels ;  so  that  it  may  convey  to 


RESPIRATORY  MOVEMENTS.  141 

the  Spinal  Cord  the  impression  of  imperfectly  arterialized  blood  circulating  in 
these,  such  as  the  Pneumogastric  is  believed  to  transmit  from  the  lungs.  It 
will  hereafter  be  shown,  that  an  impression  of  a  corresponding  kind  is  more  pro- 
bably the  cause  of  the  sense  of  hanger  and  thirst  than  any  which  originates 
in  the  stomach  alone  (§  437). — The  Motor  or  Efferent  nerves  concerned  in  the 
function  of  Respiration,  are  those  which  Sir  C.  Bell  has  grouped  together  in 
his  respiratory  system.  The  most  important  of  these,  the  Phrenic,  arises  from 
the  upper  part  of  the  Spinal  Cord ;  the  Intercostals  much  lower  down ;  whilst 
the  Facial  nerve  and  the  Spinal  Accessory,  to  the  latter  of  which,  as  will  here- 
after be  stated  (§  229),  the  motor  powers  of  the  par  vagum  are  chiefly  due, 
take  their  origin  in  the  Medulla  Oblongata  itself.  But  we  must  not  decide 
upon  the  connection  of  a  particular  nerve  with  a  particular  segment  of  the 
Spinal  Cord,  simply  because  it  diverges  from  it  at  that  point.  It  has  been 
shown  that,  in  the  Mollusca,  a  nerve  passing  to,  or  proceeding  from,  one  gang- 
lion, frequently  passes  through  or  over  another  which  lies  in  its  course  ;  and, 
in  the  Articulata,  this  is  a  still  more  constant  occurrence.  It  is  by  no  means 
improbable,  then,  that  the  connection  of  the  intercostal  nerves  is  really  in  part 
with  the  gray  matter  of  the  Medulla  Oblongata ;  at  any  rate,  such  a  connection 
has  not  been  -disproved.  The  white  columns  of  the  Spinal  Cord  consist  of 
fibres, 'which  bring  the  spinal  nerves  into  connection,  not  only  with  the  brain, 
but  also  with  other  segments  of  the  ganglionic  portion  of  the  cord,  being  analo- 
gous in  function,  not  merely  to  the  distinct  fibrous  tract  of  the  ventral  column 
of  the  Articulata,  but  also  to  the  fibrous  bands  that  connect  the  ganglia  them- 
selves. As  the  Medulla  Oblongata,  in  Vertebrate  animals,  is  the  chief  centre 
of  the  actions  of  Respiration,  it  can  scarcely  be  doubted  that  all  the  nerves  con- 
cerned in  that  function  have  a  direct  structural  connection  with  it. 

186.  That  the  Respiratory  movements,  as  ordinarily  performed,  are  essen- 
tially independent  of  the  Will,  appears  not  only  from  our  own  consciousness, 
but  also  from  cases  of  paralysis  ;  in  some  of  which  the  power  of  the  will  over 
the  muscles  has  been'lost,  whilst  the  movements  have  been  kept  up  by  the 
reflex  action  of  the  medulla  oblongata  or  respiratory  ganglion ;  whilst  in 
others,  some  of  the  respiratory  muscles  have  been  motionless  during  ordinary 
breathing,  and  yet  have  remained  under  the  power  of  the  will.  Such  cases 
are  mentioned  by  Sir  C.  Bell,  in.  the  appendix  to  his  work  on  the  Nervous 
System.  That  consciousness  is  not  a  necessary  link  in  the  chain  of  causes 
that  produce  the  respiratory  movements,  we  are  enabled  to  judge  from  the 
phenomena  presented  by  the  human  being  in  sleep  and  coma,  by  anencepha- 
lous  foetuses,  and  by  decapitated  animals.  Further,  Dr.  Ley*  has  put  on  re- 
cord a  case,  which  confirms  this  particular  inference,  just  in  the  same  manner 
as  the  cases  already  related  confirm  the  general  doctrine  of  the  non-existence 
of  sensibility  in  the  Spinal  Cord.  He  had  under  his  care  a  patient  in  whom 
the  par  vagum  appeared  to  be  diseased ;  the  lungs  suffered  in  the  usual  way 
in  consequence,  and  the  patient  had  evidently  laborious  breathing ;' but  he 
distinctly  said  that  he  felt  no  uneasiness  in  his  chest.  The  experience  of 
every  one  informs  him,  that  Respiratory  movements  are  partly  under  the  con- 
trol and  direction  of  the  will,  though  frequently  unrestrainable  by  it.  In 
ordinary  circumstances,  when  the  blood  is  being  perfectly  aerated,  and  there 
is  a  sufficient  amount  of  arterial  blood  in  the  system  to  carry  on  the  functions 
of  life  for  a  short  time,  we  can  suspend  the  respiratory  actions  during  a  few 
seconds  without  any  inconvenience.  If,  however,  we  endeavour  to  prolong 
the  suspension,  the  stimulus  conveyed  by  the  excitor  nerves  to  the  Medulla 
Oblongata  becomes  too  strong,  and  we  cannot  avoid  making  inspiratory  efforts ; 
and  if  the  suspension  be  still  further  prolonged,  the  whole  body  becomes  agi- 

*  On  Laryngismus  Stridulus,  p.  417. 


142  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

tated  by  movements  which  are  almost  of  a  convulsive  nature  ;  and  no  effort 
of  the  will  can  then  prevent  the  ingress  of  air.*  It  is  easy  to  understand  why, 
in  the  higher  animals  at  least,  and  more  especially  in  Man,  the  respiratory 
actions  should  thus  be  placed  under  the  control  of  the  will ;  since  they  are 
subservient  to  the  production  of  those  sounds  by  which  individuals  commu- 
nicate their  feelings  and  desires  to  each  other  ;  and  which,  when  articulate, 
are  capable  of  so  completely  expressing  what  is  passing  in  the  mind  of  the 
speaker.  If  the  respiratory  muscles  of  Man  were  ho  more  under  his  control 
than  they  appear  to  be  in  the  Insect  or  Molluscous  animal,  he  might  be  pro- 
vided with  the  most  perfect  apparatus  of  speech,  and  yet  he  would  not  be 
able  to  employ  it  to  any  advantage. 

187.  The  motor  power  of  the  respiratory  nerves  is  exercised,  however,  not 
only  on  the  muscles  which  perform  the  inspiratory  and  expiratory  movements, 
but  on  those  which  guard  the  entrance  to  the  wind-pipe,  and  also  on  certain 
other  parts.     The  movements  of  the  internal  respiratory  apparatus  are  chiefly, 
if  not  entirely,  effected  through  the  medium  of  the  motor  fibres,  which  the 
Par  Vagum  contains.     These  motor  fibres  exist  in  very  different  amount  in  its 
different  branches.     For  example,  the  pharyngeal  and  ossophageal  branches, 
by  which  (as  will  hereafter  appear)  the  muscles  of  deglutition  are  excited 
to  contraction,  possess  a  much  larger  proportion  of  them,  and  exhibit  much 
less  sensibility  when  irritated,  than  do  other  divisions  of  the  trunk.     Between 
the  superior  and  inferior  laryngeal  nerves,  again,  there  is  an  important  differ- 
ence, which  anatomical  and  experimental  research  have  now  very  clearly 
demonstrated.     It  has  long  been  known,  that  section  of  the  Par  Vagum  in  the 
neck,  above  the  inferior   laryngeals,  is  frequently  followed  by  suffocation, 
resulting  from  closure  of  the  glottis ;  and  hence  it  has  been  inferred,  that  the 
office  of  the  inferior  laryngeals  was  to  call  into  action  the  dilater%  of  the 
larynx,  whilst  the  superior  laryngeals,  were  supposed  to  stimulate  the  con- 
strictors. This  view,  however,  is  incorrect.  It  is  inconsistent  with  the  results, 
just  stated,  of  anatomical  examination  into  the  respective  distribution  of  these 
two  trunks ;  and  it  has  been  completely  overthrown  by  the  very  careful  and 
satisfactory  observations  and  experiments  of  Dr.  J.  Reid,  which  have  esta- 
blished that,  whilst  the  inferior  laryngeal  is  the  motor  nerve  of  nearly  all  the 
laryngeal  muscles,  the  superior  laryngeal  is  the  excitor  or  afferent  nerve, 
conveying  to  the  medulla  oblongata  the  impressions  by  which  muscular  move- 
ments are  excited.     Its  motor  endowments  are   limited  to  the  crico-thyroid 
muscle,  to  which  alone  of  all  the  muscles  its  filaments  can  be  traced,  the 
remainder  being  distributed  beneath  the  mucous  surface  of  the  larynx ;  and 
its  sensibility  is  very  evident,  when  it  is  pinched  or  irritated  during  experi- 
ments upon  it.     On  the  other  hand,  the  motor  character  of  the  inferior  laryn- 
geal branch  is  shown  by  its  very  slight  sensibility  to  injury,  its  nearly  exclu- 
sive distribution  to  muscles,  and  its  influence  in  exciting  contraction  of  these 
when  its  separated  trunk  is  stimulated. 

188.  It  has  been  ascertained  by  Dr.  Reid  that,  if  the  inferior  laryngeal 
branches  be  divided,  or  the  trunk  of  the  par  vagum  be  cut  above  their  origin 
from  it,  there  is  no  constriction  of  the  glottis,  but  a  paralyzed  state  of  its  mus- 

*  It  is  asserted  by  M.  Bourdon  (Recherches  sur  le  Mecanisme  de  la  Respiration,  p. 
81,)  that  no  person  ever  committed  suicide,  though  many  have  attempted  to  do  so,  by 
simply  holding  the  breath  ;  the  control  of  the  will  over  the  respiratory  muscles  not  being 
sufficiently  great  to  antagonize  the  stimulus  of  the  "besoin  de  respirer,"  when  this  has 
become  aggravated  by  the  temporary  cessation  of  the  action.  But  such  persons  have 
succeeded  better  by  holding  the  face  beneath  the  surface  of  water;  because  here  an- 
other set  of  muscles  is  called  into  action,  which  are  much  more  under  the  control  of  the 
will  than  are  those  of  respiration;  and  a  strong  volition  applied  to  these  can  prevent  all 
access  of  air  to  the  lungs,  however  violent  may  be  the  inspiratory  efforts. 


RESPIRATORY  MOVEMENTS.  143 

cles.  After  the  first  paroxysm  occasioned  by  the  operation,  a  period  of  qui- 
escence and  freedom  from  dyspnoea  often  supervenes,  the  respirations  being 
performed  with  ease  so  long  as  the  animal  remains  at  rest ;  but  an  unusual 
respiratory  movement,  such  as  takes  place  at  the  commencement  of  a  struggle, 
induces  immediate  symptoms  of  suffocation, — the  current  of  air  carrying  in- 
wards the  arytenoid  cartilages,  which  are  tendered  passive  by  the  paralyzed 
state  of  their  muscles ;  and  these  falling  upon  the  opening  of  the  glottis  like 
valves,  obstruct  the  entrance  of  air  into  the  lungs.  '  The  more  effort  is  made, 
the  greater  will  be  the  obstruction  :  and  accordingly,  it  is  generally  necessary 
to  counteract  the  tendency  to  suffocation,  when  it  is  desired  to  prolong  the 
life  of  the  animal  after  this  operation,  by  making  an  opening  into  the  trachea. 
Dr.  Reid  further  ascertained,  that  the  application  of  a  stimulus  to  the  inferior 
laryngeal  nerves,  when  separated  from  the  trunk,  would  occasion  distinct 
muscular  contractions  in  the  larynx,  whilst  a  corresponding  stimulus  applied 
to  the  superior  laryngeal  occasioned  no  muscular  movement,  except  in  the 
crico-thyroid  muscle.  But  when  the  superior  laryngeals  were  entire,  irrita- 
tion of  the  mucous  surface  of  the  larynx,  or  of  the  trunks  themselves,  pro- 
duced contraction  of  the  glottis  and  efforts  to  cough ;  effects  which  were  at 
once  prevented  by  dividing  those  nerves,  and  thereby  cutting  off  their  com- 
munication with  the  medulla  oblongata.  There  can  be  no  doubt,  then,  that 
the  superior  and. inferior  laryngeal  branches  constitute  the  circle  of  incident 
and  motor  nerves,  by  which  the  aperture  of  the  glottis  is  governed,  and  by 
which  any  irritation  of  the  larynx  is  made  to  close  the  passage,  so  as  to  pre- 
vent the  entrance  of  improper  substances  ;  whilst  the  superior  laryngeal  nerve 
also  excites  the  muscles  of  expiration,  so  as  to  cause  the  violent  ejection  of  a 
blast  of  air,  by  which  the  offending  gas,  fluid  or  solid,  may  be  carried  off'. 
The  effect  of  carbonic  acid  in  causing  spasmodic  closure  of  the  glottis  is  well 
known,  and  affords  a  beautiful  example  of  the  protective  character  of  this 
system  of  nerves.  The  mucous  surface  of  the  trachea  and  bronchi  appears, 
from  the  experiments  of  Valentin,  to  be  endowed  with  impressibility,  so- that 
stimuli  applied  to  it  produce  expiratory  movements  ;  and  this  evidently  ope- 
rates through  the  branches  of  the  par  vagum  distributed  upon  the  membrane. 
Here,  as  elsewhere,  we  find  that  a  stimulus  applied  to  the  surface  has  a  much 
more  decided  influence  than  irritation  of  the  trunk  of  the  nerve  supplying  it. 
Valentin  has  succeeded  in  producing  distinct  contractions  of  the  ri$g$  of  the 
trachea,  by  irritating  the  par  vagum  in  the  rabbit ;  and  he  thinks  it  "probable 
that  a  similar  action  might  be  induced  in  the  bronchi  and  their  ramifications ; 
but  this  he  has  not  succeeded  in  procuring.  The  phenomena  of  asthma,  how- 
ever, leave  little  room  for  doubt,  that  spasmodic  contraction  of  the  air-passages 
takes  place  as  a  reflex  action,  excited  by  various  causes ;  and  no  other  nerve 
but  the  par  vagum  can  be  concerned  in  producing  it. 

189.  The  actions  of  sighing,  yawning,  sobbing,  laughing,  coughing  and 
sneezing,  are  nothing  else  than  simple  modifications  of  the  ordinary  move- 
ments of  respiration,  excited  either  by  mental  emotions,  or  by  some  stimulus 
originating  in  the  respiratory  organs  themselves.  Sighing  is  nothing  more 
than  a  very  long-drawn  inspiration,  in  which  a  larger  quantity  of  air  than 
usual  is  made  to  enter  the  lungs.  This  is  continually  taking  place  to  a  mode- 
rate degree  (§  530)  ;  and  we  notice  it  particularly,  when  the  attention  is  re- 
leased, after  having  been  fixed  upon  an  object,  which  has  excited  it  strongly, 
and  which  has  prevented  our  feeling  the  insufficiency  of  the  ordinary  move- 
ments of  respiration.  Hence  this  action  is  only  occasionally  connected  with 
mental  emotion.  Yawning  is  a  still  deeper  inspiration,  which  is  accompanied 
by  a  kind  of  spasmodic  contraction  of  the  muscles  of  the  jaw,  and  also  by  a  very 
great  elevation  of  the  ribs,  in  which  the  scapulae  partake.  The  purely  in- 
voluntary character  of  this  movement  is  sometimes  seen,  in  a  remarkable  man- 


144  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

ner,  in  cases  of  palsy,  in  which  the  patient  cannot  raise  his  shoulder  by  an 
effort  of  the  will,  but  does  so  in  the  act  of  yawning.  Nevertheless  this  act 
may  be  performed  by  the  will,  though  not  completely  ;  and  it  is  one  that  is 
particularly  excited  by  an  involuntary  tendency  to  imitation  ;  as  every  one 
must  have  experienced  who  has  ever  been  in  company  with  a  set  of  yawners. 
Sobbing  is  the  consequence  of  a  series  of  short  convulsive  contractions  of  the 
diaphragm  ;  and  it  is  usually  accompanied  by  a  closure  of  the  glottis,  so  that 
no  air  really  enters.  In  Hiccup,  the  same  convulsive  inspiratory  movement 
occurs  ;  and  the  glottis  closes  suddenly  in  the  midst  of  it ;  the  sound  is  occa- 
sioned by  the  impulse  of  the  column  of  air  in  motion  against  the  glottis.  In 
Laughing,  a  precisely  reverse  action  takes  place  ;  the  muscles  of  expiration 
are  in  convulsive  movement,  more  or  less  violent,  and  send  out  the  breath  in 
a  series  of  jerks,  the  glottis  being  open.  This  sometimes  goes  on,  until  the 
diaphragm  is  more  arched,  and  the  chest  is  more  completely  emptied  of  air, 
than  it  could  be  by  an  ordinary  movement  of  expiration.  The  act  of  Crying, 
though  occasioned  by  a  contrary  emotion,  is,  so  far  as  the  respiration  is  con- 
cerned, very  nearly  the  same  as  the  last.  Every  one  knows  the  effect  of 
mixed  emotions,  in  producing  an  expression  of  them  which  is  "  between  a 
laugh  and  a  cry."  The  purposes  of  the  acts  of  coughing  and  sneezing  are, 
in  both  instances,  to  expel  substances  from  the  air-passages  which  are  sources 
of  irritation  there ;  and  this  is  accomplished  in  both,  by  a  violent  expiratory 
effort,  which  sends  forth  a  blast  of  air  from  the  lungs.  Coughing  occurs, 
when  the  source  of  irritation  is  situated  at  the  back  of  the  mouth,  in  the 
trachea,  or  bronchial  tubes.  The  irritation  may  be  produced  by  acrid  vapours, 
or  by  liquids  or  solids,  that  have  found  their  way  into  these  passages  ;  or  by 
secretions  which  have  been  poured  into  them  in  unusual  quantity,  as  the 
result  of  disease  ;  or  by  the  simple  entrance  of  air  (especially  if  cold),  when 
the  membrane  is  in  a  peculiarly  irritable  state.  Any  of  these  causes  may 
produce  an  impression  upon  the  excitor  fibres  of  the  Par  Vagum,  which, 
being  conveyed  to  the  Medulla  Oblongata,  shall  give  rise  to  the  transmission 
of  motor  impulses  to  the  several  muscles,  that  shall  combine  them  in  the  act 
of  coughing.  This  act  consists, — 1st,  in  a  long  inspiration,  which  fills  the 
lungs ;  2d,<  in  the  closure  of  the  glottis  at  the  moment  when  expiration  com- 
mences; and  3d,  in  the  bursting  open  (as  it  were)  of  the  glottis,  by  the  vio- 
lence of>4he  expiratory  movement ;  so  that  a  sudden  blast  of  air  is  forced  up 
the  air-passages,  carrying  before  it  any  thing  that  may  offer  an  obstruction. 
The  difference  between  coughing  and  Sneezing  consists  in  this, — that  in  the 
latter,  the  communication  between  the  larynx  and  the  mouth  is  partly  or 
entirely  closed,  by  the  drawing  together  of  the  sides  of  the  velum  palati  over 
the  back  of  the  tongue  ;  so  that  the  blast  of  air  is  directed,  more  or  less  com- 
pletely, through  the  nose,  in  such  a  way  as  to  carry  off  any  source  of  irrita- 
tion that  may  be  present  there. 

190.  The  influence  of  the  Spinal  Cord,  and  of  its  system  of  nerves,  on  the 
movements  of  Respiration,  affords  an  excellent  example  of  the  importance  of 
this  organ,  as  supplying  the  conditions  immediately  requisite  for  the  mainte- 
nance of  the  organic  functions.  We  have  seen  that,  strictly  speaking,  the 
act  of  Respiration,  as  we  commonly  understand  it,  is  not  Respiration  itself ; 
for  this  consists  in  the  interchange  of  ingredients  between  the  blood  and  the 
surrounding  medium,  which  is  effected  in  the  air-cells  of  the  lungs,  and  which 
takes  place  in  the  lower  animals  (as  in  plants)  without  any  muscular  effort. 
But,  in  proportion  to  the  necessity  for  the  energetic  exercise  of  this  function, 
do  we  find  a  special  provision  in  the  higher  classes,  for  the  constant  renewal 
of  that  portion  of  the  surrounding  medium  which  is  in  contact  with  the  aerat- 
ing surface;  and  this  comes  to  be  so  necessary,  that  asphyxia  might  be  pro- 
duced, without  any  interruption  to  the  ingress  of  air  through  the  trachea,  by 


DEGLUTITION  AND  DEFECATION.  145 

merely  breaking  the  circle  of  nervous  action,  through  which  the  movements 
of  Respiration  are  effected.  It  is  an  interesting  circumstance,  however,  which 
shows  the  provision  made  in  the  animal  frame  to  meet  its  necessities,  that  a 
very  small  portion  only  of  the  nervous  centres  is  involved  in  this  action  ;  and 
that,  even  in  the  highest  Animals,  all  the  rest  may  be  removed,  or  may  be 
rendered  functionally  inactive,  without  checking  it.  This  fact,  which  was 
ascertained  by  Legallois,  harmonizes  well  with  that  which  Comparative 
Anatomy  has  brought  under  our  notice  ;  for  it  has  been  shown  that,  in  the 
lowest  groups  of  Mollusca,  but  a  single  ganglion  exists  ;  and  that  this  is 
almost  exclusively  concerned  in  regulating  the  entrance  and  egress  of  the 
currents  of  water,  the  most  constant  office  of  which  is  the  aeration  of  the 
blood  (§  133). 

X.     Deglutition,  Defecation,  8fc. 

191.  Another  very  important  function  of  the  Spinal  Cord  (and  of  the 
ganglia  corresponding  to  it  in  the  Invertebrata),  is  the  control  which  it  exer- 
cises over  the  entrance  and  termination  of  the  Alimentary  Canal ;  and  this 
reflex  action  might  probably  be  traced  in  some  animals,  in  which  the  neces- 
sity for  that  of  Respiration  does  not  exist.  In  all  beings  which  are  une- 
quivocally of  an  animal  character,  a  stomach  or  digestive  cavity  exists  ;  and 
a  means  must  be  provided  for  the  introduction  of  food  into  it.  This  is  partly 
accomplished  by  the  power  with  which  its  entrance  is  endowed,  of  contracting- 
upon,  and  of  attempting  to  draw  inwards,  whatever  comes  in  contact  with  it ; 
as  we  may  readily  observe  in  the  Star-Fish,  or  Sea-Anemone,  where  the 
mouth  is  simply  the  aperture  of  the  stomach.  From  the  analogy  of  the  higher 
animals,  as  well  as  from  what  has  been  observed  in  the  lower,  it  seems  pro- 
bable that  this  action  is  of  a  reflex  character,  depending  upon  an  impression 
conveyed  to  the  nervous  centres,  and  reflected  back  to  the  muscular  fibres. 
But  we  almost  always  find  some  more  special  apparatus  than  this  for  bring- 
ing food  within  reach  of  the  orifice  of  the  stomach.  In  the  Sea-Anemone,  the, 
Hydra,  and  other  Polypes,  for  example,  we  find  that  aperture  surrounded  by 
tentacula ;  which  have  an  evident  tendency  to  lay  hold  of  any  thing  that 
touches  them,  so  as  to  bring  it,  by  their  contraction,  within  reach  of  tjjeJfctrscles 
immediately  surrounding  the  orifice.  This  is  just  the  purpose  of  ^IsHfearyn- 
geal  muscles  of  Man.  The  lower  part  of  the  oesophagus,  near  its  te^ilhation 
in  the  stomach,  has  the  same  simple  tendency  to  contraction  from  above  down- 
wards (so  as  to  convey  into  the  stomach  any  thing  which  is  brought  within  its 
reach)  as  have  the  muscles  surrounding  the  mouth  of  the  Polype ;  but  there 
is  need  of  some  more  complex  apparatus,  for  the  purpose  of  laying  hold  of  the 
food,  and  of  conducting  it  into  its  grasp.  This  is  provided  for,  in  the  higher 
animals,  in  the  muscles  of  that  funnel-like  entrance  to  the  oesophagus,  which 
is  called  the  Pharynx.  The  actions  of  these  are  most  distinctly  reflex  ;  and  it 
is  interesting  to  remark,  that  the  movements  can  neither  be  caused  nor  con- 
trolled by  the  direct  influence  of  the  will.  In  the  case  of  the  movements  of 
respiration,  we  found  sufficient  provision  made  for  their  constant  maintenance ; 
and  yet,  for  secondary  purposes,  they  were  placed  in  a  considerable  degree 
under  the  control  of  the  brain.  But  here  there  are  no  secondary  purposes  to 
be  answered ;  the  introduction  into  the  stomach  of  food,  brought  by  the  will 
within  reach  of  the  pharyngeal  muscles,  is  the  only  object  contemplated  by 
them ;  and  they  are  accordingly  placed  under  the  sole  government  of  the 
Spinal  Cord.  No  attempts,  on  our  own  part,  will  succeed  in  producing  a 
really  voluntary  act  of  deglutition.  In  order  to  excite  it,  we  must  supply  some 
stimulus  to  the  fauces.  A  very  small  particle  of  sojid  matter,  or  a  little  fluid, 
(saliva,  for  instance,)  or  the  contact  of  the  back  of  the  tongue  itself,  will  be 
13 


146  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

sufficient ;  but  without  either  of  these  we,  cannot  swallow  at  will.  Nor  can 
we  restrain  the  tendency,  when  it  is  thus  excited  by  a  stimulus ;  every  one 
knows  how  irresistible  it' is,  when  the  fauces  are  touched  in  any  unusual  man- 
ner ;  and  it  is  equally  beyond  the  direct  control  of  the  will,  in  the  ordinary 
process  of  eating, — voluntary  as  we  commonly  regard  this.  The  only  mode 
in  which  the  will  can  influence  it,  is  by  regulating  the  approach  of  the  stimu- 
lus necessary  to  excite  it ;  thus,  we  voluntarily  bring  a  morsel  of  food,  or  a 
little  fluid,  into  contact  with  the  surface  of  the  fauces,  and  an  act  of  deglutition 
is  then  involuntarily  excited ;  or  we  may  voluntarily  keep  all  stimulus  at  a 
distance,  and  no  effort  of  the  will  can  then  induce  the  action.  Moreover,  this 
action  is  performed,  like  that  of  respiration,  when  the  power  of  the  will  is  sus- 
pended, as  in  profound  sleep,  or  in  apoplexy  affecting  only  the  brain ;  and  it 
does  not  seem  to  be  at  all  affected  by  the  entire  removal  of  the  brain,  in  an 
animal  that  can  sustain  the  shock  of  the  operation ;  being  readily  excitable, 
on  stimulating  the  fauces,  so  long  as  the  nervous  structure  retains  its  functions. 
This  has  been  experimentally  proved  by  Dr.  M.  Hall;  and  it  harmonizes  with 
the  natural  experiment  sometimes  brought  under  our  notice  in  the  case  of  an 
anencephalous  infant,  in  which  the  power  of  swallowing  seems  as  vigorous  as 
in  the  perfect  one.  But,  if  the  nervous  circle  be  destroyed,  either  by  division 
of  the  trunks,  or  by  injury  of  any  kind  to  the  portion  of  the  nervous  centres 
connected  with  them,  the  action  can  no  longer  be  performed ;  and  thus  we  see 
that,  when  the  effects  of  apoplexy  are  extending  themselves  from  the  brain  to 
the  spinal  cord,  whilst  the  respiration  becomes  stertorous,  the  power  of  Deglu- 
tition is  lost,  and  then  respiration  also  speedily  ceases. 

192.  Our  knowledge  of  the  nerves  specially  concerned  in  this  action  is 
principally  due  to  the  very  careful  and  well-conducted  experiments  of  Dr.  J. 
Reid.*  The  distribution  of  the  Glosso-Pharyngeal  evidently  points  it  out  as 
in  some  way  connected  with  it;  and  Sir  C.  Bell,  misled  by  imperfect  know- 
ledge of  its  anatomy,  pronounced  it  to  be  a  muscular  nerve,  whose  function 
was  to  excite  the  combined  movements  of  the  tongue  and  pharynx,  which  are 
required  in  deglutition,  and  also  in  some  acts  of  respiration.  He  was  not 
aware  that  such  a  combination  of  movements  may  be  due  as  much  to  the 
excitor  nerve,  and  its  termination  in  the  Spinal  Cord,  as  to  the  motor,  and  its 
particular  distribution  to  muscles.  The  function  of  the  Glosso-Pharyngeal 
nerve  hasf  been  for  some  time  one  of  the  qusestiones  vexatx  of  physiology ; 
and  the  results  obtained  by  different  experimenters  are  so  strangely  at  variance, 
as  almost  to  lead  to  the  belief  that  they  have  operated  on  different  nerves.  In 
this  dilemma,  we  may  advantageously  have  recourse  to  anatomical  examina- 
tion of  its  distribution ;  and  this,  when  carefully  conducted,  discloses  the  im- 
portant fact,  that  the  nerve  scarcely  sends  any  of  its  branches  to  the  muscles 
which  they  enter ;  but  that  these  mostly  pass  through  them,  to  be  distributed 
to  the  superjacent  mucous  surface  of  the  tongue  and  fauces.  Further,  when 
the  trunk  is  separated  from  the  nervous  centres,  irritation  scarcely  ever  pro- 
duces muscular  movements.  Hence  it  is  not  in  any  great  degree  an  efferent 
or  motor  nerve  ;  and  its  distribution  would  lead  us  to  suppose  its  function  to 
be,  the  conveyance  of  impressions  from  the  surface  of  the  fauces  to  the  me- 
dulla oblonganta.  This  inference  is  fully  confirmed  by  the  fact,  that,  so  long 
as  its  trunk  is  in  connection  with  the  Medulla  Oblongata,  and  the  other  parts 
are  uninjured,  pinching,  or  other  severe  irritation  of  the  Glosso-Pharyngeal  will 
excite  distinct  acts  of  deglutition.  Such  irritation,  however,  may  excite  only 
convulsive  twitches,  instead  of  the  regular  movements  of  swallowing ;  and  it 
is  evident  that,  here  as  elsewhere,  the  impressions  made  upon  the  extremities 
of  the  nerves  are  much  more  powerful  exciters  of  reflex  movement  than  those 

*  Edinb.  Med.  and  Surg.  Journ.,  vol.  xlix. 


DEGLUTITION  AND  DEFECATION.  147 

made  upon  the  trunk,  though  the  latter  are  more  productive  of  pain.  It  was 
further  observed  by  Dr.  Reid,  that  this  effect  was  produced  b*y  pinching  the 
pharyngeal  branches  only  ;  no  irritation  of  the  lingual  division  being  effectual 
to  the  purpose. 

193.  If,  then,  the  muscles  of  deglutition  are  not  immediately  stimulated  to 
contraction  by  the  Glosso-Pharyngeal  nerve,  it  remains  to  be  inquired,  by  what 
nerve  the  motor  influence  is  conveyed  to  them  from  the  Medulla  Oblongata ; 
and  Dr.  Reid  has  been  equally  successful  in  .proving  that  this  function  is  per- 
formed by  the  pharyngeal  branches  of  the  Par  Vagum.    Anatomical  examina- 
tion of  their  distribution  shows  that  they  lose  themselves  in  the  musdes  of  the 
pharynx ;  and  whilst  no  decided  indications  of  suffering  can  be  produced  by 
irritating  them,  evident  contractions  are  occasioned  when  the  trunk,  separated 
from  the  brain,  is  pinched  or  otherwise  stimulated.     It  appears,  however,  that 
neither  is  the  Glosso-Pharyngeal  the  sole  excitor  nerve,  nor  are  the  pharyn- 
geal branches  of  the  Par  Vagum  the  sole  motor  nerves,  concerned  in  deglu- 
tition ;  for  after  the  former  has  been  perfectly  divided  on  each  side,  the  usual 
movements  can  still  be  excited,  though  with  less  energy ;  and,  after  the  latter 
have  been  cut,  the  animal  retains  the  means  of  forcing  small  morsels  through 
the  pharynx,  by  the  action  of  the  muscles  of  the  tongue  and  neck.     From  a 
careful  examination  of  the  actions  of  deglutition,  and  of  the  influence  of  various 
nerves  upon  them,  Dr.  Reid  draws  the  following  conclusions : — The  impres- 
sions are  conveyed  to  the  Medulla  Oblongata  chiefly  through  the  Glosso-Pha- 
ryngeal, but  also  along  the  branches  of  the  Fifth  pair  distributed  upon  the 
fauces,  and  probably  along  the  branches  of  the  Superior  Laryngeal  distributed 
upon  the  pharynx.     The  motor  influence  passes  chiefly  along  the  pharyngeal 
branches  of  the  Vagus  ;  along  the  branches  of  the  Hypoglossal,  distributed  to 
the  muscles  of  the  tongue,  and  to  the  sterno-hyoid,  sterno-thyroid,  and  thyro- 
hyoid  muscles  ;  along  the  motor  filaments  of  the  Recurrents,  ramifying  upon 
the  larynx ;  along  some  of  the  branches  of  the  Fifth,  supplying  the  elevator 
muscles  of  the  lower  jaw ;   along  the  branches  of  the  Portio  Dura,  ramifying 
upon  the  digastric  and  stylo-hyoid  muscles,  and  upon  the  muscles  of  the  lower 
part  of  the  face ;   and  probably  along  some  of  the  branches  of  the  Cervical 
plexus  which  unite  themselves  to  the  descendens  noni. 

194.  When  the  food  has  been  propelled  downwards  by  the  pharyngeal 
muscles  as  far  as  their  action  extends,  its  further  progress  through  the  oeso- 
phagus is  effected  by  the  peristaltic  movement  of  the  muscular  coat  of  the  tube 
itself.     This  movement  is  not,  however,  due  only  to  the  direct  stimulus  of  the 
muscular  fibre  by  the  pressur^  of  the  food,  as  it  seems  to  be  in  the  lower  part 
of  the  alimentary  canal ;  for  Dr.  J.  Reid  has  found,  by  repeater!  experiment, 
that  the  continuity  of  the  oesophageal  branches  of  the  Par  Vagum  with  the 
Spinal  Cord,  is  necessary  for  the  rapid  propulsion  of  the  food ;  so  that  it  can 
scarcely  be  doubted,  that  an  impression  made  upon  the  mucous  surface  of  the 
oesophagus,  conveyed  by  the  afferent  fibres  of  these  nerves  to  the  Medulla 
Oblongata,  and  reflected  downwards  along  the  motor  fibres,  is  the  real  cause 
of  the  muscular  contraction.     If  the  Par  Vagum  be  divided  in  the  rabbit,  on 
each  side,  above  the  oesophageal  plexus,  but  below  the  pharyngeal  branches, 
and  the  animal  be  then  fed,  it  is  found  that  the  food  is  delayed  in  the  oeso- 
phagus, which  becomes  greatly  distended.     Further,  if  the  lower  extremity 
of  the  par  vagum  be  irritated,  distinct  contractions  are  seen  in  the  oesophageal 
tube,  proceeding  from  above   downwards,  and  extending  over  the  cardiac 
extremity  of  the  stomach.     We  have  here,  then,  a  distinct  case  of  reflex  action 
without  sensation,  occurring  as  one  of  the  regular  associated  movements  in 
the  natural  condition  of  the  animal  body ;  and  it  is  very  interesting  to  find  this 
following  upon  a  reflex  action  with  sensation  (that  of  the  pharynx),  and  pre- 
ceding an  action  which  is  altogether  unconnected  wTith  the  Spinal  Cord,  (that 


148  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

of  the  lower  part  of  the  alimentary  canal.)  The  use  of  sensation  in  the  former 
case  will  presently  appear.  The  muscular  fibres  of  the  oesophagus  are  also 
excitable,  though  usually  in  a  less  degree,  by  direct  stimulation  ;  for  it  appears 
that,  in  some  animals  (the  Dog,  for  example),  section  of  the  pneumogastric 
does  not  produce  that  check  to  the  propulsion  of  the  food  which  it  occasions 
in  the  Rabbit ;  and  even  in  the  Rabbit,  as  Dr.  M.  Hall*  has  lately  remarked, 
the  simple  contractility  of  the  muscular  fibre  occasions  a  distinct  peristaltic 
movement  along  the  tube,  after  its  nerves  have  been  divided ;  causing  it  to 
discharge  its  contents,  when  cut  across. t 

195.  It  will  be  desirable  here  to  revert  for  a  short  time  to  the  actions  which, 
in  the  higher  animals,  precede  those  of  Deglutition.     There  can  be  no  doubt 
that,  in  the  Human  being,  the  motions  adapted  to  the  ingestion  and  mastica- 
tion of  aliment  originally  result,  in  part  at  least,  from  distinct  operations  of  the 
Will ;  but  it  would  appear  almost  equally  certain,  that,  in  time,  they  come  to 
be  of  so  habitual  a  character,  that  the  will  only  exerts  a  general  controlling 
influence  over  them,  each  individual  act  being  excited  through  the  shorter 
channel  already  alluded  to  (§  183).     Every  one  is  conscious  that  the  act  of 
mastication  may  be  performed  as  well,  when  the  mind  is  attentively  dwelling 
on  some  other  object,  as  when  directed  to  it;  but,  in  the  former  case,  one  is 
rather  apt  to  go  on  chewing  and  re-chewing  what  is  already  fit  to  be  swallowed, 
simply  because  the  will  does  not  exert  itself  to  check  the  action,  and  to  carry 
the  food  backwards  within  the  reach  of  the  muscles  of  deglutition,     We  now 
see  why  sensation  should  be  associated  with  the  latter  process.     The  convey- 
ance of  food  backwards  to  the  fauces  is  a  distinctly  voluntary  act ;  and  it  is 
necessary  that  it  should  be  guided  by  the  sensation  there  resulting  from  the 
contact  which  it  induces.     If  the  surface  of  the  pharynx  were  as  destitute  of 
sensation  as  is  the  lower  part  of  the  oesophagus,  we  should  not  know  when 
we  had  done  what  was  necessary  to  excite  its  muscles  to  operation.     The 
muscles  concerned  in  the  Mastication  of  food  are  nearly  all  supplied  by  the 
third  branch  of  the  Fifth  pair,  a  large  proportion  of  which  is  well  known  to 
have  a  motor  character.     Many  of  these  muscles,  especially  those  of  the 
cheeks,  are  also  supplied  by  the  portio  dura  of  the  Seventh  ;  and  yet,  if  the 
former  be  paralyzed,  this  cannot  stimulate  them  to  the  necessary  combined 
actions.     Hence  we  see  that  the  movements  are  of  an  associated  character, 
their  due  performance  being  dependent  on  the  part  of  the  nervous  centres  from 
which  the  motor  influence  originates.     If  the  Fifth  pair,  on  the  other  hand,  be 
uninjured,  whilst  the  Seventh  is  paralyzed,  the  movements  of  Mastication  are 
performed  wUhout  difficulty ;   whilst  those  connected  in  any  way  with  the 
Respiratory  function,  or  with  Expression,  are  paralyzed. 

196.  Comparative  anatomy  supplies  us  with  the  key  to  the  explanation  of 
these  phenomena.     It  has  been  seen  that,  in  the  lower  animals,  the  Respira- 
tory organs  are   completely  unconnected  with  the  mouth,  and  that  a  very 

*  Third  Memoir  on  the  Nervous  System,  §  201. 

f  There  are  many  cases  in  which  this  direct  contractility  does  not  manifest  itself  in 
the  ordinary  condition  of  the  system,  but  in  which  it  becomes  evident  when  the  muscu- 
lar structure  has  gained  an  increase  of  irritability  by  diseased  action,  as  we  frequently 
have  to  notice  in  the  intestinal  canal.  For  example ;— in  many  cases  of  disease  or  injury 
of  the  Spinal  Cord,  the  bladder  ceases  to  expel  its  contents,  through  the  interruption  of 
the  circle  of  reflex  actions  hereafter  to  be  described;  but,  after  a  time,  it  ceases  to  become 
necessary  to  draw  off  the  urine  by  the  catheter;  for  the  fluid  is  constantly  expelled,  as 
soon  as  it  has  accumulated  in  small  quantities.  In  such  cases,  the  mucous  coat  is  found 
after  death  to  be  thickened  and  inflamed;  and  the  muscular  coat  is  greatly  increased  in 
strength,  and  contracted  upon  itself.  Here,  then,  the  muscularicoat,  which  is  not  excited 
to  contraction  as  long  as  the  mucous  coat  is  in  a  healthy  condition,  acquires  a  degree  of 
abnormal  irritability  which  is  sufficient  to  enable  it  of  itself  to  expel  the  urine ;  but  this 
could  not  be  the  case,  unless  it  had  originally  been  possessed  of  independent  contractility. 


DEGLUTITION  AND  DEFECATION.  149 

distinct  set  of  muscles  is  provided  to  keep  them  in  action.  These  muscles 
have  distinct  ganglia  as  the  centres  of  their  operations  ;  and  these  ganglia  are 
only  connected  indirectly  with  those  of  the  sensori-volitional  system.  The 
same  would  appear  to  be  the  case  in  regard  to  the  introduction  of  the  food 
into  the  digestive  apparatus.  It  has  been  shown  that  the  muscles  concerned 
in  this  operation  have  their  own  centres, — the  stomato-gastric  and  pharyngeal 
ganglia, — which  are  not  very  closely  connected  with  the  cephalic,  or  with  the 
respiratory,  or  with  those  of  general  locomotion.  Now  in  the  Vertebrata,  the 
distinct  organs  have  been  so  far  blended  together,  that  the  same  muscles  serve 
the  purposes  of  both ;  but  the  different  sets  of  movements  of  these  muscles  are 
excited  by  different  nerves  ;  and  the  effect  of  division  of  either  nerve  is  to 
throw  the  muscle  out  of  connection  with  the  function  to  which  that  nerve 
previously  rendered  it  subservient,  as  much  as  if  the  muscle  were  separated 
from  the  nervous  system  altogether.  There  is  an  apparent  exception  to  this 
view  of  the  matter,  in  the  case  of  the  Portio  Dura ;  this  being  the  source  of 
those  movements  of  the  upper  lip  which,  in  many  animals,  are  essential  to 
the  prehension  of  food.  These  movements,  however,  are  dependent  upon 
sensations  conveyed  through  the  Fifth  pair,*  being  completely  checked  by 
division  of  its  infra-orbital  trunk  ;  and  it  can  scarcely  be  doubted,  from  their 
general  character,  that  they  are  of  a  strictly  voluntary  nature,  and  are  not  to 
be  regarded  as  part  of  the  reflex  associated  movements  in  which  that  nerve  is 
concerned. 

197.  Now  although,  in  the  adult  Human  being,  the  movements  required  to 
convey  the  food  to  the  pharynx  are  under  the  control  of  the  Will,  if  not  con- 
stantly dependent  upon  it,  there  is  good  reason  to  believe  that  this  is  not  the 
case  in  regard  to  those  remarkable  associated  movements  which  constitute  the 
act  of  suction  in  the  Infant.     The  experiments  provided  for  us  by  nature,  in 
the  production  of  anencephalous  monstrosities,  fully  prove  that  the  nervous 
connection  of  the  lips  and  respiratory  organs  with  the  Spinal  Cord,  is  alone 
sufficient  for  its  execution  ;  and  Mr.  Grainger  has  sufficiently  established  the 
same,  by  experiment  upon  puppies  whose  brain  had  been  removed.     He  adds 
that,  as  one  of  the  puppies  lay  on  its  side,  sucking  the  finger  which  was  pre- 
sented to  it,  it  pushed  out  its  feet  in  the  same  manner  as  young  pigs  exert  theirs 
against  the  sow's  dugs.     On  the  whole,  however,  the  act  of  suction  belongs 
more  to  the  Respiratory  ganglion  (so  to  speak)  than  to  the  Stomato-gastric 
system  of  nerves ;  and  hence  we  can  understand  why,  even  in  the  highest 
animals,  it  should  be  purely  instinctive  ;  the  movements  of  Respiration  being 
so  from  the  first,  whilst  those  ordinarily  concerned  at  a  later  period  in  the 
ingestion  of  the  -food  are  more  directed  by  the  will.      The  actions  of  the 
mammary  foetus  of  the  kangaroo,  described  by  Mr.  Morgan,  furnish  a  very 
interesting  exemplification  of  the  same  function  of  the  Spinal  Cord  ;  this  crea- 
ture, resembling  an  earth-worm  in  appearance,  arid  only  about  fourteen  lines 
in  length,  with  a  brain  corresponding  in  degree  of  development  to  that  of  a 
human  fostus  of  the  ninth  week,  executes  regular,  but  slow,  movements  of 
respiration,  adheres  firmly  to  the  point  of  the  nipple,  and  moves  its  limbs  when 
disturbed.     The  milk  is  forced  into  the  oesophagus  by  a  compressor  muscle, 
with  which  the  mamma  of  the  parent  is  provided.     "Can  it  be  imagined," 
very  justly  asks  Mr.  Grainger,  "  that  in  this  case  there  are  sensation  and 
volition,  in  what  can  be  proved  anatomically  to  be  a  foetus  ?" 

198.  We  now  return  to  the  question  of  the  influence  of  the  Spinal  Cord 

*  Hence  originated  one  of  Sir  C.  Bell's  early  errors.  He  found  that  an  ass,  in  which 
the  infra-orbital  branch  of  the  fifth  was  divided,  would  not  pick  up  oats  with  its  lip, 
although  they  were  in  contact  with  it;  hence  he  concluded  that  its  power  of  motion  was 
destroyed, — when  it  was  in  reality  only  the  sensation  necessary  to  excite  the  will  to 
cause  the  motion  that  was  deficient. 

13* 


150  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

upon  the  lower  part  of  the  alimentary  canal.  It  has  been  already  stated,  that 
the  motor  function  of  the  Par  Vagum  appe'ars  to  terminate  at  different  points 
in  different  animals ;  and  this  may  in  part  explain  the  great  variety  in  the 
results  obtained  by  different  experimenters,  in  regard  to  the  effect  of  section 
of  the  par  vagum  upon  the  function  of  digestion.  Valentin  agrees  with  Dr. 
Reid  in  stating,  that  distinct  movements  of  the  stomach  may  be  excited  in  the 
rabbit  by  irritation  of  the  par  vagum ;  and  he  adds,  as  a  precaution,  that  the 
experiment  should  be  performed  very  soon  after  death,  as  the  irritability  of  the 
stomach  is  soon  lost ;  and  that  the  stimulation  of  the  nerve  should  not  be  per- 
formed too  high  up,  but  rather  in  the  lower  part  of  the  neck,  or  in  the  thorax. 
Various  experiments  upon  living  animals  have  led  to  the  belief,  that  the  motions 
of  the  muscular  parietes  of  the  stomach,  which  perform  a  very  important  part 
in  chymification,  are  due  to  the  influence  of  this  nerve ;  food  taken  in  shortly 
before  or  subsequently  to  its  division,  having  been  found  to  be  only  dissolved 
on  the  surface  of  the  mass,  where  it  was  in  contact  with  the  mucous  membrane. 
But  these  experiments  have  been  made  for  the  most  part  upon  Herbivorous 
animals,  such  as  horses,  asses,  and  rabbits,  whose  food  is  bulky  and  difficult 
of  solution,  requiring  to  be  constantly  changed  in  its  position,  so  that  every 
part  of  it  may  be  successively  brought  to  the  exterior.  On  the  other  hand, 
Dr.  Reid  found,  in  his  experiments  upon  Dogs,  that,  after  the  first  shock  of 
the  operation  had  gone  off,  solution  of  the  food  in  the  stomach,  and  absorption 
of  chyle,  might  take  place ;  and  hence  it  may  be  inferred,  that  no  influence  of 
this  nerve  upon  the  muscular  parietes  of  the  stomach  is  essential  to  digestion 
in  that  species.  This  conclusion  harmonizes  well,  therefore,  with  the  fact 
already  stated  respecting  the  absence  of  such  influence  in  the  lower  part  of  its 
oesophagus  ;  and  it  may,  perhaps,  be  explained  by  the  consideration,  that  the 
natural  food  of  the  dog  is  much  less  bulky  and  more  easy  of  solution  than  that 
of  the  animals  already  named  ;  so  that  there  is  not  so  much  need  of  the  peculiar 
movement  which  is  in  them  so  important  an  aid  to  the  process  of  reduction. 

199.  In  regard  to  the  functions  of  the  afferent  portion  of  the  gastric  branches 
of  the  Par  Vagum,  there  has  also  been  considerable  difference  of  opinion ;  some 
physiologists  maintaining  that  it  is  by  impressions  on  them  alone  that  the  sense 
of  Hunger  or  satiety  is  occasioned ;  whilst  others  deny  that  it  has  any  power 
of  transmitting  such  impressions,  and  maintain  that  they  do  not  originate  in 
the  stomach  at  all.     Dr.  Reid  has  arrived  at  the  conclusion,  from  his  numerous 
experiments,  that  the  par  vagum  is  the  channel  through  which  the  mind 
becomes  cognisant  of  the  condition  of  the  stomach ;  but  that  it  is  not  the  sole 
excitor  of  the  sense  of  hunger.     Animals  which  have  sustained  section  of  the 
nerve  on  both  sides  will  eagerly  take  food,  if  they  have  not  received  too  great 
a  shock  from  the  operation  ;  but  they  seem  to  experience  no  feeling  of  satiety 
when  the  stomach  is  loaded.     This  inference  is  confirmed  by  Valentin,  who 
mentions  that  puppies  after  the  operation  will  take  three  times,  and  even  more, 
the  same  quantity  of  milk  as  uninjured  individuals  of  the  same  age  ;  so  that  the 
abdomen  is  greatly  distended.     The  act  of  Vomiting  has  been  now  sufficiently 
shown  to  be  excitable  through  the  par  vagum;   an  impression  propagated 
through  which  to  the  Medulla  Oblongata  excites  to  contraction  a  considerable 
number  of  muscles.    But,  as  in  the  case  of  hunger,  although  the  sense  of  nausea 
and  the  tendency  to  vomit  may  be  excited  by  various  irritating  causes  operating 
through  this  nerve  only,  it  may  be  produced  also  through  other  channels. 
Thus  severe  vomiting  has  been  excited  by  the  injection  of  a  solution  of  tartar 
emetic  or  of  emetin  into  the  blood-vessels ; — a  fact  of  which  it  has  been  pro- 
posed to  take  advantage  in  extreme  cases  of  narcotic  poisoning,  when  the  nervous 
system  has  become  so  torpid,  that  emetics  administered  in  the  ordinary  manner 
are  of  no  avail  (See  §  300). 

200.  That  the  ordinary  peristaltic  movements  of  the  intestinal  canal,  from 


DEGLUTITION  AND  DEFECATION.  151 

the  stomach  to  the  rectum,  may  take  place  without  any  connection  with  the 
nervous  system,  being  due  to  the  direct  stimulation  of  the  contact  of  food,  there 
is  now  ample  evidence  ;  and  though  some  may  still  be  found  who  deny  the 
Hallerian  doctrine,  that  muscular  fibre  possesses  in  itself  the  property  of  con- 
tractility, so  much  additional  evidence  of  its  truth  has  been  recently  adduced, 
whilst  the  fact  itself  is  so  conformable  to  the  analogy  supplied  by  others,  that 
it  will  be  here  unhesitatingly  adopted  (See  Chapter  V.).  Mr.  Grainger  and 
some  other  physiologists  have  supposed  that  the  peristaltic  movements  of  the 
alimentary  canal  are  due  to  a  sort  of  reflex  action,  taking  place  through  the 
ganglia  of  the  Sympathetic  system  of  nerves,  especially,  of  course,  the  semiJunar. 
This  supposition,  however,  has  little  or  no  evidence  to  support  it;  for  it  has 
been  fully  proved  that  the  muscular  contractions  will  continue  long  after  the 
tube  has  been  separated  from  its  nervous  connections  through  its  whole  extent ; 
and  the  only  evidence  in  its  favour  is  derived  from  the  contractions  which 
may  sometimes  be  induced  in  parts  of  the  tube  which  are  at  rest  when  the 
sympathetic  nerves  supplying  them  are  irritated.  Some  very  interesting 
experiments  have  been  recently  published  by  Valentin,  by  which  the  fact  that 
such  contractions  may  be  induced  (which  has  been  denied  by  some)  is  clearly 
substantiated ;  but  it  is  also  shown  that  the  motor  influence  does  not  originate 
in  the  Sympathetic  ganglia,  but  in  the  Spinal  Cord.  The  following  are  the 
general  results  of  upwards  of  three  hundred  experiments,  so  far  as  they  apply 
to  this  subject. — The  pharynx  may  not  only  be  excited  to  contraction  by  irri- 
tation of  the  pharyngeal  branches  of  the  Par  Vagum,  or  of  the  roots  of  the 
Spinal  Accessory,  from  which  their  motor  power  is  derived  (as  will  be  hereafter 
explained),  but  also  by  stimulating  the  roots  of  the  first  two  Cervical  nerves; 
and  the  lower  part  of  the  cesophagus  in  the  neck  is  made  to  contract  peristalti- 
cally  from  above  downwards,  by  irritation  of  the  roots  of  the  first  three  Cervical 
nerves,  and  of  the  cervical  portion  of  the  Sympathetic,  through  which  last  the 
former  evidently  operate.  The  thoracic  portion  of  the  oesophagus  is  made 
to  contract,  by  irritation  of  the  lowest  Sympathetic  ganglion  of  the  neck,  and 
of  the  higher  thoracic  ganglia,  and  also  of  the  roots  of  the  lower  Cervical 
spinal  nerves.  Muscular  contractions  of  the  stomach  are  produced  by  irrita- 
tion of  the  roots  of  the  4th,  5th,  6th  and  7th  Cervical  nerves,  and  of  the  first 
thoracic  in  the  rabbit ;  so  that  a  distinct  furrow  is  evident  between  the  cardiac 
and  pyloric  portion  of  the  viscus;  and  the  lower  the  nerve  irritated,  the 
nearer  the  pylorus  do  the  contractions  extend.  Irritation  of  the  first  thoracic 
ganglion  of  the  Sympathetic  produces  the  same  effect.  Contractions  of  the 
intestinal  tube,  varying  in  place  according  to  the  part  of  the  Spinal  Cord 
experimented  on,  may  be  excited  by  irritation  of  the  roots  of  the  dorsal,  lumbar, 
and  sacral  nerves,  and  of  the  trigeminus ;  and  similar  effects  are  produced  by 
irritation  of  the  lower  part  of  the  thoracic  portion  of  the  lumbar,  and  of  the 
sacral  portions  of  the  Sympathetic, — also  of  the  splanchnic,  and  of  the  gastric 
plexus. 

201.  From  these  facts  it  is  evident,  that  the  movements  of  the  Intestinal 
tube  may  be  influenced  by  the  Spinal  Cord;  and  that  what  is  commonly  termed 
the  Sympathetic  nerve,  is  the  channel  of  that  influence,  by  the  fibres  which  it 
derives  from  the  Spinal  system.  But  it  by  no  means  thence  follows,  that  the 
ordinary  peristaltic  actions  of  the  muscles  in  question  are  dependent  on  a 
stimulus  reflected  through  the  spinal  cord,  rather  than  on  one  directly  applied 
to  themselves.  It  is  clear  that,  although  these  movements  are  of  the  first  im- 
portance to  the  welfare  of  the  system,  such  means  of  sustaining  them  are  feeble, 
compared  to  those  which  we  find  provided  for  the  maintenance  of  the  distinctly 
reflex  actions  of  deglutition,  respiration,  &c.  The  difficulty  with  which  any 
evidence  can  be  obtained  of  the  connection,  is  a  sufficient  proof  of  this.  On 
the  other  hand,  we  do  know  that  these  peristaltic  movements  are  influenced 


152  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

by  particular  states  of  mind,  or  by  conditions  of  the  bodily  system ;  and  the 
"Connection  just  traced  satisfactorily  accounts  for  this,  and  is  itself  sufficiently 
explained.  The  intestinal  tube,  then,  from  the  stomach  to  the  rectum,  is  not 
dependent  upon  the  Spinal  Cord  for  its  contractility,  but  is  enabled  to  propel 
its  contents  by  its  own  inherent  powers ;  still  we  find  that  here,  as  in  other 
instances,  the  nervous  centres  exert  a  general  control  over  even  the  organic 
functions, — doubtless  for  the  purpose  of  harmonizing  them  with  each  other,  and 
with  the  conditions  of  the  organs  of  animal  life. 

202.  On  examining  the  outlets  by  which  the  excretions  are  voided,  we  find 
that  they  are  placed,  like  the  entrances,  under  the  guardianship  of  the  Spinal 
Cord;  subject,  however,  to  some  control  on  the  part  of  the  Will.  In  the  lowest 
animals,  the  act  of  discharging  excrementitious  matter  is  probably  as  involuntary 
as  are  the  acts  immediately  concerned  in  the  introduction  of  nutriment ;  and  is 
performed  as  often  as  there  is  any  thing  to  be  got  rid  of.  In  the  higher  classes, 
however,  such  discharges  are  much  less  frequent ;  and  reservoirs  are  provided 
yi  which  the  excrementitious  matter  may  accumulate  in  the  intervals.  The 
associated  movements  required  to  empty  these,  are  completely  involuntary  in 
their  character ;  and  are  excited  by  the  quantity,  or  stimulating  quality,  of  the 
contents  of  the  reservoir.  But,  had  volition  no  control  over  them,  great  incon- 
veniences would  ensue ;  hence  sensation  is  excited  by  the  same  stimulus  which 
produces  the  movements ;  in  order  that,  by  arousing  the  will,  the  otherwise 
involuntary  motions  maybe  restrained  and  directed.  There  can  be  little  doubt, 
from  the  experiments  of  Dr.  M.  Hall,  as  well  as  from  other  considerations,  that 
the  associated  movements,  by  which  the  contents  of  the  rectum  and  bladder  are 
discharged,  correspond  much  with  those  of  Respiration, — being  in  their  own 
nature  involuntary,  but  capable  of  a  certain  degree  of  voluntary  restraint  and 
assistance :  whilst  the  discharge  of  the  contents  of  the  vesiculae  seminales 
would  seem  to  be  completely  automatic ;  thus  corresponding  with  the  act  of 
deglutition.  On  the  other  hand,  the  sphincters,  which  antagonize  the  expellent 
action,  are  usually  maintained  in  a  state  of  moderate  contraction,  so  as  to  afford 
a  constant  check  to  the  egress  of  the  contents  of  the  cavities;  and  this  condition 
has  been  fully  proved  by  Dr.  M.  Hall  to  result  from  their  connection  with  the 
Spinal  Cord,  ceasing  completely  when  this  is  interrupted.  On  the  other  hand, 
the  sphincter  is  certainly  in  part  controlled  by  the  will,  and  is  made  to  act  in 
obedience  to  the  warning  given  by  sensation ;  and  this  voluntary  power  is  fre- 
quently destroyed  by  injuries  of  the  Brain,  whilst  the  Spinal  Cord  remains 
able  to  perform  all  its  own  functions,  so  that  discharge  of  the  urine  and  faeces 
occurs.  In  their  moderate  action,  the  expulsors  and  the  sphincters  may  be 
regarded  as  balancing  one  another,  so  far  as  their  reflex  action  is  concerned, — 
the  latter  having  rather  the  predominance,  so  as  to  restrain  the  operation  of  the 
former.  But  when  the  quantity  or  quality  of  the  contents  of  the  cavity  gives 
an  excessive  stimulus  to  the  former,  their  action  predominates,  unless  the  will 
is  put  in  force  to  strengthen  the  resistance  of  the  sphincter ;  this  we  are  fre- 
quently experiencing,  sometimes  to  our  great  discomfort.  On  the  other  hand, 
if  the  stimulus  is  deficient,  the  will  must  aid  the  expulsors,  in  order  to  overcome 
that  resistance  which  is  due  to  the  reflex  contraction  of  the  sphincters  ;  of  this 
also  we  may  convince  ourselves,  when  a  sense  of  propriety,  or  a  prospective 
regard  to  convenience,  occasions  us  to  evacuate  the  contents  of  the  rectum  or 
bladder  without  a  natural  call  to  do  so.  The  muscular  coat  of  the  Bladder  is 
commonly  regarded  as  having,  like  that  of  the  intestinal  tube,  no  connection 
with  the  Spinal  Cord ;  but  the  experiments  of  Valentin  have  shown  that  a  con- 
nection exists,  as  in  the  former  case,  through  the  sympathetic  nerve,  affecting 
not  only  the  bladder  but  also  the  ureters.  That  physiologist  states,  that  a  very 
distinct  and  powerful  peristaltic  action  of  the  ureter,  proceeding  from  the 
kidneys  to  the  bladder,  may  be  produced,  by  irritating  the  abdominal  ganglia 


PROTECTING  AGENCY  OF  THE  SPINAL  CORD.  153 

of  the  Sympathetic,  or  the  roots  of  the  superior  abdominal  Spinal  nerves ;  and 
that  strong  contractions  of  the  bladder  are  excited,  by  irritation  of  the  inferior 
portion  of  the  abdominal  Sympathetic,  but  especially  of  its  sacral  portion,  and 
of  the  roots  of  the  middle  and  inferior  abdominal  nerves  of  the  Spine.  In  these, 
as  in  former  cases,  no  effect  is  produced  by  irritation  of  the  Spinal  Nerves, 
unless  the  portion  of  the  Sympathetic  connected  with  the  particular  organ 
be  entire. 

203.  The  influence  of  the  Spinal  Cord  on  the  Genital  organs  is  of  a  simi- 
lar character.     The  muscular  contractions  involved  in  the  Emissio  Seminis 
are  clearly  of  a  reflex  nature ;  being  independent  of  the  will,  and  not  capable 
of  restraint  by  it,  when  once  fully  excited ;  and  being  producible  in  no  other 
way,  than  (like  those  concerned  in  Deglutition)  by  a  particular  local  irritation. 
That  this  irritation  need  not  amount  to  a  sensation,  is  proved  by  the  cases 
already  referred  to  (§  182) ;  and  it  has  been  also  shown  by  experiment,  that 
section  of  the  Spinal  Cord  in  the  lumbar  region  does  not  prevent  the  act  from 
being  performed,  the  lower  division  only  being  concerned  in  the  reflexion  of 
the  impression.     It  appears,  also,  from  the  experiments  of  Valentin,  that  the 
Spinal  Cord  may  operate  on  the  Genital  organs  through  the  Sympathetic  sys- 
tem.    Contractions  were  excited  in  the  vas  deferens  and  vesiculse  seminales, 
especially  of  the  Guinea  Pig  at  the  time  of  heat,  by  irritation  of  the  inferior 
lumbar  and  highest  sacral  portions  of  the  Sympathetic ;   and  the  Fallopian 
tubes,  as  well  as  the  Uterus  itself,  may  be  excited  to  contraction,  by  irritation 
of  the  same  nerves  as  those  which  excite  the  rectum, — namely,  the  lower  lum- 
bar and  first  sacral  nerves  of  the  Spine.     This  last  fact  is  important,  in  regard 
to  the  rationale  of  the  operation  of  certain  medicines,  such  as  aloes,  which  are 
known  to  have  an  influence  on  both  parts.     In  regard  to  the  act  of  Parturition, 
there  would  seem  reason  to  believe,  from  the  evidence  of  cases  of  paraplegia, 
that,  of  the  muscles  whose  operation  is  associated  in  it,  the  diaphragm,  abdomi- 
nal muscles,  &c.,  are  called  into  action  (as  in  Defecation)  through  the  Spinal 
Cord  ;  but  that  the  contractions  of  the  Uterus  itself  are  independent  of  all  con- 
nection with  the  nervous  centres.     Of  the  reason  why  the  muscles,  which 
were  up  to  that  time  inert,  should  then  combine  in  this  extraordinary  manner, 
and  with  such  remarkable  energy,  Physiology  can  afford  no  certain  informa- 
tion.    There  can  be  little  doubt,  however,  that  the  stimulus  usually  originates 
in  the  uterus,  or  in  some  of  the  neighbouring  organs  which  are  incommoded 
by  the  pressure ;  but  it  may  also  result  from  some  condition  of  the  general 
system,  in  which  the  uterus  itself  is  but  little  concerned.     It  is  an  interesting 
fact,  which  has  been  more  than  once  observed,  that  the  fetus  may  be  expelled 
from  the  dying  body  of  the  mother,  even  after  the  respiratory  movements  have 
ceased.     This  would  appear  due  to  the  contraction  of  the  Uterine  fibres  alone, 
which,  like  those  of  the  heart  and  alimentary  canal,  retain  their  irritability 
longer  than  those  of  the  muscles  supplied  by  the  cerebro-spinal  nerves  ;  and 
the  power  of  these  would  be  unopposed  by  the  resistance  which  they  ordina- 
rily have  to  encounter ;  since  the  tone  of  all  the  muscles  surrounding  the  outlet 
would  be  destroyed  by  the  cessation  of  the  activity  of  the  Spinal  system  of 
nerves  (§  207). 

*'  XL     Protecting  Agency  of  the  Spinal  Cord. 

204.  From  the  foregoing  details  it  appears,  that  one  of  the  chief  functions 
of  the  Spinal  Cord  is  to  control  the  orifices  of  the  various  open  cavities  of  the 
body  ;  and  this  function  evidently  has  safety,  as  well  as  convenience,  in  view. 
It  has  been  manifestly  designed  by  the  All-wise  Creator,  .that  the  glottis  should 
close  against  agents  injurious  to  the  organs  within  ;  and  that  the  effort  to  vomit 
should  be  excited,  by  the  attempt  to  swallow  substances  so  nauseous  as  to  induce 


154  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

loathing.  There  is  another  protective  influence  exerted  by  it,  of  a  still  more 
remarkable  nature.  It  has  been  ascertained  by  Dr.  M.  Hall  that,  if  the  func- 
tions of  the  Brain  be  suspended  or  destroyed,  without  injury  to  the  Spinal 
system  of  nerves,  the  Orbicularis  muscle  will  contract,  so  as  to  occasion  the 
closure  of  the  eyelids,  upon  the  tarsal  margin  being  touched  with  a  feather. 
This  fact  is  interesting  in  several  points  of  view.  In  the  first  place,  it  is  a 
characteristic  example  of  pure  reflex  action,  occurring  under  circumstances  in 
which  volition  cannot  be  imagined  to  guide  it,  and  in  which  there  is  no  valid 
reason  to  believe  that  sensation  directs  it.  Further,  it  explains  the  almost  irre- 
sistible nature  of  the  tendency  to  winking,  which  is  performed  at  short  inter- 
vals by  the  contraction  of  the  Orbicularis  muscle ;  this  is  evidently  a  Spinal 
action,  capable  of  being  in  some  degree  restrained  (like  that  of  respiration)  by 
the  will,  but  only  until  such  time  as  the  stimulus  (resulting,  perhaps,  from  the 
collection  of  minute  particles  of  dust  upon  the  eyes,  or  from  the  dryness  of  its 
surface  in  consequence  of  evaporation),  becomes  too  strong  to  be  any  longer 
resisted.  Again,  we  have  in  sleep  or  in  apoplexy  an  example  of  this  purely 
spinal  action,  unbalanced  by  the  influence  of  the  will,  which,  in  the  waking 
state,  antagonizes  it  by  calling  the  levator  palpebrae  into  action.  As  soon  as 
the  will  ceases  to  act,  the  lids  droop,  and  close  over  the  eye  in  order  to  protect 
it ;  and  if  those  of  a  sleeping  person  be  separated  by  the  hand,  they  will  be 
found  presently  to  return.  Here,  as  in  studying  the  respiratory  and  other 
movements,  we  are  led  to  perceive,  that  it  is  the  Brain  alone  which  is  torpid 
during  sleep,  and  whose  functions  are  affected  by  this  torpidity.  As  Dr.  M. 
Hall  very  justly  remarks,  the  Spinal  system  never  sleeps  ;  it  is  constantly  in 
activity ;  and  it  is  thus  that,  in  all  periods  and  phases  of  life,  the  movements 
which  are  essential  to  its  continued  maintenance  are  kept  up  without  sensible 
effort. 

205.  The  closure  of  the  Pupil  against  a  strong  light  is  another  movement 
of  the   same  protective  tendency.      The  channel  through  which  that  just 
named  is  performed,  is  completed  by  the  first  branch  of  the  Fifth  and  the 
Portio  Dura  of  the  seventh.     The  contraction  of  the  pupil  is  immediately 
caused  by  the  Third  pair,  or  Motor  Oculi,  as  is  easily  shown  by  irritating 
the  trunk  of  that. nerve  and  observing  the  result.     But  it  is  not  easy  to  speak 
with  certainty  as  to  the  afferent  nerve,  by  which  the  motor  influence  is  excited. 
Although  the  contraction  of  the  pupil  is  usually  in  close  accordance  with  the 
sensation  occasioned  by  the  impression  of  light  upon  the  retina,  yet  there  is 
no  want  of  evidence  to  prove  that  the  sensation  of  light  is  not  always  necessary ; 
for,  even  when  the  sight  of  both  eyes  has  been  entirely  destroyed  by  amau- 
rosis,  the  regular  actions  have  been  witnessed  in  the  pupil,  in  accordance 
with  varying  degrees  of  light  impinging  on  the  retina.     This  fact  may  be 
explained  in  two  ways.     It  may  either  be  imagined  that  the  requisite  stimu- 
lus is  not  that  of  light  conveyed  through  the  optic  nerve,  but  that  of  heat 
conveyed  through  the  ophthalmic  branch  of  the  Fifth  pair.     Or  it  may  be 
still  supposed,  that  the  motion  results  from  an  impression  upon  the  retina, 
which  impression,  being  conducted  to  the  Brain,  ordinarily  produces  a  sensa- 
tion ;  whilst  in  these  curious  cases,  no  sensation  is  produced,  on  account  of  a 
disordered  state  of  the  part  of  the  Brain,  in  which  the  Optic  nerve  terminates ; 
though  some  filaments  of  that  nerve,  being  connected  with  the  Spinal  Cord, 
and  not  with  the  Brain,  can  produce  a  reflex  action  through  the  ,  Third  pair, 
although  no  sensation  accompany  it.     In  either  view,  the  rarity  of  the  occur- 
rence is  at  once  accounted  for ;  since  in  most  cases  of  amaurosis,  the  disease 
lies  in  the  trunk  of  the  nerve,  and  thereby  checks  both  its  spinal  and  its  cerebral 
actions. 

206.  The  physiologist  has  not  at  present  any  knowledge  of  any  similar 
protective  movements,  in  the  Human  being,  designed  to  keep  the  organ  of 


OTHER  FUNCTIONS  OF  THE  SPINAL  CORD.  155 

Hearing  from  injury  ;  but  there  can  be  little  doubt  that  those  which  we  are 
constantly  witnessing  in  other  animals,  possessing  large  external  ears,  are 
reflex  actions  excited  by  the  irritation  applied  to  them.  In  regard  to  the  Nose, 
we  find  a  remarkably  complex  action — that  of  Sneezing — adapted  to  drive  off' 
any  cause  of  irritation  (§  189).  It  will  Hereafter  be  shown  that  the  stimulus 
is  conveyed,  in  this  case,  not  through  the  Olfactory  nerve,  but  through  the 
Fifth  pair ;  so  that  it  is  not  dependent  upon  the  excitement  of  the  sensation  of 
smell.  The  act  of  Coughing,  also,  may  be  regarded  of  a  protective  character, 
being  destined  to  remove  sources  of  irritation  from  the  air-passages. 

XII.     Other  Functions  of  the  Spinal  Cord. 

207.  The  influence  of  the  Nervous  Centres  in  maintaining  what  is   com- 
monly designated  as  the  tone  of  the  muscular  system,  was  first  distinctly 
limited  by  Dr.  M.  Hall  to  the  Spinal  Cord,  and  the  system  of  nerves  connected 
with  it.     By  the  expression  in  question  is  meant,  that  state  of  moderate  con- 
traction which  causes  all  the  muscles  to  present  a  certain  degree  of  firmness, 
by  their  antagonism  with  each  other,  when  none  of  them  are  particularly  con- 
tracted or  relaxed.     The  following  experiments  by  Dr.  M.  Hall  clearly  prove 
the  influence  of  the  Spinal  Cord  on  this  functional  condition  : — "  Two  Rabbits 
were  taken  ;  from  one  the  head  was  removed  ;   from  the  other  also  the  head 
was  removed,  and  the  spinal  marrow  was  cautiously  destroyed  with  a  sharp 
instrument :  the  limbs  of  the  former  retained  a  certain  degree  of  firmness  and 
elasticity ;  those  of  the  second  were  perfectly  lax."     "  The  limbs  and  tail  of  a 
decapitated  Turtle  possessed  a  certain  degree  of  firmness  or  tone,  recoiled  on 
being  drawn  from  their  position,  and  moved  with  energy  on  the  application 
of  a  stimulus.     On  withdrawing  the  spinal  marrow  gently  out  of  its  canal,  all 
these  phenomena  ceased.     The  limbs  were  no  longer  obedient  to  stimuli,  and 
became  perfectly  flaccid,  having  lost  all  their  resilience.     The  sphincter  lost 
its  circular  form  and  contracted  state,  becoming  lax,  flaccid,  and  shapeless. 
The  tail  was  flaccid  and  unmoved  on  the  application  of  stimuli."     It  is  proba- 
ble that  this  tonic  contraction  is  strictly  a  reflex  action ;    an  impression  of 
the  condition  of  the  muscle,  corresponding  with  the  "  muscular  sense"  of  Sir 
C.  Bell,  but  not  necessarily  accompanied  by  sensation,  being  conveyed  to  the 
Spinal  Cord,  and  producing  the  stimulus  to  contraction.     The  want  of  this 
tone  is  seen  in  the  relaxation  of  the  sphincters ;  and  also  in  the  distortion  of 
the  face,  produced  by  paralysis  of  the  Portio  Dura,  and  resulting  from  the 
tonic  contraction  of  the  muscles  on  one  side  of  the  face,  unbalanced  by  that 
of  the  other  side.     Cases  have  occasionally  presented  themselves,  in  which 
the  portio  dura  has  been  paralyzed  to  the  influence  of  the  Will  (owing  to 
disease  affecting  its  Cerebral  termination),  whilst  its  Spinal  connections  have 
not  been  affected  ;  so  that  the  tone  of  the  muscles  has  been  preserved,  and  no 
distortion  of  the  face  has  'manifested  itself,  until  the  muscles  were  stimulated 
by  a  voluntary  impulse,  to  which  those  of  one  side  only  would  respond. 

208.  Nearly  allied  to  this  function  of  the  Spinal  Cord,  is  that  by  which  it  is 
subservient  to  the  maintenance  of  the  contractility  of  muscles  paralyzed  to  the 
influence  of  the  will.     It  is  well  known  that,  in  ordinary  cases  of  paralysis, 
the  muscles  lose  their  irritability  in  the  course  of  a  few  weeks,  so  that  no 
stimulus  excites  them  to  contraction;   and  it  is  also  \Vfell  known  that  their 
characteristic  structure  is  so  greatly  affected,  that,  in  progress  of  time,  no  true 
muscular  fibres  can  be  detected  in  their  place.     Experiments  on  animals,  in 
which  portions  have  been  removed  from  the  nerves  supplying  the  limbs,  con- 
duct to  exactly  the  same  result  as  the  experiments  made  for  us  by  diseased 
conditions  in  Man.     Now  Dr.  M.  Hall  has  pointed  out  that, — in  cases  where 
the  muscles  are  paralyzed  to  the  influence  of  the  will,  through  disease  of  the 


156  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Brain  or  of  the  upper  part  of  the  Spinal  Cord,  but  retain  their  power  of  reflex 
action,  (the  nervous  circle  which  operates  through  the  Spinal  Cord  not  being 
interrupted) — the  contractility  of  the  muscles  is  not  diminished,  but  appears 
to  be  sometimes  even  increased  ;  and  he  has  suggested  that  this  fact  may  be 
made  available  as  a  means  of  diagnosis  in  obscure  cases  of  paralysis.  Thus, 
in  some  cases  of  Paraplegia,  the  reflex  actions  may  be  excited  ;  in  others  they 
cannot  be.  In  the  former,  the  disease  must  be  in  the  dorsal  or  cervical  portion 
of  the  Spinal  Cord,  leaving  its  lumbar  portion  free  to  carry  on  the  reflex  actions, 
though  its  connection  with  the  brain  is  interrupted.  In  the  latter,  the  disease 
is  probably  within  the  lumbar  vertebrae,  involving  that  portion  of  the  Spinal 
Cord  through  which  the  reflex  actions  of  the  lower  extremities  are  produced. 
In  like  manner,  in  paralysis  of  a  single  arm  or  of  one  leg,  if  the  reflex  actions, 
and  the  contractility  of  the  muscles  on  the  application  of  a  direct  stimulus 
(such  as  galvanism),  remain  unimpaired,  the  cause  is  probably  seated  in.  the 
Brain  ;  whilst,  if  the  tone  of  the  muscles  be  completely  lost,  and  no  contraction 
can  be  induced  in  them,  the  cause  of  the  paralysis  is  probably  somewhere  in 
the  neighbourhood  of  the  roots  of  the  nerves  of  the  part  affected.  There  is  no 
good  ground  for  believing,  however,  that  the  contractility  of  the  muscles  is 
directly  dependent  on  their  connection  with  the  Spinal  Cord, — a  doctrine 
which  is  inconsistent  (as  will  be  shown  hereafter)  with  well-established  facts. 
It  is  well  known  that  muscular  structure  requires,  for  its  perfect  nutrition,  to 
be  kept  in  a  state  of  functional  activity.  If  the  muscles  of  the  leg,  for  example, 
be  disused  for  a  long  time,  their  nutrition  is  greatly  impaired,  and  their  con- 
tractility is  almost  suspended  ;  even  though  they  retain  their  connection  with 
the  nervous  centres,  and  the  latter  be  in  their  normal  condition.  It  is  to  be 
expected,  then,  that,  if  a  muscle  be  completely  put  out  of  the  pale  of  nervous 
influence,  its  nutrition  should  be  speedily  impaired,  and  its  contractility  alto- 
gether lost ;  but  if  the  influence  of  the  Brain  only  be  withdrawn  from  it,  and 
its  connection  with  the  Spinal  Cord  be  uninterrupted,  it  will  be  in  a  state  of 
continual  action,  by  the  operation  of  various  reflected  stimuli ;  and  this  action 
will  be  sufficient  to  maintain  its  nutrition,  and  to  -prevent  the  loss  of  its  con- 
tractility (See  Chap.  V.). 

209.  The  fact,  that  the  action  of  the  Heart  is  in  some  degree  under  the 
control  of  the  Spinal  Cord,  has  long  been  known.     It  is  not  a  little  curious 
that,  although  its  movements  will  continue  regularly,  after  complete  section  of 
all  its  nerves,  any  sudden  and  severe  impression  upon  a  large  part  of  the 
Nervous  Centres, — such  as  crushing  the  Brain  or  Spinal  Cord, — will  produce 
a  great  diminution  in  their  frequency,  or  will  even  occasion  their  entire  cessa- 
tion, if  the  nervous  connection  be  entire.     It  will  be  hereafter  shown,  that  the 
influence  is  partly  communicated  by  the  Par  Vagum ;  but  it  appears,  from  the 
experiments  of  Valentin,  that  the  Sympathetic  is  in  part,  as  in  the  case  of  the 
motions  of  the  alimentary  canal,  the  channel  by  which  it  is  transmitted.     He 
found  that,  when  the  heart  had  ceased  to  beat,  its  contractions  might  be  re- 
newed by  irritation  of  the  roots  of  the  Spinal  Accessory  nerve,  and  of  the  first 
four  Cervical  nerves,  and  also  of  the  first  cervical  ganglion  of  the  Sympathetic. 
He  tjiinks  that  he  has  also  witnessed  distinct  contractions  of  the  thoracic  aorta, 
of  the  inferior  cavity,  and  of  the  thoracic  duct,  upon  irritation  of  the  neigh- 
bouring portion  of  the  Sympathetic  system,  which  evidently  derives  its  whole 
motor  power  from  the  Spinal  Cord.    The  ductus  choledocus  has  also  been  seen 
by  him  to  contract  on  irritation  of  the  right  splanchnic  nerve. 

210.  Lastly,  we  have  to  inquire  how  far  the  Reflex  action  of  the  Spinal 
Cord  is  concerned  in  the  locomotive  actions  of  the  lower  extremities  in  Man. 
It  will  be  remembered  that,  in  the  Dytiscus  whose  head  had  been  removed, 
(§  146,)  the  stimulus  of  the  contact  of  water  immediately  excited  regular  and 
continued  locomotive  actions,  which  lasted  for  some  time.     So  in  the  cases 


OTHER  FUNCTIONS  OF  THE  SPINAL  CORD.  157 

already  quoted,  (§§  177,  8,)  when  the  control  of  the  will  over  the  lower  extre- 
mities was  lost,  powerful  muscular  actions  were  excited  in  them  through  the 
Spinal  Cord  alone.  In  the  healthy  condition  of  the  Human  system,  when  the 
Will  is  controlling  all  the  movements  which  are  not  immediately  concerned  in 
the  maintenance  and  regulation  of  the  organic  functions,  no  such  actions  can 
be  excited ;  but,  in  proportion  as  its  control  is  lost,  does  the  independent  power 
of  the  Spinal  Cord  manifest  itself.  The  more  such  actions  are  of  a  simple 
rhythmical  character,  similar  to  those  of  Respiration,  the  more  does  it  seem 
that  they  may  with  probability  be  referred  to  the  Spinal  system ;  and  if  we 
attribute  to  this  (as  we  can  scarcely  help  doing)  the  rapid  vibration  of  the 
wings  of  Insects,  there  seems  no  reason  why  we  should  not  extend  the  same 
view  to  the  wings  of  Birds.  Such  an  explanation  of  their  movements  will 
account  for  their  occasional  continuance,  without  apparent  fatigue,  during  a 
period  through  which  no  known  voluntary  effort  can  endure ;  for  it  is  one  of 
the  attributes  of  the  Spinal  system  of  nerves,  well  pointed  out  by  Dr.  M.  Hall, 
that  the  exercise  of  the  muscles  excited  by  it  does  not  occasion  fatigue,  the 
sense  of  which  is  Cerebral  only.  It  would  seem  to  the  Author  more  probable, 
however,  that  those  movements  which  guide  the  body,  and  which  must  them- 
selves be  directed  by  Sensation,  are  to  be  referred  to  a  class  intermediate 
between  the  Voluntary  and  the  Reflex,  which  may  be  properly  termed  Instinc- 
tive. Several  actions  in  Man,  which  were  at  first  Voluntary,  appear  at  last  to 
be  performed  as  instinctively,  or  intuitively,  as  they  are  in  the  lower  animals 
from  the  commencement  of  their  existence.  (See  Section  xvm.  of  the  present 
Chapter.) 

211.  It  would  not  be  right  to  conclude  this  account  of  the  principal  functions 
.of  the  Spinal  Cord,  without  adverting  to  some  of  the  leading  Pathological 
applications  of  the  physiological  doctrines,  which  have  been  developed  in  it. 
A  large  part  of  these  were  first  pointed  out  by  Dr.  M.  Hall  ;*  and  they  are 
receiving  continual  and  important  extensions  from  his  own  labours  and  those 
of  other  practical  inquirers.     It  may  be  remarked,  in  the  first  place,  that  the 
power  of  the  whole  Spinal  system  is  capable  of  being  morbidly  diminished  or 
augmented.     It  may  even  be  for  a  time  almost  completely  suspended,  as  in 
Syncope ;  which  state  maybe  induced  by  sudden  and  violent  impressions,  either 
of  a  mental  or  physical  nature,  that  operate  upon  the  whole  nervous  system  at 
once,— commencing,  however,  in  the  Brain.     It  is  to  be  remarked  that,  in 
recovering  from  these,  it  is  the  Spinal  system  of  which  the  activity  is  first 
renewed, — the  respiratory  movements  recommencing,  and  the  power  of  swal- 
lowing being  restored,  before  any  voluntary  actions  can  be  performed.     A  cor- 
responding state  may  be  induced  in  particular  portions  of  the  system,  by  con- 
cussion ;  as  is  seen  in  severe  injuries  of  the  Spinal  Cord,  which  are  almost 
invariably  followed  for  a  time  by  the  suspension  of  its  functions.     Again,  the 
power  of  the  whole  Spinal  Cord  may  be  diminished  by  various  causes,  such  as 
enfeebled  circulation,  pressure,  &c.;  and  then  we  have  torpidity  of  the  whole 
muscular  system.    If  oppression  exists  in  the  brain,  the  functions  of  the  Medulla 

.  oblongata  will  be  especially  affected ;  and  if  it  be  prolonged  and  sufficiently 
severe,  Asphyxia  will  result  from  the  interruption  of  the  respiratory  movements 
which  it  occasions. 

212.  On  the  other  hand,  the  excitability  of  the  whole  Cord,  or  of  particular 
parts  of  it,  may  be  morbidly  increased.     This  is  especially  seen  in  Tetanus, 
Hydrophobia,  and  the  artificial  tetanus  induced  by  Strychnine  ;  so  that  the 
slightest  external  stimulus  is  sufficient  to  induce  reflex  actions  in  their  most 
terrific  forms.     It  is  interesting  to  remark,  that,  in  these  formidable  diseases, 

*  See  especially  his  Treatise  on  the  Diseases  and  Derangements  of  the  Nervous 
System. 

14 


158  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  functions  of  the  muscles  controlling  the  various  orifices  are  those  most 
affected ;  and  it  is  by  the  spasms  affecting  the  organs  of  respiration  or  deglu- 
tition that  life  is  commonly  terminated.  Various  remedial  agents  will  probably 
be  found  to  operate,  by  occasioning  increased  excitability  in  some  particular 
segments  of  the  Cord  ;  so  that  the  usual  stimuli  applied  to  the  parts  connected 
with  these,  will  occasion  increased  muscular  action.  This  seems  to  be  the 
case,  for  example,  in  regard  to  the  influence  of  aloes  on  the  rectum  and  uterus, 
cantharides  on  the  neck  of  the  bladder  and  adjoining  parts,  and  secale  cornu- 
tum  on -the  uterus.  The  mode  of  influence  of  cantharides  is  illustrated  by  a 
curious  case,  related  by  Dr.  M.  Hall,  of  a  young  lady  who  lost  the  power  of  reten- 
tion of  urine  in  consequence  of  a  fatty  tumour  in  the  spinal  canal,  which 
gradually  severed  the  Spinal  Cord,  and  induced  paraplegia.  The  power  of 
retaining  the  urine  was  always  restored  for  a  time  by  a  dose  of  tincture  of 
cantharides,  which  augmented  the  excitability  of  the  segment  of  the  cord, 
with  which  the  sphincter  vesicae  is  connected.  The  researches  of  Valentin, 
when  grafted  (as  it  were)  on  the  doctrines  of  Dr.  M.  Hall,  afford  the  key  to 
the  explanation  of  the  numberless  sympathetic  influences  of  the  organs  of 
nutrition,  &c.,  upon  one  another ;  by  showing  that  they  are  all  connected  with 
the  Spinal  Cord ;  and  that  the  muscular  structure,  with  which  they  are  all 
provided,  may  be  excited  to  contraction  through  it.  And,  lastly,  t%he  more 
recent  observations  of  Dr.  M.  Hall,  in  regard  to  the  peculiar  excitor  power 
that  belongs  to  the  nervous  fibres  distributed  on  various  serous  and  fibrous 
membranes,  will  probably  lead,  when  they  have  been  fully  carried  out,  to  the 
explanation  of  the  various  convulsive  actions  that  result  from  pressure  or 
irritation  affecting  these  parts. 

XIII.   Comparative  Anatomy  of  the  Encephalon. 

213.  The  assistance  which  the  Physiologist  has  hitherto  derived  from  the 
study  of  the  Comparative  Anatomy  of  the  Encephalon  in  Vertebrata,  is  not  so 
great  as  might  have  been  expected  ;  there  can  be  little  doubt,  however,  that 
much  is  yet  to  be  learned  from  it.  Certain  general  inferences  appear  well 
established;  and  it  is  chiefly  in  questions  of  detail  that  difficulties  still  exist. 
The  Encephalon  may  be  described  as  consisting  of  the  Cerebral  Hemispheres, 
the  Cerebellum,  and  the  Medulla  Oblongata  with  its  chain  of  ganglia.  The 
relative  proportion  of  the  two  former  to  the  latter  is  such  in  Man,  that  their 
character  would  not  be  readily  understood  by  the  inspection  of  his  Brain  alone ; 
and  it  is  one  of  the  most  interesting  results  of  the  comparison  of  it  with  the 
brains  of  animals  of  the  inferior  tribes  that  the  great  change  which  we  there 
find  in  the  proportion  of  the  parts,  makes  evident  the  importance  of  what 
would  have  been  otherwise  considered  subordinate  appendages.  This  is 
peculiarly  the  case  in  Fishes.  There  may  be  noticed  in  the  Encephalon  of 
that  class  four  distinct  ganglionic  enlargements;  of  which  the  posterior  is 
usually  on  the  median  line,  whilst  the  others  are  in  pairs.  The  posterior, 
from  its  position  and  connections,  is  evidently  to  be  regarded  in  the  light  of  a 
Cerebellum;  and  it  bears  a  much  larger  proportion  to  the  rest,  in  this  class, 
than  in  any  other.  The  pair  in  front  of  this  are  not  the  hemispheres  of  the 
Cerebrum,  as  their  large  size  in  some  instances  (the  Cod  for  instance)  might 
lead  us  to  suppose ;  but  they  are  immediately  connected  with  the  Optic  nerve, 
which,  in  fact,  terminates  in  them,  and  are  therefore  to  be  considered  (like 
the  chief  part  of  the  cephalic  masses  of  In vertebrated  animals)  as  Optic  Ganglia. 
In  front  of  these  are  the  Cerebral  Hemispheres,  which  are  small,  generally 
destitute  of  convolutions,  and  possess  no  ventricle  in  their  interior, — except 
in  the  Sharks  and  Rays,  in  which  they  are  much  more  highly  developed  than 
in  the  Osseous  Fishes.  Anterior  to  these  is  another  pair  of  ganglionic 


Pike. 


COMPARATIVE  ANATOMY  OF  THE  ENCEPHALON. 

Fig.  27. 
Cod, 


159 


Brains  of  Fishes,  after  Leuret;  A,  olfactive  lobes  or  ganglia;  B,  cerebral  hemispheres;  c,  optic  lobes;  D, 
cerebellum;  o  I,  olfactory  nerve ;  o  p,  optic  nerve;  p  a,  patheticus;  m  o,  motor  oculi;  a  b,  abducens ;  t  r  t, 
trifacial ;  fa,  facial ;  a  M,  auditory ;  v  a  g,  vagus ;  1 1:  tubercles  or  ganglia  of  the  trifacial ;  t  r,  tubercles  of 
the  vagus. 

enlargements,  from  which  the  Olfactory  nerves  arise;  and* these  are,  therefore, 
correctly  designated  as  the  Olfactive  tubercles  or  ganglia.  In  some  instances, 
these  ganglia  are  not  immediately  seated  upon  the  prolonged  spinal  cord, 
but  are  connected  with  it  by  long  peduncles  ;  this  is  the  case  in  the  Sharks  : 
and  we  are  thus  led  to  perceive  the  real  nature  of  the  portion  of  the  trunk  of 
the  Olfactory  nerve  in  Man,  which  lies  within  the  cranium,  and  of  its  bulbous 
expansion  on  the  Ethmoid  bone.  Besides  these  principal  ganglionic  enlarge- 
ments, there  are  often  smaller  ones,  with  which  other  nerves  are  connected. 
Thus  in  the  Shark,  we  find  a  pair  of  tubercles  of  considerable  size,  at  the 
origin  of  the  Trifacial  nerves;  and  another  pair  in  most  Fishes,  at  the  roots  of 
the  Vagi.  In  some  instances,  too,  distinct  Auditory  ganglia  present  themselves. 
214.  The  Optic  Lobes  of  Fishes  have  no  analogy  whatever  with  the  Thai- 
ami  optici  of  Mammalia;  the  connection  of  which,  with  the  Optic  nerves,  is 
apparent  only.  They  are  rather  to  be  compared  with  the  Tubercula  Quadri- 
gemina,  which  are  the  real  ganglia  of  the  Optic  nerve.  Their  analogy  is  not 
so  complete,  however,  to  these  bodies  in  the  fully-formed  Brain  of  Man,  as  it 
is  to  certain  parts  which  occupy  their  place  at  an  earlier  period.  The  Third 
Ventricle^  which  is  quite  distinct  from  the  Corpora  Q,uadrigemina,  is  hollowed 
out,  as  it  we%,  from  the  floor  of  the  Optic  Lobes  of  Fishes;  and  the  Anterior 
Commissure  bounds  its  front :  hence  these  must  be  considered  as  analogous  to 
the  parts  surrounding  the  Third  Ventricle,  as  well  as  to  the  Corpora  Cluadri- 
gemina.  This  is  made  evident  by  the  fact,  observed  by  Miiller,  that,  in  the  • 
Lamprey,  there  is  a  distinct  Lobe  of  the  third  ventricle,  replacing  the  Optic 
Lobes  of  other  fishes,  and  partly  giving  origin  to  the  optic  nerves ;  and  a  sepa- 
rate vesicle,  analogous  to  the  Corpora  Quadrigemina.  With  this  condition, 
the  early  state  of  the*  Brain  in  the  embryo  of  the  Bird  and  Mammiferous 


160 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


Fig.  28. 


Human  embryo  of  sixth  week,  enlarged 
about  thret  times;  a,  vesicle  of  corpora  quad- 
rigemina;  b,  vesicle  of  cerebral  hemispheres; 
c.  vesicle  of  thalami  optici  and  third  ventricle ; 
rf,  vesicle  for  cerebellum  and  medulla  oblon- 
gata;  e,  auditory  vesicle;  f,  olfactory  fossa; 
A,  liver;  **,  caudal  extremity.  (After  Wag- 
ner.) 


animal,  and  even  in  Man  himself,  bears  a 
very  close  correspondence.  The  Erice- 
phalon  consists,  at  this  time,  of  a  series  of 
vesicles,  arranged  in  a  line  with  each  other, 
of  which  those  that  represent  the  Cerebrum 
are  the  smallest,  whilst  that  which  repre- 
sents the  Cerebellum  is  the  largest.  The 
latter,  as  in  Fishes,  is  single,  covering  the 
fourth  ventricle  on  the  dorsal  surface  of  the 
Medulla  Oblongata.  Anterior  to  this,  is 
the  single  vesicle  of  the  Corpora  Gluadri- 
gemina,  from  which  the  Optic  nerve  chiefly 
arises :  this  has  in  its  interior  a  cavity,  the 
ventricle  of  Sylvius,  which  exists  even  in 
the  adult  Bird,  where  the  Corpora  duadri- 
gemina  are  pushed,  as  it  were,  from  each 
other  by  the  increased  development  of  the 
Cerebral  hemispheres.  In  front  of  this 
the  vesicle  of  the  Third  Ventricle, 


is 


which  contains  also  the  Thalami:  as  de- 
velopment proceeds,  this,  like  the  preced- 
ing, is  covered  by  the  enlarged  hemi- 
spheres; whilst  its  roof  becomes  cleft 
anteriorly  on  the  median  line,  so  as  to 
form  the  anterior  entrance  to  the  cavity.  Still  more  anteriorly  is  the  double 
vesicle,  which  represents  the  hemispheres  of  the  Cerebrum:  this  has  a  cavity 
on  each  side,  the  floor  of  which  is  formed  by  the  corpora  striata.  The  cavity 
of  the  cerebral  vesicles  has  at  first  no  opening,  except  into  that  of  the  third 
ventricle ;  at  a  later  period  is  formed  that  fissure  on  the  inferior  and  posterior 
side,  whick  (under  the  name  of  the  fissure  of  Sylvius)  enables  the  membranes 
enveloping  the  brain  to  be  reflected  into  the  lateral  ventricles. 

215.  Thus  it  will  be  seen  that  the  real  analogy  between  the  brain  of  the 
Human  foetus  and  that  of  the  adult  Fish,  is  not  so  close  as,  from  the  resem- 
blance in  their  external  form,  might  have  been  supposed.  In  the  small  pro- 
portion which  the  Cerebral  Hemispheres  bear  to  the  other  parts,  there  is 
evidently  a  very  close  correspondence ;  and  this  extends  also  to  the  general 
simplicity  of  their  structure,  the  absence  of  convolutions,  and  the  deficiency  of 
commissures.  But  there  is  a  much  nearer  analogy  between  the  fatal  brain 
of  the  Fish,  and  the  fatal  brain  of  the  Mammal ;  indeed,  at  the  earliest  period 
of  their  formation,  they  could  not  be  distinguished ;  during  their  advance  to  the 
permanent  condition,  however,  each  undergoes  changes,  which  are  so  much 
more  decided  in  the  higher  animals  than  in  the  lower,  that  in  the  latter  there 
seems  but  little  departure  from  the  festal  condition,  whilst  in  the  former  the 
condition  appears  entirely  changed.  Hence  it  is  not  correct  to  assert,  as  is 
frequently  done, — that  the  Brain,  or  any  other  organ,  in  the  higher  animals, 
passes  through  a  series  of  forms,  which  are  parallel  to  the  permanent  forms  of 
the  same  organ  in  different  parts  of  the  animal  scale  :  since  the  Ja.ct  is  rather, 
that  the  more  nearly  all  are  traced  back  to  their  first  origin,  the  closer  will 
their  conformity  be  found  to  be ;  the  subsequent  development  of  each  taking 
place  not  only  in  various  degrees,  but  in  different  modes  or  directions ;  so  that 
the  resemblances  presented  by  the  higher,  at  different  epochs  of  their  evolution, 
to  the  permanent  conditions  of  the  lower,  are  often  far  from  being  complete.* 

*  For  a  fuller  examination  of  this  interesting  question,  see  Gfeneral  and  Comparative 
Physiology,  §  244.  ^ 


COMPARATIVE  ANATOMY  OF  THE  ENCEPHALON. 


161 


Fig.  29. 


This  we  have  seen  to  be  the  case  in  the  present  instance  ;  the  vesicle  of  the 
Corpora  Q,uadrigemina,  and  that  of  the  Third  Ventricle,  uniting  to  form  the 
Optic  Lobes  of  Fishes,  whilst  in  the  higher  Vertebrata  they  remain  distinct ; 
so  that  there  is  no  single  part  with  which  the  Optic  Lobes  can  be  properly 
compared,  either  in  the  fetal  or  perfect  state  of  the  Human  Brain. 

216.  The  Brain  of  Reptiles  does  not  show  any  con- 
siderable advance  in  its  general  structure  above  that 
of  Fishes  ;  but  the  Cerebral  Hemispheres  are  usually 
much  larger  in  proportion  to  the  Optic  lobes ;  whilst 
the  Cerebellum  is  smaller.     The  very  low  develop- 
ment of  the  Cerebellum  is  especially  seen  in  the  Frog 
(Fig.  16),  in  which  it  is  so  small  as  not  even  to  cover- 
in  the  Fourth  Ventricle ;  but  it  is  common  to  nearly 
the  whole  group.     The  deficiency  in  commissures  still 
exists  to  a  great  extent.     The  Anterior  Commissure 
in    front  of  the  third  ventricle,  is   the  only  uniting 
band  which  can  be  distinctly  traced  in  Fishes ;  and 
Reptiles  have,  in  addition  to  this,  a  layer  of  uniting 
fibres  which  may  be  compared  to  the  Fornix  ;  but  as 
yet  there  is  no  vestige  of  a  true  Corpus  Callosum, 
or  great  transverse  commissure  of  the  hemispheres. 
The  distinction  between  the  tubercula  quadrigemina, 
and  the  parts  enclosing  the  third  ventricle,  is  more 
obvious  than  in  Fishes ;  in  fact  the  Optic  ganglia  of 
Reptiles  correspond  pretty  closely  with  the  Vesicle  of 
the  tubercula  quadrigemina  in  the  brain  of  the  foetal 
Mammal. 

217.  This  is  still  more  evident  in  Birds,  in  whose 
Encephalon  the  Tubercula  duadrigemina   or  Optic 
Ganglia,  and  the  Thalami  with  their  included  ventri- 
cle, are  obviously  very  distinct  parts.     The  Cerebral 
Hemispheres  attain  a  great  increase  of  development, 

and  arch  backwards,  so  as  partly  to  cover  the  Optic  ganglia ;  and  these  are 
separated  from  one  another,  and  thrown  to  either  side.  The  Cerebellum  also 
is  much  increased  in  size,  proportionably  to  the  Medulla  Oblongata  and  its 


Brain  of  Turtle ;  A,  olfactive 
ganglia;  B,  cerebral  hemi- 
spheres; c,  optic  ganglia;  D, 
cerebellum. 


Fig.  30. 


thai 


Brain  of  Buzzard ;  the  olfactive  ganglia  are 
concealed  beneath  B,  the  hemispheres ;  c,  op- 
tic ganglia;  D,  cerebellum;  g,  pineal  gland. 


The  hemispheres,  B,  drawn  to  either  side  to 
show  the  subjacent  parts;  c,  the  optic  lobes; 
D,  cerebellum;  thai,  thalamus  optic  us ;  e  s} 
corpus  striattun. 


162 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 


ganglia;  and  it  is  sometimes  marked  with  transverse  lines,  which  indicate 
the  intermixture  of  gray  and  white  matter  in  its  substance ;  there  is  as  yet, 
however,  no  appearance  of  a  division  into  hemispheres.  On  drawing  apart 
the  hemispheres  of  the  Cerebrum,  the  Corpora  Striata,  Optic  Thalami,  and 
Tubercula  duadrigemina  or  Optic  Ganglia,  are  seen  beneath  them;  the 
size  of  the  last  still  bears  a  considerable  proportion  to  that  of  the  whole 
Encephalon.  The  Optic  Ganglia  are  still  hollow,  as  they  are  in  the  embryo 
condition  of  Man.  Indeed  the  Brain  of  the  Human  foetus  about  the  twelfth 
week  will  bear  comparison,  in  many  respects,  with  that  of  the  Bird.  The 
Cerebral  hemispheres,  much  increased  in  size,  and  arching  back  over  the 

Fig.  31. 


e..- 


Brain  of  human  embryo  at  twelfth  week;  A,  seen  from  behind;  B,  side  view;  c,  sectional  view •  a  cor- 
pora quadrigemina;  b  b,  hemispheres ;  rf,  cerebellum;  e,  medulla  oblongata ;/,  optic  thalamus;  g,  floor  of 
third  ventricle ;  i,  olfactory  nerve.  (After  Tiedemann.) 

Thalami  and  Optic  ganglia,  but  destitute  of  convolutions  and  imperfectly  con- 
nected by  commissures, — the  large  cavity  still  existing  in  the  Optic  ganglia, 
and  freely  communicating  with  the  third  ventricle, — and  the  imperfect  evolu- 
tion of  the  Cerebellum, — make  the  correspondence  in  the  general  condition  of 
the  two  very  considerable. 

218.  The  Brain  of  the  lowest  Mammalia  presents  but  a  slight  advance  upon 
that  of  Birds,  in  regard  both  to  the  relative  proportions  of  its  parts,  and  to  their 
degree  of  development.  Thus,  in  the  Marsupialia,  the  Cerebral  hemispheres 
exhibit  no  convolutions ;  and  the  great  transverse  commissure, — the  Corpus 

Fig.  32. 


•Agr 


Upper  and  under  surface  of  Brain  of  Rabbit;  A,  B,  „,  as  before ;  o  I,  olfactive  lobes;  o  Coptic  nerve- 
m  o  motor  ocuh ;  c  m  corpora  mamillaria ;  c  c,  crus  cerebri ;  „  ,,  pons  varolii ;  p  a,  patheticus ;  t  r  i,  trifa' 
cial ;  a  b,  abducens ;  fa  c,  facial ;  a  u,  auditory ;  „  a  g,  vagus ;  ,,  spinal  accessory ;  h  y  p,  hypoglossal. 


COMPARATIVE  ANATOMY  OF  THE  ENCEPHALON.  163 

Callosum, — is  deficient.  There  is  gradually  to  be  noticed,  however,  in  ascend- 
ing the  scale,  a  backward  prolongation  of  the  Cerebral  hemispheres  ;  so  that 
first  the  Optic  ganglia,  and  then  the  Cerebellum,  are  covered  by  them.  The 
latter  partly  shows  itself,  however,  in  all  but  the  Q,uadrumana,  when  we  look 
at  the  brain  from  above  downwards  ;  in  the  Rabbit,  which  is  among  the  lowest 
in  this  respect  of  the  true  Viviparous  Mammajia,  nearly  the  whole  of  the  Cere- 
bellum is  uncovered.  In  proportion  to  the  increase  of  the  Cerebral  hemi- 
spheres, there  is  a  diminution  in  the  size  of  the  ganglia  immediately  connected 
with  the  organs  of  sense  ;  and  this  in  comparison,  not  only  with  the  rest  of  the 
Encephalon,  but  even  with  the  Spinal  Cord ;  so  that  in  Man  the  Tubercula 
Q,uadri gemma  are  absolutely  smaller  than  they  are  in  many  animals  of  far 
inferior  size.  The  internal  structure  of  the  hemispheres  becomes  more  com- 
plex in  the  same  proportion  as  their  size  and  the  depth  of  the  convolutions 
increase  ;  and  in  Man  all  these  conditions  present  themselves  in  a  far  higher 
degree  than  in  any  other  animal.  In  fact  it  is  only  among  the  Ruminantia, 

[Fig.  33. 


A  view  of  the  base  of  the  Cerebrum  and  Cerebellum,  together  with  their  nerves;  1,  anterior  extremity 
of  the  fissure  of  the  hemispheres  of  the  brain;  2,  posterior  extremity  of  the  same  fissure;  3.  the  anterior 
lobes  of  the  cerebrum;  4,  its  middle  lobe;  5,  the  fissure  of  Sylvius;  6,  the  posterior  lobe  of  the  cerebrum; 
7,  the  point  of  the  infundibulum ;  8,  its  body;  9,  the  corpora  albicantia;  10,  cineritious  matter;  11,  the  crura 
cerebri;  12,  the  pons  varolii;  13,  the  top  of  the  medulla  oblongata;  14,  posterior  prolongation  of  the  pons 
varolii;  15,  middle  of  the  cerebellum;  16,  anterior  part  of  the  cerebellum;  17,  its  posterior  part  and  the 
fissure  of  its  hemispheres;  18,  superior  part  of  the  medulla  spinalis;  19,  middle  fissure  of  the  medulla 
oblongata;  20,  the  corpus  pyramidale;  21,  the  corpus  restiforme;  22,  the  corpus  olivare;  23,  the  olfactory 
nerve;  24,  its  bulb;  25,  its  external  root;  23,  its  middle  root;  27,  its  internal  root;  28,  the  optic  nerve 
beyond  the  chiasm;  29,  the  optic  nerve  before  the  chiasm;  30,  the  motor  oculi,  or  third  pair  of  nerves ; 
31,  the  fourth  pair,  or  pathetic  nerves;  32,  the  fifth  pair,  or  trigemini  nerves;  33,  the  sixth  pair,  or  motor 
externus;  34,  the  facial  nerve;  35,  the  auditory— the  two  making  the  seventh  pair;  36,  37,  38,  the  eighth 
pair  of  nerves.  (The  ninth  pair  is  not  here  seen.)  ] 


164  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Pachydermata,  Carnivora,  and  Quadrumana,  that  regular  convolutions  can  be 
said  to  exist.  The  correspondence  between  the  bulbous  expansion  of  the 
Olfactive  Nerves  in  Mammalia,  and  the  Olfactive  lobes  of  the  lower  Vertebrata, 
is  made  evident  by  the  presence,  in  both  instances,  of  a  cavity  which  commu- 
nicates with  the  lateral  ventricle  on  each  side ;  it  is  in  Man  only  that  this  cavity 
is  wanting.  The  external  form  of  the  Corpora  Q,uadrigemina  of  Mammalia, 
differs  from  that  of  the  Optic  ganglia  of  Birds,  owing  to  the  division  of  the 
former  into  anterior  and  posterior  eminences,  (the  nates  and  testes) ;  and  there 
is  also  an  internal  difference,  occasioned  by  the  contraction  of  the  cavity  or 
ventricle,  which  now  only  remains  as  the  Aqueduct  of  Sylvius.  The  Cere- 
bellum is  chiefly  remarkable  for  the  development  of  its  lateral  parts  or  hemi- 
spheres ;  the  central  portion,  sometimes*called  the  vermiform  process,  is  rela- 
tively less  developed  than  in  the  lower  Vertebrata,  in  which  it  forms  the  whole 
of  the  organ. 

XIV.  Functions  of  the  Cephalic  Nerves. 

219.  Before  proceeding  to  inquire  into  the  functions  of  the  different  parts  of 
the  Encephalon,  it  seems  desirable  to  bring  together  what  is  known  in  regard 
to  the  functions  of  the  Nerves  specially  connected  with  them ;   so  that,  by 
tracing  their  connections,  we  may  be  able  to  obtain  some  light  upon  this  very 
obscure,  though  most  interesting  and  important  subject. 

220.  That  the  First  pair,  or  Olfactory  nerves,  minister  to  the  sense  of  Smell, 
has  long  been  known;  yet  it  could  not  be  .  predicated  without  experimental 
inquiry,  that  it  is  not  a  conductor  of  the  impressions  which  produce  ordinary 
sensation;  nor  that  it  is  destitute  of  all  power  of  exciting  muscular  movement, 
either  by  direct  or  reflex  action.     Anatomical  examination  of  the  distribution 
of  this  nerve,  proves  that  it  is  not  one  which  directly  conveys  motor  influence 
to  any  muscles ;  since  all  its  branches  are  distributed  to  the  membrane  lining 
the  nasal  cavity.     Experimental  inquiry  leads  to  the  same  result ;  for  no  irri- 
tation of  the  peduncles  or  branches  excites  any  muscular  movement.     Further, 
no  irritation  of  any  part  of  this  nerve  excites  reflex  actions  through  other 
nerves.     Again,  it  is  not  a  nerve  of  common  sensation;  for  animals  exhibit  no 

[Fig-  34. 


A  view  of  the  First  pair,  or  Olfactory  Nerves,  with  the  Nasal  Branches  of  the  Fifth  pair :  1,  frontal  sinus; 
2,  sphenoidal  sinus;  3,  hard  palate  ;  4,  bulb  of  the  olfactory  nerve;  5,  branches  of  the  olfactory  nerve  on 
the  superior  and  middle  turbinated  bones;  G,  spherio-palatine  nerves  from  the  second  branch  of  the  fifth 
pair;  7,  internal  nasal  nerve  from  the  first  branch  of  the  fifth:  8,  branches  of  7  to  the  Schneiderian  mem- 
brane;  9.  ganglion  of  Cloquet  in  the  foramen  incisivum;  10,  anastomosis  of  the  branches  of  the  fi.th  pair 
on  the  inferior  lurbinated  bone.] 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  1C5 

sign  of  pain  when  it  is  subjected  to  any  kind  of  irritation.  Neither  the  divi- 
sion of  the  nerve,  nor  the  destruction  of  the  olfactive  ganglia,  seems  to  incon- 
venience them  materially.  They  take  their  food,  move  with  their  accustomed 
agility,  and  exhibit  the  usual  appetites  of  their  kind.  The  common  sensibility 
of  the  parts  contained  in  the  olfactive  organ  is  in  no  degree  impaired,  as  is 
shown  by  the  effect  of  irritating  vapours ;  but  the  animals  are  destitute  of  the 
sense  of  smell,  as  is  shown  by  the  way  in  which  these  vapours  affect  them. 
At  first  they  appear  indifferent  to  their  presence,  and  then  suddenly  and  vehe- 
mently avoid  them,  as  soon  as  the  Schneiderian  membrane  becomes  irritated. 
Moreover,  if  two  dogs,  with  the  eyes  bandaged,  one  having  the  olfactory 
nerves  and  ganglia  sound,  and  the  other  having  had  them  destroyed,  are 
brought  into  the  neighbourhood  of  the  dead  body  of  an  animal,  the  former 
will  examine  it  by  its  smell ;  whilst  the  latter,  even  if  he  touches  it,  pays  no 
attention  to  it.  This  experiment  Valentin  states  that  he  has  repeated  several 
times,  and  always  with  the  same  results.  Further,  common  observation  shows 
that  sensibility  to  irritants,  such  as  snuff,  and  acuteness  of  the  power  of  smell, 
bear  no  constant  proportion  to  one  another;  and  there  is  ample  pathological 
evidence  that  the  want  of  this  sense  is  connected  with  some  morbid  condition 
of  the  olfactory  nerves  or  ganglia.  It  is  well  known  that  Magendie  has  main- 
tained that  the  Fifth  pair  in  some  way  furnishes  conditions  requisite  for  the 
enjoyment  of  the  sense  of  smell,  asserting  that,  when  it  is  cut,  the  animal  is 
deprived  of  this.  But  his  experiments  were  made  with  irritating  vapours, 
which  excite  sternutation  or  other  violent  muscular  actions,  not  through  the 
olfactory  nerve,  but  through  the  fifth  pair:  and  the  experiments  of  Valentin, 
just  related,  fully  prove  that  the  animals  are  not  sensitive  to  odours,  strictly  so 
called,  after  the  Olfactory  has  been  divided.  It  is  by  no  means  improbable, 
however,  that  the  acuteness  of  the  true  sense  of  smell  may  be  diminished  by 
section  of  the  Fifth  pair ;  since  the  olfactory  membrane  is  no  longer  duly  moist- 
ened by  its  proper  secretion ;  and,  when  dry,  it  is  not  so  susceptible  of  the 
impressions  made  by  those  minute  particles  of  odoriferous  substances  to  which 
the  excitement  of  the  sensation  must  be  referred. 

221.  That  the  Second  pair,  or  Optic  nerves,  have  an  analogous  character, 
appears  alike  from  anatomical  and  experimental  evidence.  No  chemical  or 
mechanical  stimulus  of  the  nerve  produces  direct  muscular  motion,  nor  does  it 
give  rise,  as  far  as  can  be  ascertained,  to  indications  of  pain;  whence  it  may 
be  concluded  that  this  nerve  is  not  one  of  common  sensation.  That  the  ordi- 
nary sensibility  of  the  eyeball  remains,  when  the  functions  of  the  Optic  nerve 
are  completely  destroyed,  is  well  known,  as  is  also  the  fact  that  division  of  it 
puts  an  end  to  the  power  of  vision.  Valentin  states  that,  although  the  Optic 
nerve  may,  like  other  nerves,  be  in  appearance  completely  regenerated,  he 
has  never  been  able  to  obtain  any  evidence  that  the  power  of  sight  has  been 
in  the  least  degree  recovered.  He  remarks  that  animals  suddenly  made  blind 
exhibit  great  mental  disturbance  and  perform  many  unaccustomed  movements ; 
and  that  the  complete  absence  of  the  power  of  vision  is  easily  ascertained. 
Morbid  changes  are  sometimes  observed  to  take  place  in  eyes  whose  Optic 
nerve  has  been  divided;  but  these  are  by  no  means  so  constant  or  so  extensive 
as  when  the  Fifth  pair  is  paralyzed;  and  they  may  not  improbably  be  attri- 
buted to  the  injury,  occasioned  by  the  operation  itself,  to  the  parts  within  the 
orbit.  It  is  well  known  that,  when  amaurosis  is  produced  by  a  morbid  condi- 
tion of  the  Optic  nerve  alone,  the  eye  retains  its  usual  appearance ;  but,  if  the 
amaurosis  be  complete,  the  texture  of  the  Retina  undergoes  a  remarkable 
change,  ceasing  to  exhibit  that  peculiar  structure  which  normally  characterizes 
it.  Neither  primitive  nervous  fibrils  nor  nucleated  globules  can  be  distin- 
guished in  it;  and  the  yellow  spot  of  Soemmering  becomes  paler,  and  is  at 
last  undistinguishable.  But,  if  a  very  slight  degree  of  sensibility  to  light 


166  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

remain,  these  changes  are  much  less  decided.  Further,  it  is  well  known  that, 
when  the  sight  is  destroyed  by  a  disease  or  injury,  which  prevents  the  passage 
of  light  through  the  pupil,  the  whole  eye  becomes  more  or  less  atrophied  ;  and 
the  Retina  and  Optic  nerve,  although  previously  sound,  are  found  after  death 
(if  the  morbid  condition  have  lasted  sufficiently  long)  to  have  lost  their  charac- 
teristic structure.  It  seems  evident,  then,  that  the  continuance  of  the  functional 
operations  of  nerves,  is  a  necessary  condition  of  the  maintenance  of  their  nor- 
mal organization ;  and  we  can  very  well  understand  that  this  should  be  the 
case,  from  the  analogy  of  other  parts  of  (the  system. 

222.  The  Optic  nerve,  though  analogous  to  the  Olfactory  in  all  the  points 
hitherto  mentioned,  differs  from  it  in  one  important  respect;  that  it  has  the 
power  of  conveying  impressions  which  shall  excite  reflex  muscular  motions. 
This  is  especially  the  case  in  regard  to  the  Iris,  the  ordinary  actions  of  which 
are  regulated  by  the  degree  of  light  impinging  on  the  retina.   When  the  optic 
nerve  is  divided,  a  contraction  of  the  pupil  takes  place ;  but  this  does  not  occur 
if  the  connection  of  this  nerve  with  the  third  pair,  through  the  nervous  cen- 
tres, be  in  any  way  interrupted.     After  such  division  (if  complete),  the  state 
of  the  pupil  is  not  affected  by  variations  in  the  degree  of  light  impinging  on 
the  retina,  except  in  particular  cases  in  which  it  is  influenced  through  other  chan- 
nels.   Thus,  in  a  patient  suffering  under  amaurosis  of  one  eye,  the  pupil  of  the 
affected  eye  is  often  found  to  vary  in  size,  in  accordance  with  that  of  the  other 
eye;  but  this  effect  is  produced  by  the  action  of  light  on  the  retina  of  the 
sound  eye,  which  produces  a  motor  change  in  the  third  pair  on  both  sides. 
Further,  as  has  been  formerly  stated  (§  205),  the  impression  only  of  light  upon 
the  retina  may  give  rise  to  contraction  of  the  pupil,  by  reflex  action,  when  the 
optic  nerve  is  itself  sound;  whilst  no  sensations  are  received  through  the  eye, 
in  consequence  of  disease  in  the  sensorial  portion  of  the  nervous  centres. 
Another  cause  has  been  pointed  out  by  Valentin,  for  the  influence  of  light  in 
causing  contraction  of  the  pupil,  and  vice  versa;  that,  if  the  rays  impinge  upon 
the  iris,  a  reflex  stimulation  is  produced  through  the  fifth  pair;  and  he  remarks 
that  the  susceptibility  of  the  iris  to  this  kind  of  influence  seems  much  increased 
after  the  optic  nerve  has  been  divided.     Besides  the  contractions  of  the  pupil, 
another  action,  which  has  been  sometimes  spoken  of  as  reflex,  is  produced 
through  the  optic  nerve — the  contraction  of  the  orbicularis  under  the  influence 
of  strong  light,  or  when  a  foreign  body  is  suddenly  brought  near  the  eye.    But 
this  cannot  be  produced  by  any  mechanical  stimulation,  and  it  evidently  in- 
volves sensation;  in  fact,  it  is  a  movement  of  an  emotional  kind  (Sect,  xvui.), 
produced  by  the  painful  effect  of  light,  which  gives  rise  to  the  condition  well 
characterized  by  the  term  photophobia.     The  involuntary  character  of  it  must 
be  evident  to  every  one  who  has  been  engaged  in  the  treatment  of  diseases  of 
the  eyes;  and  the  effect  of  it  is  aided  by  a  similarly  involuntary  movement  of 
the  eyeball  itself,  which  is  rotated  upwards  and  inwards  to  a  greater  extent  than 
the  Will  appears  able  to  effect. 

223.  It  will  be  convenient  next  to  advert  to  the  Auditory  nerve,  or  Portio 
Mpllis  of  the  Seventh ;  the  functions  of  which  are  easily  determined  by  anato- 
mical examination  of  its  distribution,  and  by  observation  of  pathological  pheno- 
mena, to  be  analogous  to  triose  of  the  two  preceding.     Atrophy  or  lesion  of 
the  trunk  destroys  the  sense  of  Hearing ;  whilst  irritation  of  it  produces  audi- 
tory sensations,  but  does  not  occasion  pain.     From  experiments  made  upon 
the  nerve  before  it  leaves  the  cranial  cavity,  it  appears  satisfactorily  ascer- 
tained, that  this  nerve  has  no  motor  power  either  of  a  direct  or  reflex  charac- 
ter, and  that  it  is  not  endowed  with  common  sensibility.     It  is  interesting  to 
remark,  that  microscopic   examination  of  its  structure   clearly  indicates   its 
intermediate  character,  between  the  nerves  of  special  sensation  issuing  from 
the  anterior  part  of  the  cranium, — namely,  the  Optic  and  Olfactory,— -and  those 


FUNCTIONS  OF  THE  CEPHALIC  NERVES. 


167 


A  view  of  the  origin  and  distribution  of  the  Portio 
Mollis  of  the  Seventh  pair  or  Auditory  Nerve;  1,  the 
medulla  oblongata ;  2,  the  pons  varolii ;  3,  4,  the  crura 
cerebelli  of  the  right  side ;  5.  the  eighth  pair  of  nerves  ; 
6,  the  ninth  pair;  7,  the  auditory  nerve  distributed  to 
the  cochlea  and  labyrinth;  8,  the  sixth  pair  of  nerves; 
9,  the  portio  dura  of  the  seventh  pair;  10,  the  fourth 
pair;  11,  the  fifth  pair.] 


whose  function  is  to  minister,  either  [Fig.  35. 

to  common  sensation,  or  to  that  of 
taste  which  approaches  nearly  to  it, 
— namely,  the  Fifth  pair  and  the 
Glosso-pharyngeal,  —  which  issue 
from  the  posterior  part  of  the  Ence- 
phalon,  and  are  more  nearly  analo- 
gous to  the  Spinal  nerves.  The 
primitive  fibres  are  not  so  soft  as 
those  of  the  Olfactive,  nor  so  slender 
as  those  of  the  Optic ;  and  they  are 
softer  than  those  of  the  Glosso-pha- 
ryngeal.  Moreover,  the  Auditory 
never  forms  a  plexus  with  the  Fa- 
cial, to  which  there  is  no  analogy 
in  the  Optic  and  Olfactive  nerves, 
but  to  which  a  similar  one  exists  in 
the  Glosso-pharyngeal.  This  inter- 
mediate structural  character  is  inte- 
resting, when  we  compare  it  with 
the  intermediate  character  of  the 
function  ;  for  the  impressions  made 
upon  the  sense  of  Hearing  are  pro- 
duced through  vibrations  of  a  mate- 
rial fluid, — instead  of  being,  as  in  the  case  of  Sight,  the  result  of  changes  so 
subtle  as  to  be  almost  inscrutable  to  our  means  of  research, — or,  as  in  the  case 
of  Taste  and  Touch,  being  produced  by  the  direct  contact  of  the  substance 
which  gives  rise  to  the  sensation. 

224.  Passing  by  for  the  present  the  Motor  nerves  of  the  Orbit,  as  consti- 
tuting a  distinct  subject  for  future  inquiry,  we  may  advantageously  proceed 
with  the  other  Sensory  nerves  connected  with  the  Encephalon.     It  should  be 
noticed,  however,  that  the  Third  pair,  or  Motor  Oculi,  certainly  possesses  some 
degree  of  sensibility,  as  is  evidenced  by  the  signs  of  pain  given  by  the  animal 
when  it  is  cut  or  compressed ;  but  this  sensibility  is  not  nearly  so  great  as  that 
of  the  Fifth  pair ;  and  it  may  be  doubted  whether  it  is  possessed  by  it,  in 
virtue  of  its  direct  connection  with  the  nervous  centres,— or  whether  it  does 
not  derive  it  by  its  anastomosis  with  the  Fifth  pair,  some  filaments  of  which 
may  pass  backwards  as  well  as  forwards,  so  as  to  confer  sensibility  on  the 
Third  pair,  both  before  and  after  their  junction  with  it.     No  sensory  fibres 
can  be  proved  to  exist  in  the  Fourth  and  Sixth  nerves. 

225.  We  next  come  to  the  Fifth  pair,  or  Trifacial,  the  true  nature  of  the 
functions  of  which  was  ascertained  in  part  by  Sir  C.  Bell;  his  views  receiving 
modification,  however,  from  the  experimental  researches  of  others.     As  for- 
merly stated,  it  possesses  two  distinct  sets  of  roots,  of  which  one  is  much  larger 
than  the  other ;  on  the  larger  root,  as  on  the  posterior  root  of  the  spinal  nerves, 
is  a  distinct  ganglion ;  and  the  fibres  arising  from  the  smaller  root  do  not  blend 
with  the  others,  until  after  the  latter  have  passed  through  this  ganglion.    The 
trunk  of  the  nerve  separates,  as  is  well  known,  into  three  divisions, — the 
Ophthalmic,  the  Superior  Maxillary,  and  the  Inferior  Maxillary ;  and  it  can 
easily  be  shown  by  careful  dissection,  that  the  fibres  of  the  smaller  root  pass 
into  the  third  of  these  divisions  alone.     When  the  distribution  of  this  nerve 
is  carefully  examined,  it  is  found  that  the  first  and  second  divisions  of  it  pro- 
ceed almost  entirely  to  the  skin  and  mucous  surfaces,  a  very  small  proportion 
only  of  their  fibres  being  lost  in  the  muscles ;  but  of  the  branches  of  the  third 
division,  a  large  part  are  distinctly  muscular.     Hence  analogy,  and  the  facts 


168 


FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Fig.  36. 


A  diagram  showing  the  Fifth  pair  of  Nerves  with  its  Branches ;  1,  the  origin  of  the  nerve  by  two  roots; 
2,  the  nerve  escaping  from  the  crus  cerebelli ;  3,  the  Gasserian  ganglion ;  4,  its  ophthalmic  division ;  5,  the 
frontal  nerve,  giving  off  the  supra-trochlear  branch,  and  escaping  on  the  forehead  through  the  supra-orbital 
foramen;  6,  the  lachrymal  nerve ;  7,  the  nasal  fierve,  passing  at  8  through  the  anterior  ethmoidal  foramen, 
and  giving  off  the  infra-trochlear  branch ;  9,  the  communication  of  the  nasal  nerve  with  the  ciliary  ganglion ; 
10,  a  small  portion  of  the  third  nerve  with  which  the  ganglion  is  seen  communicating;  the  ganglion  gives 
off  the  ciliary  branches  from  its  anterior  aspect;  11,  the  superior  maxillary  nerve ;  12,  its  orbital  branch; 
13,  the  two  branches  communicating  with  Meckel's  ganglion ;  the  three  branches  given  off  from  the  lower 
part  of  the  ganglion  are  the  posterior  palatine  nerves;  14,  14,  the  superior  dental  nerves,  posterior,  middle 
and  anterior;  15.  the  infra-orbital  branches  distributed  upon  the  cheek;  16,  the  inferior  maxillary  nerve ; 
17,  its  anterior  or  muscular  trunk;  18,  the  posterior  trunk;  the  two  divisions  are  separated  by  an  arrow; 
19,  the  gustatory  nerve ;  20,  the  chorda  tympani  joining  it  at  an  acute  angle ;  21,  the  sub-maxillary  ganglion ; 
22,  the  inferior  dental  nerve;  23,  its  mylo-hyoidean  branch;  24,  the  auricular  nerve,  dividing  behind  the 
articulation  of  the  lower  jaw,  to  reunite  and  form  a  single  trunk ;  25,  its  branch  of  communication  with  the 
facial  nerve ;  26,  its  temporal  branch. 


[Fig.  37. 


A  view  of  the  distribution  of  the  Trifacral  or 
Fifth  pair;  1,  orbit ;-2,  antrum  highmorianum ;  3, 
tongue;  4,  lower  jaw-bone;  5,  root  of  the  fifth 
pair,  forming  the  ganglion  of  Gasser;  6,  first 
branch  of  the  fifth  pair,  or  ophthalmic;  7,  second 
branch  of  the  fifth  pair,  or  superior  maxillary; 
8,  third  branch  of  the  fifth  pair,  or  inferior  maxil- 
lary; 9,  frontal  branch,  dividing  into  external  and 
internal  frontal  nerves ;  10,  lachrymal  branch  of 
the  fifth  pair;  11,  nasal  branch;  just  under  the 
figure  is  the  long  root  of  the  lenticular  or  ciliary 
ganglion  and  a  few  of  the  ciliary  nerves ;  12, 
internal  nasal  nerve,  disappearing  through  the 
anterior  ethmoidal  foramen;  13,  external  nasal 
nerve;  14,  external  and  internal  frontal  nerve ; 
15,  infra-orbitary  nerve  ;  16,  posterior  dental 
branches;  17, middle  dental  branch;  18,  anterior 
dental  nerve;  19,  terminating  branches  of  the 
infra-orbital  nerve,  called  the  labial  and  palpe- 
bral  nerves;  20,  subcutaneous  malce,  or  orbitar 
branch;  21,  pterygoid,  or  recurrent  nerve,  from 
Meckel's  ganglion;  22,  five  anterior  branches  of 
the  third  branch  of  the  fifth  pair;  23,  lingual 
branch  of  the  fifth,  joined  by  the  chorda  tym- 
pani; 24,  inferior  dental  nerve;  25,  its  mental 
branches ;  26,  superficial  temporal  nerve ;  27, 
auricular  branches ;  28,  mylo-hyoid  branch.] 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  169 

supplied  by  anatomical  research,  would  lead  to  the  conclusion,  that  the  two 
first  divisions  are  nerves  of  sensation  only,  and  that  the  third  division  combines 
sensory  and  motor  endowments.  Such  an  inference  is  fully  borne  out  by 
experiment.  When  the  whole  trunk  is  divided  within  the  cranium  (which 
Magendie,  by  frequent  practice,  has  been  able  to  accomplish),  evident  signs  of 
acute  pain  are  given.  After  the  incision  has  been  made  through  the  skin,  the 
animal  remains  quiet  until  the  nerve  is  touched ;  and  when  it  is  pressed  or 
divided,  doleful  cries  are  uttered,  which  continue  for  some  time,  showing  the 
painful  effect  of  the  irritated  state  of  the  cut  extremity.  The  common  sensi- 
bility of  all  the  parts  supplied  by  this  nerve  is  entirely  destroyed  on  the  affected 
side.  The  jaw  does  not  hang  loosely,  because  it  is  partly  kept  up  by  the  mus- 
cles of  the  other  side  ;  but  it  falls  in  a  slight  degree  ;  and  its  movements  are 
seen,  when  carefully  observed,  to  be  somewhat  oblique.  If  the  trunk  be 
divided  on  each  side,  the  whole  head  is  deprived  of  sensibility ;  and  the  ani- 
mal carries  it  in  a  curious  vacillating  manner,  as  if  it  were  a  foreign  body. 

226.  If  the  anterior  or  Ophthalmic  branch  only  be  divided,  all  the  parts 
supplied  by  it  are  found  to  have  lost  their  sensibility,  but  their  motions  are 
unimpaired ;    and  all  experiments   and  pathological  observations  concur  in 
attributing  to  it  sensory  endowments  only.     The  only  apparent  exception  is  in 
the  case  of  the  Naso-Ciliary  branch ;  since  there  is  good  reason  to  believe  that 
the  long  root  of  the  ciliary  ganglion,  and  the  long  ciliary  nerves,  possess  motor 
powers  ;  but  these  appear  to  be  derived  from  the  Sympathetic  nerve.     When 
the  whole  nerve,  or  its  anterior  branch,  is  divided  in  the  rabbit,  the  pupil  is 
exceedingly  contracted,  and  remains  immovable ;  but  in  dogs  and  pigeons  it 
is  dilated.     The  pupil  of  the  other  eye  is  scarcely  affected ;  or,  if  its  dimen- 
sions be  changed,  it  soon  returns  to  its  natural  state.     The  eyeball  speedily 
becomes  inflamed,  however;  and  the  inflammation  usually  runs  on  to  suppura- 
tion and  complete  disorganization.    The  commencement  of  these  changes  may 
be  commonly  noticed  within  twenty-four  hours  after  the  operation ;  and  they 
appear  to  be  due  to  the  want  of  the  protective  secretion,  which  (as  will  be 
explained  when  the  direct  influence  of  the  nervous  system  upon  the  organic 
functions  is  considered)  is  necessary  to  keep  the  mucous  surface  of  the  eye  in 
its  healthy  condition,  and  which  is  not  formed  when  the  sensibility  of  that 
surface  is  destroyed. — The  Superior  Maxillary  branch,  considered  in  itself, 
is  equally  destitute  of  motor  endowments  with  the  ophthalmic ;  but  its  con- 
nections with  other  nerves,  through  the  spleno-palatine  ganglion  and  its  anasto- 
mosing twigs,  may  introduce  a  few  motor  fibres  into  it. — The  Inferior  Maxillary 
branch  is  the  only  one  which  possesses  motor  as  well  as  sensory  endowments 
from  its  origin ;  but  its  different  subdivisions  possess  these  endowments  in 
varying  proportions,  some  being  almost  exclusively  motor,  and  others  as  com- 
pletely of  a  sensory  character.     The  latter  is  probably  the  nature  of  the  Lin- 
gual branch;  and  there  seems  good  reason  to  believe,  as  will  presently  be 
shown,  that  this  ministers  not  only  to  the  tactile  sensibility  of  the  tongue,  but 
to  the  sense  of  taste.     The  muscles  put  in  action  by  this  division  of  the  Fifth 
pair,  are  solely  those  concerned  in  the  masticatory  movements. 

227.  The  Portio  Dura  of  the  Seventh  pair,  or  Facial  nerve,  has  been  sup- 
posed, since  the  first  researches  of  Sir  C.  Bell,  to  be  a  nerve  of  motion  only; 
but  some  recent  physiologists  have  maintained  that  it  both  possesses  sensory 
endowments  and  arises  by  a  double  root.     The  latter  assertion  is  quite  falla- 
cious ;  and  the  most  carefully  conducted  experiments  do  not  bear  out  the  for- 
mer.   By  exposing  the  roots  of  the  Seventh  pair  within  the  cranium,  Valentin 
ascertained  that  it  possesses  no  sensory  endowments  at  its  origin ;  since,  when 
these  were  touched,  the  animals  gave  no  signs  of  pain,  though  violent  mus- 
cular movements  were  excited  in  the  face.     Subsequently  to  its  first  entrance 
into  the  canal  by  which  it  emerges,  however,  it  anastomoses  with  other  nerves ; 

15 


170  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Fig.  38. 


The  distribution  of  the  Facial  Nerve,  and  the  branches  of  the  Cervical  Plexus;  1,  the  facial  nerve, 
escaping  from  the  stylo-mastoid  foramen,  and  crossing  the  ramus  of  the  lower  jaw;  the  parotid  gland  has 
been  removed  in  order  to  see  the  nerve  more  distinctly ;  2,  the  posterior  auricular  branch;  the  digastric 
and  stylo-mastoid  filaments  are  seen  near  the  origin  of  this  branch  ;  3,  temporal  branches,  communicating 
with  (4)  the  branches  of  the  frontal  nerve;  5,  facial  branches,  communicating  with  (6)  the  infra-orbital 
nerve;  7,  facial  branches,  communicating  with  (6)  the  mental  nerve;  9,  cervico-facial  branches,  commu- 
nicating with  (10)  the  superficialis  colli  nerve,  and  forming  a  plexus  (11)  over  the  sub-maxillary  gland  ;  the 
distribution  of  the  branches  of  the  facial  in  a  radiated  direction  over  the  side  of  the  face,  constitutes  the 
pes  anserimus;  12,  the  auricularis  magnus  nerve,  one  of  the  ascending  branches  of  the  cervical  plexus  ; 
13,  the  occipitalis  minor,  ascending  along  the  posterior  border  of  the  sterno-mastoid  muscle ;  14,  the  super- 
ficial and  deep-descending  branches  of  the  cervical  plexus  ;  15,  the  spinal  accessory  nerve,  giving  off  a 
branch  to  the  external  surface  of  the  trapezius  muscle :  10,  the  occipitalis  major  nerve,  the  posterior 
branch  of  the  second  cervical  nerve. 

and  thus  sensory  fibres  are  introduced  into  it  from  many  different  sources — 
anteriorly,  from  the  Fifth  pair;  and  posteriorly,  from  the  Cervical  nerves — 
which  cause  irritation  of  several  of  its  branches  to  produce  pain.  The  number 
and  situation  of  the  anastomoses  vary  much  in  different  animals ;  so  that  it  is 
impossible  to  make  any  very  comprehensive  statement  in  regard  to  them. 
Experimental  researches  leave  no  doubt  that  the  Portio  Dura  is  the  general 
motor  nerve  of  the  face,  ministering  to  the  influence  of  Volition  and  of  Emo- 
tion, and  also  being  the  channel  of  the  Reflex  movements  concerned  in  respi- 
ration and  other  associated  movements  of  the  muscles,  but  not  being  in  the  least 
concerned  in  the  act  of  mastication.* 

228.  The  functions  of  the  Glosso-Pharyngeal  nerve  have  been  heretofore 

*  The  distinctness  of  the  Spinal  and  Cerebral  portions  of  this  nerve  is  made  evident 
by  the  not  nnfrequent  occurrence  of  paralysis  in  either  of  them,  without  the  other  being 
affected.  Thus  we  may  see  the  mouth 'drawn  to  one  side  (in  consequence  of  the  loss  of 
tone  which  the  muscles  have  experienced),  and  all  the  Reflex  and  Emotional  actions  of 
the  face  performed  only  on  one  side;  and  yet  Voluntary  power  may  remain  unaffected. 
Thus,  in  ordinary  winking,  the  lid  of  the  affected  side  does  not  close,  though  the  patient 
can  shut  the  eye  by  an  effort  of  the  will.  On  the  other  hand,  the  tone  of  the  muscles 
may  remain  unimpaired,  and  all  their  Reflex  and  Emotional  actions  may  be  performed 
as  usual,  and  yet  distortion  may  be  at  once  apparent,  when  Voluntary  actions  are 
attempted,  in  consequence  of  paralysis  of  the  Cerebral  portion  of  the  nerve  on  one  side. 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  171 

alluded  to  in  part ;  but  there  still  remain  several  questions  to  be  discussed  in 
regard  to  them.  Reasons  have  been  given  for  the  belief,  that  it  is  chiefly  an 
afferent  nerve, — scarcely  having  any  direct  power  of  exciting  muscular  con- 
traction, but  conveying  impressions  to  the  Medulla  Oblongata,  which  produce 
reflex  movements  of  the  other  nerves  (§  192).  Some  experimenters  assert, 
that  they  have  succeeded  in  exciting  direct  muscular  actions  through  its  trunk. 
This  is  by  no  means  impossible ;  but  if  the  truth  of  the  statement  be  admitted, 
it  does  not  invalidate  the  inferences  regarding  the  general  function  of  the 
nerve,  deduced  by  Dr.  Reid  from  minute  anatomical  investigation,  and  from  a 
large  number  of  experiments.  Much  controversy  has  taken  place  on  the 
question,  whether  this  nerve  is  to  be  regarded  as  ministering,  partly  or  exclu- 
sively, to  the  sense  of  Taste;  and  many  high  authorities  have  ranged  them- 
selves on  each  side.  The  question  involves  that  of  the  function  of  the  Lingual 
branch  of  the  Fifth  pair ;  and  it  is  partly  to  be  decided  by  the  anatomical  rela- 
tions of  the  two  nerves  respectively.  The  glosso-pharyngeal  is  principally 
distributed  on  the  mucous  surface  of  the  fauces,  and  on  the  back  of  the  tongue. 
According  to  Valentin,  it  sends  a  branch  forwards,  on  either  side,  somewhat 
beneath  the  lateral  margin,  which  supplies  the  edges  and  inferior  surface  of 
the  tip  of  the  tongue,  and  inosculates  with  the  Lingual  branch  of  the  Fifth 
pair.  On  the  other  hand,  the  upper  surface  of  the  front  of  the  tongue  is  sup- 
plied by  this  lingual  branch.  The  experiments  of  Dr.  Alcock,  whose  conclu- 
sions are  borne  out  by  Dr.  J.  Reid,  decidedly  support  the  conclusion,  that  the 
gustative  sensibility  of  this  part  of  the  tongue  is  due  to  the  latter  nerve,  being 
evidently  impaired  by  division  of  it.  Moreover,  cases  are  by  no  means  rare, 
in  which  the  gustative  sensibility  of  the  anterior  part  of  the  tongue  has  been 
destroyed,  with  its  tactual  sensibility ;  when  there  was  no  reason  to  suppose 
that  any  other  than  the  Fifth  pair  of  nerves  was  involved.*  On  the  other 
hand,  it  is  equally  certain,  that  the  sense  of  taste  is  not  destroyed  by  section  of 
the  Lingual  nerve  on  each  side ;  and  it  seems  also  well  ascertained,  that  it  is 
impaired  by  section  of  the  Glosso-pharyngeal  nerve.  Considering  how  nearly 
allied  is  the  sense  of  taste  to  that  of  touch,  and  bearing  in  mind  the  respective 
distribution  of  these  two  nerves,  it  does  not  seem  difficult  to  arrive  at  the  con- 
clusion, that  both  nerves  are  concerned  in  this  function ;  but  there  seems  good 
reason  to  believe  the  Glosso-pharyngeal  to  be  exclusively  that  through  which 
the  impressions  made  by  disagreeable  substances  taken  into  the  mouth  are 
propagated  to  the  Medulla  Oblongata,  so  as  to  produce  nausea  and  to  excite 
efforts  to  vomit. 

229.  The  functions  of  the  Par  Vagum  at  its  roots  have  lately  been  made 
the  subject  of  particular  examination  by  Valentin;  and  he  has  arrived  at  the 
very  interesting  result,  that  it  there  possesses  no  motor  power,  but  is  entirely 
a  sensory  or  rather  an  afferent  nerve.  He  states  that,  if  the  roots  be  carefully 
separated  from  those  of  the  Glosso-Pharyngeal,  and  (which  is  a  matter  of  some 
difficulty)  from  those  of  the  Spinal  Accessory  nerve,  and  be  then  irritated,  no 
movements  of  the  organs  supplied  by  it  can  be  observed.  On  the  other  hand, 
if  the  roots  be  irritated  whilst  in  connection  with  the  nervous  centres,  muscular 
contractions,  evidently  of  a  reflex  character,  result  from  the  irritation ;  and 
strong  evidences  of  their  sensibility  are  also  given.  On  the  other  hand,  again, 
when  the  roots  of  the  Spinal  Accessory  nerve  are  irritated,  no  indications  of 
sensation  'are  given  ;  but  the  muscular  parts  supplied  by  the  Par  Vagum,  as 
well  as  by  its  own  trunk,  are  made  to  contract,  even  when  the  roots  are  sepa- 
rated from  the  nervous  centres ;  so  that  these  roots  must  be  regarded  as  the 
channel  of  the  motor  influence,  transmitted  to  them  from  the  Medulla  Oblon- 
gata. When  the  Par  Vagum  swells  into  the  jugular  ganglion,  an  interchange 

*  Romberg,  in  Mailer's  Archiv.  1838,  Heft  iii. 


172  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Fig.  39.  [Fig.  40. 


Origin  and  distribution  of  the  Eighth  pair  of  nerves ; 
1,  3,  4,  the  medulla  oblongaja;  1,  the  corpus  pyra- 
midale  of  one  side;  3,  the  corpus  olivare  ;  4,  the  cor- 
pus restiforme;  2,  the  pons  varolii;  5,  the  facial 
nerve ;  6,  the  origin  of  the  glosso-pharyngeal  nerve ; 
7,  the  ganglion  of  Andersch ;  8,  the  trunk  of  the  nerve  ; 
9,  the  spinal  accessory  nerve  ;  10,  the  ganglion  of  the 
pneumogastric  nerve;  11,  its  plexiform  ganglion;  12, 
its  trunk  ;  13,  its  pharyngeal  branch  forming  the  pha- 
ryngeal  plexus  (14)  assisted  by  a  branch  from  the 
glosso-pharyngeal  (8)  and  one  from  the  superior  laryn- 
geal  nerve  (15) ;  16,  cardiac  branches ;  17,  recurrent 
laryngeal  branch;  18,  anterior  pulmonary  branches; 
19,  posterior  pulmonary  branches;  20,  cesophageal 
plexus;  21,  gastric  branches;  22,  origin  of  the  spinal 
accessory  nerve ;  23,  its  branches  distributed  to  the 
sterno-mastoid  muscle ;  24,  its  branches  to  the  trape- 
zius  muscle. 


A,  view  of  the  distribution  of  the  Glosso-Pha- 
ryngeal  Pneumogastric  and  Spinal  Accessory 
NeBres,orthe  Eighth  pair;  l,the  inferior  maxillary 
nerve;  2,  the  gustatory  nerve;  3,  the  chorda-tym- 
pani;  4,  the  auricular  nerve;  5,  its  communication 
with  the  portio  dura;  6.  the  facial  nerve  coming 
out  of  the  stylo-mastoid  foramen;  7,  the  glonso- 
pharyngeal  nerve;  8,  branches  to  the  stylo-pha- 
ryngeus  muscle;  9,  the  pharyngeal  branch  of  the 
pneumogastr  c  nerve  descending  to  form  the  pha- 
ryngeal plexus;  10,  branches  of  the  glosso-pha- 
ryngeal to  the  pharyngeal  plexus ;  11,  the  pneumo- 
gastric nerve;  12,  the  pharyngeal  plexus;  13,  the 
superior  laryngeal  branch;  14,  branches  to  the 
pharyngeal  plexus  ;  15,  15,  communication  of  the 
superior  and  inferior  laryngeal  nerves;  16,  car- 
diac branches ;  17,  cardiac  branches  from  the  right 
pneumogastric  nerve ;  18,  the  left  cardiac  gan- 
glion and  plexus;  19,  the  recurrent  or  inferior 
laryngeal  nerve ;  20,  branches  sent  from^the  curve 
of  the  recurrent  nerve  to  the  pulmonary  plexus; 
21,  the  anterior  pulmonary  plexus;  22,22,  the  osso- 
phagcal  plexus.] 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  173 

of  fibres  takes  place  between  it  and  the  Spinal  Accessory ;  but  many  more 
fibres  can  be  traced  from  the  latter  into  the  former  than  from  the  former  into 
the  latter.  Hence  it  results  that,  of  the  branches  into  which  the  Par  Vagum 
subsequently  divides,  many  enjoy  a  high  degree  of  motor  power;  whilst  those 
of  the  Spinal  Accessory  do  not  appear  to  possess  any  great  share  of  sensibility. 
The  pharyngeal  branches  are  among  the  most  decidedly  motor  of  all  those 
given  off  from  the  Pn.eumogastric ;  and  these  may  in  great  part  be  traced 
backwards  into  the  Spinal  Accessory.  Hence  the  idea  of  Arnold  and  Scarpa, 
— that  the  Par  Vagum  and  Spinal  Accessory  are  together  analogous  to  a 
spinal  nerve,  the  former  answering  to  the  posterior  roots,  and  the  latter  to  the 
anterior, — appears  sufficiently  probable.  In  regard  to  its  trunk,  however,  the 
Par  Vagum  must  of  course  be  considered  as  a  nerve  of  double  endowments. 
The  chief  function  of  its  afferent  portion  is  to  convey  to  the  Medulla  Oblongata 
the  impression  produced  by  venous  blood  in  the  capillaries  of  the  lungs,  or  of 
carbonic  acid  in  the  air-cells  ;  this  impression  may  give  rise,  as  we  have  seen, 
to  the  respiratory  movements,  without  producing  sensation ;  but,  if  it  be  from 
any  cause  stronger  than  usual,  the  sense  of  uneasiness  which  it  occasions  is 
very  distressing.  This  impression  may  be  imitated  by  pressure  on  the  nerve, 
which  induces  an  immediate  inspiratory  movement.  That  the  nerve  is  capa- 
ble of  conveying  those  impressions,  which  become  sensations  when,  communi- 
cated to  the  sensorium,  is  further  evident  from  the  fact  that,  when  its  trunk 
is  pinched,  the  animal  gives  signs  of  acute  pain.  Besides  the  pulmonary 
impressions,  this  nerve  also  conveys  to  the  Medulla  Oblongata  those  which 
originate  in  the  mucous  surface  of  the  larynx,  trachea  and  bronchi,  as  well  as 
on  the  lower  part  of  the  ossophagus  and  on  the  walls  of  the  stomach.  The 
purpose  of  these  is  to  stimulate  various  movements,  which  are  performed 
through  the  motor  portion  of  the  nerve ;  this  excites  the  actions  of  the  muscles 
of  the  pharynx  and  larynx,  of  the  oesophagus,  and,  in  some  degree,  of  the 
stomach  and  respiratory  tubes. 

230.  The  section  of  the  Par  Vagum  produces,  as  would  readily  be  expected, 
great  disorder  of  the  functions  of  Respiration  and  Digestion,  to  which  it  minis- 
ters.    It  is  an  operation  which  has  been  very  frequently  performed;  and  the 
statements  of  its  results  vary  considerably  amongst  each  other,  being  generally 
influenced,  in  some  degree,  by  the  preconceived  views  of  the  experimenter.* 
The  section  of  the  Par  Vagum,  when  practised  with  the  view  of  ascertaining 
the  influence  of  the  nerve  upon  the  lungs  and  stomach,  is  usually  made  in 
the  neck,  between  the  origins  of  the  superior  and  inferior   (or  recurrent) 
laryngeal  branches.     Hence  the  muscles  of  the  larynx  are  paralyzed;  'and,  if 
the  animal  should  struggle  violently,  the  ingress  of  air  is  likely  to  be  ob- 
structed by  the  flapping  down  of  the  arytenoid  cartilages,  and  by  the  closure 
of  the  glottis.     This  is  especially  the  case  in  young  animals,  in  which  the 
larynx  is  small.    But  in  those  that  are  full  grown,  and  ha've  a  large  larynx,  an 
adequate  quantity  of  air  may  still  find  its  way  through  the  aperture,  if  the 
animal  refrain  from  any  violent  effort.    In  a  considerable  number  of  Dr.  Reid's 
experiments,  therefore,  he  did  not  find  it  necessary  to  introduce  the  trachea- 
tube,  which  other  experimenters  have  generally  employed.     An  opening  was 
made  into  the  trachea,  however,  in  those  instances  in  which,  from  any  cause, 
the  entrance  of  air  was  obstructed. 

231.  The  real  character  of  the  morbid  changes  in  the  lungs  which  are 
induced  by  cutting  the  Par  Vagum,  the  order  in  which  they  arise,  and  the  causes 
to  which  they  are  immediately  due,  constitute  very  interesting  subjects  of 

*  The  Author  employs,  as  in  his  opinion  the  most  worthy  of  confidence,  the  experi- 
ments of  Dr-.  J.  Reid,  (Edinb.  Med.  &  Surg.  Journ.,  Vols.  xiix.  and  li.,)  on  whose  accu- 
racy he  has  strong  personal  reasons  for  placing  reliance;  and  whose  anatomical  and 
pathological  attainments  are  such  as  to  render  him  fully  competent  to  the  task. 

15* 


174  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

investigation;  and  the  knowledge  of  them  will  probably  throw  light  upon 
many  ill-understood  morbid  phenomena.  In  the  first  place,  it  has  been  fully 
established  by  Dr.  Reid,  that  section  of  the  Vagus  on  one  side  only  does  not 
necessarily,  or  even  generally,  induce  disease  of  that  lung;  and  hence  the 
important  inference  may  be  drawn,  that  the  nerve  does  not  exercise  any  imme- 
diate influence  on  its  functions.  When  both  Vagi  are  divided,  however,  the 
animal  rarely  survives  long ;  but  its  death  frequently  results  from  the  disorder 
of  the  digestive  functions.  Nevertheless,  the  power  of  digestion  is  sometimes 
restored  sufficiently  to  re-invigorate  the  animals ;  and  their  lives  may  then  be 
prolonged  for  a  considerable  time.  In  fifteen  out  of  seventeen  animals  experi- 
mented on  by  Dr.  Reid,  the  lungs  were  found  more  or  less  unfit  for  the 
healthy  performance  of  their  functions.  The  most  common  morbid  changes 
were  a  congested  state  of  the  blood-vessels,  and  an  effusion  of  frothy  serum 
into  the  air-cells  and  bronchial  tubes.  In  eight  out  of  the  fifteen,  these  changes 
were  strongly  marked.  In  some  portions  of  the  lungs,  the  quantity  of  blood 
was  so  great  as  to  render  them  dense.  The  degree  of  congestion  varied  in 
different  parts  of  the  same  lung ;  but  it  was  generally  greatest  at  the  most 
depending  portions.  The  condensation  was  generally  greater  than  could  be 
accounted  for  by  the  mere  congestion  of  blood  in  the  vessels ;  and  probably 
arose  from  the  escape  of  the  solid  parts  of  the  blood  into  the  tissue  of  the 
lung.  In  some  instances,  the  condensation  was  so  great  that  considerable  por- 
tions of  the  lung  sank  in  water  and  did  not  crepitate ;  but  they  did  not  present 
the  granulated  appearance  of  the  second  stage  of  ordinary  pneumonia.  In  five 
cases,  in  which  the  animals  had  survived  a  considerable  time,  portions  of  the 
lungs  exhibited  the  second,  and  even  the  third  stages  of  pneumonia,  with  puri- 
form  effusion  into  the  small  bronchial  tubes ;  and,  in  two,  gangrene  had  super- 
vened. 

232.  One  of  the  most  important  points  to  ascertain,  in  an  investigation  of 
this  kind,  is  the  first  departure  from  a  healthy  state, — to  decide  whether  the 
effusion  of  frothy  reddish  serum,  by  interfering  with  the  usual  change  in  the 
lungs,  causes  the  congested  state  of  the  pulmonary  vessels  and  the  laboured 
respiration ;  or  whether  the  effusion  is  the  effect  of  a  previously  congested 
state  of  the  blood-vessels.     The  former  is  the  opinion  of  many  physiologists, 
who  have  represented  the  effusion  of  serum  as  a  process  of  morbid  secretion, 
directly  resulting  from  the  disorder  of  that  function,  produced  by  the  section  of 
the  nerve.     The  latter  appears  the  unavoidable  inference  from  the  carefully 
noted  results  of  Dr.  Reid's  experiments.     In  several  of  these,  only  a  very 
small  quantity  of  frothy  serum  was  found  in  the  air-tubes,  even  when  the 
lungs  were  found  loaded  with  blood,  and  when  the  respiration  before  death 
was  very  laboured.     This  naturally  leads  us  to  doubt  whether  the  frothy 
serum  is  the  cause  of  the  laboured  respiration,  and  of  the  congested  state 
of  the  pulmonary  vessels,  in  those  cases  where  it  is  present ;  though  there 
can  be  no  doubt   that,  when   once  it   is   effused,  it  must  powerfully  tend 
to  increase  the  difficulty  of  respiration,  and  still  further  to  impede  the  cir- 
culation through  the  lungs.     Dr.  R.   has  satisfied  himself  of  an  important 
point,  which  has  been  overlooked  by  others — that  this  frothy  fluid  is  not 
mucus,  though  occasionally  mixed  with  it;  but  that  it  is  the  frothy  serum  so 
frequently  found  in  cases  where  the  circulation  through  the  lungs  has  been 
impeded  before  death.     From  this  and  other  facts,  Dr.  R.  concludes  "that  the 
congestion  of  the  blood-vessels  is  the  first  departure  from  the  healthy  state  of 
the  lung,  and  that  the  effusion  of  frothy  serum  is  a  subsequent  effect." 

233.  The  next  point,  therefore,  to  be  inquired  into,  is  the  cause  of  this  con- 
gestion; and  this  is  most  satisfactorily  explained  upon  the  general  principles 
regulating  the  circulation  of  the  blood,  by  remembering  that  section  of  the  Par 
Vagum  greatly  diminishes  the  frequency  of  the  respiratory  movements,  and 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  175 

that  the  quantity  of  air  introduced  into  the  lungs  is,  therefore,  very  insufficient 
for  the  due  aeration  of  the  blood.  We  shall  hereafter  see  reason  to  regard  it 
as  one  of  the  best-established  principles  in  Physiology,  that  the  activity  of  the 
changes  which  the  blood  undergoes,  in  the  capillary  vessels,  does,  in  some 
way  or  other,  regulate  its  movement  through  them;  that,  when  these  changes 
are  proceeding  with  activity,  the  capillary  circulation  is  proportionably  acce- 
lerated; and  that,  when  they  are  abnormally  low  in  degree,  the  movement  of 
the  blood  in  the  capillaries  is  stagnated.  There  is  now  abundant  evidence,  in 
regard  to  the  Pulmonary  circulation  in  particular,  that,  to  prevent  the  admis- 
sion of  oxygen  in  the  lungs,  either  by  causing  the  animal  to  breathe  pure 
nitrogen  or  hydrogen,  or  by  occlusion  of  the  air-passages,  is  to  bring  the  circu- 
lation through  their  capillaries  to  a  speedy  check.  Hence  we  should  at  once 
be  led  to  infer,  that  diminution  in  the  number  of  Respiratory  movements  would 
produce  the  same  effect;  and  as  little  or  no  difference  in  their  frequency  is 
produced  by  section  of  one  Vagus  only,  the  usual  absence  of  morbid  changes 
in  the  lung  supplied  by  it  is  fully  accounted  for.  The  congestion  of  the  ves- 
sels, induced  by  insufficient  aeration,  satisfactorily  accounts,  not  only  for  the 
effusion  of  serum,  but  also  for  the  tendency  to  pass  into  the  inflammatory  con- 
dition, sometimes  presented  by  the  lungs,  as  by  other  organs  similarly  affected. 
Dr.  Reid  confirms  this  view,  by  the  particulars  of  cases  of  disease  in  the 
human  subject,  in  which  the  lungs  presented,  after  death,  a  condition  similar 
to  that  observed  in  the  lower  animals  after  section  of  the  Vagi ;  and,  in  these 
individuals,  the  respiratory  movements  had  been  much  less  frequent  than 
natural  during  the  latter  part  of  life,  owing  to  a  torpid  condition  of  the  nervous 
centres.  The  opinion  (held  especially  by  Dr.  Wilson  Philip)  that  section  of 
the  par  vagum  produces  the  serous  effusion,  by  its  direct  influence  on  the 
function  of  Secretion,  is  further  invalidated  by  the  fact  stated  by  Dr.  Reid,— 
that  he  always  found  the  bronchial  membrane  covered  with  its  true  mucus, 
except  when  inflammation  was  present. 

234.  "  The  experimental  history  of  the  Par  Vagum,"  it  is  justly  remarked 
by  Dr.  Reid,  "  furnishes  an  excellent  illustration  of  the  numerous  difficulties 
with  which  the  physiologist  has  to  contend,  from  the  impossibility  of  insu- 
lating any  individual  organ  from  its  mutual  actions  and  reactions,  when  he 
wishes  to  examine  the  order  and  dependence  of  its  phenomena."  In  such 
investigations,  no  useful  inference  can  be  drawn  from  one  or  two  experiments 
only  ;'in  order  to  avoid  all  sources  of  fallacy,  a  large  number  must  be  made  ; 
the  points  in  which  all  agree  must  be  separated  from  others  in  which  there  is 
a  variation  of  results ;  and  it  must  be  then  inquired,  to  what  the  latter  is  due. 
These  observations  apply  equally  to  the  other  principal  subject  of  inquiry  in 
regard  to  the  functions  of  the  Par  Vagum, — its  influence  upon  the  process  of 
Digestion.  The  results  obtained  by  different  experimenters  have  led  to  differ- 
ences of  opinion  as  to  its  action  no  less  remarkable  than  those  on  the  question 
just  discussed.  Dr.  Wilson  Philip  has  long  maintained  that  the  par  vagum 
controls  the  secretion  of  gastric  juice,  which  he  stated  to  cease  when  the  nerve 
is  divided ;  and  he  further  stated,  that  the  influence  of  galvanism,  propagated 
along  the  nerve,  would  re-establish  the  secretion.  This  statement  has  been 
quoted  and  re-quoted  as  an  established  physiological  position ;  and,  when 
united  with  the  well-known  fact  that  galvanism  would  excite  muscular  con- 
traction, it  has  seemed  to  Dr.  W.  Philip  and  other  physiologists  sufficient  to 
establish  the  important  position,  that  galvanism  and  nervous  influence  are 
identical.  The  statement,  however,  has  been  disputed  by  many  other  experi- 
menters, who  have  satisfied  themselves  that  the  secretion  of  gastric  juice  con- 
tinued, and  that  the  impairment  of  the  digestive  power,  which  is  certainly  a 
result  (for  a  time  at  least)  of  the  operation,  may  be  attributed  to  paralysis  of 
the  muscular  coat  of  the  stomach. 


176  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

235.  The  experiments  of  Dr.  Reid  do  not  furnish  grounds  for  a  positive 
determination  of  the  functions  of  the  gastrk  portion  of  the  Par  Vagum ;  but 
they  furnish  important  correction  of  the  results  obtained  by  others.     He  has 
succeeded,  as  formerly  stated  (§  198),  in  producing  movements  of  the  stomach, 
by  irritation  of  the  Vagi ;  but  that  these  movements  may  be  excited  in  other 
ways,  is  evident  from  the  fact  that,  in  several  of  his  experiments,  food  was 
digested  and  propelled  into  the  duodenum  subsequently  to  the  operation.    The 
same  fact,  which  he  appears  to  have  fully  substantiated,  is  an  incontrovertible 
proof,  that  the  secretion  of  gastric  juice  is  not  dependent  on  nervous  influence 
supplied  by  the  Par  Vagum,  though  doubtless  in  part  regulated  by  it.     The 
first  effects  of  the  operation,  however,  are  almost  invariably  found  to  be  vomit- 
ing (in  those  animals  capable  of  it),  loathing  of  food,  and  arrestment  of  the 
digestive  process ;  and  it  is  not  until  after  four  or  five  days,  that  the  power 
seems  re-established.     In  the  animals  which  died  before  that  time,  no  indica- 
tion of  it  could  be  discovered  by  Dr.  R.;  in  those  which  survived  longer,  great 
emaciation  took  place  ;  but  when  life  was  sufficiently  prolonged,  the  power  of 
assimilation  seemed  almost  completely  restored.     This  was  the  case  in  four 
out  of  the  seventeen  dogs  experimented  on ;  and  the  evidence  of  this  restora- 
tion consisted  in  the  recovery  of  flesh  and  blood  by  the  animals,  the  vomiting 
of  half-digested  food  permanently  reddening  litmus  paper,  the  disappearance 
of  a  considerable  quantity  of  alimentary  matter  from  the  intestinal  canal,  and 
the  existence  of  chyle  in  the  lacteals.    It  may  serve  to  account  in  some  degree 
for  the  contrary  results  obtained  by  other  experimenters,  to  state  that  seven 
out  of  Dr.  R.'s  seventeen  experiments  were  performed  before  he  obtained  any 
evidence  of  digestion  after  the  operation ;  and  that  the  four  which  furnished 
this  followed  one  another  almost  in  succession ;  so  that  it  is  easy  to  understand 
why  those,  who  were  satisfied  with  a  small  number  of  experiments,  should 
have  been  led  to  deny  it  altogether.  [*] 

236.  Another  series  of  experiments  was  performed  by  Dr.  Reid,  for  the  pur- 
pose of  testing  the  validity  of  the  results  obtained  by  Sir  B.  Brodie,  relative  to 
the  effects  of  section  of  the  Par  Vagum  upon  the  secretions  of  the  stomach, 
after  the  introduction  of  arsenious  acid  into  the  system.     According  to  that 
eminent  Surgeon  and  Physiologist,  when  the  poison  was  introduced  after  the 
Par  Vagum  had  been  divided  on  each  side,  the  quantity  of  the  protective 

[*  M.Bernard  has  instituted  fresh  experiments  to  determine  this  still-debated  question, 
making  use  of  the  artificial  fistulous  openings  into  the  stomach,  invented  by  M.  Blondlot. 
A  dog's  digestion  had  been  thus  watched  for'eight  days,  and  had  always  been  well 
effected.  On  the  ninth  day,  after  a  day's  fast,  M.  Bernard  sponged  out  the  stomach, 
which  contracted  on  the  contact  of  the  sponge,  and  at  once  secreted  a  large  quantity  of 
gastric  fluid;  he  then  divided  the  pneumogastric  nerves  in  the  middle  of  the  neck,  and 
immediately  the  mucous  membrane,  which  had  been  turgid,  became  pale,  as  if  exsan- 
guine, its  movements  ceased,  the  secretion  of  gastric  fluid  was  instantaneously  put  a  stop  to, 
and  a  quantity  of  ropy  neutral  mucus  was  soon  produced  in  its  place.  After  this,  no 
digestion  was  duly  performed,  and  milk  was  no  longer  coagulated;  raw  meat  remained 
unchanged,  and  the  food  (meat,  milk,  bread  and  sugar,  which  the  dog  had  before  tho- 
roughly digested)  remained  for  a  long  time  neutral,  and  at  last  acquired  acidity  only  from 
its  own  transformation  into  lactic  acid.  In  the  stomachs  of  other  dogs  after  the  division 
of  the  nerves,  he  traced  the  transformation  of  cane-sugar  into  grape-sugar  in  three  or 
four  hours;  and  in  ten  or  twelve  hours  the  transformation  into  lactic  acid  was  complete. 
In  others,  when  the  food  was  not  capable  of  an  acid  transformation,  it  remained  neutral 
to  the  last.  In  no  case  did  any  part  of  the  food  pass  through  the  peculiar  changes  of 
chymification.  In  a  last  experiment,  he  gave  to  each  of  two  dogs,  in  one  of  which  he 
had  cut  the  nerves,  a  dose  of  emulsine  and  half  an  hour  after,  a  dose  of  amygdaline 
(substances  which  are  innocent  alone,  but  when  mixed  produce  hydrocyanic  acid).  The 
dog,  whose  nerves  were  cut,  died  in  a  quarter  of  an  hour,  the  substances  being  absorbed 
unaltered  and  mixing  in  the  blood:  in  the  other,  the  emulsine  was  changed  by  the  action 
of  the  gastric  fluid  before  the  amygdaline  was  administered,  and  it  survived. —  Gazette 
Mid.,  Juin  1,  1844,  from  the  Report  of  the  Acad.  des  ScL,  seance  du  27  Mai,  1844.— M.  0.] 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  177 

mucous  and  watery  secretions  was  much  less  than  usual,  although  obvious 
marks  of  inflammation  were  present.  In  order  to  avoid  error  as  much  as  pos- 
sible, Dr.  Reid  made  five  sets  of  experiments,  employing  two  dogs  in  each,  as 
nearly  as  possible  of  equal  size  and  strength,  introducing  the  same  quantity  of 
the  poison  into  the  system  of  each  in  the  same  manner,  'but  cutting  the  Vagi 
in  one,  and  leaving  them  entire  in  the  other.  This  comparative  mode  of 
experimenting  is  obviously  the  only  one  admissible  in  such  an  investigation. 
Its  result  was  in  every  instance  opposed  to  the  statements  of  Sir  B.  Brodie ; 
the  quantity  of  the  mucous  and  watery  secretions  of  the  stomach  being  nearly 
the  same  in  each  individual  of  the  respective  pairs  subjected  to  experiment; 
so  that  they  can  no  longer  be  referred  to  the  influence  of  the  Eighth  pair  of 
nerves.  Moreover,  the  appearances  of  inflammation  were,  in  four  out  of  the 
five  cases,  greatest  in  the  animals  whose  Vagi  were  left  entire ;  and  this  seemed 
to  be  referable  to  the  longer  duration  of  their  lives  after  the  arsenic  had  been 
introduced.  The  results  of  Sir  B.  Brodie's  experiments  may  perhaps  be  ex- 
plained, by  the  speedy  occurrence  of  death  in  the  subjects  of  them,«consequent 
(it  may  JDC)  upon  the  want  of  sufficiently  free  respiration,  which  was  carefully 
guarded  against  by  Dr.  Reid. 

2*37.  So  far  as  the  results  of  Dr.  Reid's  experiments  may  be  trusted  to, 
therefore,  (and  the  Author  is  himself  disposed  to  rely  on  them  almost  impli- 
citly,) all  me  arguments  which  have  been  drawn,  in  favour  of  the  doctrine  that 
secretion  depends  upon  nervous  agency,  from  the  effects  of  lesion  of  the  Vagi 
upon  the  functions  of  the  stomach,  must  be  set  aside.  That  this  nerve  has  an 
important  influence  on  the  gastric  secretion,  is  evident  from  the  deficiency  in 
its  amount,  soon  after  the  operation,  as  well  as  from  other  facts.  But  this  is  a 
very  different  proposition  from  that  just  alluded  to;  and  the  difference  has 
been  very  happily  illustrated  by  Dr.  R.  "  The  movements  of  a  horse,"  he 
observes,  "are  independent  of  the  rider  on  his  back;  in  other  words,  the  rider 
does  not  furnish  the  conditions  necessary  for  the  movements  of  the  horse ;  but 
every  one  knows  how  much  these  movements  may  be  influenced  by  the  hand 
and  heel  of  the  rider."  It  may  be  hoped,  then,  that  physiologists  will  cease 
to  adduce  the  oft-cited  experiments  of  Dr.  Wilson  Philip,  in  favour  of  the 
hypothesis  (for  such  it  must  be  termed)  that  secretion  is  dependent  upon 
nervous  influence,  and  that  this  is  identical  with  galvanism.  Additional  evi- 
dence of  their  fallacy  is  derived  from  the  fact  mentioned  by  Dr.  Reid,  that  the 
usual  mucous  secretions  of  the  stomach  were  always  found ;  and  they  are  fur- 
ther invalidated  by  the  testimony  of  Miiller,  who  denies  that  galvanism  has 
any  influence  in  re-establishing  the  gastric  secretion,  when  it  has  been  checked 
by  secretion  of  the  nerves. 

238.  It  only  remains  to  notice  the  influence  of  section  of  the  Vagi  upon  the 
actions  of  the  Heart.  It  has  been  already  stated  that  mechanical  irritation  of 
these  nerves,  especially  at  these  roots,  has  a  tendency  to  excite  or  accelerate 
the  heart's  action.  It  remains  to  inquire,  if  its  movements  are  dependent  upon 
their  influence ;  or  if  these  nerves  form  the  channel  through  which  they  are 
affected  by  emotions  of  the  mind,  or  by  conditions  of  the  bodily  system.  In 
regard  to  the  first  point,  no  doubt  can  be  entertained,  since  the  regular  move- 
ments of  the  heart  are  but  little  affected  by  section  of  the  Vagi.  With  respect 
to  the  second,  there  is  more  difficulty,  since  the  number  of  causes  which  may 
influence  the  rapidity  and  pulsations  of  the  heart,  is  very  considerable.  For 
example,  when  the  blood  is  forced  on  more  rapidly  towards  the  heart,  as  in  exer- 
cise, struggling,  &c.,  the  stimulus  to  its  contractions  is  more  frequently  renewed, 
and  they  become  more  frequent;  and  when  the  current  moves  on  more  slowly, 
as  in  a  state  of  rest,  their  frequency  becomes  proportionabry  diminished.  If 
the  contractions  of  the  heart  were  not-  dependent  upon  the  blood,  and  their 
•ttumber  were  not  regulated  by  the  quantity  flowing  into  its  cavities,  very 


178  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

serious  and  inevitably  fatal  disturbances  of  the  heart's  action  would  soon  result. 
That  this  adjustment  takes  place  otherwise  than  through  the  medium  of  the 
nervous  centres, '  is  evident  from  the  fact  that,  in  a  dog,  in  which  the  par 
vagum  and  sympathetic  had  been  divided  in  the  neck  on  each  side,  violent 
struggling,  induced  by  alarm,  raised  the  number  of  pulsations  from  130  to  260 
per  minute.  It  is  difficult  to  ascertain,  by  experiment  upon  the  lower  animals, 
whether  simple  emotion,  unattended  with  struggling  or  other  exertion,  would 
affect  the  pulsation  of  the  heart,  after  section  of  the  Vagi ;  but  when  the  large 
proportion  of  the  Sympathetic  nerves  proceeding  to  this,  organ  is  considered, 
and  when  it  is  also  remembered  that  irritation  of  the  roots  of  the  upper  cervi- 
cal nerves  stimulates  the  action  of  the  heart  through  these,  we  can  scarcely 
doubt  that  both  may  serve  as  the  channels  of  this  influence,  especially  in  such 
animals  as  the  dog,  in  which  the  two  freely  inosculate  in  the  neck. 

239.  In  regard  to  the  functions  of  the  Spinal  Accessory  nerve,  also,  there 
has  been  great  difference  of  opinion;  the  peculiarity  of  its  origin  and  course 
having  led  to  the  belief  that  some  very  especial  purpose  is  answered  by  it. 
We  shall  first  examine  what  evidence  of  its  character  may  be  obtained  from 
its  anatomy  only.  Its  filaments  come  off  from  the  middle  column  of  the  Spinal 
Cord,  most  frequently  as  low  down  as  the  origins  of  the  sixth  and  seventh 
Cervical  nerves.  In  its  course  upwards  to  the  foramen  magnum,  it  lies 
between  the  posterior  roots  of  the  spinal  nerves  and  the  ligamentum  denticu- 
latum.  It  sometimes  receives  filaments  from  these  roots,  and  is  generally 
connected  especially  with  the  first  cervical.  According  to  Bellingeri,  however, 
who  has  paid  great  attention  to  the  subject,  the  filaments  coming  from  the  pos- 
terior roots  do  not  form  part  of  the  trunk  of  the  nerve,  but  leave  it  again  to 
enter  the  posterior  root  of  the  first  cervical.  It  may  be  doubted  whether  this 
is  entirely  true ;  as  some  experiments  appear  to  show  that  the  Spinal  Acces- 
sory is  in  some  degree  a  sensory  nerve,  even  at  its  roots.  As  the  trunk  passes 
through  'the  foramen  lacerum,  it  divides  into  two  branches ;  of  which  the 
internal,  after  giving  off  some  filaments  that  assist  in  forming  the  pharyngeal 
branch  of  the  Par  Vagum,  becomes  incorporated  with  the  trunk  of  that  nerve, 
whilst  the  external  proceeds  outwards,  and  is  finally  distributed  to  the  sterno- 
cleido-mastoideus  and  trapezius  muscles,  some  of  its  filaments  inosculating 
with  those  of  the  cervical  plexus.  It  is  interesting  to  remark,  that  the  junction 
of  the  anterior  branch  with  the  Par  Vagum,  beyond  the  point  at  which  the 
latter  swells  out  into  its  superior  ganglion,  increases  the  analogy,  which  has 
been  sustained  upon  other  grounds,  between  the  compound  trunk  thus  formed 
and  that  of  the  spinal  nerves  ;  the  Par  Vagum  being  regarded  as  the  sensory 
root,  and  the  Spinal  Accessory  as  the  motor.  According  to  Valentin,  however, 
there  is  not  a  mere  passage  of  filaments  from  the  Spinal  Accessory  to  the  Par 
Vagum,  but  an  absolute  interchange ;  the  trunk  of  the  former  containing  some 
sensory  fibres  derived  from  the  latter.  When  the  roots  of  the  Spinal  Acces- 
sory are  irritated,  as  appears  from  the  experiments  of  Valentin,  no  decided 
indications  of  sensation  can  be  obtained ;  but  all  the  motor  actions  of  the  Par 
Vagum  manifest  themselves.  When  the  external  branch  is  irritated,  before  it 
perforates  the  sterno-mastoid  muscle,  vigorous  convulsive  movements  of  that 
muscle,  and  of  the  trapezius,  are  produced;  and  the  animal  does  not  give  any 
signs  of  pain,  unless  the  nerve  is  firmly  compressed  between  the  forceps,  or 
is  included  in  a  tight  ligature.  Hence  it  may  be  inferred  that  the  functions  of 
this  nerve  are  chiefly  motor,  and  that  its  sensory  filaments  are  few  in  number. 
Further,  when  the  nerve  has  been  cut  across,  or  firmly  tied,  irritation  of  the 
lower  end  is  attended  by  the  same  convulsive  movements  of  tlie  muscles ; 
whilst  irritation  of  the  upper  end,  in  connection  with  the  spinal  cord,  is  unat- 
tended with  any  muscular  movement.  Hence  it  is  clear  that  the  motions 
occasioned  by  irritating  it  are  of  a  direct,  not  of  a  reflex  character.  The  same1 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  179 

muscular  movements  are  observed  on  irritating  the  nerve  in  the  recently  killed 
animal,  as  during  life. 

240.  According  to  SirC.  Bell,  the  Spinal  Accessory  is  a  purely  Respiratory 
nerve,  whose  office  it  is  to  excite  the  involuntary  or  automatic  movements  of 
the  muscles  it  supplies,  which  share  in  the  act  of  respiration  ;    and  he  states 
that  the  division  of  it  paralyzes  the  muscles  to  which  it  is  distributed,  as 
muscles  of  respiration  ;   though  they  still  perform  the  voluntary  movements, 
through  the  medium  of  the  spinal  nerves.     Both  Valentin  and  Dr.  Reid,  how- 
ever, positively  deny  that  this  is  the  case.     Dr.  Reid's  method  of  experiment- 
ing was  well  adapted  to  test  the  truth  of  the  assertion.     Considering  that,  in 
the  ordinary  condition  of  the  animal,  it  might  be  difficult  to  distinguish  the 
actions  of  particular  muscles,  beneath  the  skin,  when  those  in  the  neighbour- 
hood were  in  operation ;  and  also  that  the  usual  automatic  movements  might 
be  stimulated  by  voluntary  action,  when  the  breathing  might  be   rendered 
difficult ;  he  adopted  the  following  plan  : — A  small  dose  of  prussic  acid  was 
given  to  an  animal,  in  which  the  Spinal  Accessory  had  been  previously  divided 
on  one  side  ;  and  after  the  convulsive  movements  produced  by  it  had  ceased, 
the  animal  was  generally  found  in  a  state  similar  to  that  which  we  sometimes 
see  in  apoplexy,— the  action  of  the  heart  going  on,  the  respirations  being  slow 
and  heaving,  and  the  sensorial  functions  appearing  to  be  completely  suspended. 
The  Respiratory  movements  always  ceased  before  the  action  of  the  heart ; 
but  they  continued,  in  several  of  the  animals  experimented  on,  sufficiently 
long  to  allow  the  muscles  of  the  anterior  part  of  the  neck  to  be  laid  bare,  so 
that  accurate  observations  could  be  made  upon  their  contractions.     In  the  dog 
and  cat,  the  sterno-mastoid  does  not  appear  to  have  much  participation  in  the 
ordinary  movements  of  respiration  ;    for  in  several  instances  it  could  not  be 
seen  to  contract  on  either  side,  though  the  head  was  forcibly  pulled  towards 
the  chest  at  each  inspiratory  movement,  chiefly  by  the  action  of  the  sterno- 
hyoid  and  thyroid  muscles.     In  two  dogs  and  one  cat,  however,  in  which  the 
head  was  fixed,  and  these  respiratory  movements  were  particularly  vigorous, 
distinct  contractions  were  seen  in  the  exposed  sterno-mastoid  muscles,  syn- 
chronous with  the  other  movements  of  respiration:    these  were,  perhaps, 
somewhat  weaker  on  the  side  on  which  the  nerve  had  been  cut,  but  were 
still  decidedly  present.     In  one  of  these  dogs,  similar  movements  were  ob- 
served in  the  trapezius,  on  the  side  on  which  the  nerve  had  been  divided. 
As  the  condition  of  the  animal  forbade  the  idea  that  volition  could  be  the  cause 
of  these  movements,  it  can  scarcely  be  questioned  that  Sir  C.  Bell's  statement 
was  an  erroneous  one.     As  far,  therefore,  as  these  experiments  afford  any 
positive  data,  in  regard  to  the  functions  of  this  nerve,  it  may  be  concluded 
that  they  are  the  same  as  those  of  the  cervical  plexus,  with  which  it  anasto- 
moses freely.     "Future  anatomical  researches,"  as  Dr.  Reid  justly  remarks, 
"  may  perhaps  explain   to  us  how  it  follows  this   peculiar  course,  without 
obliging  us  to  suppose  that  it  has  a  reference  to  any  special  function  in  the 
adult  of  the  human  species."     Thus,  the  study  of  the  history  of  development 
has  accounted  satisfactorily  for  the  peculiar  course  of  the  recurrent  laryngeal, 
which  may  be  traced  passing  directly  from  the  par  vagum  to  the  larynx,  at  a 
time  when  the  neck  can  scarcely  be  said  to  exist,  and  when  that  organ  is 
buried  in  the  thorax.     As  this  rises  in  the  neck,  the  nerve  which  at  first  came 
off  below  the  great  transverse  blood-vessels,  has  both  its  origin  and  its  termina- 
tion carried  upwards  ;  whilst  it  is  still  tied  down  by  these  vessels  in  the  middle 
of  its  course. 

241.  The  Hypoglossal  nerve,  or  Motor  Liriguse,  is  the  only  one  which,  in 
the  regular  order,  now  remains  to  be  considered.     That  the  distribution  of 
this  nerve  is  restricted  to  the  muscles  of  the  tongue,  is  a  point  very  easily 
established  by  anatomical  research  ;  and  accordingly  we  find  that,  long  before 


180  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  time  of  Sir  C.  Bell,  Willis  spoke  of  it  as  the  nerve  of  the  motions  of  articu- 
lation, whilst  to  the  Lingual  branch  of  the  fifth  pair  he  attributed  the  power  of 
exercising  the  sense  of  taste ;  and  he  distinctly  stated,  that  the  reason  of  this 
organ  being  supplied  with  two  nerves  is  its  double  function.  The  inference 
that  it  is  chiefly,  if  not  entirely,  a  motor  nerve,  which  has  been  founded  on  its 
anatomical  distribution,  is  supported  also  by  the  nature  of  its  origin,  which  is 
usually  from  a  single  root,  corresponding  to  the  anterior  root  of  the  Spinal 
nerves.  Experiment  shows  that,  when  the  trunk  of  the  nerve  is  stretched, 
pinched,  or  galvanized,  violent  motions  of  the  whole  tongue,  even  to  its  tip, 
are  occasioned ;  and  also,  that  similar  movements  take  place  after  division  of 
the  nerve,  when  the  cut  end  most  distant  from  the  brain  is  irritated.  In  regard 
to  the  degree  in  which  this  nerve  possesses  sensory  properties,  there  is  some 
difference  of  opinion  amongst  physiologists,  founded,  as  it  would  seem,  on  a 
variation  in  this  respect  between  different  animals.  Indications  of  pain  are 
usually  given,  when  the  trunk  is  irritated  after  its  exit  from  the  cranium  ;  but 
these  may  proceed  from  its  free  anastomosis  with  the  cervical  nerves,  which 
not  improbably  impart  sensory  fibres  to  it.  But  in  some  Mammalia,  the  hypo- 
glossal  nerve  has  been  found  to  possess  a  small  posterior  root  with  a  ganglion  : 
this  is  the  case  in  the  ox,  and  also  in  the  rabbit ;  and  in  the  latter  animal, 
Valentin  states  that  the  two  trunks  pass  out  from  the  cranium  through  separate 
orifices,  and  that,  after  their  exit,  one  may  be  shown  to  be  sensory,  and  the 
other  to  be  motor.  Hence  this  nerve,  which  is  the  lowest  of  those  that  ori- 
ginate in  the  cephalic  prolongation  of  the  spinal  cord  generally  known  as  the 
medulla  oblongata,  approaches  very  closely  in  some  animals  to  the  regular 
type  of  the  spinal  nerves  ;  and  though  in  Man  it  still  manifests  an  irregularity, 
in  having  only  a  single  root,  yet  this  irregularity  is  often  shared  by  the  first 
cervical  nerve,  which  also  has  sometimes  an  anterior  root  only. 

342.  The  Hypoglossal  nerve  is  distributed  not  merely  to  the  tongue,  but  to 
the  muscles  of  the  neck  which  are  concerned  in  the  movements  of  the  larynx ; 
and  the  purpose  of  this  distribution  is  probably  to  associate  them  in  those 
actions  which  are  necessary  for  articulate  speech.  Though  all  the  motions 
of  the  tongue  are  performed  through  the  medium  of  this  nerve,  yet  it  would 
appear,  from  pathological  phenomena,  to  have  at  least  two  distinct  connections 
with  the  nervous  centres  ;  for  in  many  cases  of  paralysis,  the  masticatory 
movements  of  the  tongue  are  but  little  affected,  when  the  power  of  articula- 
tion is  much  injured  or  totally  destroyed  ;  and  the  converse  may  be  occa- 
sionally noticed.  When  this  nerve  is  paralyzed  on  one  side,  in  hemiplegia, 
it  will  be  generally  observed  that  the  tongue,  when  the  patient  is  directed  to 
put  it  out,  is  projected  towards  the  palsied  side  of  the  face  :  that  is  due  to  the 
want  of  action  of  the  lingual  muscles  of  that  side,  which  do  not  aid  in  pushing 
forward  the  tip;  the  point  is  consequently  directed  only  by  the  muscles  of  the 
other  side,  which  will  not  act  in  a  straight  direction,  when  unantagonized  by 
their  fellows.  It  is  a  curious  fact,  however,  that  the  hypoglossal  nerve  seems 
not  to  be  always  palsied  on  the  same  side  with  the  facial,  but  sometimes  on 
the  other.  This  has  been  suggested  to  be  due  to  the  origination  of  the  roots 
of  this  nerve  from  near  the  point  at  which  the  pyramids  of  the  medulla 
oblongata  decussate  :  so  that  some  of  its  fibres  come  off,  like  those  of  the  spinal 
nerves,  without  crossing ;  whilst  others  are  transmitted  to  the  opposite  side, 
like  those  of  the  higher  cerebral  nerves ;  and  the  cause  of  paralysis  may 
affect  one  or  other  of  these  sets  of  roots  mortfparticularly.  Whatever  may  be 
the  validity  of  this  explanation,  the  circumstance  is  an  interesting  one,  and 
well  worthy  of  attention.* 

*  It  may  be  questioned,  however,  whether  the  Hypoglossal  is  really  paralyzed  on  the 
opposite  side  from  the  facial  in  such  cases.  An  instance  has  been  communicated  to  the 


FUNCTIONS  OF  THE  CEPHALIC  NERVES.  181 

[Fig.  41. 


The  course  and  distribution  of  the  Hypo-Glossal  or  Ninth  pair  of  nerves;  the  deep-seated  nerves  of  the 
neck  are  also  seen;  1,  the  hypo-glossal  nerve  ;  2,  branches  communicating  with  the  gustatory  nerve;  3,  a 
branch  to  the  origin  of  the  hyoid  muscles ;  4,  the  descendens  noni  nerve;  5,  the  loop  formed  with  the  branch 
from  the  cervical  nerves;  6,  muscular  branches  to  the  depressor  muscles  of  the  larynx;  7,  a  filament  from 
the  second  cervical  nerve,  and  8,  a  filament  from  the  third  cervical,  uniting  to  form  the  communicating 
branch  with  the  loop  from  the  descendens  noni;  9,  the  auricular  nerve;  10,  the  inferior  dental  nerve;  11,  its 
mylo-hyoideau  branch;  12,  the  gustatory  nerve;  13,  the  chorda-tympani  passing  to  the  gustatory  nerve ; 
14,  the  chorda-tympani  leaving  the  gustatory  nerve  to  join  the  sub-maxillary  ganglion ;  15,  the  sub-maxil- 
lary ganglion ;  16,  filaments  of  communication  with  the  lingual  nerve;  17,  the  glosso-pharyngeal  nerve; 
18,  the  pneumogastric  or  par  vagum  nerve;  19,  the  three  upper  cervical  nerves;  20,  the  four  inferior  cer- 
vical nerves ;  21,  the  first  dorsal  nerve ;  22, 23,  the.brachial  plexus ;  24;  25,  the  phrenic  nerve ;  26,  the  carotid 
artery ;  27,  the  internal  jugular  vein.] 

243.  The  character  of  the  Cephalic  nerves,  as  distinguished  from  the 
Spinal,  is  a  point  of  much  interest,  when  considered  in  relation  to  Compara- 
tive Anatomy,  and  to  Embryology.  It  appears,  from  what  has  heen  already 
stated,  that  the  Par  Vagum,  Spinal  Accessory,  Glosso-pharyngeal,  and  Hypo- 
glossal  nerves,  may  be  considered  nearly  in  the  light  of  ordinary  Spinal 
nerves.  They  all  take  their  origin  exclusively  in  the  Medulla  Oblongata ; 
and  the  want  of  correspondence  in  position,  between  their  roots  and  those  of 
the  Spinal  nerves,  is  readi]y  accounted  for,^by  the  alteration  in  the  direction 
of  the  columns  of  the  Spinal  Cord,  which, — as  long  since  pointed  out  by 
Rosenthal,  and  lately  stated  prominently  by  Dr.  Reid, — not  only  decussate 
laterally,  but,  as  it  were,  from  behind  forwards  (§  171).  The  Hypoglossal, as 
just  stated,  not  unfrequently  possesses  a  sensory  in  addition  to  its  motor  root. 
The  Glosso-pharyngeal,  which  is  principally  an  afferent  nerve,  is  stated  by 
Arnold  and  others  to  have  a  small  motor  root ;  at  any  rate,  the  motor  fibres 
which  belong  to  it  are  to  be  found  in  the  Par  Vagum.  That  the  Par  Vagum 
and  a  portion  of  the  Spinal  Accessory  together  make  up  a  spinal  nerve,  has 
been  already  stated  as  probable.  Leaving  these  nerves  out  of  the  question, 

author  by  Dr.  W.  Budd,  in  which  the  hypoglossal  nerve  was  completely  divided  on  one 
side;  and  yet  the  tip  of  the  tongue,  when  the  patient  was  desired  to  put  it  out,  was  some- 
times directed  from  and  sometimes  towards  the  palsied  side  ;  showing  that  the  muscles 
of  either  half  are  sufficient  to  give  any  required  direction  to  the  whole. 
16 


182  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

therefore,  we  proceed  to  the  rest.  Comparative  anatomy,  and  the  study  of 
Embryonic  development,  alike  show  that  the  Spinal  Cord  and  Medulla  Ob- 
longata  constitute  the  most  essential  part  of  the  nervous  system  in  Vertebrata  ; 
and  that  the  Cerebral  Hemispheres  are  superadded,  as  it  were,  to  this.  At 
an  early  period  of  development,  the  Encephalon  consists  chiefly  of  three 
vesicles,  which  correspond  with  the  gang-home  enlargements  of  the  nervous 
cord  of  the  Articulata,  and  mark  three  divisions  of  the  cerebro-spinal  axis ; 
and,  in  accordance  with  this  view,  the  Osteologist  is  able  to  trace,  in  the  bones 
of  the  cranium,  the  same  elements  which  would  form  three  vertebras,  in  a 
much  expanded  and  altered  condition.  However  improbable  such  an  idea 
might  seem,  when  the  cranium  of  the  higher  Vertebrata  alone  is  examined,  it 
at  once  reconciles  itself  to  our  reason,  when  we  direct  our  attention  to  that  of 
Reptiles  and  Fishes  ;  in  which  classes  the  size  of  the  Cerebral  or  hemispheric 
ganglia  is  very  small,  in  comparison  with  that  of  the  Ganglia  of  special  sensa- 
tion ;  and  in  which  the  latter  evidently  form  but  a  continuation  of  the  Spinal 
Cord,  modified  in  its  function :  so  that,  when  we  trace  upwards  the  cavity  of 
the  spinal  column  into  that  of  the  cranium,  we  encounter  no  material  change, 
either  in  its  size  or  direction.  The  three  pairs  of  nerves  of  special  sensation 
make  their  way  out  through  these  three  cranial  vertebrae  respectively.  At  a 
later  period  of  development,  other  nerves  are  interposed  between  these ;  which, 
being  intervertebral,  are  evidently  more  analogous  to  the  Spinal  nerves,  both 
in  situation  and  function.  A  separation  of  the  primitive  fibres  of  these  takes 
place,  however,  during  the  progress  of  development,  so  that  their  distribution 
appears  irregular.  Thus,  the  greater  part  of  the  sensory  fibres  are  contained 
in  the  large  division  of  the  Trigeminus ;  whilst,  of  the  motor  fibres,  the  ante- 
rior ones  chiefly  pass  forwards  as  the  Oculo-motor  and  Patheticus ;  and  of  the 
posterior,  some  form  the  small  division  of  the  Trigeminus,  and  others  unite 
with  the  first  pair  from  the  medulla  oblongata,  to  form  the  Facial.  This  last 
fact  explains  the  close  union  of  this  nerve  with  those  proceeding  more  directly 
from  the  medulla  oblongata,  which  we  find  in  Fishes  and  in  some  Amphibia. 
According  to  Valentin,  the  Glosso-pharyngeal  is  the  sensory  portion  of  the 
first  pair  from  the  medulla  oblongata,  of  which  the  motor  part  is  chiefly  com- 
prehended in  the  Facial  nerve.  It  is  very  interesting  to  trace  this  gradual 
metamorphosis  from  the  character  of  the  Spinal  nerves,  which  is  exhibited  in 
the  Cephalic,  when  they  are  traced  upwards  from  the  Medulla  Oblongata;  and 
this  is  shown,  as  formerly  pointed  out  (§  223),  as  much  in  the  nerves  of  special 
sensation  as  in  the  rest.  Although  we  are  accustomed  to  consider  the  Fifth 
pair  as  par  excellence  the  Spinal  nerve  of  the  head,  the  foregoing  statements, 
founded  upon  the  history  of  its  development,  show  that  the  nerves  of  the  Orbit 
really  belong  to  its  motor  portion ;  they  may  consequently  be  regarded  as  alto- 
gether forming  the  first  of  the  intervertebral  or  Spinal  nerves  of  the  cranium. 
The  Facial  and  Glosso-pharyngeal  appear  to  constitute  the  second ;  whilst  the 
Par  Vagum  and  Spinal  Accessory  intervene  between  this  and  the  true  Spinal, 
of  which  the  Hypoglossal  may  be  considered  as  the  first. 
/ 

XV.— Motor  Nerves  of  the  Orbit. 

244.  We  now  return  to  consider  the  functions  of  the  Third,  Fourth  and 
Sixth  pairs  of  nerves,  together  constituting  the  entire  channel  of  the  movements 
of  the  eyeball.  Their  particular  functions  are  but  ill  understood,  and  the 
movements  which  they  govern  offer  so  many  peculiarities,  that  the  inquiry 
becomes  a  very  complex  one.  It  is  of  peculiar  interest,  however,  both  on 
account  of  its  general  bearing  on  the  Physiology  of  the  Nervous  System,  and 
at  the  present  time,  more  especially,  in  consequence  of  the  assistance  iwhich 
a  correct  Jmowledge  of  these  functions  may  afford,  in  the  treatment  of  Stra- 


MOTOR  NERVES  OF  THE  ORBIT. 


183 


[Fig.  42. 


bismus,  by  the  operation  which  has  now  been  so  extensively  and  (when  exe- 
cuted with  care  and  judgment)  so  successfully  performed. 

245.  It  will  be  recollected  that,  in  the  Human  Orbit,  six  muscles  for  the 
movements  of  the  eyeball  are  found;  the  four  recti,  and  the  two  oblique  mus- 
cles. The  precise  actions  of  these  are  not  easily  established  by  experiment 
on  the  lower  animals;  for  in  all  those  which  ordinarily  maintain  the  horizontal 
position,  there  is  an  additional  muscle,  termed  the  retractor,  which  embraces 
the  whole  posterior  portion  of  the  globe,  and  passes  backwards  to  be  attached 
to  the  bottom  of  the  orbit.  This  muscle  is  most  developed  in  Ruminating 
animals,  which,  during  their  whole  time  of  feeding,  carry  their  heads  in  a 
dependent  position.  In  most  Carnivorous  animals,  instead  of  the  complete 
hollow  muscular  cone,  (the  base  enclosing  the  eyeball,  whilst  the  apex  sur- 
rounds the  optic  nerve,)  which  we  find  in  the  Ruminants,  there  are  four  dis- 
tinct strips,  almost  resembling  a  second  set  of  recti  muscles,  but  deep-seated, 
and  inserted  into  the  posterior  instead  of  the  anterior  portion  of  the  globe.  It 
is  obvious  that  the  actions  of  these  must  greatly  affect  the  results  of  any  opera- 
tions which  we  may  perform  upon  the  other  muscles  of  the  Orbit ;  and,  as  it 
is  impossible  to  divide  the  former,  without  completely  separating  the  eye  from 
its  attachments,  we  have  no  means 
of  correcting  such  results  but  by 
reasoning  alone.  Experiments  upon 
animals  of  the  order  of  Q,uadru- 
mana,  most  nearly  allied  to  Man, 
would  be  more  satisfactory,  as  in 
them  the  retractor  muscle  is  almost 
or  entirely  absent.  If  the  origin 
and  insertion  of  the  four  Recti  mus- 
cles be  examined,  however,  no  doubt 
can  remain  that  each  of  them,  act- 
ing singly,  is  capable  of  causing  the 
globe  to  revolve  in  its  own  direction 
— the  superior  rectus  causing  the 
pupil  to  turn  upwards — the  internal 
rectus  causing  it  to  roll  towards  the 
nose — and  so  on.  A  very  easy  and 
direct  application  of  the  laws  of  me- 
chanics wrill  further  make  it  evident 
to  us,  that  the  combined  action  of 
any  two  of  the  Recti  muscles  will 
cause  the  pupil  to  turn  in  a  direc- 
tion intermediate  between  the  lines 
of  their  single  action,  and  that  any 
intermediate  position  may  thus  be 
given  to  the  eyeball  by  these  mus- 
cles alone.  This  fact,  which  has 
not  received  the  attention  it  de- 
serves, leads  us  to  perceive  that  the 
Oblique  muscles  must  have  some 
supplementary  function'  It  may  be  objected  that  this  is  a  theoretical  statement 
only,  and  that  there  may  be  some  practical  obstacle  to  the  performance  of 
diagonal  movements  by  the  Recti  muscles,  wThich  renders  the  assistance  of 
the  Obliques  essential  for  this  purpose.  But  to  this  it  may  be  replied,  that  no 
single  muscle  can  direct  the  ball  either  downwards  and  inwards,  or  upwards 
and  outwards,  and  that,  as  we  have  good  reason  to  believe  these  movements  to 


A  view  of  the  Third,  Fourth  and  Sixth  pairs  of  Nerves; 
1,  ball  of  the  eye  and  rectus  externus  muscle ;  2,  the 
superior  maxilla;  3,  the  third  pair,  or  motores  oculi, 
distributed  to  all  the  muscles  of  the  eye  except  the  su- 
perior oblique  and  external  rectus;  4,  the  fourth  pair, or 
pathetici,  going  to  the  superior  oblique  muscle;  5,  one 
of  the  branches  of  the  seventh  pair;  6,  the  sixth  pair, 
or  motor  externus,  distributed  to  the  external  rectus 
muscle;  7,  spheno-palatine  ganglion  and  branches;  S, 
ciliary  nerves  from  the  lenticular  ganglion,  the  short 
root  of  which  is  seen  to  connect  it  with  the  third  pair.] 


184  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

be  affected  by  the  combination  of  the  Recti  muscles,  there  is  no  reason  why 
the  other  diagonal  movements  should  not  also  be  due  to  them. 

246.  The  action  of  the  Superior  Oblique  muscle  has  been  a  patter  of  dis- 
pute.    Unlike  the  other  muscles  which  arise  from  the  back  of  the  orbit,  its 
tendon  is  not  inserted  into  the  front  hemisphere  of  the  eye,  but  into  a  point 
behind  its  vertical  axis ;  and  we  should,  therefore,  be  led  to  suppose  that  its 
operation  is  to  move  the  pupil  in  a  direction  contrary  to  that  in  which  its  ten- 
don is  inserted ;  that  is  to  say,  as  its  tendon  passes,  from  its  insertion  towards 
the   trochea,  upwards  and  somewhat  inwards,  we   should  suppose  that,  in 
shortening,  it  would  draw  the  back  of  the  eyeball  in  that  direction,  and  turn 
the  pupil  in  the  contrary  one — namely,  downwards  and  a  little  outwards. 
This  theory  of  its  action  is  borne  out  by  experiments,  both  upon  the  muscle 
and  the  nerve  which  supplies  it ;  for  by  laying  bare  the  muscle,  without  dis- 
turbing the  eyeball  or  the  neighbouring  parts,  and  then   exercising  gentle 
traction  upon  it,  so  as  to  draw  the  tendon  in  the  same  manner  as  ordinary 
contraction  of  the  muscle  would  have  done,  the  eyeball  is  turned  downwards 
and   somewhat  outwards.      The  same  effect  is  produced  when  the  Fourth 
pair  of  nerves  is  irritated,  either  mechanically  or  by  galvanism,  after  it  has 
been  separated  from  the  brain.     On  the  other  hand,  the  Inferior  Oblique  mus- 
cle may  be  shown,  by  experiments  upon  itself,  to  roll  the  eye  upwards  and 
inwards ;  the  inward  movement  is  much  greater  than  the  outward  movement 
caused  by  the  Superior  Oblique ;  so-that  these  two  muscles  are  not  exactly 
antagonists  of  each  other. 

247.  The  distribution  of  nerves  to  these  muscles  is  very  peculiar.     The 
Superior  Oblique  has  a  nerve  for  itself  alone,  namely,  the  Fourth  pair ;  this 
was  formerly  called  the  Patheticus  nerve,  from  its  being  supposed  to  govern 
that  rotation  of  the  ball  upwards  and  inwards,  which  gives  a  pathetic  expres- 
sion to  the  countenance  ;  but,  as  just  shown,  its  real  action  is  the  reverse.    By 
Sir  C.  Bell,  this  nerve  was  considered  as  belonging  to  his  Respiratory  system; 
ahd  he  endeavoured  to  show,  that  the  sudden  movement  of  the  pupil  upwards 
and  imvards,  which  takes  place  in  coughing  and  sneezing,  and  the  fixation  of 
the  ball  in  a  similar  position  during  sleep,  are  due  to  its  operation.     The 
ascertained  action  of  the  muscle,  however,  constrained  him  to  suppose,  that 
the  operation  of  the  nerve  was  not  to  cause  contraction,  but  relaxation,  of  this ; 
by  which  the  antagonist  muscles  might  be  free  to  occasion  the  movement. 
This  idea  affords  a  remarkable  exemplification  of  the  degree  in  which  theory 
may,  in  some  minds,  usurp  the  place  of  observation.     There  is,  as  we  have 
formerly  seen,  no  ground  for  the  assumption  of  a  system  of  Respiratory  nerves 
distinct  from  those  forming  the  general  Excito-Motor  system,  from  which  a 
part  of  every  motor  trunk  in  the  body  is  derived ;  and  the  supposition  that  the 
action  of  a  nerve  is  ever  to  cause  relaxation  in  a  muscle,  is  at  variance  with 
all  sound  physiological  induction.     In  this  particular  instance,  it  is  at  once 
refuted,  by  such  experiments  on  the  trunk  of  the  nerve  as  those  just  adverted 
to. — It  may  further  be  added,  in  regard  to  this  nerve,  that  there  is  no  decided 
reason  to. believe  that  it  contains  any  sensory  fibres.     Its  distribution  is  entirely 
restricted  to  the  Superior  Oblique  muscle ;  but  since  in  this,  as  in  other  mus- 
cles of  the. orbit,  there  is  certainly  a  degree  of  sensibility,  as  is  experienced  by 
the  fatigue  to  which  the  long  fixation  or  violent  straining  of  them  gives  rise,  it 
may  be  questioned  whether  the  Fourth  pair  of  nerves  is  entirely  motor.     Its 
course  within  the  cranium  renders  it  very  unlikely  that  this  point  can  be 
satisfactorily  determined  by  experiment.     Muhler  states   that  a  connection 
exists  between  this  nerve  and  the  ophthalmic  branch  of  the  Fifth  pair ;  so  that 
it  is  not  improbable  that,  as  in  other  instances,  its  sensory  endowments  are 
derived  from  this  source. 

248.  Tine  same  may  be  said  of  the  Sixth  pair,  which  is  termed  the  M- 


MOTOR  NERVES  OF  THE  ORBIT.  185 

ducens  nerve,  from  its  being  solely  distributed  to  the  Rectus  externus  muscle. 
There  is  no  reason  to  believe  that  the  actions  of  either  of  the  two  last-mentioned 
nerves  are  ever  involuntary;  on  the  contrary,  there  will  appear  reason  to 
suppose  that  they  are,  with  a  branch  of  the  third  pair,  the  sources  of  the 
voluntary  movements  of  the  eyes.  Cases  occasionally  present  themselves  in 
which  this  nerve  alone  is  paralyzed;  and  the  outward  motion  of  the  ball  is 
then  almost  entirely  lost. 

249.  The  three  other  Recti  muscles,  together  with  the  Levator  Palpebra3, 
and  Inferior  Oblique,  are  supplied  by  the  Third  pair,  commonly  termed  Oculo- 
motor. The  general  question,  how  far  this  nerve  is  to  be  regarded  as  exclu- 
sively motor,  has  been  already  considered  (§  224);  that  it  is  chiefly  so,  there 
can  be  no  doubt.  But  we  have  now  to  inquire,  whether  there  is  any  ground 
for  believing  that  different  branches  of  the  nerve  are  subservient  to  motions  of 
a  different  character — some,  for  example,  being  more  connected  with  the 
Reflex  function  of  the  Spinal  Cord;  others  with  that  instinctive  tendency 
which  causes  opposite  muscular  actions  to  take  place  in  the  two  orbits  by  one 
effort  of  the  will;  and  others  being  immediately  directed  and  controlled  by  the 
will.  It  will  be  remembered  that  this  nerve  subdivides  into  two  principal 
branches  ;  of  which  one  supplies  the  Levator  Palpebra3  and  Superior  Rectus; 
whilst  the  other  is  distributed  to  the  Internal  and  Inferior  Recti,  and  to  the 
Inferior  Oblique.  Now  the  action  of  the  former  appears  to  be  of  a  purely 
voluntary  character.  We  have  no  instance  of  the  upper  lid  being  elevated  by 
any  other  than  an  effort  of  the  will ;  and,  if  this  be  suspended,  the  Orbicularis 
may  be  made  to  depress  it,  by  the  reflexion  of  a  stimulus  applied  to  the  edge 
of  the  tarsi.  Moreover,  when  a  strong  light  causes  the  lids  to  contract  invo- 
luntarily, we  feel  conscious  that  a  voluntary  effort  is  required  to  keep  them 
apart.  The  same  may  be  said  of  the  directly  upward  movement  of  the  eye- 
ball, wrhich  is  caused  by  the  Superior  Rectus  alone:  it  is  never  any  thing  but 
a  voluntary  act;  for  the  upward  and  inward  movement  adverted  to  by  Sir  C. 
Bell,  is  evidently  occasioned  by  the  inferior  oblique  acting  alone.  On  the 
other  hand,  it  is  certain  that  some,  at  least,  of  the  actions  of  the  second  branch 
are  of  a  simply  reflex  nature ;  and  that  others  cannot  be  said  to  be  voluntary, 
but  are  rather  of  an  instinctive  character.  It  is  from  this  branch  that  the 
twigs  proceed,  which  enter  the  ciliary  ganglion,  and  which  govern  the  move- 
ments of  the  pupil ;  movements  which  have  been  already  shown  to  be  of  a 
simply  reflex  nature.  Some  have  attempted  to  show,  that  the  actions  of  the 
iris  are  in  a  slight  degree  voluntary,  because,  by  an  effort  of  the  will,  they 
could  occasion  contraction  of  the  pupil ;  but  this  so-called  voluntary  contraction 
is  always  connected  with  a  change  in  the  place  of  the  eyeball  itself,  occasioned 
by  an  action  of  some  of  its  muscles.  It  is  principally  noticed  under  the  two 
following  conditions.  1.  When  an  object  is  brought  very  near  the  eye,  and 
we  steadily  fix  our  attention  upon  it,  the  axes  of  the  two  eyes  are  made  to 
converge  ;  and  if  this  convergence  be  carried  to  a  considerable  extent,  so  that 
the  pupils  of  both  eyes  are  sensibly  directed  towards  the  inner  canthus,  a 
contraction  of  the  pupil  takes  place.  The  final  cause  or  purpose  of  this  con- 
traction is  very  evident.  When  an  object  is  brought  near  the  eye,  the  rays 
proceeding  from  it  would  enter  the  pupil  (if  it  remained  of  its  usual  size)  at 
an  angle  of  divergence  so  much  greater  than  that  which  would  allow  them  to 
be  properly  refracted  to  a  focus,  that  indistinct  vision  would  necessarily  result. 
By  the  contraction  of  the  pupil,  however,  the  extreme  or  most  divergent  rays 
are  cut  off,  and  the  pencil  is  reduced  within  the  proper  angle.  The  principle 
is  precisely  the  same  as  that  on  which  the  optician  applies  a  stop  behind  his 
lenses,  which  reduces  their  aperture  in  proportion  to  the  shortness  of  their 
focal  distance.  2.  Contraction  of  the  pupil  is  also  noticed,  when  the  eyeball 
is  performing  that  rotation  upwards  and  inwards  which  has  been  already 

16* 


186  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

spoken  of  as  occasioned  by  the  contraction  of  the  Inferior  Oblique  muscle ; 
and  which,  when  performed  along  with  violent  respiratory  actions,  or  during 
sleep,  must  be  regarded  as  involuntary.  This  rotation  also  takes  place,  to  a 
slight  degree,  when  the  eyelid  is  depressed,  as  in  ordinary  winking;  and  it 
is  obvious  that,  in  this  manner,  the  surface  of  the  eye  is  more  effectually  swept 
free  from  impurities  which  m&y  have  gathered  upon  it,  than  it  would  be  by 
the  downward  motion  ofthe  lid  alone.  But  the  pupil  is  not  contracted  when 
the  eyeball  is  voluntarily  rotated  upwards  and  inwards, — an  action  which 
\rnay  be  effected  by  the  Superior  Rectus,  some  fibres  of  which  are  sufficiently 
rar  removed  from  the  central  axis  of  the  globe  to  give  it  an  internal  direction. 
There  is  good  reason  to  believe,  therefore,  that  the  actions  of  the  inferior 
branch  of  the  Third  nerve  are  in  great  part  automatic,  whilst  those  of  the 
superior  branch  are  purely  voluntary.  Upon  this  reasoning,  Valentin  has 
founded  a  very  ingenious  theory  of  the  consensual  movements  of  the  eyeball, 
which  will  now  be  explained ;  and  this  wrill  be  conveniently  followed  by  an 
inquiry  into  the  nature  of  this  class  of  movements,  as  distinguished  from  the 
Reflex  on  the  one  hand,  and  the  Volitional  on  the  other. 
/ 

XVI. — Consensual  Movements  of  the  Eye. 

•^  * 

250.  From  the  foregoing  observations  it  appears,  that  the  Rectus  Superior, 
Obliquus  Superior,  and  Rectus  Externus,  which  are  supplied  from  the  superior 
branch  of  the  Third  pair,  and  by  the  Fourth  and  Sixth  pairs,  are  all  to  be 
regarded  as  purely  voluntary  muscles  ;  and  Valentin  considers  them  analogous 
to  the  Extensors  of  the  limbs,  spine,  &c.,  which  are  for  the  most  part  distin- 
guished by  the  same  character.     By  the  actions  of  these  three  muscles,  singly 
or  combined,  the  eyeball  may  be  moved  in  nearly  all  directions.     On  the 
other  hand,  the  Inferior  and  Internal  Recti,  and  the  Inferior  Oblique,  supplied 
by  the  inferior  branch  of  the  Third  pair,  are  more  or  less  automatic  in  their 
action  ;  and  these  are  compared,  by  Valentin,  to  the  flexors.     By  the  single 
or  combined  actions  of  these  muscles  also,  the  eyeball  may  be  moved  towards 
almost  any  point,  except  in  an  upward  and  outward  direction ;  and  any  one 
who  tries  the  experiment  will  find  that  this  is,  of  all  the  movements  of  the 
eye,  the  one  that  is  attended  with  the  most  constrained  action  of  the  muscles. 

251.  On  studying  the  conjoint  movements  of  the  eyeball,  we  are  led  to 
observe^ the  very  curious  fact,  that  they  are  not  so  much  symmetrical  as 
harmonious ;  that  is  to  say,  the  corresponding  muscles  on  the  two  sides  are 
rarely  in  action  at  once ;  whilst  such  a  harmony  or  consent  exists  between 
the  actions  of  the  muscles  of  the  two  orbits,  that  they  work  to  one   common 
purpose,  namely,  the  direction  of  both  eyes  toward  the  required  object.     In 
order  to  study  them  properly,  it  is  necessary  to  reduce  them  to  seme  kind  of 
classification.     1.  If  one  eye  be  rotated  imvards,  and  the  other  outwards,  the 
Internal  Rectus  of  one  eye,  and  the  External  Rectus  of  the  other,  a^e  evidently 
put  in  action  together.     This  movement  is  harmonious  or  consensual,  but  not 
symmetrical.     2.  Both  eyeballs  are  elevated,  by  the  contraction  of  the  two 
Superior  Recti.     3.  Both  eyeballs  are  depressed;  this  is  effected  by  the  con- 
joint action  of  the  Inferior  Recti  muscles  ;  and  the  movement  is,  like  the  preced- 
ing, both  harmonic  and  symmetrical.     4.  Both  are  drawn  directly  inwards 
and  downwards,  as  when  $e  look  at  an  object  placed  on  or  near  the  nose ;  this 
movement  is  symmetrical,*  }>ut  not  harmonic ;  and  it  is  effected  by  the  action 
of  the  Internal  Rectus,  joined  either  with  the  Inferior  Rectus  or  the  Superior 
Oblique.     5.  When  one  eye  is  rolled  upwards  and  inwards,  and  the  other 
upwards  and  outwards,  the  Inferior  Oblique  is  probably  operating  on  one  side, 
whilst  the  Superior  Rectus  unites  its  action  with  that  of  the  External  on  the 
other.     And,  6,  when  one  eye  is  drawn  downwards  and  inwards,  and  the 


CONSENSUAL  MOVEMENTS  OF  THE  EYE.  187 

other  downwards  and  outwards,  the  Inferior  Rectus  Is  probably  operating, 
along  with  the  Internal  Rectus,  on  one  side,  whilst  the  Superior  Oblique  is  the 
chief  cause  of  the  latter  movement. — All  these  movements  may  be  voluntarily 
performed  by  Man ;  but  it  is  not  so  clear  that  the  muscles  by  which  they  are 
effected,  are  equally  influenced  by  volition  in  each  case  ;  and  there  are  some 
curious  diversities  in  our  power  of  operating  on  different  muscles,  which  throw 
some  light  on  the  matter.  Of  those  which  are  entirely  subjected  to  the  will, 
we  can  only  put  that  pair  in  action  together  which  will  operate  without  de- 
stroying the  symmetrical  position  of  the  two  eyes,  namely,  the  Superior  Recti. 
We  cannot  voluntarily  abduct  both  eyes,  nor  roll  them  downwards  and  out- 
wards by  the  conjoint  action  of  the  two  External  Recti  or  Superior  Obliques. 
Nor,  again,  can  we  bring  any  of  these  voluntary  muscles — the  Superior 
Obliques  and  Superior  Rectus,  for  example — to  act  against  each  other  in  the 
two  eyes,  so  as  to  destroy  their  symmetry.  Thus,  as  remarked  by  Valentin, 
in  almost  every  movement,  in  which  the  harmony  of  the  two  eyes  is  preserved, 
whilst  the  symmetry  is  destroyed  (as  in  those  of  the  1st,  5th,  and  Oth  of  the 
foregoing  classes),  one  or  more  muscles  of  voluntary  motion  are  acting  on  one 
eye,  and  one,  or  more  of  the  automatic  grouj5  are  chiefly  concerned  in  produc- 
ing the  rotation  of  the  faker.  This  idea  is  an  extremely  ingenious  one,  and 
will  be  found  to  be  supported  by  other  facts. 

252.  But  there  are  two  kinds  of  movement  of  the  Eyeballs  which  are  not 
at  all  voluntary.     In  the  first  of  these,  both  eyeballs  are  rotated  upwards  and 
imuards,  by  the  action  of  both  Inferior  Obliques.     In  the  other,  both  eyeballs 
are  directed  inwards,  by  the  action  of  both  Internal  Recti.     Now  in  both  these 
cases,  the  harmony  of  the  movements  is  destroyed  :  but  it  is  by  two  similar 
muscles,  both  acting  automatically,  and  subjected,  therefore,  to  the  same  stimu- 
lus.    In  the  first  of  these  cases,  the  stimulus  may  originate  in  some  part  very 
distant  from  the  eye  itself,  and  may  be  of  a  purely  reflex  kind ;  as  when  the 
eye  is  rotated  under  the  lid,  in  the  acts  of  .sneezing,  coughing,  winking,  &c. 
The  latter  we  shall  find  to  be  another  result  of  the  same  cause  as  that  which 
secures  the  usual  harmonic  movements  of  the  eyeball  (§  255). 

253.  It  may  be  stated  as  a  physiological  fact,  that  single  vision  with  two 
eyes  is  dependent  upon  the  formation  of  the  image  upon  parts  of  the  two 
retinae  which  are  accustomed  thus  to  act  with  each  other.     In  many  physio- 
logical works,  it  is  asserted,  that  single  vision  is  the  result  of  the  impressions 
being  made  on  corresponding  parts  of  the  two  retina,- — that  is  to  say,  on  parts 
equally  distant  from  the  axis,  on  one  side  or  the  other:  but  this  seems  to  be 
disproved  by  the  fact,  that  patients  who  have  been  long  affected  with  Con- 
vergent Strabismus,  and  who  see  equally  well  with  both  eyes  (as  many  do), 
are  not  troubled  with  double  vision.     On  the  other  hand,  when  a  person  whose 
eyes  look  straight  before  him,  is  the  subject  of  a  disorder  which  renders  their 
motions  in  any  degree  irregular,  he  is  at  once  affected  with  double  vision  ;  and 
the  same  has  been  noticed  to  be  a  common  immediate  result  of  the  successful 
operation  for  the  cure  of  strabismus,  where  vision  is  good  in  both  eyes.     Al- 
though the  images  were  previously  formed  on  parts  of  the  retinae  which  were 
very  far  from  corresponding  with  each  other,  yet  no  sooner  is  the  position  of 
the  eyes  rectified  (so  that  the  relation  between  the  situation  of  the  images  is 
the  same  as  it  would  have  been  in  a  sound  eye"),  than  the  patient  sees  double. 
Now  in  these  cases  the  difficulty  very  speedily  diminishes,  and  the  patient 
soon  learns  to  see  single.     It  can  scarcely  be  imagined,  then,  that  to  any  other 
cause  than  habit,  is  to  be  attributed  the  long-discussed  phenomenon  of  single 
vision  with  two  eyes.     The  mind  receives  the  two  images,  frequently  com- 
bining them  together  (as  Mr.  Wheatstone's  ingenious  experiments  with  the 
Stereoscope  have  most  satisfactorily  shown,  §  339)  to  produce  a  picture  in 
relief;  and  so  long  as  these  are  conveyed  to  it  in  the  accustomed  manner,  it  / 


188  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

reconciles  them  together,  even  if  the  parts  of  the  retinae  on  which  they  are 
formed  do  not  correspond ;  but  if  any  circumstance  break  this  chain,  and 
cause  the  imag'es  to  be  transmitted  to  the  sensorium  through  a  new  channel, 
the  mind  requires  some  little  time  to  adapt  itself  to  this  impression,  as  it  does 
by  habit  to  almost  every  other.* 

*  That  there  is  a  greater  tendency  to  consent  between  the  images,  when  they  are  formed 
upon  corresponding  parts  of  the  retinae,  the  Author  readily  admits;  and  he  thinks  that 
this  is  a  principle  of  some  importance,  in  explaining  the  re-adjustment  of  the  eyes,  after 
the  operation  for  Strabismus.  Every  one  who  has  seen  much  of  this  operation  is  aware, 
that  the  re-adjustment  of  the  eye  is  not  always  immediate,  but  that,  after  the  muscle  has 
been  freely  divided,  the  eye  often  remains  somewhat  inverted  for  a  few  days,  gradually 
acquiring  its  straight  position.  The  Author  has  known  one  case,  in  which,"  after  such  a 
degree  of  temporary  inversion  as  seemed  to  render  the  success  of  the  operation  very 
doubtful,  eversion  actually  took  place  for  a  short  time  to  a  considerable  extent;  after 
which  the  axes  became  parallel,  and  have  remained  so  ever  since. 

Another  argument,  derived  from  the  results  of  this  operation,  in  favour  of  the  con- 
sensual movement  being  chiefly  dependent  upon  the  place  of  the  impressions  on  the 
retina  is,  that  it  is  much  more  successful  in  those  cases  in  which  the  sight  of  the  most 
displaced  eye  is  good,  than  in  those  in  which  (as  not  unfrequently  happens  from  long 
disuse)  it  is  much  impaired.  In  cases  of  the  latter  class,  the  cure  is  seldom  complete. 
There  is  another  curious  fact,  which  may  be  adverted  to  in  reference  to  this  subject: 
Strabismus  not  unfrequently  arises  from  the  formation  of  an  opaque  spot  on  the  centre 
of  the  cornea,  which  prevents  the  formation  of  any  images  on  the  retina,  except  by  the 
oblique  rays;  and  nature  seems  to  endeavour  (so  to  speak)  to  repair  the  mischief,  by 
causing  the  eye  to  assume  the  position  most  favourable  for  the  reception  of  these. 

To  one  more  point  only,  connected  with  the  subject  of  Strabismus,  would  the  Author 
now  allude.  He  is  well  convinced,  from  repeated  observation,  that  those  Surgeons  are 
in  the  right,  who  have  maintained,  in  a  recent  controversy,  that,  in  a  large  proportion  of 
cases,  strabismus  is  caused  by  an  affection  of  both  sets  of  muscles  or  nerves,  and  not  of 
one  only;  and  that  it  then  requires,  for  its  perfect  cure,  the  division  of  the  corresponding 
muscle  on  both  sides.  Cases  will  be  frequently  met  with,  in  which  this  is  evident;  the 
two  eyes  being  employed  to  nearly  the  same  extent,  and  the  patient  giving  to  both  a 
slight  inward  direction,  when  desired  to  look  straight  forwards.  In  general?  however, 
one  eye  usually  looks  straight  forwards,  whilst  the  other  is  greatly  inverted;  and  the 
sight  of  the  inverted  eye  is  frequently  affected  to  a  considerable  degree  by  disuse ;  so 
that,  when  the  patient  voluntarily  rotates  it  into  its  proper  axis,  his  vision  with  it  is  far 
from  being  distinct.  Some  Surgeons  have  maintained,  that  the  inverted  eye  is  usually 
the  only  one  in  fault,  and  consider  that  the  division  of  the  tendon  of  its  Internal  Rectus 
is  sufficient  for  the  cure.  They  would  even  divide  its  other  tendons,  if  the  parallelism 
be  not  restored  rather  than  touch  the  other  eye.  The  Author  is  himself  satisfied,  how- 
ever, that  the  restriction  of  the  abnormal  state  to  a  single  eye,  is  the  exception,  and  not 
the  rule,  in  all  but  very  slight  cases  of  strabismus;  and  to  this  opinion  he  is  led  both  by 
the  consideration  of  the  mode  in  which  strabismus  first  takes  place,  and  by  the  results 
of  the  operations  which  have  come  under  his  notice.  If  the  eyes  of  an  infant  affected 
with  cerebral  disease  be  watched,  there  will  frequently  be  observed  in  them  very  irregu- 
lar movements;  the  axes  of  the  two  being  sometimes  extremely  convergent,  and  then 
very  divergent.  This  irregularity  is  rarely  or  never  seen  to  be  confined  to  one  eye. 
Now,  in  a  large  proportion  of  cases  of  Strabismus,  the  malady  is  a  consequence  of  some 
cerebral  affection  during  infancy  or  childhood,  which  we  can  scarcely  suppose  to  have 
affected  one  eye  only.  Again,  in  other  instances  we  find  the  Strabismus  to  have  resulted 
from  the  constant  direction  of  the  eyes  to  very  near  objects,  as  in  short-sighted  persons; 
and  here,  too,  the  cause  manifestly  affects  both.  Now  it  is  easy  to  understand,  why  one 
eye  of  the  patient  should  appear  to  be  in  its  natural  position,  whilst  the  other  is  greatly 
inverted.  The  cause  of  strabismus  usually  affects  the  two  eyes  somewhat  unequally, 
so  that  one  is  much  more  inverted  than  the  other.  We  will  call  the  least  inverted  eve 
A,  and  the  other  B.  In  the  ordinary  acts  of  vision,  the  patient  will  make  most  use  "of 
the  least  inverted  eye,  A,  because  he  can  most  readily  look  straight  forwards  or  outwards 
with  it;  but  to  bring  it  into  the  axis,  or  to  rotate  it  outwards,  necessitates  a  still  more 
decided  inversion  of  B.  This  remains  the  position  of  things, — the  patient  usually  look- 
ing straight  forwards  with  A,  which  is  the  eye  constantly  employed  for  the  purposes  of 
vision,— and  frequently  almost  burying  under  the  inner  canthus  the  other  eye,  B,  the 
vision  ip  which  is  of  very  little  use  to  him.  When,  therefore,  the  tendon  of  the  internal 
rectus  of  B  is  divided,  the  relative  position  of  the  two  is  not  entirely  rectified.  Some- 
times it  appears  to  be  so  for  a  time;  but  the  strabismus  then  begins  to  return,  and  it  can 


CONSENSUAL  MOVEMENTS  OF  THE  EYE.  189 

254.  If  this  be  admitted,  we  gain  an  important  step  in  the  explanation  of 
the  Consensual  movements  of  the  eye.     The  object  to  be  attained  is  evidently 
this — that  the  usual  axes  of  the  eye  should  always  be  directed  towards  the 
object  to  be  viewed;  and  this,  as  we  have  seen,  involves  the  necessity  (in  a 
great  majority  of  cases),  of  unsymmetrical  movements  being  performed  by 
the  two  eyeballs.      Now  it  is  fair  to  argue  from  the  facts  already  stated 
(respecting  the  distribution  of  the  Third  pair,  and  the  known  functions  of  its 
inferior  branch),  that,  in  directing  our  eyes  by  a  voluntary  effort  to  any  par- 
ticular object,  the  will  acts  chiefly  upon  one  eye,  and  that  the  other  follows  its 
direction  by  an  automatic  movement.     This  automatic  movement  appears  to 
be  governed  by  the  relative  place  of  the  images  upon  the  retinae.     It  is  well 
known  that,  in  children  born  blind,  the  movements  are  not  consensual ;  they 
are  frequently  very  far  from  being  so,  in  cases  of  congenital  cataract,  where  a 
considerable  amount  of  light  is  evidently  admitted,  but  where  no  distinct 
image  can  be  formed ;  and  in  such  cases,  the  movements  are  most  consensual 
where  the  object  is  bright  or  luminous,  and  a  more  vivid  impression  therefore 
made  upon  the  retina.     It  is  no  objection  to  this  theory  to  say,  that  persons 
who  have  become  blind  may  still  move  their  eyes  in  a  consensual  manner ; 
since  the  habit  of  the  association  of  particular  movements  having  been  once 
acquired,  the  known  laws  of  nervous  action  account  for  its  continuance  ;  and, 
as  a  matter  of  fact,  a  want  of  consent  may  be  often  noticed  where  the  blind- 
ness is  total.     The  peculiar  vacant  appearance,  which  may  be  noticed  in  the 
countenance  of  persons  completely  deprived  of  sight  by  amaurotic  or  other 
affections  which  do*not  alter  the  external  aspect  of  the  eyes,  seems  to  result 
from  this, — that  their  axes  are  parallel,  as  if  the  individual  were  looking  into 
distant  space,  instead  of  presenting  that  slight  convergence,  which   must 
always  exist  between  them  when  the  eyes  are  fixed  upon  a  definite  object. 
This  convergence,  which  is  of  course  regulated  by  the  Internal  Recti,  varies 
in  degree  according  to  the  distance  of  the  object ;  and  it  is  astonishing  how 
minute  an  alteration  in  the  axes  of  the  eyes  is  perceptible  to  a  person  ob- 
serving them.     For  instance,  A  sees  the  eyes  of  B  directed  towards  his  face, 
but  he  perceives  that  B  is  not  looking  at  him ;  he  knows  this  by  a  sort  of 
intuitive  interpretation  of  the  fact,  that  his  face  is  not  the  point  of  convergence 
of  B's  eyes.     But  if  B,  who  might  have  been  previously  looking  at  something 
nearer  or  more  remote  than  A's  face,  fix  his  gaze  upon  the  latter,  so  that  the 
degree  of  convergence  of  the  axes  is'altered,  without  the  general  direction  of 
the  eyes  being  in  the  least  affected,  the  change  is  at  once  perceived  by  the 
person  so  regarded ;  and  the  eyes  of  the  two  then  meet. 

255.  The  foregoing  considerations  may  be  summed  up  in  this  simple  state- 
ment ; — that,  when  the  axis  of  one  eye  is  voluntarily  directed  towards  an 

only  be  checked  by  division  of  the  tendon  of  the  other  eye,  A;  after  which,  the  cure  is 
generally  complete  and  permanent.  That  it  has  not  been  so  in  many  of  the  cases  on 
which  operations  have  been  performed,  the  author  attributes,  without  the  slightest  doubt 
in  his  own  mind,  to  the  neglect  of  the  second  operation.  As  just  now  stated,  the  sight 
of  the  most  inverted  eye  is  frequently  very  imperfect;  indeed  it  is  sometimes  impaired 
to  such  an  extent,  that  the  patients  speak  of  it  as  entirely  useless.  That  this  impair- 
ment results  in  part  from  disuse  merely,  seems  very  evident,  from  the  great  improve- 
ment which  often  succeeds  the  rectification  of  the  axes.  The  Author  cannot  help 
thinking  it  probable,  however,  that  the  same  cause  which  produced  the  distortion  of  the 
eye  may,  in  some  instances  at  least,  have  affected  the  Optic  nerve,  as  well  as  the  Motor 
nerves  of  the  orbit;  and  this  idea  is  borne  out  by  the  fact  of  the  restoration  of  sight,  in 
certain  cases  of  Amaurosis,  by  division  of  one  or  more  tendons,  where  no  Strabismus 
previously  existed  (See  Adams  on  Muscular  Amaurosis).  It  is  interesting  to  remark 
that,  in  these  cases,  Strabismus  was  usually  the  first  effect  of  the  operation;  but  that  the 
eye  generally  recovered  its  ordinary  position  within  a  short  time,  especially  when  the 
sight  was  improving. 


190  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

object,  there  is  an  instinctive  tendency,  on  the  part  of  the  Nervous  System 
and  the  Muscles  by  which  it  acts,  to  effect  a  consensual  movement  of  the  other ; 
so  that  its  accustomed  axis  also  shall  be  directed  towards  the  object.  This 
principle  fully  accounts  for  the  only  non-consensual  movement  which  can  be 
performed  in  any  way  voluntarily, — that  of  both  eyes  inwards,  or  downwards 
and  inwards,  which  is  effected  by  the  conjoint  action  of  the  Internal  Recti. 
Some  persons  possess  the  power  of  performing  this  to  a  much  greater  degree 
than  others ;  but  in  all  instances,  the  eyes  must  be  fixed  on  an  object;  and 
thus  the  movement  is  as  referable  as  any  other  to  this  principle. — It  is,  per- 
haps, desirable  to  qualify  the  classification  of  the  nerves  and  muscles  of  the 
Orbit  proposed  by  Valentin,  by  admitting  that  all  have,  in  some  degree,  a 
voluntary,  and  in  some  degree  an  automatic  action ;  but  that  voluntary  power 
predominates  in  regard  to  one  group,  whilst  the  other  is  more  commonly  acted 
on  by  an  automatic  impulse.  It  is  clear  that  the  will  must  have  some  power 
over  the  Inferior  Rectus,  for  example ;  since  both  eyes  can  be  voluntarily 
directed  downwards.  But  the  power  of  the  Will  over  this  muscle  is  much 
less  than  it  is  over  the  Superior  Rectus ;  as  is  shown  by  the  fact  that,  if  we 
direct  the  eyes  downwards,  and  then  close  the  lids,  no  effort  of  volition  can 
prevent  the  eye  from  being  rolled  upwards  by  the  Inferior  Oblique  ;  and  that, 
whilst  the  lids  remain  closed,  the  pupils  cannot  be  directed  downwards  in  any 
considerable  degree.  It  is  evident,  then,  that  the  impression  of  an  object  upon 
the  retina  is  almost  as  necessary  to  occasion  the  combined  action  of  the  Infe- 
rior as  it  is  to  produce  that  of  the  Internal  Recti.  The  case  is  very  different 
in  regard  to  the  Superior  Recti,  which  can  be  made  to  act  together,  in  any 
degree,  without  the  necessity  of  a  visual  impression. 

256.  It  has  been  pointed  out  by  Mliller,  as  an  obvious  reason  for  the  sepa- 
ration of  the  6th  from  the  3d  pair  of  nerves,  that  there  is  usually  a  great 
tendency  to  consentient  action  between  the  nerves  of  the  two  sides,  which 
pass  off  from  the  same  point  of  the  cerebro-spinal  axis — as  we  see  in  the  case 
of  Reflex  movements  of  both  sides  (such  as  that  of  the  pupil),  which  are 
excited  by  a  stimulus  applied  to  one  only ;  and  that  this  holds  good  also  in 
those  movements  of  the  eyes  which  are  effected  by  the  third  pair  exclusively 
— such  as  the  elevation  or  depression  of  both  pupils ;  but  in  the  horizontal 
movements  of  the  eyeballs,  two  different  actions  are  being  performed  on  the 
two  sides  respectively;  and  it  may  be  conceived  that  this  may  be  more  readily 
accomplished  by  two  different  nerves  than  by  branches  of  the  same.    We  may 
admit  some  truth  in  this  idea,  without  attributing  much  weight  to  it.     It  has 
been  already  stated  as  a  result  of  Embryological  research,  that  all  the  Nerves 
of  the  Orbit  do  in  reality  form  part  of  the  Spinal  nerve,  to  which  the  Fifth 
pair  alone  has  been  commonly  regarded  as  equivalent ;  and  it  is  well  known 
that  we  can  perform  many  different  actions  on  the  two  sides,  through  the 
medium  of  similar  nerves  at  the  same  time.     It  is  remarkable,  however,  that 
there  are  some  dissimilar  movements  which  it  is  impossible  to  execute  with 
any  degree  of  rapidity,  except  by  long  practice :  thus,  if  we  move  the  right  hand 
as  if  winding  on  a  reel,  and  afterwards  make  the  left  hand  revolve  in  a  con- 
trary direction,  no  difficulty  is  experienced;  but  if  we  attempt  to  move  the  two 
at  the  same  time,  in  contrary  directions,  we  shall  find  it  almost  impracticable. 

257.  There  can  be  no  doubt  that,  in  these  and  many  other  voluntary  move- 
ments, we  are  guided  by  the  sensations  communicated  through  the  afferent 
nerves,  which  indicate  to  the  mind  the  state  of  the  muscle.     Many  interesting 
cases  are  on  record,  which  show  the  necessity  of  this  muscular  sense,  for 
determining  voluntary  contraction  of  the  muscle.    Thus  Sir  C.  Bell  (who  pro- 
minently directed  attention  to  this  class  of  facts,  under  the  designation  of  the 
Nervous  Circle,)  mentions  an  instance  of  a  woman  who  was  deprived  of  it  in 
her  arms,  without  losing  the  motor  power,  and  who  stated  that  she  was 


GENERAL  FUNCTIONS  OF  THE  ENCEPHALON.  191 

obliged  to  keep  her  eyes  constantly  fixed  on  any  thing  (even  her  child)  which 
she  held  in  her  hands,  as  she  could  not  continue  the  muscular  effort  when  no 
longer  informed,  by  one  sense  or  the  other,  that  it  was  necessary.  Now,  the 
only  real  difference  between  the  case  of  the  ordinary  muscles  and  that  of  the 
muscles  of  the  eyeball,  is  (as  Dr.  Alison*  has  justly  remarked)  that  the 
guiding  sensations  are  those  received  through  the  Retina  in  the  latter  case, 
whilst  in  the  former  they  are  those  of  the  muscles  themselves.  It  may  be 
asked  in  what  such  consensual  movements,  as  those  of  the  Eye,  differ  from 
those  of  a  reflex  character?  The  answer  is,  simply,  that  the  former  cannot  be 
effected  without  consciousness,  and  some  mental  condition  supervening  upon 
it;  whilst,  in  the  latter,  sensation  has  been  shown  not  to  be  a  necessary  link. 
The  former  may  be  as  much  involuntary  as  the  latter,  as  is  shown  in  the 
effects  of  tickling,  which  could  not  be  manifested  in  an  unconscious  individual. 
Here  a  condition,  very  much  resembling  an  emotion,  is  produced;  and  from 
this,  as  from  other  emotions,  various  combined  movements  may  result,  with 
which  Volition  has  nothing  to  do.  The  same  may  probably  be  said  of  the 
Instinctive  actions  of  animals,  which,  as  will  presently  appear,  are  probably 
to  be  referred  to  the  same  category  with  the  purely  Emotional  acts  of  Man :  in 
both,  Sensation,  and  that  usually  of  a  special  kirfd,  is  a  necessary  link.  Further 
it  would  appear  that  actions,  which  were  originally  of  a  completely  voluntary 
character,  may  come  by  habit  to  be  performed  within  the  shorter  channel:  thus, 
a  musician  will  play  a  difficult  piece,  whilst  keeping  up  a  conversation  on 
an  entirely  different  subject;  and  here  the  muscular  movements  are  guided,  not 
only  by  the  sensations  produced  by  their  own  contraction,  but  also  by  the  anti- 
cipation of  the  auditory  sensations  which  will  result  from  their  operation. 
The  same  may  be  said  of  the  action  of  the  muscles  of  Voice  (§  412). 

;••'"    XVII.    General  Functions  of  the  Encephalon. 

258.  The  portion  of  the  Nervous  Centres  contained  within  the  cranium,  and 
commonly  designated  collectively  as  the-  Encephalon,  may  be  regarded  as  con- 
sisting of  four  principal  divisions:  1,  the  Cerebral  Hemispheres,  which,  in  the 
Mammalia,  and  especially  in  Man,  constitute  by  far  the  largest  portion  of  the 
whole ;  2,  the  Cerebellum,  the  complete  separation  of  which  from  the  Cerebrum, 
and  its  distinct  connections  with  the  Medulla  Oblongata,  mark  it  out  as  an  organ 
of  peculiar •  character ;  3,  the  Tuber cula  Quadrigemina  and  other  Ganglionic 
masses  at  the^Mfe  of  the  brain,  connected  with  the  nerves  of  special  sensation, 
and  analogous  to  the  Olfactive,  Optic  and  Auditory  ganglia  of  the  lower  ani- 
mals ;  and  4,  the  Medulla  Oblongata,  or  cranial  prolongation  of  the  Spinal 
Cord,  which  is  connected,  at  its  upper  end,  with  the  Ganglia  of  specral  sensa- 
tion, with  the  Thalami  optici,  which  may  probably  be  regarded  asfne  corre- 
sponding recipients  of  ordinary  sensory  impressions,  and  with  the  Corpa 
Striata,  through  which  the  motor  impulses  are  transmitted  to  it  from  the  Hemi- 
spheres.    It  has  been  already  shown  that  this  last  organ  is  peculiarly  connected 
with  the  functions  of  Respiration  and  Deglutition ;  and  we  shall  next  inquire 
what  special  function  can  be  attributed  to  the  ganglionic  enlargements  at  its 
upper  end. 

XVIIfc   Functions  of  the  Tubercula  Quadrigemina,  fyc.     Emotional  and 

Instinctive  Actions. 

259.  The  degree  in  which  animals  high  in  the  scale  of  organization  can 
perform  the  functions  of  life,  without  any  other  centre  of  action  than  the  Gang- 

*  Anatomical  and  Physiological  Inferences  from  the  Study  of  the  Nerves  of  the  Orbit, 
in  Trans,  of  Royal  Society  of  Edin.,  vol.  xv. 


192  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

lia  of  Special  sense,  the  Medulla  Oblongata,  and  the  Cerebellum,  appears  extra- 
ordinary to  those  who  are  accustomed  to  regard  the  Cerebral  Hemispheres  as 
the  centre  of  all  energy.  From  the  experiments  of  Flourens,  Hertwig,  Ma- 
gendie,  and  others,  it  appears  that  not  only  Reptiles,  but  Birds  and  Mammalia, 
may  survive  for  many  weeks  or  months  (if  their  physical  wants  be  duly  sup- 
plied) after  the  removal  of  the  whole  Cerebrum.  It  is  difficult  to  substantiate 
the  existence  in  them  of  actual  sensation ;  but  their  movements  appear  to  be 
of  a  higher  kind  than  those  resulting  from  mere  Reflex  action.  One  of  the 
most  remarkable  phenomena  in  such  a  being,  is  the  power  of  maintaining  its 
equilibrium,  which  could  scarcely  exist  without  consciousness.  If  it  be  laid 
upon  the  back,  it  rises  again ;  if  pushed,  it  walks.  If  a  Bird  thus  mutilated  be 
thrown  into  the  air,  it  flies ;  if  a  Frog  be  touched,  it  leaps.  Such  a  being, 
when  violently  aroused,  has  all  the  manner  of  an  animal  waking  -from  sleep ; 
and  it  manifests  just  about  the  same  degree  of  consciousness  with  a  sleeping 
Man,  whose  torpor  is  not  too  profound  to  prevent  his  suffering  from  an  uneasy 
position,  and  who  moves  himself  to  amend  it.  The  negative  results  of  experi- 
ments of  this  kind  are  much  more  satisfactory  than  the  positive  ;  that  is  to 
say,  if  we  are  able  to  substantiate  the  performance  of  a  particular  function, 
after  the  removal  of  a  certain  organ,  we  may  be  sure  that  the  function  is  not 
dependent  on  that  organ.  But  the  converse  does  not  hold  good ;  for  it  fre- 
quently happens  that,  when  such  violent  operations  are  practised  on  the  ner- 
vous centres,  they  occasion  an  amount  of  general  disturbance,  which  suspends 
or  modifies  functions  that  have  no  immediate  connection  with  the  organ  in 
question  ;  so  that  we  cannot  safely  attribute  the  alteration  in  them  to  the  loss 
of  it.  For  example,  Hertwig  found  that,  upon  removing  the  upper  part  of  the 
hemispheres  in  a  pigeon,  the  powers  of  sight  and  hearing  appeared  to  be 
destroyed,  and  the  animal  sat  in  one  spot,  as  if  asleep  ;  but,  being  fed  during 
a  fortnight,  the  sensibility  returned,  and  the  bird  lived  for  three  months. 

260.  Among  the  ganglia  of  special  sensation,  the  functions  of  the  Optic 
Lobes,  or  Corpora  Quadrigemina,  have  been  chiefly  examined.  The  researches 
of  Flourens  and  Hertwig  have  shown,  that  their  connection  with  the  visual 
function,  which  might  be  inferred  from  their  anatomical  relations,  is  substan- 
tiated by  experiment.     The  partial  loss  of  the  ganglion  on  one  side  produces 
partial  loss  of  power  and  temporary  blindness  on  the  opposite  side  of  the  body, 
without  necessarily  destroying  the  mobility  of  the  pupil ;  but  the  removal  of  a 
larger  portion,  or  complete  extirpation  of  it,  occasions  permanent  blindness  and 
immobility  of  the  pupil,  with  temporary  muscular  weakness,  on  the  opposite 
sides.     This  temporary  disorder  of  the  muscular  system  sometimes  manifests 
itself  in  a  tendency  to  move  on  the  axis,  as  if  the  animal  were  giddy.     No 
disturbance  of  consciousness  appears  to  be  produced  ;  and  Hertwig  states  that 
he  never  witnessed  the  convulsions  which  Flourens  mentions  as  a  consequence 
of  the  operation,  and  which  were  probably  occasioned  by  his  incision  having 
been  carried  too  deeply. — We  shall  now  inquire  what  inferences  may  be  drawn 
from  comparative  observations,  in  regard  to  the  more  general  function  of  these 
organs. 

261.  That  a  large  number  of  the  actions  of  the  lower  animals  are  immedi- 
ately prompted  by  Sensations,  without  the  intervention  of  reasoning  processes, 
is  universally  admitted  ;  and'  to  these  actions  the  term  Instinctive  is  ordinarily 
given.     They  appear  to  result  from  the  direct  operation  of  a  mental  condition, 
analogous  to  that  which  exists  in  Man,  when  the  emotions,  passions,  or  pro- 
pensities are  so  strongly  excited,  as  to  act  at  once  on  the  body  without  the 
intervention  of  the  Will.     In  the  purely  reflex  movements,  it  has  been  shown 
that  sensation  is  not  a  necessary  link.     On  the  other  hand,  in  Voluntary  acts, 
neither  sensations  nor  emotions  directly  affect  the  body,  but  only  serve  to  stimu- 
late the  reasoning  j^rocesses,  and  to  supply  motives  to  the  judgment ;  and  the 


^  EMOTIONAL  AND  INSTINCTIVE  ACTIONS.  193 

operations  of  this  terminate  in  the  formation  of  a  Volition,  the  commands  of 
which  are  conveyed  to  the  muscle,  through  a  channel  structurally  distinct,  as 
cases  of  paralysis  fully  prove,  from  that  which  is  the  medium  of  Emotional 
actions. — It  cannot  be  doubted  by  any  person,  who  has  attentively  studied  the 
characters  of  the  lower  animals,  that  many  of  them  possess  psychical  endow- 
ments, corresponding  with  those  which  we  term  the  intellectual  powers  and 
moral  feelings  in  Man ;  but  in  proportion  as  these  are  undeveloped,  in  that 
proportion  is  the  animal  under  the  dominion  of  those  Instinctive  impulses, 
which,  so  far  as  its  own  consciousness  is  concerned,  may  be  designated  as 
blind  and  aimless,  but  which  are  ordained  by  the  Creator  for  its  protection 
front  danger,  and  for  the  supply  of  its  natural  wants.  The  same  may  be  said 
of  the  Human  infant,  or  of  the  Idiot,  in  whom  the  reasoning  powers  are  unde- 
veloped. Instinctive  actions  may  in  general  be  distinguished  from  those  which 
are  the  result  of  voluntary  power  guided  by  reason,  chiefly  by  the  two  follow- 
ing characters : — Although,  in  many  cases,  experience  is  required  to  give  the 
Will  command  over  the  muscles  concerned  in  its  operations,  no  experience  or 
education  is  required,  in  order  that  the  different  actions,  which  result  from  an 
Instinctive  impulse,  may  follow  one  another  with  unerring  precision.  2.  These 
actions  are  always  performed  4)y  the  same  species  of  animal,  nearly,  if  not 
exactly,  in  the  same  manner;  presenting  no  such  variation  in  the  means 
adapted  to  the  object  in  view,  and  admitting  of  no  such  improvement  in  the 
progress  of  life,  or  in  the  succession  of  ages,  as  we  observe  in  the  habits  of 
individual  men,  or  in  the  manners  and  customs  of  nations,  that  are  adapted  to 
the  attainment  of  any  particular  ends,  by  those  voluntary  efforts  which  are 
guided  by  reason.  The  fact,  too,  that  these  instinctive  actions  are  often  seen 
to  be  performed  under  circumstances  rendering  them  nugatory,  as  reason 
informs  us,  for  the  ends  which  they  are  to  accomplish  (as  when  the  Flesh-fly 
deposits  her  egg  on  the  Carrion-plant  instead  of  a  piece  of  meat,  or  when  the 
Hen  sits  on  a  pebble  instead  of  her  egg), — is  an  additional  proof,  that  the 
Instinctive  actions  of  animals  are  prompted,  like  the  consensual  movements  we 
have  been  recently  inquiring  into,  by  an  impulse  which  immediately  results 
from  a  particular  sensation  being  felt,  and  not  by  anticipation  of  the  effect  which 
the  action  will  produce. 

262.  The  correspondence  between  the  purely  Emotional  actions  in  Man, 
and  those  actions  in  the  lower  animals  to  which  we  give  the  name  of  Instinct- 
ive, may  be  made  evident  by  a  very  simple  illustration.  The  Cuttlefish  is 
well  known  to  discharge  its  ink,  when  pursued,  and  to  tinge  fhe  water  around 
with  a  colour  so  deep,  as  to  enable  it  to  escape  under  the  cloud  thus  formed. 
Now  it  is  not  to  be  supposed  that  the  Cuttle-fish  has  any  notion  of  the  purpose 
which  this  act  will  serve ;  since  its  constancy  and  uniformity,  and  the  provi- 
sion for  its  performance  immediately  on  the  emersion  of  the  young  animal  from 
the  egg,  forbid  our  regarding  it  as  the  result  of  any  act  of  reasoning.  Further, 
the  ink  is  an  excretion  which  corresponds  to  the  urine  (having  been  found  to 
contain  urea) ;  and  every  one  knows  how  strong  an  impulse  to  discharge  this 
is  frequently  caused  by  mental  emotion.  The  same  may  be  said  of  the 
strongly  odorous  secretions  possessed  by  many  Mammalia,  which  are  dis- 
charged under  similar  circumstances,  and  evidently  with  the  same  object; 
though  of  that  object,  the  animal  itself  be  not  conscious.  The  emotion  of  fear 
involuntarily  opens  the  sphincters,  and  causes  the  contraction  of  the  receptacle, 
in  one  case  as  in  the  other:  and  the  great  difference  between  the  condition  of 
Man,  and  that  of  the  lower  animals,  in  this  respect,  is  simply  that, — in  the 
former,  the  purely  Emotional  or  Instinctive  actions  are  few  in  comparison  with 
the  whole,  whilst  in  the  latter  they  constitute  by  far  the  largest  part ;  and  also 
that  Man  has  much  greater  power  of  controlling  these  actions  by  an  effort  of 
his  Will,  than  that  which  the  lower  animals  possess.  Every  one  knows,  how- 
17  * 


194  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

ever,  that  Man  is  not  unfrequently  compelled  by  the  strength  of  his  Emotions 
to  act  against  his  Will.  Thus,  we  see  or,  hear  something  ludicrous,  which 
involuntarily  produces  laughter,  although  we  may  have  the  strongest  motives 
for  desiring  to  restrain  it.  On  the  other  hand,  a  loathsome  object,  which  excites 
the  feeling  of  disgust,  produces  nausea  and  even  vomiting.  Or,  again,  a  violent 
fright  not  unfrequently  occasions  convulsive  movements;  and  these  may  be 
brought  on,  in  some  excitable  states  of  the  nervous  system,  by  Emotions  of  a  less 
powerful  kind  (§§  298,  299).* 

283.  Dr.  M.  Hall  is  of  opinion  that  the  Spinal  system  of  nerves  constitutes 
the  channel  of  Emotional  actions.  There  is  no  other  evidence  for  this,  how- 
ever, than  the  occasional  manifestation,  in  cases  of  paralysis,  of  reflex  and 
emotional  actions,  when  voluntary  control  is  lost.  Such  cases  only  prove, 
however,  that  emotional  actions  are  not  volitional ;  they  are  far  from  proving 
them  to  be  Spinal.  If  the  essential  correspondence  between  the  purely  Emo- 
tional acts  of  Man,  and  the  Instinctive  acts  of  the  lower  animals  be  admitted, 
we  may  reasonably  localize  their  centre  more  satisfactorily,  in  that  chain  of 
ganglionic  masses,  which  only  occupies  the  centre  of  the  base  of  the  brain  in 
Man,  but  which,  in  the  lower  Vertebrata,  possesses  an  aggregate  dimension 
far  exceeding  that  of  the  Cerebral  hemispheres-.  We  are  led  to  such  a  locali- 
zation by  a  very  simple  and  satisfactory  train  of  reasoning.  The  actions  in 
question  are  not  simply  reflex  ;  since  sensation,  and  something  of  the  nature 
of  emotion,  both  involving  consciousness,  are  elements  in  their  performance  ; 
and,  moreover,  these  sensations  are  rather  of  the  special  than  of  the  common 
character,  involving,  therefore,  the  olfactory,  optic,  and  auditory  ganglia.  No 
intelligent  person  can  doubt,  that,  as  we  descend  the  scale  of  being,  instinct 
is  gradually  superseding  reason ;  and  that  in  the  lowest  Vertebrata,  the  mani- 
festations of  the  latter  are  extremely  feeble,  nearly  all  the  actions  of  life  being 
guided  by  the  former.  Now  on  looking  at  the  Encephalon,  we  perceive  a 
difference  in  the  relative  proportions  of  its  principal  divisions,  so  closely  cor- 
responding with  these,  that  it  is  difficult  to  imagine  them  unconnected.  In 
proportion  as  we  descend  the  scale,  we  find  the  Cerebral  Hemispheres  dimin- 
ishing in  relative  size,  whilst  the  Ganglia  at  the  origins  of  the  nerves  of  special 
sensation  increase  to  a  remarkable  degree ;  and  we  cannot,  therefore,  but  con- 

*  It  is  a  very  interesting  question,  how  far  actions  at  first  performed  voluntarily  by 
Man,  may  by  habit  cease  to  require  an  effort  of  the  Will ;  being  prompted,  like  the  In- 
stinctive class  of  movements,  by  the  direct  impulse  of  sensations.  Thus  we  all  know 
that,  in  walking  along  an  accustomed  road,  we  frequently  occupy  our  minds  with  some 
continuous  train  of  thought,  and  yet  our  limbs  continue  to  move  under  us  with  regular- 
ity, until  we  are  surprised  by  finding  ourselves  at  the  place  of  our  destination,  or  perhaps 
at  some  other  which  we  had  not  intended  to  visit,  but  to  which  habit  has  conducted  us. 
Or  we  may  read  aloud  for  a  long  time,  without  having  in  the  least  degree  comprehended 
the  meaning  of  the  words  we  have  uttered;  our  attention  having  been  closely  engaged 
by  some  engrossing  thoughts  or  feelings  within.  Or  a  Musician  may  play  a  well-known 
piece  of  music,  whilst  carrying  on  an  animated  conversation  ;— the  Author  has  known  a 
skilful  performer  who  could  play  at  sight  whilst  thus  occupied.  Now  in  such  a  case  it 
would  be  said  by  some  Metaphysicians  (acknowledging,  as  most  do,  that  the  mind  can- 
not will  two  different  things  at  the  same  time)  that  the  Volition  is  in  a  sort  of  vibratory 
condition  between  the  two  sets  of  actions,  now  prompting  one,  and  now  the  other.  But 
it  would  seem  much  more  conformable  to  the  analogy  afforded  by  other  psychical  phe- 
nomena, to  refer  the  habitual  series  of  actions  to  the  same  division  of  the  Nervous  System 
with  the  Instinctive;  and  perhaps  the  term  Automatic  may  be  fairly  applied  to  the  whole 
of  this  group.  It  is  well  known  that  in  cases  of  severe  injury  of  the  brain,  in  which  In- 
telligence and  Will  seem  completely  in  abeyance,  habitual  actions  may  be  often  excited. 
Thus,  Dr.  Perceval,  in  his  Essay  on  Habit,  mentions  the  case  of  a*nuff-taking  countess, 
in  whom,  when  seized  with  apoplexy,  irritation  of  the  nose  with  a  feather  produced  con- 
traction of  the  forefinger  and  thumb  of  the  right  hand  ;  and  Mr.  Travers  has  recorded  a 
similar  fact  m  the  case  of  a  boy,  who,  when  apparently  insensible  from  depressed  frac- 
ture of  the  skull  assisted  in  removing  his  clothes,  preparatorily  to  the  required  operation. 


EMOTIONAL  AND  INSTINCTIVE  ACTIONS.  195 

sicfcr  it  probable  that  these  ganglia  and  tracts  of  gray  matter,  whose  size  is  in 
Man  so  trifling,  in  comparison  to  the  bulk  of  his  Cerebral  Hemispheres,  are 
subservient  to  those  Instinctive  actions  which  are  prompted  by  sensations,  but 
in  which  volition  does  not  partake. 

204.  It  may  be  said  that,  in  attributing  to  this  division  of  the  nervous  centres 
a  function  different  from  that  of  the  Spinal  Cord,  on  the  one  hand,  and  of  the 
Brain  on  the  other,  we  are  unnecessarily  multiplying  the  systems  of  nervous 
fibres  which  must  then  be  supposed  to  exist  in  every  trunk  ; — one,  namely, 
for  reflex  actions, — another  for  the  instinctive  and  emotional, — and  a  third  for 
the  volitional.  But  the  tendency  of  Neurological  research  has  certainly  been 
to  show,  that  different  functions  are  performed  by  the  same  trunk,  in  virtu^  of 
its  containing  fibres,  which  are  connected  with  different  divisions  of  the  ner- 
vous centres ;  and  knowing,  as  we  do,  that  these  three  distinct  sources  of 
action  have  a  real  existence,  it  cannot  be  regarded  as  improbable,  that  their 
channels  also  should  be  separate  (§  227  note).  Moreover,  it  has  been  seen 
(§  172)  that  there  is  a  distinct  group  of  fibres  in  the  Medulla  Oblongata,  which 
has  its  ganglionic  centre  in  the  Corpora  Gluadrigemina,  and  cannot  be  traced 
into  the  Cerebral  hemispheres  ;  it  is  reasonable,  therefore,  to  suppose  that  it 
is  functionally  as  well  as  structurally  distinct ;  and  no  function  can  be  attri- 
buted to-  them  with  such  probability  as  that  of  producing  those  instinctive 
and  emotional  movements  of  the  body  which  are  excited  and  directed  through 
the  sense  of  Sight.  On  turning  to  the  Invertebrata,  we  find  important  con- 
firmation of  these  views  in  the  fact,  that,  in  general,  the  principal  ganglionic 
masses,  occupying  the  place  of  the  Brain  of  higher  animals,  are  closely  con- 
nected with  the  organs  of  special  sensation  situated  in  the  head,  and  are 
therefore  analogous  to  the  Optic  and  other  ganglia  in  Vertebrata ; « whilst 
scarcely  any  traces  can  be  found  of  superadded  ganglionic  bodies,  at  all 
resembling  the  Cerebral  hemispheres.  The  almost  exclusively  Instinctive 
character  of  the  actions  of  such  animals  harmonizes  well  with  the  opinion 
that  these  ganglia  are  the  chief  sources  of  them. 

265.  The  Emotions  are  concerned  in  Man,  however,  in  many  actions  which 
are  in  themselves  strictly  voluntary.  Unless  they  be  strongly  excited,  so  as 
to  get  the  better  of  the  will,  they  do  not  operate  directly  through  the  nervous 
trunks,  but  are  subservient  to  the  intellectual  operations,  to  which  they  supply 
materials  or  motives.  Thus,  of  two  individuals,  with  differently  constituted 
minds,  one  shall  judge  of  every  thing  through  the  medium  of  a  gloomy  morose 
temper,  which,  like  a  darkened  glass,  represents  to  his  judgment  the  whole 
world  in  league  to  injure  him  ;  and  all  his  determinations,  being  based  upon 
this  erroneous  view,  exhibit  the  indications  of  it  in  his  actions  ;  which  are 
themselves,  nevertheless,  of  an  entirely  voluntary  character.  On  the  other 
hand,  a  person  of  a  cheerful,  benevolent  disposition,  looks  at  the  world  around 
as  through  a  Claude  Lorraine  glass,  seeing  every  thing  in  its  brightest  and 
sunniest  aspect ;  and,  with  intellectual  faculties  precisely  similar  to  those  of 
the  former  individual,  he  will  come  to  opposite  conclusions ;  because  the 
materials  which  form  the  -basis  of  his  judgment  are  submitted  to  it  in  a  very 
different  form.  Various  forms  of  Moral  Insanity  exhibit  the  same  contrast  in 
a  yet  more  striking  light.  We  not  unfrequently  meet  with  individuals,  still 
holding  their  place  in  society,  who  are  accustomed  to  act  so  much  upon 
feeling,  and  to  be  so  little  guided  by  reason,  as  to  be  scarcely  regarded  as  sane ; 
and  a  very  little  exaggeration  of  such  a  tendency  causes  the  actions  to  be  so 
•injurious  to  the  individual  himself  or  to  those  around  him,  that  restraint  is 
required,  although*  th'e  intellect  is  in  no  way  disordered,  nor  are  any  of  the 
feelings  perverted.  Not  unfrequently  we  may  observe  similar  inconsistencies 
resulting  from  the  habitual  indulgence  of  one  particular  feeling,  or  a  morbid 
exaggeration  of  it.  The  mother  who,  through  weakness  of  will,  yields  to  her 


196  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

instinctive  fondness  for  her  offspring,  in  allowing  it  gratifications  which  she 
knows  to  be  injurious  to  it,  is  placing  herself  below  the  level  of  many  less 
gifted  beings.  The  habit  of  yielding  to  a  natural  infirmity  of  temper  often 
leads  into  paroxysms  of  ungovernable  rage,  which,  in  their  turn,  pass  into  a 
state  of  maniacal  excitement.  It  is  not  unfrequently  seen,  that  a  delusion  of 
the  intellect  (constituting  what  is  commonly  known  as  Monomania),  has  in 
reality  resulted  from  a  disordered  state  of  the  feelings,  which  have  represented 
every  occurrence  in  a  wrong  light  to  the  mind  of  the  individual.  All  such 
conditions  are  of  extreme  interest,  when  compared  with  those  which  are  met 
with  amongst  idiots,  and  animals  enjoying  a  much  lower  degree  of  intelligence  ; 
for  the  result  is  much  the  same,  in 'whatever  way  the  balance  between  the 
feelings  and  the  judgment  (which  is  so  beautifully  adjusted  in  the  well-ordered 
mind  of  Man),  is  disturbed, — whether  by  a  diminution  of  the  intelligence,  or 
by  an  exaltation  of  the  feelings.  These  views  will  probably  be  found  correct, 
whatever  be  the  truth  of  the  speculation  with  which  they  have  been  here 
connected,  as  to  the  part  of  the  Nervous  system  concerned  in  the  performance 
of  the  purely  Emotional  actions.  That  their  channel  is  alike  distinct,  how- 
ever, from  that  of  the  voluntary  movements,  and  from  that  of  reflex  operations, 
must  be  apparent  to  any  one  who  fairly  weighs  the  evidence. 

XIX.  Functions  of  the  Cerebellum. 

286.  In  regard  to  the  particular  purposes  which  are  served  by  the  Cere- 
bellum, physiologists  are  still  much  in  the  dark  ;  although  there  are  not 
wanting  those  who  consider  them  well  ascertained.  That  this  organ  has 
some  special  function,  distinct  from  that  of  the  Cerebral  hemispheres,  can 
scarcely  be  doubted ;  since  its  peculiar  structure  and  position,  its  independent 
connections  with  the  Medulla  Oblongata,  and  its  extremely  variable  size  rela- 
tively to  the  remainder  of  the  Encephalon,  point  it  out  as  an  instrument 
adapted  to  some  particular  purpose.  We  shall  inquire  briefly  into  the  nature 
of  the  evidence  respecting  its  function,  which  is  supplied  to  us  by  Comparative 
Anatomy,  by  Experiment,  and  by  Pathological  phenomena.  A  Cerebellum 
is  found  in  all  Vertebrated  animals  ;  although  it  is  in  some  extremely  small, 
looking  like  a  little  prominence  on  the  Medulla  Oblongata.  When  this  is  the 
case,  it  is  observed  that  the  whole  mass  is  not  a  miniature  (so  to  speak)  of  the 
large  Cerebellum  of  Man,  but  that  the  central  portion  (termed  the  vermiform 
process)  is  the  part  most  developed ;  the  lobes  not  presenting  themselves  until 
the  organ  has  acquired  an  increased  dimension.  The  following  table,  con- 
structed from  materials  contained  in  M.  Serres'  most  valuable  Comparative 
Anatomy  of  the  Brain,  will  afford  some  idea,  of  the  materials  for  speculating 
on  the  nature  of  the  function  of  the  Cerebellum,  which  we  obtain  from  this 
source.  The  first  column  gives  the  diameter  of  the  Spinal  Cord  at  the  second 
cervical  vertebra  ;  in  the  two  succeeding  columns  are  stated  the  transverse  and 
the  antero-posterior  diameters  of  the  Cerebellum ;  these  dimensions  are  stated 
in  hundred-thousandths  of  a  metre.  The  fourth  column  expresses,  in  round 
numbers,  the  proportion  which  the  diameters  of  the  Cerebellum  bear  to  that  of 
the  Spinal  Cord  ;  the  latter  being  reckoned  as  1. 


FUNCTIONS  OF  THE  CEREBELLUM. 


197 


MAMMALIA. 

Diameter  of  Spinal 
Cord  at  2d  Cervical 
Vertebra. 

Transverse  Diameter 
of  Cerebellum. 

Antero-posterior 
Diameter 
of  Cerebellum. 

Proportions. 

Man  . 

1100 

12,000 

6000 

11  —  5i 

Simia  Rubia 

900 

4500 

2443 

5  o| 

Bear  . 

1300 

5900 

3500 

4^  2^ 

Dog  . 

1100 

4200 

2525 

3£—  2-1- 

Dromedary 

1900 

7100 

4600 

3|  —  2£ 

Kangaroo  . 

1200 

3800 

2600 

3i—  2* 

BIRDS. 

Falcon 

400 

1350 

1100 

3£—  2£ 

Swallow    . 

3175 

500 

600 

3  —  3J 

Turkey      . 

500 

1350 

1600 

2|  —  2£ 

Ostrich 

700 

1750 

2500 

21—  33 

REPTILES. 

Crocodile  . 

300 

500 

400 

If—  1| 

Frog 

300 

300 

200 

FISHES. 

Shark 

700 

1700  . 

3100 

2£—  :!3 

Cod    . 

575 

1350 

1700 

2£—  37 

Turbot 

500 

750 

900 

li—  If 

Lamprey   . 

275 

225 

100 

*-l 

267-  This  table  affords  us  much  scope  for  interesting  speculation,  and  maybe 
applied  to  the  correction  of  hypotheses  erected  upon  other  foundations.  Before 
we  proceed  to  these,  however,  a  few  general  remarks  may  be  made  upon  it. 
In  the  first  place,  the  proportional  development  of  the  Cerebellum  is  seen  to 
be  smallest  in  the  vermiform  Fishes,  which  approach  most  nearly  to  the  Inver- 
tebrata ;  but  it  is  much  greater  in  the  higher  Fishes  than  it  is  in  Reptiles.  If 
we  consider  in  what  particular,  that  may  be  reasonably  supposed  to  have  a 
connection  with  this  organ,  the  former  surpass  the  latter,  we  should  at  once 
be  struck  with  their  superiority  in  activity  and  variety  of  movement.  Passing 
on  to  Birds,  we  remark  that  the  average  dimensions  of  the  Cerebellum  greatly 
surpass  those  of  the  organ  in  Reptiles ;  but  that  they  do  not  exceed  those 
occasionally  met  with  in  Fishes.  The  greatest  size  is  not  found  in  those 
species  which  approach  most  nearly  to  the  Mammalia  in  general  conformation, 
such  as  the  Ostrich ;  but  in  those  of  most  active  arid  varied  powers  of  flight. 
Lastly,  on  ascending  the  scale  of  Mammiferous  animals,  we  cannot  but  be 
struck  with  the  rapid  advance  in  the  proportional  size  of  the  Cerebellum,  that 
we  observe,  as  we  rise  from  the  lowest,  which  are  surpassed  in  this  respect  by 
many  Birds,  towards  Man,  in  whom  it  attains  a  development  which  appears 
enormous,  even  when  contrasted  with  that  of  the  duadrumana. 

268.  We  have  next  to  inquire  what  evidence  can  be  drawn  from  Experi- 
mental investigations  on  the  same  subject ;  and  in  reference  to  this  it  is 
desirable  to  remark,  in  the  first  place,  that  the  experimental  mode  of  inquiry 
is  perhaps  more  applicable  to  this  organ  than  to  other  parts  of  the  Encephalon ; 
inasmuch  as  it  can  be  altogether  removed  with  little  disturbance  of  the  actions 
immediately  essential  to  life  ;  and  the  animals  soon  recover  from  the  shock  of 
the  operation,  and  seem  but  little  affected,  except  in  some  easily  recognized 
particulars.  The  principal  experimenters  upon  this  subject  have  been  Rolan- 

17* 


198  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

do,  Flourens,  Magendie,  and  Hertwig.  It  is  not  to  be  expected  that  there 
should  be  an  exact  conformity  among  the  results  obtained  by  all.  Every  one 
who  has  been  engaged  in  physiological  experiments,  is  aware  of  the  amount 
of  difference  caused  by  very  minute  variations  in  their  circumstances  ;  in  no 
department  of  inquiry  is  this  more  the  case  than  in  regard  to  the  Nervous 
System ;  and  such  differences  are  yet  more  likely  to  occur  in  experiments 
made  upon  the  Nervous  Centres  than  in  those  which  concern  their  trunks. 
The  investigations  of  Flourens  are  the  most  clear  and  decisive  in  their  results  ; 
and  of  these  we  shall  accordingly  take  a  general  survey.  He  found  that,  when 
the  Cerebellum  was  mechanically  injured,  the  animals  gave  no  signs  of  sensi- 
bility, nor  were  they  affected  with  convulsions.  When  the  Cerebellum  was 
being  removed  by  successive  slices,  the  animals  became  restless,  and  their 
movements  were  irregular ;  and  by  the  time  that  the  last  portion  of  the  organ 
was  cut  away,  the  animals  had  entirely  lost  the  powers  of  springing,  flying, 
walking,  standing,  and  preserving  their  equilibrium, — in  short,  of  performing 
any  combined  muscular  movements  which  are  not  of  a  simply  reflex  character. 
When  an  animal  in  this  state  was  laid  upon  the  back,  it  could  not  recover  its 
former  posture ;  but  it  fluttered  its  wings  and  did  not  lie  in  a  state  of  stupor. 
When  placed  in  the  erect  position,  it  staggered  and  fell  like  a  drunken  man, — 
not,  however,  without  making  efforts  to  maintain  its  balance.  When  threatened 
with  a  blow,  it  evidently  saw  it,  and  endeavoured  to  avoid  it.  It  did  not  seem 
that  the  animal  had  in  any  degree  lost  voluntary  power  over  its  several  mus- 
cles ;  nor  did  sensation  appear  to  be  impaired.  The  faculty  of  combining 
the  actions  of  the  muscles  in  groups,  however,  was  completely  destroyed ; 
except  so  far  as  those  actions  (as  that  of  respiration)  were  dependent  only 
upon  the  Reflex  function  of  the  Spinal  Cord.  The  experiments  afforded  the 
same  results  when, made  upon  each  class  of  Vertebrated  animals;  and  they 
have  since  been  repeated,  with  corresponding  effects,  by  Bouillaud  and  Hert- 
wig. The  latter  agrees  with  Flourens,  also,  in  stating  that  the  removal  of  one 
side  of  the  Cerebellum  affects  the  movements  of  the  opposite  side  of  the  body ; 
and  he  further  mentions  that,  if  the  mutilation  of  the  Cerebellum  have  been 
partial  only,  its  function  is  in  great  degree  restored. 

269.  All  these  results  are  objected  to  by  those  who  assert  that  the  Cere- 
bellum is  the  seat  of  the  sexual  instinct ;  on  the  ground  that  the  observed 
aberrations  of  the  motor  functions  are  sufficiently  accounted  for,  by  the  gene- 
ral disturbance  which  an  operation  so  severe  must  necessarily  induce.     The 
fallacy  of  this  objection,  however,  is  shown  by  the  fact,  that  the  much  more 
severe  operation  of  removing  the  Hemispheres  does  not  occasion  such  an 
aberration ;  the  power  of  performing  the  associated  movements,  and  of  main- 
taining the  equilibrium,  being  remarkably  preserved  after  the  loss  of  them. 

270.  Upon  comparing  these  results  with  the  preceding  table,  a  remarkable 
correspondence  will  be  observed  between  them.     The  classes  which  have  the 
greatest  variety  of  movements,  and  which  require  for  them  the  most  perfect 
combination  of  a  large  number  of  separate  muscular  actions,  have,  taken  col- 
lectively, the  largest  Cerebellum.     Of  all  classes  of  Vertebrata,  Reptiles  are 
the  most  inert ;  and  their  motions  require  the  least  co-ordination.     The  active 
predaceous  Fishes  far  surpass  them  in  this  respect;  and  may  be  compared 
with  Birds,  in  the   energy  of  their  passage  through  the  water,  and  in  their 
facility  of  changing  their  direction  during  the  most  rapid  progression.     The 
Cerebellum,  accordingly,  bears  to  the  Spinal  Cord  in  them,  very  much  the 
same 'proportion  as  it  does  in  Birds.    On  the  other  hand,  the  Flat  Fish,  which 
lie  near  the  bottom  of  the  ocean,  and  which  have  a  much  less  variety  of 
movement,  have  a  very  much  smaller  cerebellum:  and  the  Vermiform  Fishes, 
which  are  almost  or  completely  destitute  of  fins,  and  whose  progression  is 
accomplished  by  flexion  of  the  body,  have  a  Cerebellum  so  small  as  to  be 


FUNCTIONS  OF  THE  CEREBELLUM.  190 

scarcely  discoverable :  their  motion  being,  like  that  of  the  Articulata,  almost 
entirely  of  a  reflex  character, — each  segment  being  influenced  by  its  own 
ganglionic  centre,  and  the  Spinal  Cord  constituting  by  far  the  largest  propor- 
tion of  the  nervous  centres.     On  looking  at  the  class  of  Birds,  we  observe 
that  the  active  predaceous  Falcons,  and  the  swift-winged  Swallows  (the  per- 
fect control  possessed  by  which  over  their  complicated  movements  must  hav% 
been  observed  by  every  one),  have  a  Cerebellum  much  larger  in  proportion, 
than  that  of  the  Gallinaceous  birds,  \vhose  powers  of  flight  are  small,  or  than 
that  of  the  Struthious  tribe,  in  which  they  are  altogether  absent.     Lastly,  on 
comparing  its  proportional  size  in  the  different  orders  of  Mammalia,  with  the 
number  and  variety  of  muscular  actions  requiring  combined  movements,  of 
which  they  are  respectively  capable,  we  observe   an  even  more  remarkable 
correspondence.     In  the  hoofed  Quadrupeds,  in  which  the  muscular  appara- 
tus of  the  extremities  is  reduced  to  its  greatest  simplicity,  and  in  which  the 
movements  of  progression  are   simple,  the  Cerebellum  is  relatively  smaller 
than  it  is  found  to  be  in  some  Birds ;  but  in  proportion  as  the  extremities 
acquire  the  power  of  prehension,  and  together  with  this  a  power  of  applica- 
tion to  a  great  variety  of  purposes, — still  more,  in  proportion  as  the  animal 
becomes  capable  of  maintaining  the  erect  posture,  in  which  a  constant  mus- 
cular exertion,  consisting  of  a  number  of  most  elaborately  combined  parts,  is 
required, — do  AVC  find  the  size  of  the  Cerebellum,  and  the  complexity  of  its 
structure,  undergoing  a  rapid  increase.     Thus,  even   between  the  Dog  and 
the  Bear  there  is  a  marked  difference  ;  the  latter  being  capable  of  remaining 
for  some  time  in  the   erect  posture,  and  often  spontaneously  assuming  it ; 
whilst  to  the  former  it  is  any  thing  but  natural.     In  the  semi-erect  Apes, 
again,  there  is  a  very  great  advance  in  the  proportional  size  of  the  Cerebel- 
lum ;  and  those  which  most  approach  Man  in  the    tendency   to   preserve 
habitually  the   erect  posture,  also  come  nearest  to  him  in  the  dimensions  of 
this  organ.     Now  it  is  evident  that  Man,  although  far  inferior  to  many  of  the 
lower  animals,  in  the  power  of  performing  various  particular  kinds  of  move- 
ment, far  surpasses  them  all  in  the  number  and  variety  of  the  combinations 
which  he  is  capable  of  executing,  and  in  the  complexity  of  the  combinations 
themselves.     Thus,  if  we  attentively  consider  the  act  of  walking  in  man,  we 
shall  find  that  there  is  scarcely  a  muscle  of  the  trunk  or  extremities  which  is 
not  actually  concerned  in  it,  some  being  engaged  in  performing  the  neces- 
sary movements,  and  others  in  maintaining  the  equilibrium  of  the  body,  which 
is  disturbed  by  them.     On  the  other  hand,  in  the  Horse  or  Camel,  the  mus- 
cular movements  are  individually  numerous,  but  they  do  not  require  nearly 
the  same  perfect  co-ordination.     And  in  the  Bird,  the  number  of  muscles  em- 
ployed in  the  movements  of  flight,  and  in  directing  the   course  of  these,  is 
really  comparatively  small ;  as  may  at  once  be  perceived,  by  comparing  the 
rigidity  of  the  skeleton  of  the  trunk  of  the  Bird  writh  that  of  Man,  and  by 
remembering  the   complete  inactivity  of  the  lower  extremities  during  the 
active  condition  of  the  upper.     In  fact,  the  motions  of  the  wings  are  so  simple 
and  regular,  as  to  suggest  the  idea,  that,  as  in  Insects,  their  character  is  more 
reflex  than  directly  voluntary : — an  idea  which  is  supported  by  the  length  of 
time  during  which  they  can  be  kept  up  without  apparent  fatigue,  and  also  by 
the  important  fact  already  mentioned,  wfiich  experimental  research  has  dis- 
closed (§  284).     It  is  seen,  then,  that  Comparative  Anatomy  fully  confirms 
the  idea,  which  Experimental  physiology  suggests,  respecting  the  chief  func- 
tions of  the  Cerebellum. 

271.  Some  of  Magendie's  experiments  indicate  a  further  connection  of  this 
organ  with  the  motor  function,  the  nature  of  which  is  still  obscure.  This  phy- 
siologist asserts  that,  if  a  wound  be  inflicted  on  the  Cerebellum,  the  animal 
seems  compelled  by  an  inward  force  to  retrograde  movement,  although  making 


200  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

an  effort  to  advance  ;  and  that,  if  the  Crus  Cerebelli  on  one  side  be  injured, 
the  animal  is  caused  to  roll  over  towards  the  same  side.  Sometimes  (if  Ma- 
gendie's  statements  can  be  relied  on),  the  animals  made  sixty  revolutions  in  a 
minute,  and  continued  this  movement  for  a  week  without  cessation.  Division 
of  the  second  Crus  Cerebelli  restored  the  equilibrium.  Hertwig  observed  the 
s*me  phenomenon,  when  the  Pons  Varoiii  (which  is  nothing  more  than  the 
commissure  of  the  Cerebellum,  surrounding  the  Crura  Cerebri)  was  injured 
on  one  side  ;  and  he  has  also  remarked,  that  the  movements  of  the  eyes  were 
no  longer  consensual. 

272.  On  turning  to  Pathology  for  evidence  of  the  functions  of  the  Cere- 
bellum, we  meet  with  much  that  seems  contradictory.  It  must  be  remembered 
that  a  sudden  effusion  of  blood,  even  to  a  small  extent,  in  any  part  of  the 
Encephalon,  is  liable  to  produce  the  phenomena  of  apoplexy  or  paralysis ; 
and  inferences  founded  upon  the  phenomena  exhibited  after  sudden  lesions  of 
this  description  are,  therefore,  much  less  valid  than  those  based  on  the  results 
of  more  chronic   affections.  '  In  regard  to  these  last,  however,  it  is  to  be 
observed,  that  we  are  not  yet  in  a  condition  to  be  able  to  state  with  precision, 
what  amount  of  morbid  alteration  in  any  part  of  the  nervous  centres  is  com- 
patible with  but  slightly  disturbed  performance  of  its  function ;  and  that  cases 
are  every  now  and  then  occurring,  which  would  upset  all  our  previous  notions, 
if  we  were  not  aware  that  the  same  difficulty  presents  itself  even  in  regard 
to  the  best-established  results  in  Neurology.     It  is  also  to  be  remembered,  that 
the  results  of  disease,  occasioning  pressure,  will  be  peculiarly  liable  to  affect 
the  Medulla  Oblongata,  as  well  as  the  Cerebellum1,  and  will  thus  occasion  a 
greater  loss  of  motor  power  than  would  be  occasioned  by  the  mere  suspension 
of  the  function  of  the  latter. 

273.  Pathological  phenomena,  when  examined  with   these   reservations, 
appear  to  coincide  with  the  results  of  experiment,  in  supporting  the  conclu- 
sion, that  the  Cerebellum  is  not  in  any  way  the  instrument  of  psychical  opera- 
tions.    Inflammation  of  the  membranes  covering  it,  if  confined  to  that  part, 
does  not  produce  delirium ;  and  its  almost  complete  destruction  by  gradual 
softening,  does  not  appear  necessarily  to  involve  loss  of  intellectual  power. 
"  But,"  remarks  Andral,  "  whilst  the  changes  of  intelligence  were  variable, 
inconstant  and  of  little  importance,  the  lesions  of  motion,  on  the  contrary,  were 
observed  in  all  the  cases  [of  softening  which  had  come  under  his  notice]  ex- 
cept one ;  and  in  this  it  is  not  quite  certain  that  motion  was  not  interfered 
with."     In  general,  apoplexy  of  the  Cerebellum  is  accompanied  by  paralysis  ; 
but  this  is  by  no  means  usual  in  cases  of  chronic  disease,  in  which  there  is 
rather  an  irregularity  of  movement,  with  a  degree  of  restlessness,  resembling 
that  described  by  Flourens  as  resulting  from  partial  injury  of  this  organ.     In 
a  few  cases  in  which  both  lobes  of  the  Cerebellum  have  been  seriously  affected, 
the  tendency  to  retrograde  movement  has  been  observed ;  and  instances  are 
also  on  record,  of  the  occurrence  of  rotatory  movement,  which  has  been  found 
to  be  connected  with  lesion  of  the  Crus  Cerebelli  on  the  same  side.     So  far 
as  they  can  be  relied  on,  therefore,  the  results  of  the  three  methods  of  investi- 
gation bear  a  very  close  correspondence ;  and  it  can  scarcely  be  doubted,  that 
they  afford  us  some  approximation  to  truth. 

274.  We   have  now  to  examine^  however,  another  doctrine  regarding  the 
functions  of -the  Cerebellum,  which  was  propounded  by  Gall,  and  which  is 
supported  by  the  Phrenological  school  of  physiologists.     This  doctrine — that 
the  Cerebellum  is  the  organ  of  the  sexual  instinct — is  by  no  means  incom- 
patible with  the  other  ;  and  by  some  it  has  been  held  in  combination  with  it. 
The  greater  number  of  phrenologists,  however,  regard  this  instinct  as  the 
exclusive  function  of  the  Cerebellum ;  and  assert  that  they  can  judge  of  its 
intensity,  by  the  degree  of  development  of  the  organ.    We  shall  now  examine 


FUNCTIONS  OF  THE  CEREBELLUM.  201 

the  evidence  in  support  of  this  position,  afforded  by  the  three  methods  of 
inquiry  which  have  been  already  indicated.  The  results  of  fair  observation 
as  to  the  comparative  size  of  the  Cerebellum  in  different  animals,  can  scarcely 
be  regarded  as  otherwise  than  very  unfavourable  to  the  doctrine  in  question. 
In  the  greatest  number  of  Fishes,  it  is  well  known  that  no  sexual  congress 
takes  place  ;  the  seminal  fluid  being  merely  effused,  like  any  other  excretion, 
into  the  surrounding  water ;  and  being  thus  brought  into  accidental  contact 
with  the  ova,  of  which  a  large  proportion  are  never  fertilized.  On  the  other 
hand,  in  many  Reptiles,  the  sexual  instinct  appears  extremely  strong  ;  and 
this  is  especially  the  case  in  the  Frog,  the  whole  system  of  which  is  endowed, 
at  the  season  of  fertility,  with  an  extraordinary  degree  of  excitability,  analo- 
gous to  a  morbid  condition  that  sometimes  presents  itself  in  the  Human  being. 
It  has  been  remarked  that,  if  the  head  of  a  male  Frog  be  cut  off,  during  the 
congress  (which  lasts  for  some  time),  his  embrace  will  not  be  relaxed,  and 
will  even  continue  until  the  body  of  tile  female  is  becoming  gangrenous  from 
the  pressure  ;  thus  showing  that  the  action  is  one  of  a  purely  reflex  character. 
Now,  on  comparing  the  size  of  the  Cerebellum  of  the  Frog  with  that  of  the 
Cod,  (we  exclude  the  higher  Cartilaginous  fishes,  in  which  the  reproductive 
function  has  a  more  elevated  type,)  we  find  that  it  is  not  above  one-half  the 
proportional  size.  Moreover,  not  only  is  the  size  much  inferior,  but  the  struc- 
ture is  much  less  complicated  in  the  former  than  in  the  latter.  Again,  in 
comparing  the  Gallinaceous  Birds,  which  are  polygamous,  with  the  Raptorial 
and  Insessorial  tribes,  which  live  in  pairs,  we  find  that  the  former,  instead  of 
having  a  larger  cerebellum,  have  one  of  inferior  size.  Further,  on  looking  at 
the  Mammalia,  the  same  disproportion  may  be  noticed.  A  friend  who  kept 
some  Kangaroos  in  his  garden,  informed  the  author  that  they  were  the  most 
salacious  animals  he  ever  saw  ;  yet  their  cerebellum  is  one  of  the  smallest  to 
be  found  in  the  class.  Every  one  knows,  again,  the  salacity  of  Monkeys  ; 
there  are  many  which  are  excited  to  violent  demonstrations,  by  the  sight  even 
of  a  human  female  ;  and  there  are  few  which  do  not  practise  masturbation, 
when  kept  in  solitary  confinement :  yet  in  them  the  cerebellum  is  much 
smaller  than  in  Man,  in  whom  the  sexual  impulse  is  much  less  violent.  It 
has  been  supposed  that  the  large  size  of  the  organ  in  Man  is  connected  with 
his  constant  possession  of  the  appetite,  which  is  only  occasional  in  others ; 
but  this  does  not  hold  good ;  since  among  domestic  animals,  there  are  many 
which  are  ready  to  breed  throughout  the  year, — Cats  and  Rabbits  for  instance ; 
and  in  these  we  do  not  find  any  peculiar  difference  in  the  size  of  the  Cere- 
bellum. It  is  asserted,  however,  that  the  results  of  observation  in  Man  lead 
to  a  positive  conclusion,  that  the  size  of  the  Cerebellum  is  a  measure  of  the 
intensity  of  the  sexual  instinct  in  the  individual.  This  assertion  has  been 
met  by  the  counter-statement  of  others, — that  no  such  relation  exists.  It  is 
unfortunate  that  here,  as  in  many  other  instances,  each  party  has  registered 
the  observations  favourable  to  their  own  views  rather  than  those  of  an  oppo- 
site character  ;  so  that,  until  some  additional  evidence  of  a  less  partial  nature 
has  been  collected,  we  must  consider  the  question  as  sub  judice.  The  author 
is  by  no  means  disposed  to  deny  that  such  a  correspondence  may  exist ;  but 
on  contrasting  the  degree  of  support  which  this  part  of  phrenology  really 
derives  from  pathological  evidence,  with  that  which  the  upholders  of  this 
view  represent  it  to  receive,  he  cannot  but  look  with  much  distrust  at  all  their 
observations  on  this  subject. 

275.  It  is  stated  in  Phrenological  works,  as  an  ordinary  result  of  disease  of 
the  Cerebellum,  that  there  is  an  affection  of  the  genital  organs,  manifesting 
itself  in  priapism,  turgescence  of  the  testes,  and  sometimes  in  seminal  emis- 
sions. Now  it  is  quite  true  that,  in  cases  of  apoplexy,  in  which  these  symp- 
toms manifest  themselves,  there  is  very  commonly  found  to  be  effusion  upon 


202  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

the  Cerebellum,  or  in  its  substance ;  but  it  is  to  be  remembered,  that  in  all 
such  lesions  the  Medulla  Oblongata  is  involved,  and  these  symptoms,  equally 
with  paralysis,  may  be  due  to  affection  of  that  organ.*  Further,  the  converse 
does  not  by  any  means  hold  good ;  for  the  proportion  of  cases  of  disease  of 
the  Cerebellum,  in  which  there  is  any  manifest  affection  of  the  sexual  organs, 
is  really  very  small,  being,  according  to  the  calculations  of  Burdach,  not  above 
one  in  seventeen.  The  same  physiologist  states  that  such  affections  do  pre- 
sent themselves,  although  very  rarely,  \vhen  the  Cerebrum  is  the  seat  of  the 
lesion.  A  large  number  of  facts  adduced  by  Phrenologists  in  support  of  their 
views — such  as  the  erections  and  emissions  which  often  take  place  during 
hanging — may  be  explained  as  well,  or  even  better,  on  the  hypothesis  that 
the  Cerebro-spinal  axis  (that  is,  the  Spinal  cord  with  the  Medulla  Oblongata) 
is  the  seat  of  this  instinct.  And  this  hypothesis  is  much  more  conformable  to 
the  results  of  experiment  and  disease  than  that  which  locates  it  in  the  Cere- 
bellum. For  it  has  been  found  that  mechanical  irritation  of  the  Spinal  Cord, 
and  disease  in  its  substance,  much  more  frequently  produce  excitement  of  the 
genital  organs,  than  do  lesions  of  the  Cerebellum.  This  view  is  entertained 
by  Miiller,  and  by  most  physiologists  who  have  taken  a  comprehensive  and 
unbiased  survey  of  the  phenomena  in  question. 

276.  Among  the  arguments  adduced  by  Gall  and  his  followers  in  proof  of 
the  connection  between  the  Cerebellum  and  the  sexual  instinct,  is  one  which 
would  deserve  great  attention,  if  the  facts  stated  could  be  relied  on.  It  has 
been  asserted,  over  and  over  again,  that  the  Cerebellum,  in  animals  which 
have  been  castrated  when  young,  is  much  smaller  than  in  those  which  have 
retained  their  virility, — being,  in  fact,  atrophied  from  want  of  power  to  act. 
Now  it  is  unfortunate,  that  vague  assertion,  founded  on  estimates  formed  by 
the  eye  from  the  cranium  alone,  is  all  on  which  this  position  rests ;  and  it  will 
be  presently  shown,  how  very  liable  to  error  such  an  estimate  must  be.  The 
following  is  the  result  of  a  series  of  observations  on  this  subject,  suggested  by 
M.  Leuret,t  and  carried  into  effect  by  M.  Lassaigne  : — The  weight  of  the 
Cerebellum,  both  absolutely,  and  as  compared  with  that  of  the  Cerebrum, -was 
adopted  as  the  standard  of  comparison.  This  was  ascertained  in  ten  Stallions, 
of  the  ages  of  from  nine  to  seventeen  years  ;  in  twelve  Mares,  aged  from  seven 
to  sixteen  years ;  and  in  twenty-one  Geldings,  aged  from  seven  to  seven- 
teen years.  The  average  weight  of  the  Cerebrum  in  the  Stallions  was  433 
grammes;  the  greatest  being  485  gr.,  and  the  least  (which  was  in  a  horse  of 
ten  years  old)  being  350.  The  average  weight  of  the  Cerebellum  was  61  gr.; 
the  greatest  being  65  gr.,  and  the  least  56  gr.  The  average  proportion  borne 
by  the  weight  of  the  Cerebellum  to  that  of  the  Cerebrum,  was,  therefore,  1  to 
7-07 ;  the  highest  (resulting  from  a  very  small  Cerebrum)  being  1  to  6-25 ; 
and  the  lowest  (resulting  from  an  unusually  large  Cerebrum)  being  1  to  7'46. 
Throughout  it  might  be  observed,  that  the  variation  in  the  size  of  the  Cerebellum 
was  much  less  than  in  that  of  the  Cerebrum. — In  the  twelve  Mares,  the  average 
weight  of  the  Cerebrum  was  402  gr. ;  the  highest  being  432  gr.  and  the  lowest 
336  gr.  That  of  the  Cerebellum  was  61  gr. ;  the  highest  being  66  gr.  (which 
was  in  the  individual  with  the  smallest  Cerebrum),  and  the  lowest  58  gr. 

*  A  case  has  been  recently  communicated  to  the  Author,  in  which  the  sexual  desire, 
which  had  been  always  strong  through  life,  but  which  had  been  controlled  within  the 
limits  of  decency,  manifested  itself,  during:  a  period  of  some  months  preceding  death,  in 
a  most  extraordinary  degree;  on  post  mortem  examination,  a  tumour  was  found  on  the 
Pons  Varolii.  This  fact  harmonizes  with  the  view  given  in  the  text  (§  278),  that  the 
sexual  instinct,  if  connected  with  the  cerebellum  at  all,  has  its  seat  in  the  central  lobe; 
but  it  also  corresponds  equally  well  with  the  idea,  that  the  Medulla  Oblongata  is  its 
centre. 

f  Anat.  Comp.  du  Systdme  Nerveux,  torn.  i.  p.  427. 


FUNCTIONS  OF  THE  CEREBELLUM.  203 

The  average  proportion  of  the  weight  of  the  Cerebellum  to  that  of  the  Cere- 
brum was  1  to  6-59 ;  the  highest  being  1  to  5*09,  and  the  lowest  1  to  7.  The 
proportion  was,  therefore,  considerably  higher  in  the  perfect  female  than  in 
the  perfect  male. — In  the  twenty-one  Geldings,  the  average  weight  of  the 
Cerebrum  was  419  gr. ;  the  highest  being  566  gr.,  and  the  lowest  346  gr. 
The  average  of  the  Cerebellum  was  70  gr. ;  the  highest  being  76  gr.,  and 
the  lowest  64  gr.  The  average  proportion  was,  therefore,  1  to  5-97 ;  the 
highest  being  1  to  5-16,  and  the  lowest  1  to  7'44.  It  is  curious  that  this  last 
was  in  the  individual  which  had  the  largest  Cerebellum  of  the  whole ;  but 
the  proportional  weight  of  the  Cerebrum  was  still  greater. 

277.  Bringing  together  the  results  of  these  observations,  they  are  found  to 
be  quite  opposed  to  the  statement  of  Gall.  The  weight  of  the  Cerebrum, 
reckoning  the  Cerebellum  as  1,  is  thus  expressed  in  each  of  the  foregoing 
descriptions  of  animals. 

Average.  Highest.  Lowest. 

Stallions  .         .         .         7-07        7-46  6.25 

Mares      .         .         .         6-59         7-00  5-09 

Geldings  .         .         5-97        7-44  5-16 

The  average  proportional  size  of  the  Cerebellum  in  Geldings,  therefore,  is  so 
far  from  being  less  than  that  which  it  bears  in  entire  Horses  and  Mares,  that 
it  is  positively  greater ;  and  this  depends  not  only  on  diminution  in  the  rela- 
tive size  of  the  Cerebrum,  but  on  its  own  larger  dimensions,  as  the  following 
comparison  of  absolute  weights  will  show : — 

Average.  Highest.  Lowest. 

Stallions    ...         61             65  56 

Mares        ...         61             66  58 

Geldings  ...         70            76  64 

The  difference  is  so  remarkable,  and  appears,  from  examination  of  the  indi- 
vidual results,  to  be  so  constant,  that  it  cannot  be  attributed  to  any  accidental 
circumstance,  arising  out  of  the  small  number  of  animals  experimented  on. 
The  average  weight  of  the  Cerebellum  in  the  ten  Stallions  and  twelve  Mares 
is  seen  to  be  the  same  ;  and  the  extremes  differ  but  little  in  the  two ;  whilst 
the  average  in  the  Gelding  is  more  than  one-seventh  higher,  and  the  lowest  is 
considerably  above  the  average  of  the  precedingpvhile  the  highest  far  exceeds 
the  highest  amongst  the  entire  Horses. — It  is  curious  that  Gall  would  have 
been  much  nearer  the  truth,  if  he  had  said  that  the  dimensions  of  the  cere- 
brum are  usually  reduced  by  castration ;  for  it  appears  from  the  following 
table  that  this  is  really  the  case  : — 

Average.  Greatest.  Least. 

Stallions      ...         433        485  350 

Mares          ...         402         432  336 

Geldings     .         .         .419         566  346 

The  weight  of  the  largest  Cerebrum  of  the  Gelding  is  far  above  the  highest 
of  the  Stallions ;  but  it  seems  to  be  an  extraordinary  case,  as  in  no  other  was 
the  weight  above  490  gr.  If  this  one  be  excluded,  the  average  will  be 
reduced  still  further,  being  then  about  412 ;  this  may  be  seen  by  looking  ovrr 
the  whole  table,  to  give  a  very  fair  idea  of  the'usual  weight  in  these  animals, 
which  is  therefore  less,  by  about  one-twentieth,  than  the  average  of  the  Stal- 
lions. The  increased  size  of  the  Cerebellum  in  Geldings  may  perhaps  be 
accounted  for,  by  remembering  that  this  last  class  of  horses  is  solely  employed 
for  its  muscular  power,  and  that  the  constant  exercise  of  the  organ  is  not 
unlikely  to  develop  its  size ;  whilst  Stallions,  being  kept  especially  for  the 


201  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

purpose  of  propagation,  are  much  less  applied  to  occupations,  which  call  forth 
their  motor  faculties. 

278.  The  Author  is  far  from  denying  in  toto  that  any  peculiar  connection 
exists  between  the  Cerebellum  and  the  Genital  system ;  but  if  the  evidence  at 
present  adduced,  in  support  of  the  Phrenological  position,  be  held  sufficient 
to  establish  it,  in  defiance  of  so  many  opposing  considerations,  we  must  bid 
adieu  to  all  safe  reasoning  in  Physiology.     The  weight  of  testimony  appears 
to  him  to  be  quite  decided,  in  regard  to  the  connection  of  the  Cerebellum  with 
the  regulation  of  the  motor  function.     How  far  this  invalidates  the  moderate 
phrenological  view,  which  does  not  regard  the  function  of  the  Cerebullum 
as  exclusively  devoted  to  the  sexual  instinct,  is  a  question  well  deserving  of 
attention.     There  is  nothing  opposed  to  such  an  idea,  in  the  results  of  the 
experiments  already  adverted  to  (§  268) ;  since  there  is  no  evidence  that  sex- 
ual instinct  remained  after  the  removal  of  the  Cerebellum ;  but,  on  the  other 
hand,  there  is  no  proof  that  it  was  destroyed.    A  circumstance  which  has  been 
several  times  mentioned  to  him,  that  great  application  to  gymnastic  exercises 
diminishes,  for  a  time,  the  sexual  vigour,  and  even  totally  suspends  desire, — 
seems  worthy  of  consideration  in  reference  to  such  a  view.     If  the  Cerebel- 
lum be  really  connected  with  both  kinds  of  functions,  it  does  not  seem  unrea- 
sonable that  the  excessive  employment  of  it  upon  one  should  diminish  its 
energy  in  regard  to  the  other.     Further,  it  would  seem  by  no  means  impro- 
bable that  the  Lobes  are  specially  connected  with  the  regulation  and  co-ordi- 
nation of  movements ;  whilst  the  Vermiform  processes,  which  are  very  large 
in  many  animals  in  which  the  former  scarcely  present  themselves,  are  the 
parts  connected  with  the  sexual  function.     As  an  additional  argument  in 
favour  of  the  former  part  of  this  view,  it  may  be  stated,  that  in  Man  the  lobes 
bear  a  larger  proportion  to  the  Vermiform  processes  than  in  any  other  animal ; 
and  that  they  undergo  their  most  rapid  development  during  the  first  few  years 
of  life,  when  a  large  number  of  complex  voluntary  movements  are  being 
learned  by  experience,  and  are  being  associated  by  means  of  the  muscular 
sensations  accompanying  them ;  whilst  in  those  animals  which  have,  imme- 
diately after  birth,  the  power  of  regulating  their  voluntary  movements  for 
definite  objects,  with  the  greatest  precision,  the  Cerebellum  is  more  fully 
developed  at  the  time  of  birth.     In  both  instances  it  is  well  formed  and  in 
active  operation  (so  far  as  can  be  judged  of  by  the  amount  of  circulation 
through  it),  long  before  the  s&xual  instinct  manifests  itself  in  any  perceptible 
degree. 

XX.  Functions  of  the  Cerebrum. 

279.  In  regard  to  certain  general  positions,  there  is  little  difference  of  opin- 
ion amongst  Physiologists  upon  this  much-controverted  subject;  and  it  will 
be  desirable  to  inquire  what  may  be  considered  as  firmly  established  before  we 
proceed  with  details  of  a  more  questionable  nature.    We  shall,  as  before,  apply 
to  Comparative  Anatomy,  to  Experiment  and  to  Pathology,  for  our  chief  data. 
Any  genera]   inferences,  founded  only  upon  observation  of  the  phenomena 
presented  by  Man,  must  be  looked  upon  with  suspicion ;  since  every  advance 
in  Comparative  Physiology  leads  us  to  perceive  how  close  is  the  functional 
relation  between  organs  that  are  really  of  analogous  nature  in  different  classes 
of  animals;  and  how  necessary,  therefore^  it  is  to  examine  ai^f  contrast  all  the 
facts  which  we  can  attain  in  regard  to  them,  in  order  to  impart  to  our  conclu- 
sions the  utmost  validity  of  which  they  are  capable.     Our  first  general  propo- 
sition is,  that  the  Cerebrum  is  the  sole  instrument  of  Intelligence;  by  which 
term  is  implied  the  Voluntary  adaptation  of  means  to  ends,  in  a  manner  imply- 
ing a  perception  of  the  nature  of  both.     The  actions  performed  by  the  lower 


FUNCTIONS  OF  THE  CEREBRUM.  205 

animals  are  often  such  as  to  leave  us  in  doubt  whether  they  are  the  result  of  a 
mere  instinctive  impulse  or  of  an  intelligent  adaptation  of  means  to  ends ;  and 
we  are  guided  in  our  determination  chiefly  by  the  uniformity  of  these  actions 
in  the  several  individuals  of  the  same  species.  If  we  analyze  any  of  our  own 
instinctive  actions,  we  shall  perceive  the  same  absence  of  design  on  our  own 
parts  as  that  which  we  attribute  to  the  lower  animals.  No  one  would  assert 
that  the  tendency  to  sexual  intercourse  is  the  result  of  a  knowledge  of  its  con- 
sequences, and  of  a  voluntary  adaptation  of  means  to  ends ;  or  that,  if  we  can 
imagine  a  man  newly  coming  into  the  world,  in  the  full  possession  of  all  his 
powers,  he  would  wait  to  eat,  when  hungry,  until  experience  had  taught  him 
that  the  swallowing  of  food  would  relieve  the  uneasy  feeling.  It  has  been 
already  shown  that,  in  the  infant,  the  act  of  sucking  may  be  performed  even 
without  a  Cerebrum  (§  197) ;  and  for  this,  and  other  similar  actions,  therefore, 
it  is  doubtful  whether  consciousness  is  a  requisite  condition.  Adult  animals, 
whose  Cerebral  hemispheres  have  been  removed,  will  eat  food  that  is  put  into 
their  mouths,  although  they  will  riot  go  to  seek  it;  and  this  is  the  case  with 
many  Human  idiots.  When  the  functions  of  the  Brain  are  disturbed,  or  in 
partial  abeyance,  as  in  fever,  we  often  see  a  remarkable  return  to  the  instinctive 
propensities  in  regard  to  food ;  and  the  Physician  frequently  derives  import- 
ant guidance,  as  to  the  patient's  diet  and  regimen,  (particularly  as  to  the 
administration  of  wine,)  from  the  inclination  or  disinclination  which  he  mani- 
fests. The  Intelligence  of  an  animal  may  be  further  estimated  by  its  degree 
of  educability — that  is,  the  facility  with  which  its  natural  habits  may  be 
changed  by  the  influence  of  man,  and  the  complication  of  the  mental  pro- 
cesses which  it  appears  to  perform  under  its  new  circumstances.  We  all 
know  that  Insects — the  most  active  of  all  Inv^rtebrated  animals — are  but  little 
susceptible  of  such  influence.  It  may  be  doubted  whether  there  ever  was  a 
case  in  which  an  Insect  of  any  kind  could  be  taught  to  recognize  any  one 
who  had  been  in  the  habit  of  feeding  it,  or  to  show  any  other  unequivocal 
mark  of  intelligence.  Bees  and  other  Insects  which  display  much  art  in  the 
construction  of  their  habitations,  and  which  execute  a  variety  of  most  curious 
contrivances,  beautifully  adapted  to  variations  in  their  circumstances,  appear 
to  be  entirely  guided  in  their  operations  by  instinct;  since  all  Bees  act  alike, 
under  the  same  circumstances.  We  do  not  find  one  community  or  individual 
clever,  and  another  stupid ;  and  for  a  Bee  to  be  destitute  of  its  peculiar  ten- 
dency to  build  at  certain  angles,  would  be  as  remarkable  as  a  Human  being 
without  a  tendency  to  eat.*  In  Insects,  as  already  stated,  we  can  discover 
little  or  nothing  that  is  analogous  to  the  Cerebrum  of  Vertebrata;  and  it  is 
manifest  that  their  cephalic  ganglia  correspond  chiefly  with  the  ganglionic 
enlargements  at  the  upper  end  of  the  Medulla  Oblongata,  which  are  connected 
with  the  organs  of  special  sensation,  and  which  have  been  stated  in  the  pre- 

*  The  only  manifestation  of  educability  which  the  Author  has  ever  noticed,  during  a 
pretty  long  familiarity  with  the  habits  of  Bees,  is  the  acquirement  of  a  power  of  distin- 
guishing the  entrance  of  their  hive  from  that  of  others  around.  When  a  swarm  is  first 
placed  in  a  new  box,  and  the  Bees  have  gone  forth  in  search  of  food,  they  often  seem 
puzzled,  on  their  return,  as  to  which  is  their  own  habitation;  more  especially  if  there  be 
several  hives,  with  similar  entrances,  in  one  bee-house;  and  it  has  been  proposed  to  paint 
these  entrances  of  different  colours,  in  order  to  enable  the  Bee  to  distinguish  them  more 
readily.  In  a  short  time,  however,  even  without  such  aid,  the  Bees  are  seen  to  dart  from 
a  considerable  height  in  the  air,  directly  down  to  their  proper  entrances;  showing  that 
they  have  learned  to  distinguish  these  by  a  memorial  power.  This  the  Author  has  ob- 
served most  remarkably,  in  a  case  in  which  a  hive  is  placed  in  the  drawing-room  of  a 
house,  the  entrance  to  it  being  beneath  one  of  the  windows;  the  adjoining  houses  have 
windows  precisely  similar,  except  in  the  absence  of  this  small  passage;  and  he  has  often 
noticed  that,  when  a  new  stock  has  been  placed  in  this  hive,  the  Bees  are  some  days  in 
learning  the  exact  position  of  their  house,  considerably  annoying  the  neighbours  by  flying 
in  at  their  windows. 
18 


206  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

ceding  section,  to  be  not  improbably  the  centres  of  the  instincts  and  emotions 
of  higher  animals. 

280.  On  comparing  Birds  with  Insects,  we  at  once  see  a  very  remarkable 
difference  in  the  character  of  their  actions.     Their  instinctive  tendencies  are 
of  nearly  the  same  kind;  and  the  usual  arts  which  they  exhibit  in  the  con- 
struction of  their  habitations,  in  procuring  their  food,  and  in  escaping  from 
danger,  must  be  regarded  as  intuitive,  on  account  of  the   uniformity  with 
which  they  are  practised  by  different  individuals  of  the  same  species,  and  the 
perfection  Vith  which  they  are  exercised  on  the  very  first  occasion.     But  in 
the  adaptation  of  their  operations  to  peculiar  circumstances,  Birds  display  a 
variety  and  fertility  of  resource  far  surpassing  that  which  is  manifested  by 
Insects ;  and  it  is  not  doubted,  by  those  who  have  attentively  observed  their 
habits,  that  in  such  adaptations  they  are  often  guided  by  real  intelligence. — 
This  must  be  the  case,  for  example,  when  they  make  trial  of  several  means, 
and  select  that  one  which  best  answers  the  purpose  ;   or  when  they  make  an 
obvious  improvement  from  year  to  year  in  the  comforts  of  their  dwelling ;  or 
when  they  are  influenced  in  the  choice  of  a  situation  by  peculiar  circumstances, 
which,  in  a  state  of  nature,  can  scarcely  be  supposed  to  affect  them.     The 
complete  domesticability  of  many  Birds  is  in  itself  a  proof  of  their  possessing 
a  certain  degree  of  intelligence ;  but  this  alone  does  not  indicate  the  possession 
of  more  than  a  very  low  amount  of  it ;    since  many  of  the  most  domesticable 
animals  are  of  the  humblest  intellectual  capacity,  and  seem  to  become  attached 
to  Ma*n,  principally  as  the  source  on  which  they  depend  for  the  supply  of 
their  animal  wants.     This  is  the  case  with  most  Herbivorous  quadrupeds,  and 
with  Rabbits,  Guinea-pigs,  &c.,  as  well  as  with  the  Gallinaceous  Birds.     The 
attachment  of  the  Dog  or  the  Elephant  is  evidently  of  a  much  higher  kind, 
and  involves  a  much  larger  number  of  considerations ;    and  their  actions  are 
evidently  the  result,  in  many  instances,  of  a  complex  train  of  reasoning,  differ- 
ing in  no  essential  respect  from  that  which  Man  would  perform  in  similar 
circumstances.      The  epithet, "  half-reasoning,"  commonly  applied  to  these 
animals,  does  not  express  the  whole  truth ;   for  their  mental  processes  are  of 
the  same  kind  with  those  of  Man,  and  differ  more  in  the  degree  of  control 
which  the  animal  possesses  over  them,  than  they  do  in  their  own  character. 
We  have  no  evidence  that  any  of  the  lower  animals  have  a  voluntary  power 
of  guiding,  restraining,  or  accelerating  their  mental  operations,  at  all  similar  to 
that  which  Man  possesses  ;  these  seem  to  be  of  very  much  the  same  character 
as  those  which  we  perform  in  our  dreams,  different  trains  of  thought  com- 
mencing as  they  are  suggested,  and  proceeding  according  to  the  usual  laws, 
until  some  other  disturb  them.     Although  it  is  customary  to  regard  the  Dog 
and  the  Elephant  as  the  most  intelligent  among  the  lower  animals,  it  is  not 
certain  that  we  do  so  with  justice ;   for  it  is  very  possible  that  we  are  misled 
by  that  peculiar  attachment  to  Man  which  in  them  must  be  termed  an  instinct, 
and  which  enters  as  a  motive  into  a  large  proportion  of  their  actions  ;  and  that, 
if  we  were  more  acquainted  with  the  psychical  characters  of  the  higher 
Gluadrumana,  we  should  find  in  them  a  greater  degree  of  mental  capability 
than  we  now  attribute  to  them.     One  thing  is  certain, — that,  the  higher  the 
degree  of  intelligence  which  we  find  characteristic  of  a  particular  race,  the 
greater  is  the  degree  of  variation  which  we  meet  with  in  the  characters  of 
individuals  ;   thus  every  one  knows  that  there  are  stupid  Dogs  and  clever 
Dogs,  ill-tempered  Dogs  and  good-tempered  Dogs, — as  there  are  stupid  Men 
and  clever  Men,  ill-tempered  Men  or  good-tempered  Men.     But  no  one  could 
distinguish  between  a  stupid  Bee  and  a  clever  Bee,  or  between  a  good-tem- 
pered Wasp  and  an  ill-tempered  Wasp,  simply  because  all  their  actions  are 
prompted  by  an  unvarying  instinct. 

281.  Before  inquiring  into  the  comparative  size  of  the  Cerebrum,  in  different 


FUNCTIONS  OF  THE  CEREBRUM.  207 

animals,  it  is  desirable  to  obtain  a  general  notion  of  its  structure.  Three 
principal  sets  of  fibres  may  be  distinguished  in  the  white  or  medullary  sub- 
stance, of  which  the  great  mass  of  it  is  composed.  These  are  the  Ascending 
fibres,  which  proceed  from  the  sensory  tract,  and  diverge  from  the  Thalami 
optici  to  the  periphery,  the  Descending  fibres,  which  converge  from  the  peri- 
phery towards  the  Corpora  Striata,  and  then  pass  downwards  into  the  motor 
tract ;  and  the  Commissural  fibres,  which  establish  the  connection  between 
the  various  parts  of  the  periphery  and  of  the  substance  of  the  brain. — 
It  is  on  the  very  large  proportion  which  the  commissural  fibres  bear  to 
the  rest,  that  the  bulk  of  the  brain  of  Man  and  of  the  higher  animals  chiefly 
depends ;  and  it  is  easy  to  conceive,  that  this  condition  has  an  important  rela- 
tion with  mental  operations,  whatever  be  our  view  of  the  functions  of  dif-* 
ferent  parts  of  the  Brain.  The  different  relative  distribution  of  the  gray 
and  white  matter  in  the  Cerebrum,  from  that  which  is  elsewhere  presented 
to  us  in  ganglionic  masses,  naturally  suggests  the  inquiry,  how  far  this  corre- 
sponds with  what  has  been  stated  of  their  probable  functions.  The  amount  of 
ordinary  vascular  action  in  the  gray  substance,  as  compared  with  that  which 
takes  place  in  the  white,  is  an  important  circumstance  in  favour  of  the  view, 
that  it  is  the  part  in  which  all  changes  originate,  and  that  the  fibrous  portion, 
like  the  trunk  of  the  nerve,  serves  only  to  conduct  or  transmit  the  influence 
of  those  changes.  This  position  derives  additional  support  from  the  effects  of 
disease.  It  has  been  frequently  remarked  that,  if  we  compare  those  cases  of 
cerebral  disease  in  which  there  is  delirium,  with  those  in  which  it  does  not 
occur,  we  shall  find  that  it  is  most  common  in  cases  in  which  there  is  an 
inflammatory  affection  of  the  surface,  or  of  the  membranes, — extending  from, 
them  into  it ;  whilst  in  deep-seated  inflammation,  the  most  important  symptoms 
are  those  which  result  from  sympathetic  affections  of  the  muscular  system. 
It  has  been  even  proposed  to  establish  a  diagnosis  between  inflammation  of  the 
membranes  (especially  of  the  arachnoid),  and  inflammation  of  the  substance  of 
the  brain,  upon  this  general  fact ;  but  it  is  to  be  remembered  that  (to  use  the 
words  of  Lallemand)  "  it  is  impossible  that  the  arachnoid  should  be  inflamed, 
without  the  surface  of  the  brain  in  contact  with  it  being  also  affected ;  but  its 
tissue  not  being  altered,  there  merely  results  from  this  vicinity  exaltation  in 
its  functions."  All  the  cases,  therefore,  which  have  been  referred  to  in  sup- 
port of  this  diagnosis,  really  tend  to  establish  the  proposition,  that  the  superficial 
portion  of  the  Cerebrum  is  the  part  really  affected.  It  is  absurd  to  suppose 
that  inflammation  of  the  membranes,  without  any  abnormal  condition  of  the 
Brain  itself,  can  seriously  affect  the  mental  operations. — It  has  been  further 
remarked,  that  arachnitis  of  the  convexity  of  the  Brain  is  more  frequently 
attended  with  delirium  and  other  symptoms  of  excitement  than  similar  in- 
flammation affecting  the  base,  in  which  coma  supervenes  earlier,  with  little  or 
no  previous  disturbance  of  the  intellect ;  this,  too,  corresponds  with  the  doc- 
trine just  referred  to ;  since  the  influence  of  any  effusion  aboirt  the  origins  of 
the  nerves  and  the  Medulla  Oblongata,  is  well  known  to  be  prejudicial  to  their 
functions  as  conductors,  even  entirely  suspending  them;  whilst, from  the  infe- 
rior vascularity  of  these  parts,  they  are  not  so  liable  to  manifest  symptoms  of 
excitement,  from  the  contiguity  of  an  inflamed  membrane.  In  fact,  inflamma- 
tion of  the  white  substance  of  the  Brain  is  itself  attended  rather  with  a  state 
of  torpor,  or  of  partial  suspension  of  its  usual  operations,  than  with  excitement ; 
irregular  convulsive  actions  are  not  unfrequently  seen  as  a  result  of  it ;  but 
these  are  often  manifested,  when  the  power  of  the  will  over  the  muscles,  is 
destroyed.  It  may  not  be  difficult  to  account  for  this  difference  of  symptoms, 
by  reflecting,  that  a  large  proportion  of  the  medullary  substance  of  the  Brain 
consists  of  a  sort  of  extremely  delicate  areolar  tissue,  by  which  the  fibres  are 
connected  together,  and  through  which  the  blood-vessels  are  distributed ;  and 
it  is  probably  in  this  that  the  principal  changes  take  place,  of  which  the  early 


308  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

stages  of  the  inflammatory  process  consist.  These  changes,  being  accompanied 
by  turgescence  of  the  vessels,  and  by  effusion  into  the.  tissue  surrounding 
them,  must  occasion  a  degree  of  pressure  on  the  enclosed  fibres,  which  de- 
stroys their  conducting  power,  and  thus  cuts  off  the  body  from  connection 
with  the  centre  of  the  intellectual  operations ;  whilst  they  may  at  the  same 
time  give  rise  to  many  irregular  and  involuntary  movements  of  the  muscles, 
to  which  the  fibres  thus  affected  are  distributed. 

282.  This  view  is  further  supported  by  the  researches  of  Foville,  on  the  alte- 
rations of  the  Brain  which  are  connected  with  insanity.     His  observations  are 
deserving  of  great  confidence,  both  for  the  sake  of  his  own  high  character  and 
attainments,  and  on  account  of  the  careful  manner  in  which  they  were  made. 
*To  avoid  trusting  to  his  memory  for  comparison,  Foville  has  been  in  the  habit 
of  examining  the  brain  of  a  person  who  died  without  any  disease  in  this 
organ,  at  the  same  time  with  that  of  one  who  died  insane.     In  acute  cases  of 
Insanity,  he  frequently  found  the  cineritious  portion  intensely  red,  but  without 
adhesion  to  the  membranes  ;  whilst  in  chronic  cases,  he  found  the  cortical 
substance  indurated  and  adherent  to  the  membranes.     In  nearly  all  cases  of 
Insanity  accompanied  with  general  Paralysis,  he  has  found  the  white  portion 
of  the  brain  injected  and  indurated  ;  and  he  conceives  that  the  fibres  had 
become  adherent  to  each  other.     It  has  been  supposed  by  Calmeil,  that  the 
paralysis  of  the  insane  is  connected  with  disease  of  the  cineritious  substance ; 
but  Foville  states  that  he  and  his  colleagues  have  made  many  hundreds  of 
observations  on  cases,  in  which  there  were  well-marked  alterations  of  the 
cortical  substance  of  the  brain,  without  any  other  manifestations  during  life 
than  disorder  of  the  intellect.     This  view  is  supported  by  Bouillaud,  and  by 
several  other  eminent  pathologists ;  as  is  also  the  other  part  of  the  proposition, 
— that  morbid  alterations  in  the  medullary  portion  are  connected  with  dis- 
order in  the  transmission  of  motor  impulses  to  the  muscles. 

283.  It  is  important  to  bear  in  mind  the  view  to  which  we  are  thus  con- 
ducted,— in  regard  to  the  relative  offices  of  the  gray  and  white  matter, — when 
forming  our  opinions  upon  the  functions  of  the  Cerebrum  in  general,  or  of  its 
several  parts,  from  the  various  data  supplied  to  us  by  Comparative  Anatomy, 
and  by  experimental  and  pathological  inquiry.     For  in  regard  to  the  first  of 
these  sources  it  is  to  be  remarked,  that  the  size  of  the  brain  does  not,  con- 
sidered alone,  afford  a  means  of  judgment  as  to  its  power.     The  quantity  of 
gray  matter  on  its  surface  should  rather  be  our  guide  ;  and  this  we  may  judge 
of,  not  only  by  the  depth  of  the  layer,  but  by  the  complexity  of  the  convolu- 
tions by  which  the  surface  is  extended.  *  In  no  class,  save  in  Mammalia,  do 
we  find  the  surface  marked  with  convolutions;  and  in  general  we  do  not  meet 
with  that  fissure  between  the  hemispheres  which  greatly  increases  the  extent 
of  surface.     In  forming  comparisons  as  to  the  connection  between  the  size  of 
the  Brain,  and  the  intelligence,  in  different  animals,  we  must  not  be  at  all 
guided  by  its  simple  proportional  dimensions  ;  since  it  is  very  evident,  that  it 
is  rather  the  proportion  of  the  bulk  of  the  brain  to  that  of  the  whole  body, 
upon  which  we  should  found  our  comparison.     But  even  this  is  not  alto- 
gether a  safe  guide;   and   many  Physiologists  have   endeavoured   to   com- 
pare the  size  of  the  brain  with  the  aggregate  bulk  of  the  nerves  proceeding 
from  it.     This  is  a  much  fairer  measure ;  but  it  cannot  be  taken  without  great 
difficulty.     For  all  practical  purposes,  the  comparison  of  the  bulk  of  the  Brain 
with  that  of  the  Spinal  Cord  will  probably  answer  very  well.     The  following 
table,  the  materials  of  which  are  drawn  from  M.  Serre's  Comparative  Anatomy 
of  the  Brain,  exhibits  the  three  diameters  of  the  Brain  of  a  number  of  different 
animals,  and  the  diameter  of  the  Spinal  Cord  at  the  second  cervical  vertebrae. 
The  last  three  columns  present  in  round  numbers,  the  three  diameters  of  the 
Brain,  reckoning  that  of  the  Spinal  Cord  as  1,  for  the  sake  of  easy  comparison. 


FUNCTIONS  OF  THE  CEREBRUM. 


209 


Diameter 
of  Spinal 
Cord. 

DIMENSIONS  OF  CEREBRUM. 

Proportional  Dimensions. 

AHt.-post. 

Transv. 

Vertical. 

Man  . 

1100 

17000 

7500 

9000 

l—i  5i 

1—  6f 

1—84 

Dolphin 
Mandril 

1000 
950 

9500 
8100 

5850 
3200 

8200 
4900 

1-9* 

1-4 

1—  3£ 

ilSl 

1—5 

Tiger 

1600 

9400 

4250 

6400 

1  52 

1  2f 

1—4 

Dromedary 

1900 

10500 

5050 

5800 

1  5* 

1  2f 

1—3 

Kangaroo 

1200 

5300 

2350 

3800 

l-4f 

1—2 

1-3* 

Vulture 

800 

3200 

2200 

1550 

1—4 

1—  2| 

1—2 

Falcon 

500 

1900 

1450 

1200 

1—  3| 

1—3 

1—  2f 

Swallow     . 

175 

1000 

600 

550 

1  —  5f 

—3* 

1-31 

Pie     . 

450 

2000 

1400 

1200 

1—  4| 

—3 

1—  2| 

Turkey 

500 

1750 

1250 

1200 

1—  3| 

2* 

Parroquet  . 

400 

2900 

1400 

1700 

1—  7* 

—  3* 

1—4! 

Tortoise      . 

300 

1600 

500 

1—  5| 

—  1* 

Crocodile    . 

300 

800 

500 

1—2* 

—  1* 

Viper 

200 

600 

300 

1—2 

—  li 

Frog  . 

300 

500 

400 

1-lf 

-i* 

Shark 

710 

2300 

IJOO 

1—  3s 

—l4 

Cod    . 

575 

725 

800 

1—1$ 

i| 

Lamprey    . 

275 

400 

300 

1—  li 

—  H 

Angler 

400 

400 

300 

1  —  1 

—if 

284.  As  might  be  expected,  the  Brain  of  Man  bears  by  far  the  highest 
proportion ;  but  this  proportion  is  not  so  large  in  the  transverse  and  vertical 
diameters,  as  in  the  antero-posterior ;  in  fact,  in  the  proportion  of  the  vertical 
diameter,  the  brain  of  Man  is  equaled  by  that  of  the  Dolphin,  and  nearly  so 
in  that  of  the  transverse  diameter.  In  the  complexity  of  the  convolutions, 
however,  and  in  the  thickness  of  the  gray  matter,  the  Cerebrum  of  Man  far 
surpasses  that  of  this  Cetaceous  animal.  In  these  respects  the  higher  Q,uad- 
rumana  present  the  nearest  approach  to  it ;  but  their  brain  is  much  inferior 
in  size.  In  descending  the  scale  of  Mammalia,  there  may  be  observed  a 
gradual  simplification  in  the  general  structure  of  the  Brain,  depending  upon 
a  great  diminution  in  the  amount  of  commissural  fibres ;  until  in  the  Marsu- 
pialia  the  Brain  presents  nearly  the  same  condition  which  it  offers  in  Birds 
(§  218).  These  animals  manifest  a  much  lower  degree  of  intelligence  than 
many  Birds  evidently  possess ;  and  it  is  interesting  to  remark,  that  their  cere- 
bral hemispheres  are  proportionably  smaller  than  those  which  we  find  in 
many  Birds  :  the  diminution  in  their  relative  size  not  being  counterbalanced 
(as  it  is  in  some  other  instances)  by  increased  complexity  of  structure.  In 
the  class  of  Birds  we  observe  that  the  Vulture  and  the  Falcon,  whose  preda- 
ceous  instincts  give  them  a  considerable  amount  of  general  energy,  are  much 
inferior  in  the  size  of  their  brains  to  the  Insessorial  Birds,  which  are  more 
intelligent ;  and  that  of  all,  there  is  none  in  which  the  brain  is  so  proportion- 
ally large,  as  it  is  in  the  Parrot  tribe,  the  educability  of  which  is  familiar  to 
every  one ;  whilst  the  easily  domesticable,  but  unintelligent  Turkey,  has  a 
brain  of  scarcely  half  the  proportional  size.  The'  very  small  size  of  the  Cere- 
brum in  Reptiles  and  Fishes,  completely  harmonizes  with  the  same  view ; 
these  animals  presenting  for  the  most  part  but  feeble  indications  of  intelli- 
gence. Among  Reptiles,  the  Tortoise  has  a  Cerebrum  comparable  in  length 

18* 


210  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

to  that  of  Birds  ;  but  its  breadth  and  depth  are  far  less.  The  largest  Cerebra 
among  Fishes  are  found  in  the  Shark  tribe;  the  superior  intelligence  of 
which  is  well  known  to  those  who  have  had  the  opportunity  of  observing 
their  habits ;  and  it  is  interesting  to  remark,  that  their  surface  occasionally 
presents  an  appearance  of  rudimentary  convolutions. 

285.  Comparative  Anatomy,  then,  fully  bears  out  the  general  doctrine, 
that  the  Cerebrum  constitutes  the  organ  of  Intelligence,  as  distinguished  from 
those  mere  Instincts  by  which  many  of  the  lower  animals  seem  to  be  almost 
entirely  guided.  By  Intelligence,  we  do  not  mean,  however,  the  reasoning 
faculties  only,  but  the  combination  of  those  powers  which  are  of  an  educable 
character,  and  which  become  the  springs  of  voluntary  action  in  very  different 
proportions  in  different  animals  of  the  same  tribe ; — as  distinguished  from 
those  which  have  an  immediate  relation  to  the  wants  of  the  corporeal  system, 
and  which  are  automatic  and  invariable  in  the  several  individuals  of  the  same 
species.  Observation  of  the  Human  species  exhibits  the  same  distinction. 
When  the  Brain  is  fully  developed,  it  offers  innumerable  diversities  of  form 
and  size,  among  various  individuals  ;  and  there  are  as  many  diversities  of  cha- 
racter. It  may  be  doubted  if  two  individuals  were  ever  exactly  alike  in  this 
respect.  That  a  Brain  which  is  greatly  under  the  average  size,  is  incapable 
of  performing  its  proper  functions,  and  that  the  possessor  of  it  must  neces- 
sarily be  more  or  less  idiotic,  there  can  be  no  reasonable  doubt.  On  the  other 
hand,  that  a  large  well-developed  Brain  is  found  to  exist  in  persons,  who 
have  made  themselves  conspicuous  in  thfc  world  by  their  attainments  or  their 
achievements,  may  be  stated  as  a  proposition  of  equal  generality.  In  these 
opposite  cases,  we  witness  most  distinctly  the  antagonism  between  the  in- 
stinctive and  voluntary  powers.  Those  unfortunate  beings,  in  whom  the  Brain 
is  but  little  developed,  are  guided  almost  solely  by  their  instinctive  tendencies, 
which  frequently  manifest  themselves  with  a  degree  of  strength  that  would 
not  have  been  supposed  to  exist :  and  occasionally  new  instincts  present 
themselves,  of  which  the  Human  being  is  ordinarily  regarded  as  destitute.* 
On  the  other  hand,  those  who  have  obtained  most  influence  over  the  under- 
standings of  others,  have  always  been  themselves  persons  of  strong  volitional 
powers  ;  in  whom  the  instinctive  tendencies  have  been  subordinate  to  the  wih1, 
and  who  have  given  their  whole  energy  to  the  particular  object  of  their  pur- 
suit. It  is  very  different,  however,  with  those  who  are  actuated  by  what  is 
ordinarily  termed  genius;  and  whose  influence  is  rather  upon  the  feelings 
than  upon  the  understandings,  of  those  around  them.  Such  persons  are  often 
very  deficient  in  the  power  of  even  comprehending  the  ordinary  affairs  of 
life  ;  and  still  more  commonly,  they  show  an  extreme  want  of  judgment  in 
the  management  of  them,  being  under  the  immediate  influence  of\their  pas- 
sions and  emotions,  and  not  having  brought  these  under  the  control  of  their 
intelligent  will.  The  life  of  a  genius,  whether  his  bent  be  towards  poetry, 
music,  painting,  or  pursuits  of  a  more  material  character,  is  seldom  one  which 
can  be  held  up  for  imitation.  In  such  persons,  the  general,  power  of  the 
mind  being  low,  the  Brain  is  not  usually  found  of  any  great  size.  The  mere 
comparative  size  of  the  Brain,  however,  affords  no  accurate  measure  of  the 
amount  of  mental  power ;  we  not  unfrequently  meet  with  men  possessing 
large  and  well-formed  heads,  whilst  their  capacity  is  not  greater  than  that  of 
others,  the  dimensions  of  whose  crania  have  the  same  general  proportion,  but 
are  of  much  less  absolute  size.  Large  brains,  with  deficient  activity,  are 

*  A  remarkable  instance  of  this  has  been  recently  published.  A  perfectly  idiotic  girl, 
in  Paris,  having  been  seduced  by  some  miscreant,  was  delivered  of  a  child  without 
assistance.  It  was  found  that  she  had  gnawed  the  umbilical  cord  in  two ;  in  the  same 
manner  as  is  practised  by  the  lower  animals.  It  is  scarcely  to  be  supposed  that  she  had 
any  idea  of  the  object  of  this  separation. 


FUNCTIONS  OF  THE  CEREBRUM.  211 

commonly  found  in  persons  of  what  has  been  termed  the  phlegmatic  tempera- 
ment, in  whom  the  general  processes  of  life  seem  in  a  torpid  and  indolent 
state  ;  whilst  small  brains  and  great  activity  betoken  what  are  known  as  the 
sanguine  and  nervous  temperaments.  These  distinctions  come  to  be  very 
important,  where  we  proceed  further  in  our  inquiries,  and  attempt  to  deter- 
mine the  particular  modes  of  development  of  the  Brain,  which  coincide  with 
certain  manifestations  of  the  mind. 

286.  Having  now  inquired  into  the  evidence  of  the  general  functions  of  the 
Cerebrum,  which  may  be  derived  from  examination  of  its  comparative  deve- 
lopment, we  proceed  to  our  other  sources  of  information — Experiment  and 
Pathological  phenomena.     The  effects  of  the  entire  removal  of  the  Hemi- 
spheres have  been  already  described  (§  264).     In  these  and  similar  experi- 
ments, it  has  been  constantly  remarked  that  injuries  of  the  Cerebral  substance 
do  not  occasion  signs  of  pain,  and  that  they  do  not  give  rise  to  any  convulsive 
movements.     Even  the  Thalami  and  Corpora  Striata  may  be  wounded,  with- 
out the  excitement  of  convulsions ;  but  if  the  incisions  involve  the  Tubercula 
Q,uadrigemina,  or  the  Medulla  Oblongata,  convulsions  uniformly  occur.     This 
result  perfectly  accords  with  what  has  been  observed  in  Man ;  for  it  has  been 
frequently  remarked,  when  it  has  been  necessary  to  separate  protruded  por- 
tions of  the  Brain  from  the  healthy  part,  that  it  has  given  rise  to  no  sensation, 
even  in  cases  in  which  the  mind  has  been  perfectly  clear  at  the  time.     The 
effect  of  pressure  upon  the  Brain  is  well  known  to  be  the  suspension  of  all  its 
operations :  this  has  been  substantiated  by  experiments  upon  animals,  and 
also  by  similar  experiments  on  persons  who  have  had  a  portion  of  th  *cranium 
removed,  so  as  to  expose  the  membranes  of  the  Brain.     The  pressure  of  the 
finger  upon  the  membranes  occasions  a  state  of  immediate  unconsciousness, 
resembling  profound  sleep,  which  ceases  as  soon  as  the  pressure  is  withdrawn. 
Such  pressure  will,  of  course,  affect  the  whole  Encephalon,  and  not  the  Cere- 
brum alone.     Experiment  does  not  throw  much  light  on  the  particular  func- 
tions of  the  Corpus  Callosum  and  other  Commissures;  since  they  can  scarcely 
be  divided  without  severe  general  injury.    It  would  appear,  however,  that  the 
partial  or  entire  absence  of  these  parts,  reducing  the  Cerebrum  to  the  level  of 
that  of  the  Marsupial  quadruped,  or  of  the  Bird,  is  by  no  means  an  unfre- 
quent  cause  of  idiocy. 

287.  The  information  afforded  by  Pathological  phenomena  is  far  from  being 
definite.     Many  instances  are  on  record,  in  which  extensive  disease  has  oc- 
curred in  one  Hemisphere,  so  as  almost  entirely  to  destroy  it,  without  either 
any  obvious  injury  to  the  mental  powers,  or  any  interruption  of  the  influence  of 
the  mind  upon  the  body.     But  there  is  no  case  on  record,  of  severe  lesion  of 
both  hemispheres,  in  which  morbid  phenomena  were  not  evident  during  life. 

,  It  is  true  that,  in  Chronic  Hydrocephalus,  a  very  remarkable  alteration  in  the 
condition  of  the  Brain  sometimes  presents  itself,  which  might  a  priori  have 
been  supposed  destructive  to  its  power  of  activity ;  the  ventricles  being  so 
enormously  distended  with  fluid,  that  the  cerebral  matter  has  seemed  like  a 
thin  lamina,  spread  over  the  interior  of  the  enlarged  cranium.  But  there  is 
no  proof  that  absolute  destruction  of  any  part  was  thus  occasioned;  and  it 
would  seem  that  the  very  gradual  nature  of  the  change  gives  to  the  structure 
time  for  accommodating  itself  to  it.  This,  in  fact,  is  to  be  noticed  in  all  dis- 
eases of  the  Encephalon.  A  sudden  lesion,  so  trifling  as  to  escape  observation, 
unless  this  be  very  carfully  conducted,  will  occasion  very  severe  symptoms  ; 
whilst  a  chronic  disease  may  gradually  extend  itself,  without  any  external 
manifestation.  It  will  usually  be  found  that  sudden  paralysis,  of  which  the 
seat  is  in  the  Brain,  results  from  some  slight  effusion  of  blood  in  the  substance 
or  neighbourhood  of  the  Corpora  Striata;  whilst,  if  it  follow  disorder  of  the 
Brain  of  long  standing,  a  much  greater  amount  of  lesion  will  usually  present 


212  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

itself.  In  either  case,  the  paralysis  occurs  in  the  opposite  side  of  the  body,  as 
we  should  expect  in  the  decussation  of  the  pyramids ;  but  it  may  occur  either 
in  the  same  or  on  the  opposite  side  of  the /ace — the  cause  of  which  is  not  very 
apparent.  If  convulsions  accompany  the  paralysis,  we  may  infer  that  the 
Corpora  Quadrigemina,  or  the  parts  below,  are  involved  in  the  injury ;  and, 
in  this  case,  it  is  usually  found  that  the  convulsions  are  on  the  paralyzed  side 
of  the  body— the  effect  of  the  lesion,  both  of  the  Cerebrum  and  of  the  Corpora 
Quadrigemina,  being  propagated  to  the  opposite  side  by  the  decussation  of  the 
pyramids.  Where,  as  not  unfrequently  happens,  there  is  paralysis  of  one 
side,  accompanying  convulsions  on  the  other,  it  is  commonly  the  result  of  a 
lesion  affecting  the  base  of  the  Brain  and  Medulla  Oblongata,  on  the  side  on 
which  the  convulsions  take  place.  Here  the  effect  of  the  lesion  has  to  cross 
from  the  Brain,  whilst  its  influence  on  the  Medulla  Oblongata  is  shown  on  the 
same  side.  Many  apparent  anomalies  present  themselves,  however,  which 
are  by  no  means  easy  of  explanation  in  the  present  state  of  our  knowledge. 

288.  The  general  result  of  such  investigations  is,  that  the  Cerebrum  is  the 
organ  through  which  all  those  impressions  are  received  which  give  rise  to 
Voluntary  actions ;  and  that  it  affords  the  power  of  occasioning  muscular 
contraction,  in  obedience  to  the  influence  of  the  will :  but  that  the  fibres  com- 
posing its  medullary  portion  are  not  susceptible  of  being  thrown  into  action 
by  mechanical  irritation,  in  the  same  manner  as  are  those  of  the  Spinal  Cord 
and  Nerves,  a  peculiarity  which  may,  perhaps,  be  connected  with  the  differ- 
ence of  their  structure,  formerly  explained  (§  110).     There  is  no  positive 
reason  for  the  belief,  that  the  Cerebrum  is  essential  to  the  purely  Emotional 
actions ;  and  analogy,  as  we  have  seen,  applied  to  the  explanation  of  patho- 
logical phenomena,  would  lead  to  the  belief  that  their  channel  is  different. 
It  can  scarcely  be  denied,  however,  that  in  the  Cerebrum  resides  that  power 
by  which  the  attention  of  the  mind  is  directed  to  any  sensation;  and  by 
which,  through  the  medium  of  a  brief  reasoning  process,  a  notion  is  formed 
regarding  its  nature  :  this  operation  is  altogether  designated  as  perception, — 
which  term,  however,  is  also  applied  to  its  result.     Now  it  will  be  presently 
seen,  that  the  formation  of  such  elementary  notions  in  us,  is  often  a  complex 
process,  though  a  rapid  one  ;  whilst,  in  many  of  the  lower  animals,  it  appears 
to  be  very  much  simpler, — as  to  all  those  points,  at  least,  which  concern  the 
instinctive  actions  necessary  for  their  well-being.     Such  intuitive  perceptions 
occasionally  take  place  in  ourselves  ;  but  it  will  probably  appear,  from  exami- 
nation of  them,  that  they  are  connected  either  with  the  mere  Instincts,  or  with 
the  Emotions. 

289.  Some  metaphysicians  have  confounded  Perception  with  Sensation ; 
but  the  difference  may  be  easily  made  evident.     In  order  that  a  sensation 
should  be  produced,  a  conscious  state  of  the  mind  is  all  that  is  required.     Its 
whole  attention  may  be  directed  towards  some  other  object,  and  the  sensation 
calls  up  no  new  ideas  whatever ;  yet  it  will  produce  some  change  in  the 
sensorium,  which  causes  it  to  be  (as  it  were)  registered  there  for  a  time,  and 
which  may  become  the  object  of  subsequent  attention ;  so  that,  when  the 
mind  is  directed  towards  it,  that  idea  or  notion  of  the  cause  of  the  sensation 
is  formed  which  constitutes  a  perception.     For  example,  a  student,  who  is 
directing  his  thoughts  to  some  object  of  earnest  pursuit,  does  not  receive  any 
intimation  of  the  passage  of  time  from  the  striking  of  a  clock  in  his  room. 
The  sensation  must  be  produced,  if  there  be  no  defect  in  his  nervous  system. ; 
but  it  is  not  attended  to,  because  the  mind  is  bent  upon  another  object.     It 
may  produce  so  little  impression  on  the  mind,  as  not  to  recur  spontaneously, 
when  the  train  of  thought  which  previously  occupied  the  mind  has  been 
closed,  leaving  the  attention  ready  to  be  directed  to  any  other  object ;  or,  the 
impression  having  been  stronger,  it  may 'so  recur,  and  at  once  excite  an  idea 


FUNCTIONS  OF  THE  CEREBRUM.  213 

in  the  mind.  Again,  the  individual  may  then  be  able  only  to  say,  that  ho 
heard  the  clock  strike  ;  or  he  may  be  able  to  retrace  the  number  of  strokes. 
Now,  in  either  case,  a  simple  perception  is  formed,  without  his  being  aware 
that  any  mental  operation  has  intervened.  He  would  say  that  he  remembers 
hearing  the  clock  strike  ;  but  this  would  not  express  the  truth.  That  which 
he  remembers  is  a  certain  series  of  sonorous  impressions,  which  was  commu- 
nicated to  his  mind ;  and  he  recognizes  them  as  the  striking  of  a  clock,  by  a 
process  in  which  memory  and  judgment  are  combined, — which  process  may 
further  inform  him,  that  the  sounds  proceeded  from  his  own  particular  clock. 
If  he  had  never  heard  a  clock  strike,  and  the  sound  produced  by  it  had  never 
been  described  to  him,  he  would  not  have  been  able  to  form  that  notion  of  the 
object  giving  rise  to  the  sensation,  which,  simple  as  it  appears  to  be  at  the 
time,  is  the  result  of  complex  mental  operations.  But  when  these  operations 
have  been  frequently  performed,  the  perception  or  notion  of  the  object  be- 
comes inseparably  connected  with  the  sensation  ;  and  thus  it  is  excited  by  the 
latter,  without  any  knowledge,  on  the  part  of  the  individual,  that  a  mental 
operation  has  taken  place.  Such  perceptions  are  termed  acquired,  in  contra- 
distinction to  the  intuitive  perceptions,  of  which  the  lower  animals  seem  to 
possess  a  large  number.  The  idea  of  the  distance  of  an  object,  for  example, 
is  one  derived  in  Man  from  many  sources,  and  is  the  result  of  a  long  experi- 
ence ;  the  infant,  or  the  adult  seeing  for  the  first  time,  has  to  bring  the  senses 
of  sight  and  of  touch  to  bear  upon  one  another,  in  order  to  obtain  it ;  but, 
when  once  the  power  of  determining  it  is  acquired,  the  steps  of  the  process 
are  lost  'sight  of.  In  the  lower  tribes  of  animals,  however,  in  which  the 
young  receive  no  assistance  from  their  parents,  there  is  an  evident  necessity 
for  some  immediate  power  of  forming  this  determination ;  since  they  would 
not  be  able  to  obtain  their  food  without  it.  Accordingly  they  manifest  in  their 
actions  a  perception  of  governing  idea  of  distances,  which  can  only  be  gained 
by  Man  after  long  experience.  A  Fly-catcher,  for  example,  just  come  out  of 
its  shell,  has  been  seen  to  peck  at  an  insect,  with  an  aim  as  perfect,  as  if  it 
had  been  all  its  life  engaged  in  learning  the  art  (§  341). 

290.  In  some  instances,  animals  learn  that,  by  intuitive  perception,  at  which 
Man  could  only  arrive  by  the  most  refined  processes  of  reasoning,  or  b£  the 
careful  application  of  the  most  varied  experience.  Thus,  a  little  fish,  named 
the  ChsRtodon  rostratus,  is  in  the  habit  of  ejecting  from  its  prolonged  snout, 
drops  of  fluid,  which  strike  insects  that  happen  to  be  near  the  surface  of  the 
water,  and  cause  them  to  fall  into  it,  so  as  to  come  within  its  own  reach. 
Now,  by  the  laws  of  refraction  of  light,  the  place  of  the  Insect  in  the  air  will 
not  really  be  that,  at  which  it  appears  to  the  Fish  in  the  water ;  but  it  will  be 
a  little  below  its  apparent  place,  and  to  this  point  the  aim  must  be  directed. 
But  the  difference  between  the  real  and  the  apparent  place  will  not  be  con- 
stant ;  for  the  more  perpendicularly  the  rays  enter  the  water,  the  less  will  be 
the  variation ;  and,  on  the  other  hand,  the  more  oblique  the  direction,  the 
greater  will  be  the  difference.  Now  it  is  impossible  to  imagine  but  that,  by 
an  intuitive  perception,  the  real  plac^of  the  Insect  is  known  to  the  Fish  in 
every  instance,  as  perfectly  as  it  could  be  to  the  most  sagacious  Human 
mathematician,  or  to  a  clever  marksman,  who  had  learned  the  requisite  allow- 
ance in  each  case  by  a  long  experience.  In  Man,  the  acquirement  of  per- 
ceptions is  clearly  a  cerebral  operation  ;  but  their  intuitional  formation  in  the 
lower  animals  is  probably  to  be  regarded  as  one  of  those  processes,  to  which 
the  ganglia  connected  with  the  organs  of  special  sense,  that  are  in  them  of  so 
great  a  proportional  size,  are  subservient.  The  same  may  be  said  of  many  of 
the  intuitive  perceptions  in  Man,  which,  if  analyzed,  are  found  to  be  con- 
nected rather  with  the  instinctive  and  emotional  tendencies  than  with  the 
intellectual  powers ; — the  perceptions  which  minister  to  the  exercise  of  these 


214  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

last,  being  the  result  of  experience.  Thus,  it  has  been  well  remarked  by  Dr. 
Alison,  that  the  changes  which  Emotions  occasion  in  the  countenance,  ges- 
tures, &c.,  of  one  individual,  are  instinctively  interpreted  by  others  ;  for  these 
signs  of  mental  affection  are  very  early  understood  by  young  children,  sooner 
than  any  associations  can  be  supposed  to  have  been  formed,  by  experience, 
of  their  connection  with  particular  modes  of  conduct ;  and  they  affect  us  more 
quickly  and  strongly,  and  with  nicer  varieties  of  feeling,  than  when  it  is 
attempted  to  convey  the  same  feelings  in  words,  which  are  signs  addressed  to 
the  intellect. 

291.  Many  Physiologists  and  Metaphysicians  are  of  opinion,  that  every 
sensation  actually  experienced  may  become  the  subject  of  a  perception  at  any 
future  time,  though  beyond  the  voluntary  power  of  the  memory  to  retrace  ; 
and  the  phenomena  of  dreams  and  delirium,  in  which  these  sensations  often 
recur  with  extraordinary  vividness,  afford  much   support  to  this    doctrine. 
Some  of  the  instances  upon  record  are  remarkable,  as  proving  that  the  sensa- 
tions may  be  thus  remembered,  without  any  perceptions  being  attached  to 
them ;  these  sensations  having  been  of  such  a  nature,  as  not  to  excite  any 
notion  or  idea  in  the  mind  of  the  individual.     A  very  extraordinary  case  of 
this  kind  has  been  recorded,  in  which  a  woman,  during  the  delirium  of  fever, 
continually  repeated  sentences  in  a  language  unknown  to  those  around  her, 
which  proved  to  be  Hebrew  and  Chaldaic ;  of  these  she  stated  herself,  on  her 
recovery,  to  be  perfectly  ignorant ;  but  on  tracing  her  former  history,  it  was 
found  that,  in  early  life,  she  had  lived  as  servant  with  a  clergyman,  who  had 
been  accustomed  to  walk  up  and  down  the  passage,  repeating  or  reading 
aloud  sentences  in  these  languages,  which  she  must  have  retained  in  her 
memory  unconsciously  to  herself.     Of  the  nature  of  the  change,  by  which 
sensations  are  thus  registered,  it  is  in  vain  to  speculate ;  and  it  does  not  seem 
likely  that  we  shall  ever  become  acquainted  with  it.     This  is  certain,  how- 
ever,— that  disease  or  injury  of  the  brain  will  destroy  this  power,  or  will  affect 
it  in  various  remarkable  modes.     We  not  unfrequently  meet  with  cases,  in 
which  the  brain  has  been  weakened  by  attacks  of  epilepsy  or  apoplexy,  in 
such  a  manner  as  to  prevent  the  reception  of  any  new  impressions  ;  so  that 
the  patient  does  not  remember  any  thing  that  passes  from  day  to  day ;  whilst 
the  impressions  of  events,  which  happened  long  before  the  commencement  of 
his  malady,  recur  with  greater  vividness  than  ever.     On  the  other  hand,  the 
memory  of  the  long-since-past  is  sometimes  entirely  destroyed ;  whilst  that  of 
events  which  have  happened  subsequently  to  the  malady  is  but  little  weakened. 
The  memory  of  particular  classes  of  ideas  is  frequently  destroyed ; — that  of  a 
certain  language,  or  some  branch  of  science,  for  example.     The  loss  of  the 
memory  of  words  is  another  very  curious  form  of  this  disorder,  which  is  not 
unfrequently  to  be  met  with  :  the  patient  understands  perfectly  well  what  is 
said,  but  is  not  able  to  reply  in  any  other  terms  than  yes  or  no, — not  from  any 
paralysis  of  the  muscles  of  articulation,  but  from  the  incapability  of  expressing 
the  ideas  in  language.     Sometimes  the  memory  of  a  particular  class  of  words 
only,  such  as  nouns  or  verbs,  is  destroyed  ;  or  it  may  be  impaired  merely,  fco 
that  the  patient  mistakes  the  proper  terms,  and  speaks  a  most  curious  jargon. 
These  cases  have  a  peculiar  interest,  in  reference  to  the  final  subject  of  our 
inquiry. 

292.  That  the  different  portions  of  the  Cerebrum  have  different  functions 
in  the  complex  operations  of  thought,  must  be  admitted  to  be  by  no  means  an 
improbable  speculation ;  and  it  is  well  known  that,  under  the  name  of  Phre- 
nology, or  the  Science  of  Mind,  a  systematic  allocation  has  been  made,  of 
what  have  been  regarded  as  the  several  fundamental  powers  and  faculties  of 
the   mind,  to   certain   parts  of  the  Cerebral  hemispheres.     This  was   first 
attempted  by  Gall,  who  stated  that  he  was  guided  in  his  determinations,  by 


FUNCTIONS  OF  THE  CEREBRUM.  215 

observing  on  the  heads  of  those  who  manifested  any  remarkable  faculty  or 
tendency,  a  corresponding  prominence  ;  and  to  have  found  confirmation  of  his 
inferences,  by  comparing  in  like  manner  the  skulls  of  the  lower  animals  with 
their  peculiar  powers  and  dispositions.  Both  these  branches  of  inquiry  have 
been  taken  up  by  numerous  observers  ;  and  a  large  amount  of  evidence  has 
been  adduced  by  them  in  support  of  Gall's  views,  which  appears  in  itself 
plausible,  and  which  is  regarded  by  many  physiologists  of  much  intelligence 
as  quite  decisive.  Nevertheless,  it  does  not  appear  that  the  doctrine  is  widely 
received  amongst  those  whose  peculiar  attention  to  the  Physiology  and  Patho- 
logy of  the  Nervous  System  gives  them  the  highest  authority  on  the  subject ; 
and  much  additional  proof  would  seem  to  be  requisite,  before  it  can  take  rank 
as  substantially  true.  It  may  be  freely  admitted  that  Mankind  is  in  the  habit 
of  forming  an  impression  of  an  individual's  intellectual  capacity,  by  the  height 
and  expansion  of  his  forehead ;  and  that  a  low  forehead  and  crown,  with  great 
development  of  the  occipital  portion  of  the  brain,  generally  accompany  a  cha- 
racter in  which  the  influence  of  the  animal  passions  is  predominant ;  and 
correspondences  even  more  detailed  may  be  admitted,  without  the  inference 
being  then  conclusive,  that  these  several  parts  are  the  distinct  organs  of  the 
several  faculties,  or  that  the  size  of  the  organ  is  a  measure  of  its  functional 
power.  It  may  be  thought  to  be,  in  regard  to  the  form  of  the  head,  very 
much  as  in  respect  to  the  character  of  the  face, — that  we  may  draw  from  it  a 
general  idea  as  to  the  character  of  the  mind,  and  may  not  unfrequently  be 
able  to  predicate  correctly  some  minute  details ;  and  yet  that  an  attempt  to 
localize  the  organs  more  minutely,  may  be  as  destitute  of  truth  as  were  the 
details  of  the  system  of  Lavater.  Moreover,  a  fundamental  doubt  hangs  over 
every  determination  of  function,  which  results  from  a  comparison  of  the  size 
of  the  supposed  organ  or  region  in  different  cases.  If  it  be  true  that  the  gray 
matter  only  is  the  source  of  power,  and  that  the  white  is  merely  a  conductor, 
we  have  no  right  to  assume  that  the  total  size  of  the  organ  affords  a  measure 
of  its  power,  until  it  has  been  shown  that  the  thickness  of  the  cortical  substance 
can  be  judged  of  by  the  size  of  the  Brain,  or  of  any  part  of  it.  Certainly 
there  is  a  considerable  variation  in  this  respect  among  different  individuals ; 
and  it  is  yet  to  be  proved  that  the  relation  is  constant  in  different  parts  of  the 
same  individual  Brain.  Until  this  is  substantiated,  all  inferences  drawn  from 
correspondence  between  the  prominence  of  a  certain  part  of  the  brain,  and  the 
intensity  of  a  particular  function,  are  invalid ;  that  is,  if  the  general  doctrine 
of  the  relative  functions  of  the  gray  and  white  matter  be  true.— Further,  there 
is  unfortunately  a  considerable  uncertainty  attending  all  Phrenological  obser- 
vations, which  are  made  upon  the  cranium,  rather  than  upon  the  brain ;  this 
we  have  seen  from  the  discrepancy  between  the  statements  of  Gall,  and  the 
facts  ascertained  regarding  the  comparative  weight  of  the  Cerebellum  in 
castrated  and  entire  horses.  It  appears  to  the  Author,  too,  that  Comparative 
anatomy  and  psychology  are  very  far  from  supporting  the  system,  when  their 
evidence  is  fairly  weighed.*  It  is  a  very  curious  circumstance,  that  the 
difference  in  the  antero-posterior  diameter,  between  the  brain  of  Man  and  that 
-  of  the  lower  Mammalia,  principally  arises  from  the  shortness  of  the  posterior 
lobes  in  the  latter,  these  being  seldom  long  enough  to  cover  the  Cerebellum ; 
yet  it  is  in  these  posterior  lobes  that  the  animal  propensities  are  regarded  by 

*  Much  is  said  by  Phrenologists  respecting  M.  Vimont's  examination  of  this  question, 
and  of  the  affirmative  decision  to  which  he  has  come;  but  they  are  not  so  ready  to  men- 
tion, that  M.  Leuret,  from  at  least  equally  extensive  observations,  has  arrived  at  an  oppo- 
site conclusion.  Of  these  two,  if  authority  is  to  decide  the  matter,  the  Author  would 
certainly  give  the  preference  to  M.  Leuret,  as  a  man  of  general  eminence,  and  one  who 
had  a  reputation  to  lose;  whilst  M.  Vimont  was  previously  unknown,  and  had  only 
brought  himself  into  notoriety  by  his  advocacy  of  Phrenology. 


216  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

phrenologists  as  having  their  seat.  On  the  other  hand,  the  anterior  lobes,  in 
which  the  intellectual  faculties  are  considered  as  residing,  bear,  in  many  ani- 
mals,' a  much  larger  proportion  to  the  whole  bulk  of  the  brain  than  they  do 
in  Man.  Again,  Comparative  Anatomy  and  Experiment  alike  sanction  the 
conclusion,  that  the  purely  Instinctive  propensities  have  not  their  seat  in  the 
Cerebrum.  These  examples,  and  many  similar  ones  that  might  easily  be 
added,  collectively  show  the  uncertainty,  to  say  the  least,  of  the  inferences 
which  are  by  many  regarded  as  firmly  established. 

293.  The  evidence  of  Pathology,  again,  tends  to  show  that  particular  dis- 
orders of  function  may  result  from  lesions  of  any  part  of  the  Cerebral  hemi- 
spheres.    This  has  been  especially  noticed,  for  example,  in  regard  to  the  loss 
of  the  Memory  of  Words,  which  Phrenologists  locate  in  the  organ  of  Lan- 
guage ;  there,  of  course,  the  lesion  might  be  expected,  on  their  system,  to 
present  itself;  but  this  is  by  no  means  constantly,  or  even  generally,  the  case. 
Phrenologists  lay  great  stress  on  the  effects  of  local  injury,  in  causing  loss 
of  memory  of  a  particular  subject;   but  this  principle,  if  carried  to  its  full 
extent,  would  require  us  to  regard  each  organ  as  split  up  into  a  large  number 
of  subdivisions — the  organ  of  language,  for  example,  having  one  store-house 
for  Latin,  another  for  Greek,  &c. ;  either  of  which  may  be  destroyed,  without 
the  other  being  affected.    A  very  important  source  of  evidence  is  that  afforded 
by  the  correspondence  between  the  several  kinds  of  Monomania,  and  the  forms 
of  the  brains  of  the  persons  exhibiting  them;  and  the  number  of  those  who, 
having  studied  this  question,  have  given  in  their  adhesion  to  the  phrenological 
system,  is  one  of  the  most  weighty  evidences  of  its  containing  much  truth. 
The  doubts  which  have  been  expressed  on  the  subject  would  have  much  less 
weight,  if  the  coincidence  of  Phrenological  determinations  of  character  with 
truth,  were  more  constant.     The  fairest  tests  of  these  are  to  be  found,  as  Dr. 
Holland  has  justly  remarked,  "  not  in  vague  and  ill-defined  moral  propensities, 
but  in  a  few  simple  and  well-marked  faculties,  such  as  those  of  numerical 
calculation,  language  or  music,  which  have  no  others  in  actual  opposition  to 
them,  and  the  degree  of  perfection  in  which  can  be  clearly  defined."     We 
hear  much  from  Phrenologists,  as  to  their  successful  application  of  these  tests ; 
but  we  do  not  hear  of  the  instances  of  failure.    The  Author's  own  experience 
of  their  determinations,  however,  has  certainly  led  him  to  the  belief  that  failure 
is  nearly  as  frequent  as  success.     Without  wishing  to  set  himself  up  as  an 
opponent  to  Phrenology,  he  perfectly  agrees  with  Dr.  Holland,  in  thinking 
that  an  impartial  view  of  it  requires,  "  not  that  the  doctrine  should  be  put 
aside  altogether,  but  that  great  abatement  should  be  made  of  its  pretensions  as 
a  system."     In  particular,  he  thinks  that  those  who  pursue  it  are  bound  to 
make  themselves  first  acquainted  with  what  dan  be  established  as  the  general 
functions  of  the  Brain,  before  descending  to  particulars. 

XXI.  General  Recapitulation  and  Pathological  Applications. 

294.  A  general  summary  of  the  views  here  propounded,  in  regard  to  the 
Functions  of  the'Cerebro-Spinal  division  of  the  Nervous  System,  may  proba- 
bly be  useful  in  assisting  the  Student  to  gain  clear  ideas  regarding  them. 
The  fibres  of  the  Nervous  trunks  may  be  divided,  according  to  the  direction 
o£  their  influence,  into  two  classes— the  afferent  or  centripetal — and  the  effe- 
rint  or  centrifugal.     The  afferent  may  be  said  td  commence  at  the  periphery, 
Specially  on  the  skin,  mucous  surfaces,  &c.,  and  to  terminate  in  the  gray 
matter  of  the  nervous  centres ;  whilst  the  efferent  originate  in  that  gray  matter, 
and  terminate  in  the  muscles.*     Every  fibre  runs  a  distinct  course  from  its 

*  The  terms  originate  and  terminate  cannot  be  used  with  strict  correctness ;  since,  as 


RECAPITULATION  AND  PATHOLOGICAL  APPLICATIONS.  217 

origin  to  its  termination ;  and  it  is  not  improbable  that  there  are  several  distinct 
endowment!  in  the  different  fibres  composing  each  trunk.  There  is  no  evi- 
dence that  the  fibrous  structure  serves  any  different  purpose  than  that  of  a 
mere  conductor;  and  there  seems  good  reason  to  believe  that  all  the  active 
operations,  of  which  the  nervous  system  is  the  instrument,  originate  in  the 
gray  matter.  A  mass  of  gray  matter,  connected  with  nervous  trunks,  forms 
a  ganglion.  In  the  Invertebrata,  the  ganglia  are  frequently  numerous,  and 
are  scattered  through  the  system,  without  much  connection  with  each  other—- 
each having  a  distinct  function.  In  Vertebrated  animals,  on  the  other  hand, 
they  are  united  into  one  mass — partly,  it  would  seem,  for  the  sake  of  the 
protection  afforded  them  by  the  bony  skeleton — and  partly  in  order  that  more 
complete  consentaneousness  of  action  may  be  attained.  Still,  several  distinct 
divisions  may  be  traced  in  the  centres  of  the  Cerebro-Spinal  System — partly 
by  the  determination  of  their  respective  functions,  as  indicated  by  observation 
and  experiment — and  partly  by  the  study  of  the  distribution  of  the  nerves 
proceeding  from  them.  In  this  manner  we  arrive  at  the  knowledge  of  several 
distinct  ganglionic  centres,  of  which  the  following  may  be  considered  as  a 
general  account. 

I.  The  true  Spinal  Cord,  consisting  of  a  nucleus  of  gray  matter,  receiving 
afferent  fibres,  and  giving  origin  to  efferent;  by  these  it  is  connected  with  all 
parts  of  the  body,  but  especially  with  the  surface  and  muscles  of  the  extremi- 
ties.    The  actions  of  this  centre  may  be  performed  without  consciousness  on 
the  part  of  the  individual;  and  they  consist  in  the  reflexion  of  a  motor  im- 
pulse along. an  efferent  nerve,  on  the  reception  of  a  stimulus  conveyed  by  an 
afferent  or  excitor  nerve.     These  reflex  movements  can  be  best  excited  when 
the  muscles  are  removed  from  the  control  of  the  Will,  which  otherwise  gene- 
rally antagonizes  them.     Some  of  them  are  connected  with  the  maintenance 
of  the  organic  functions ;  and  others  with  the  protection  or  withdrawal  of  the 
body  from  injury.     Muscular  movements  may  also  be  excited,  by  a  stimulus 
directly  applied  to  the  Spinal  Cord  itself  (§  157 — 212). 

II.  The  Medulla  Oblongata,  or  cranial  prolongation  of  the  Spinal  Cord.  The 
actions  of  this  do  not  essentially  differ  from  those  of  the  true  Spinal  Cord;  but 
they  are  connected  with  different  organs.     This  part  consists  chiefly  of  the 
centres  of  the  nerves  of  Respiration  and  Deglutition — two  functions,  of  which 
the  continual  maintenance  is  essential  to  the  life  of  the  being;  and  it  would 
seem  as  if  these  were  placed  within  the  cranium,  to  be  more  secured  from 
accidental  injury.     The  movements  concerned  in  Respiration  and  Deglutition 
are,  like  those  excited  through  the  true  Spinal  Cord,  of  a  strictly  reflex  cha- 
racter, oeing,  in  all  instances,  due  to  an  impression,  or  stimulus,  originating 
in  the  periphery  of  the  system,  which,  being  conveyed  to  the  centre,  excites 
there  a  motor  impulse ;  and  they,  also,  are  independent  of  Sensation  (§  184 — 
194). 

III.  The  ganglia  of  the  nerves  of  Special  Sensation,  which  form,  as  it 
were^  the  continuation  of  the  Medulla  Oblongata.     These,  also,  appear  to 
minister  to  actions,  which  do  not  differ  widely  from  the  Reflex  in  character — 
being  almost  necessarily  excited  by  certain  stimuli,  and  being  only  in  a  degree 
controllable  by  the  will.  But  their  actions  differ  in  this,  that  they  are  attended 
with  consciousness,  and  also,  it  would  appear,  with  certain  peculiar  feelings.' 
Reasons  have  been  given  for  the  belief  that  these  ganglia  are  the  centres  of 
those  actions  which  are  commonly  termed  instinctive  in  the  lower  animals, 
and  consensual  and  emotional  in  ourselves.     These  all  correspond  in  being 

formerly  explained  (§  112),  there  is  probably  never  an  actual  termination  of  nervous 
fibres,  either  in  the  muscles  or  in  gray  matter;  but  they  cease  to  run  in  their  previous 
direction,  after  forming  their  terminal  loops;  and  their  course,  as  afferent  or  efferen, 
fibres,  may  consequently  be  said  to  begin  or  to  end  at  these  points, 
19 


218  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

performed  without  any  idea  of  a  purpose,  and  without  any  direction  of  the 
will,  being  frequently  in  opposition  to  it  (258 — 265). 

IV.  The  Cerebral  Hemispheres,  or  Ganglia,  which  are  evidently  the  instru- 
ments or  organs  of  the  intellectual  faculties.     These  are  connected  by  fibres 
of  communication  with  almost  all  parts  of  the  body ;  and  from  their  propor- 
tional size  in  Man,  it  seems  probable  that  many  of  the  nervous  trunks  are 
principally  composed  of  such  fibres.     It  is  probably  by  them  alone  that  ideas 
or  notions  of  surrounding  objects  are  acquired,  and  that  these  ideas  are  made 
the  groundwork  of  mental  operations.     They  would  seem,  also,  to  be   the 
exclusive  seat  of  Memory.     The  results  of  these  operations  are  manifested  on 
the  bodily  frame,  through  the  Will,  which  is  capable  of  acting,  in  greater  or 
less  degree,  on  all  the  muscles  forming  part  of  the  system  of  Animal  life 
(279—292). 

V.  The  Cerebellum,  which  appears  to  be  concerned  in  the  regulation  and 
harmonization  of  Muscular  movement,  whether  instinctive  or  voluntary  (§  266 
—278). 

Tabular  View  of  the  Nervous  Centres. 

Cerebral  Ganglia, 

the  centres  of  the  operations 

of  Intelligence  and  Will. 

Nerves  of  Special  sensa-^i          Ganglia  of  Snerial  SPHSP  fNerves  of  Special  sensa- 

tion.-Motor  fibres  min-  (  \**>          I  tion.-Motor  fibres  min- 


.  ^-        the  centres  of  Consensual,        -^     ,    ,      ., 
"   5tinctive,and  Emotional  actions.  !  f  tgjem 

Cerebellic  Ganglia, 

for  harmonization  of  general 

muscular  actions. 


Afferent  and  Motor  Nerves  J  Respiratory  I  Afferent  and  Motor  Nerves 

of  Respiration,  Deglutition,  >          and  stomato-gastric          2  of  Respiration,  Deglutition, 
&c.  >  Ganglia.  f  &c. 


Trunks  of  Spinal  nerves,  composed""!  o  g  £  ^  0  f  Trunks  of  Spinal  nerves,  composed 
of  fibres  from  true  Spinal  Cord,  and  |  c  o  ^  g  g  |  of  fibres  from  true  Spinal  Cord,  and 
from  Cerebrum,  Cerebellum,  and  I  £  T?;=  '&  *s  \  from  Cerebrum,  Cerebellum,  and 
Medulla  Oblongata;  each  group  f§  £  cc  §  g  ]  Medulla  Oblongata;  each  group 
containing  afferent  and  efferent  $^  §>~  «T  containing  afferent  and  efferent 
fibres.  J  5  S'oJ  =  U 


295.  The  distinctness  of  the  operations  of  these  several  centres  is  shown  in 
various  ways :  but  especially  by  conditions  of  the  bodily  system,  in  which 
one  or  more  of  them  is  in  a  state  of  inaction,  whether  temporary  or  perma- 
nent ;  or  is  prevented,  by  the  interruption  of  the  usual  channel  of  communi- 
cation, from  operating  on  particular  parts.  Thus,  in  ordinary  profound  Sleep, 
which  is  a  state  of  complete  unconsciousness,  it  is  evident  that  the  Cerebral 
Hemispheres,  and  the  Ganglia  of  Special  Sense,  are  at  rest ;  as  the  Cerebel- 


RECAPITULATION  AND  PATHOLOGICAL  APPLICATIONS.  219 

Jum,  also,  may  be  considered  to  be  :  but  the  Medulla  Oblongata  and  Spinal 
Cord  must  be  in  complete  functional  activity.  The  same  is  the  case  in  pro- 
found Coma,  resulting  from  effusion  of  blood,  or  from  narcotic  poisons,  but  not 
affecting  the  j)ower  of  breathing  or  swallowing.  It  may  be  frequently  ob- 
served, that  the  sleep  is  not  so  profound  as  entirely  to  suspend  the  conscious- 
ness of  the  individual ;  and  that  various  movements  of  an  adaptive  character 
are  performed,  tending  to  relieve  uneasiness  resulting  from  various  causes. 
In  this  condition  it  seems  not  improbable,  that  the  sensory  ganglia  are  in  some 
degree  awake,  and  that  the  movements  are  of  an  instinctive  nature ; — the 
mind  of  the  individual  not  being  sufficiently  active  to  discern  the  cause  of  the 
uneasiness,  or  to  employ  his  intelligence  in  the  removal  of  it.  Whenever 
Dreaming  takes  place,  it  is  evident  that  the  Cerebrum  is  in  a  state  of  partial 
activity.  The  state  of  Dreaming,  and  many  forms  of  Insanity,  have  consider- 
able analogy  with  each  other ;  especially  in  the  absence  of  the  power,  which 
is  so  characteristic  of  the  well-regulated  mind  of  Man,  of  controlling  and  regu- 
lating the  current  of  thought.  One  idea  calls  up  another,  according  to  their 
previous  associations  ;  and  the  most  incongruous  combinations  are  frequently 
the  result ;  but  it  will  generally,  if  not  always,  be  found,  that  the  ideas  them- 
selves have  been  previously  in  the  mind,  and  that  no  entirely  new  train  of 
thought  is  started.  Of  the  degree  in  which,  when  the  mind  is  thus  closed  to 
the  external  world,  the  hidden  stores  of  Memory  are  opened  to  its  search, 
many  very  curious  instances  are  recorded. 

296.  The  state  of  Somnambulism  appears  to  be  nearer  to  that  of  wakeful 
activity  of  the  whole  mind,  than  is  that  of  Dreaming.  In  the  latter  condition, 
the  individual  is  unconscious  of  external  objects  ;  for,  if  they  produce  an  effect 
upon  him,  it  is  in  modifying  the  current  of  ideas,  frequently  in  some  very 
ludicrous  manner :  and  he  does  not  form  any  true  perception  or  idea  of  their 
nature.  But  in  Somnambulism,  his  senses  are  partly  awake,  so  that  impres- 
sions made  upon  them  may  be  properly  represented  to  the  mind,  and  excite 
there  the  ideas  with  which  they  are  connected ;  moreover,  the  Cerebellum  is 
also  awake,  so  that  the  movements  which  the  individual  performs  are  per- 
fectly adapted  to  their  object ;  indeed  it  has  frequently  occurred,  that  the 
power  of  balancing  the  body  has  been  so  remarkably  exercised  in  this  condi- 
tion, that  sleep-walkers  have  traversed  narrow  and  difficult  paths,  over  which 
they  could  not  have  passed  in  open  day,  when  conscious  of  their  danger.  In 
^Somnambulism,  as  in  Dreaming,  there  is  an  evident  want  of  voluntary  control 
over  the  thoughts  ;  their  succession  is  more  influenced,  however,  by  impres- 
sions received  from  without,  than  it  is  in  dreaming ;  and  hence  the  mind  may 
sometimes  be  easily  guided  into  a  particular  train,  by  properly  directing  the 
impressions  made  upon  the  sensory  organs.  It  may  be  remarked,  however, 
that  impressions  which  do  not  in  some  degree  harmonize  with  the  train  of 
ideas,  are  not  received  by  the  mind ;  or,  at  any  rate,  they  are  not  applied  to 
the  correction  of  the  erroneous  notions  which  possess  it.  But  there  are  many 
different  shades  in  the  condition  of  the  mind,  between  Dreaming  and  Som- 
nambulism, the  individual  being,  in  some  cases,  much  less  conscious  of  ex- 
ternal objects  than  he  is  in  others.  In  some  instances  it  appears  as  if  the 
mind  was  so  wholly  engrossed  in  a  particular  train  of  thought,  that  it  could 
not  be  affected  by  any  new  sensations,  so  that  there  is  even  an  unconscious- 
ness of  those  which  produce  pain ;  this  has  its  parallel  in  the  waking  state. 
A  very  remarkable  characteristic  of  the  state  of  Somnambulism,  is  the  com- 
plete isolation  which  commonly  exists  between  the  trains  of  thought  which 
then  occupy  the  mind  and  its  operations  during  the  waking  hours ;  so  that 
in  neither  state  is  there  a  remembrance  of  what  passes  in  the  other.  There 
is  usually  this  difference,  however ; — that  the  mental  operations  which  take 
place  in  Somnambulism  are,  like  those  of  dreaming,  frequently  suggested  by 


220  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

what  has  previously  been  occupying  the  mind  ;  whilst  these  seem  to  leave  no 
impression  to  be  retraced  in  the  waking  state,  though  all  that  passes  in  one 
fit  of  Somnambulism  may  be  recollected  in  the  next.  This  has  been  most 
remarkably  observed  in  the  phenomena  of  that  curious  state  ^jjjiich  is  known 
under  the  name  of  Double  Consciousness  ;*  in  this,  the  form  of  Somnambulism 
in  which  there  is  a  consciousness  of  external  impressions,  seems  to  alternate 
with  the  condition  of  ordinary  mental  activity,  and  the  individual  leads  (as  it 
were)  two  distinct  lives,  recollecting  in  each  condition  what  happened  in 
previous  states  of  the  same  character,  but  knowing  nothing  of  the  occurrences 
of  the  other.t 

297.  We  have  thus  witnessed  several  varieties  in  the  condition  of  the  bodily 
system,  depending  upon  partial  or  complete  suspension  of  the  functional  activity 
of  the  Cerebrum,  Cerebellum,  and  Sensory  ganglia.     There  is  no  normal  con- 
dition of  the  Spinal  system,  which  at  all  corresponds  with  these  ;    since  its 
operations  are  so  closely  connected  with   the  maintenance  of  the  organic 
functions,  that  the  suspension  of  them  necessarily  induces  the  cessation  of  the 
latter.     This  is  especially  the  case,  however,  in  regard  to  the  Respiratory 
ganglion  ;  for  the  whole  remainder  of  the  Spinal  Cord  maybe  removed,  with- 
out the  interruption  of  the  movements  which  are  dependent  on  that  segment 
of  it.     Cases  have  occurred,  however,  in  which  the  natural  performance  even 
of  these  has  been  partially  or  entirely  suspended ;  and  in  which  the  main- 
tenance of  life  has  for  a  time  been  effected,  by  a  voluntary  exertion  of  the 
muscles  of  Respiration.     The  influence  of  the  Will  upon  the  general  motor 
apparatus  of  Man,  seems  to  predominate  so  greatly  over  the  Reflex  action  of 
the  Spinal  Cord,  that  few  phenomena  which  are  attributable  to  the  latter 
ordinarily  present  themselves ;   these  are  manifested,  however,  when  the  in- 
fluence of  the  Brain  over  any  part  is  cut  ofl^  as  is  seen  in  certain  cases  of 
paralysis.     These  morbid  conditions  present  us,  also,  with  illustrations  of  other 
effects  of  the  interruption  of  the  communication  between  the  nervous  centres 
and  particular  sets  of  muscles.     Thus,  the  influence  of  the  Will  may  be  cut 
off,  although  that  of  the  Instincts,  Emotions,  and  Reflex  Function  may  remain ; 
or  the  respondence  of  the  muscles  to  Emotion  may  be  prevented,  whilst  they 
are  still  capable  of  Voluntary  control,  or  of  Reflex  action.     Such  cases  seem 
to  point  very  clearly  to  three  distinct  primary  centres  of  nervous  agency  ; — 
and  to  these,  the  Cerebrum,  Sensory  Ganglia,  and  Spinal  Cord  (including  the 
Medulla  Oblongata)  have  been  here  assigned  as  the  instruments.     We  shall 
next  inquire  into  some  other  morbid  conditions  of  the  system,  which  seem  due 
to  the  irregular  action  of  these  ;  and  in  this  we  shall  be  chiefly  guided  by  the 
researches  of  Dr.  M.  Hall,  which  have  been  already  slightly  glanced  at  (§'211, 

298.  Of  the  Convulsive  diseases,  it  appears  that  the  greater  part,  if  not  the 
whole,  may  be  attributed  to  a  morbid  state  of  the  Spinal  System  of  nerves. — 
So  completely  does  the  power  of  producing  convulsive  movements  appear 
limited  to  that  and  to  the  Emotional  system,  (no  mechanical  irritation  of  the 
Cerebral  substance  being  effectual  in  exciting  such  movements,  §  286)  that, 

*  Much  interesting  information  on  this  and  other  subjects  alluded  to  in  this  section 
may  be  found  in  Dr.  Abercrombie's  Treatise  on  the  Intellectual  Functions. 

f  In  regard  to  the  curious  phenomena  which  are  produced  by  the  so-called  Mesmeric 
influence,  the,  author  prefers  not  offering,  for  the  present,  any  decided  opinion."  He  has 
seen  enough  to  satisfy  him  that  they  are  deserving  of  investigation  ;  and  to  the  inquiry 
into  their  true  character  and  causes,  he  purposes  to  devote  himself  as  opportunity  may 
serve.  But  there  are  so  many  sources  of  fallacy  in  the  mode  in  which  such  inquiries 
have  been  usually  conducted,  that  he  cannot  satisfy  himself  by  relying  on  the  testimony 
of  others,  however  elevated  their  characters  may  be  above  the  mere  suspicion  of 
deception,  and  however  firmly  he  might  resf  upon  their  evidence,  in  regard  to  subjects 
of  a  less  complex  nature. 


RECAPITULATION  AND  PATHOLOGICAL  APPLICATIONS.  221 

where  convulsions  present  themselves  during  diseases  which  appear  limited 
to  the  Brain,  we  may  infer  that  one  of  these  systems  is  involved.  Dr.  M. 
Hall  has  recently  pointed  out,  that  this  complication  is  due  to  the  impressions 
made  upon  the  fibres  of  the  Spinal  nerves  distributed  upon  the  Dura  Mater, 
and  other  serious  and  fibrous  membranes ;  for  convulsive  actions  may  be  in- 
duced by  pinching  these  membranes,  or  otherwise  irritating  them.  Of  the 
distinct  forms  or  combinations,  of  which  the  class  of  convulsive  disorders  is 
composed,  Tetanus  is  one  of  the  most  interesting  and  instructive.  This  disease 
is  evidently  dependent  upon  a  state  of  undue  excitability  of  the  whole  Spinal 
System ;  and  this  may  be  produced  by  different  causes.  That  which  is 
termed  the  idiopathic  form  of  the  disease  has  its  origin  in  the  centres ;  it  may 
result  in  Man  from  the  operation  of  various  predisposing  and  exciting  causes  ; 
and  may  be  artificially  induced  in  Animals  by  the  administration  of  Strychnia. 
In  the  traumatic  form  of  the  disease,  the  morbid  state  has  its  origin  in  a  local 
injury;  and  the  irritation  propagated  from  this,  and  operating  through  the 
Spinal  Cord,  may  be  itself  a  cause  of  many  of  the  convulsive  movements. 
But,  when  the  irritable  state  is  once  established  in  the  nervous  centres,  con- 
vulsive action  of  the  muscles  may  be  excited  by  any  stimuli,  and  even  almost 
entirely  without  external  causes.  Hence  it  is  that,  whilst  the  amputation  of 
the  injured  part  is  not  unfrequently  the  means  of  saving  the  patient,  if  per- 
formed sufficiently  early,  it  is  attended  with  no  benefit  if  delayed.  The 
Cerebral  apparatus  is  entirely  unaffected  in  this  disorder ;  but  the  nerves  of 
deglutition  are  usually  those  first  influenced  by  it ;  those  of  respiration,  how- 
ever, being  soon  affected,  as  also  those  of  the  trunk  in  general.  The  condition 
termed  Hydrophobia  is  nearly  allied  to  that  of  traumatic  Tetanus,  differing 
chiefly  in  the  mode  in  which  the  cerebro-spinal  axis  is  affected.  The  irritable 
state  of  the  nervous  centres  results  from  a  local  injury  of  a  peculiar  kind;  and 
here,  too,  the  early  removal  of  the  part  is  very  desirable  as  a  means  of  pre- 
vention ;  although,  when  the  malady  has  once  reached  the  centres,  it  is  of  no 
use.  The  muscles  of  respiration  and  deglutition  are,  as  in  Tetanus,  those 
spasmodically  affected  in  the  first  instance  ;  but  there  is  this  curious  difference- 
in  the  mode  in  which  they  are  excited  to  action, — that,  whilst  in  Tetanus  the 
stimulus  operates  through  the  true  Spinal  Cord  (either  centrally,  or  by  being 
conveyed  from  the  periphery),  in  Hydrophobia  it  is  often  conducted  from  the 
ganglia  of  special  sense,  or  even  from  the  brain ;  so  that  the  sight  or  sound  of 
fluids,  or  even  the  idea  of  them,  occasions — equally  with  their  contact,  or  with 
that  of  a  current  of  air — the  most  distressing  convulsions.  It  would  seem 
therefore,  as  if  the  Emotional  system  of  nerves  was  involved  in  it. 

299.  Epilepsy  is  another  convulsive  disease,  principally  involving  the  Spinal 
Cord,  but  partly  affecting  the  Brain.  The  predisposition  to  convulsive  move- 
ments may  depend  upon  many  causes  ;  but  the  movements  themselves  are  in 
general  immediately  excited  by  some  local  irritation,  as  by  the  presence  of  undi- 
gested matter  in  the  stomach,  of  worms  in  the  intestines,  &c.,  although  fre- 
quently also  from  causes  purely  mental.  The  convulsive  movements  usually 
affect  the  muscular  system  very  extensively  ;  acting  especially  upon  the  mus- 
cles of  ingestion  and  egestion.  The  Brain  is  evidently  much  concerned  in  the 
disease,  however;  as  is  evident  from  the  numerous  instances  in  which  it  has 
been  clearly  traced  to  some  local  affection  of  that  organ,  as  well  as  from  the 
loss  of  consciousness  which  accompanies  the  convulsion.  Many  forms  of  that 
protean-  malady,  Hysteria,  are  attended  with  a  similar  irritability  of  the  Ner- 
vous Centres  ;  but  there  is  this  remarkable  difference  in  the  two  cases, — that 
the  morbid  phenomena  of  Hysteria,  whilst  they  often  simulate  those  of  Teta- 
nus, Hydrophobia,  Epilepsy,  &c.,  are  evidently  dependent  upon  a  state  of  the 
system  of  -a  much  less  abnormal  character,  being  relieved  by  very  mild  reme- 
dies, and  being  often  capable  of  prevention  by  a  strong  effort  of  the  will.  Dr. 

19* 


222  FUNCTIONS  OF  THE  NERVOUS  SYSTEM. 

Hall  has  pointed  out  an  important  distinction  between  Epilepsy  and  Hysteria, 
which  materially  influences  the  proximate  danger  of  the  paroxysm  of  each 
respectively;  in  the  former,  the  larynx  is  convulsively  closed  and  partial 
asphyxia  is  the  necessary  result,  if  the  access  of  air  be  too  long  prevented,  so 
that  venous  congestion  ensues,  increasing  the  disorder  of  the  nervous  centres 
even  to  a  fatal  degree ;  in  Hysteria,  on  the  contrary,  much  as  the  larynx  is 
affected,  it  is  not  usually  closed.  Cases  sometimes  present  themselves,  how- 
ever, in  which  the  Hysteric  paroxysm  assumes  the  Epileptic  character,  the 
larynx  being  closed  during  expiration,  so  as  to  produce  alarming  results. 

300.  The  foregoing  are  the  chief  general  spasmodic  diseases  in  which  the 
Spinal  system  of  nerves  is  evidently  involved  ;*  but  there  are  many  others  of 
a  more  local  character.  Such  are  the  various  forms  of  Spasmodic  Asthma,  the 
attacks  of  which  generally  result  from  some  internal  irritation,  either  in  the 
lungs  themselves  or  in  the  digestive  system,  producing  a  reflex  action  upon  the 
muscular  fibres  of  the  bronchial  tubes.  The  Croup-like  Convulsion,  or  Crow- 
ing Inspiration  of  Infants,  again,  is  an  obstruction  to  the  passage  of  the  air 
through  the  glottis,  by  a  spasmodic  contraction  of  the  constrictors  of  the  larynx. 
This  spasmodic  action  may  be  induced  by  various  kinds  of  irritation  ;  such  as 
that  occasioned  by  teething,  by  the  presence  of  undigested  food,  or  by  intestinal 
disorder.  In  the  crowing  inspiration,  the  larynx  is  partially  closed ;  when  the 
spasm  is  severe,  however,  there  is  complete  occlusion  of  the  passage ;  and 
forcible  efforts  at  expiration  are  made,  which  induce,  as  in  epilepsy,  a  severe 
degree  of  venous  congestion,  and  this  reacts  upon  the  nervous  centres,  aggra- 
vating the  previous  disorder  of  their  condition.  The  present  increased  know- 
ledge of  the  functions  of  the  laryngeal  nerves,  and  of  the  symptoms  of  this 
disease,  appears  to  render  inadmissible  the  explanation  of  it  given  not  long 
since  by  Dr.  H.  Ley,  who  attributed  it  to  paralysis  of  the  pneumogastric  nerves 
occasioned  by  pressure.  Spasmodic  closure  of  the  larynx  may  occur  from 
other  causes.  When  the  rima-glottidis  is  narrowed,  by  effusion  of  fluid  into 
the  substance  of  its  walls,  it  is  very  liable  to  be  completely  closed  by  spas- 
modic action,  to  which  the  unduly  irritable  condition  of  the  mucous  membrane 
will  furnish  many  sources  of  excitement.  Choking,  again,  does  not  result  so 
much  from  the  pressure  of  the  Food  on  the  air-passages  themselves,  as  from  the 
spasmodic  action  of  the  larynx,  excited  by  this ;  and  the  dislodgment  of  the 
morsel  by  an  act  of  vomiting  is  the  most  effectual  means  of  obtaining  relief. 
Tenesmus  and  Strangury  are  well-known  forms  of  spasmodic  muscular  con- 
traction, excited  by  local  irritation  acting  through  the  Spinal  system.  The 
abnormal  action  which  leads  to  Abortion  is  frequently  excited  in  the  same 
manner  ;  how  far  the  uterus  itself  is  called  into  contraction  by  the  ordinary 
spinal  nerves,  is  a  question  as  yet  undecided  ;  but  the  facts  already  stated  leave 
no  doubt,  that  stimuli  operating  on  these  may  act  upon  it  through  the  Sympa- 
thetic, into  which  their  fibres  pass  (§  203).  It  will  be  borne  in  mind,  how- 
ever, that,  in  abortion,  as  in  ordinary  parturition,  many  muscles  are  called  in, 

*  Chorea  is  ranked  by  Dr.  M.  Hall  as  a  disease  of  the  Spinal  System  of  nerves;  but 
this  can  scarcely  be  regarded  as  a  correct  determination.  It  is  true  that  there  is  consi- 
derable irregularity  in  the  ordinary  Reflex  actions;  but  the  irregularity  is  still  greater  in 
those  to  which  Volition  or  Emotion  is  the  stimulus.  Moreover,  the  body  is  at  rest  during 
sleep;  and  the  "Spinal  system  never  sleeps."  The  frequent  origin  "of  the  disease  in 
causes  which  have  excited  strong  mental  emotions,  and  the  effect  of  even  moderate  excite- 
ment of  the  feelings  in  greatly  aggravating  ihe  movements  of  the  body,  seem  to  indicate 
the  connection  of  this  disease  with  the  Emotional  system  of  nerves.  Stammering  may 
be  regarded  as  a  sort  of  Chorea  affecting  the  muscles  of  voice:  of  this,  more  hereafter 
(CHAP.  vr.).  In  Paralysis  Agitans,  it  may  be  usually  observed  that  the  voluntary  actions 
are  much  more  affected  than  the  reflex;  the  latter,  indeed,  not  in  general  manifesting  any 
disturbance.  An  interesting  and  well-marked  case  of  this  disease  has  been  mentioned 
to  the  author  by  Dr.  W.  Budd,  in  which  softening  was  found  in  the  Crura  Cerebri. 


RECAPITULATION  AND  PATHOLOGICAL  APPLICATIONS.  223 

to  aid  the  contractions  of  the  uterus,  which  are  strictly  under  the  dominion  of 
the  Spinal  system.  There  is  a  form  of  Incontinence  of  urine,  which  is  very 
analogous  to  the  morbid  action  just  described ;  the  sphincter  has  its  due 
power;  but  the  stimulus  to  the  evacuation  of  the  bladder  is  excessive  in 
strength  and  degree,  owing  to  the  acridity  of  the  urine  or  other  causes.  The 
part  of  the  bladder  upon  which  this  appears  chiefly  to  act,  is  the  trigonum 
(which  is  well  known  to  be  more  sensitive  to  the  irritation  of  calculi  than  the 
rest  of  the  internal  surface) ;  and  Sir  C.  Bell  advises  young  persons  who  suf- 
fer during  the  night  from  this  very  disagreeable  complaint,  to  lie  upon  the 
belly  instead  of  the  back,  so  that  the  contact  of  the  urine  with  the  trigonum 
may  be  delayed  as  long  as  possible. 

301.  One  of  the  most  familiar  examples  of  the  pathological  excitement  of 
the  true  Spinal  system,  is  the  act  of  Vomiting ;  and,  as  Dr.  M.  Hall  justly 
remarks,  the  special  function  of  this  system  nowhere  receives  better  illustra- 
tion. The  act  may  be  excited  in  various  ways.  Thus,  it  results  from  the 
tickling  of  the  fauces  with  a  feather  or  with  the  finger ;  but  if  the  feather  be 
carried  too  far  down,  an  act  of  deglutition  is  induced,  instead  5f  vomiting.* 
In  this  instance  the  glosso-pharyngeal,  and  perhaps  also  the  fifth  pair,  are  the 
nerves  by  which  the  stimulus  is  conveyed  to  the  Medulla  Oblongata.  Vomit- 
ing, again,  may  be  induced  by  substances  introduced  into  the  stomach ;  and 
here  the  pneumogastric  is  evidently  the  exciter.  When  it  takes  place  as  a 
result  of  pregnancy,  or  of  some  intestinal  irritation,  the  stimulus  must  be  con- 
veyed either  through  one  of  the  ordinary  Spinal  nerves  or  through  the  Sym- 
pathetic. But  it  may  also  be  occasioned  by  the  sight,  smell,  or  taste  of  any 
disagreeable  object,  or  by  the  mere  conception  of  it,  or  by  mental  emotion 
simply.  In  this  case,  the  stimulus  appears  to  be  received  by  the  ganglia  of 
special  sense,  and  to  be  transmitted  by  them  to  the  muscles  concerned,  as  by 
the  Spinal  Cord  or  Medulla  Oblongata  in  the  former  case.  When  Vomiting 
is  excited  by  the  introduction  of  emetic  substances  into  the  blodti  (§  199),  it  is 
probable  that  their  stimulation  chiefly  operates  through  the  extended  plexus 
of  nerves,  spread  out  by  the  Sympathetic  upon  the  walls  of  the  blood-vessels ; 
but  the  irritant  action  of  the  substance  upon  the  nervous  centres  may  be  also 
concerned.  In  regard  to  the  mechanism  by  which  the  act  of  Vomiting  is 
produced,  considerable  difference  of  opinion  has  existed.  The  old  doctrine 
was,  that  it  was  occasioned  by  the  simple  contraction  of  the  stomach  itself; 
but  Magendie  proved  that  this  could  not  be  the  case,  by  substituting  a  bladder 
for  the  stomach  of  an  animal,  and  then  injecting  a  solution  of  tartarized  anti- 
mony into  its  blood,  which  immediately  caused  the  emptying  of  the  bladder, 
by  the  pressure  of  the  surrounding  muscles ;  these  muscles  he  considered  to 
be  the  diaphragm  and  abdominal  muscles,  the  conjoint  actions  of  which  would 
be  a  peculiarity  observed  in  no  other  instance.  By  Dr.  M.  Hall,  on  the  other 
hand,  it  is  maintained  that  the  act  of  vomiting  is,  like  the  expulsion  of  the 
foetus,  urine,  fa3Ces,  &c.,  an  expiratory  effort,  modified  in  its  effects  by  the 
peculiar  condition  of  the  sphincters.  It  bears,  indeed,  great  resemblance  to 
the  act  of  coughing ;  differing  chiefly  in  this,  that  in  Vomiting  the  larynx  is 
closed  during  the  whole  operation,  whilst  it  is  only  closed  momentarily  in 
coughing ;  and  also  that  in  coughing  the  cardiac  'orifice  of  the  stomach  is 
closed,  whilst  in  vomiting  it  is  opened.  In  this  view,  the  accuracy  of  which 

*  This  has  been  the  cause  of  many  accidents.  Patients  have  tickled  the  fauces  with 
a  feather,  in  order  to  excite  vomiting;  and,  having  introduced  it  too  far  into  the  pha- 
rynx, it  has  been  drawn  out  of  their  fingers,  by  the  muscles  of  deglutition,  and  carried 
into  the  oasophagus.  Similar  accidents  have  occurred  with  the  rectum-bougie,  and 
female  catheter,  as  well  as  with  probes,  &c.,  introduced  into  the  male  urethra;  all  the 
orifices  being  furnished  with  a  kind  of  ingestive  power,  which  is  clearly  the  result  of 
Reflex  action. 


224  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

has  been  proved  by  experiment,  the  diaphragm  is  quite  inert.  A  curious  case 
has  been  recorded  by  Drs.  Graves  and  Stokes,*  in  which  vomiting  took  place 
from  the  stomach  of  a  man,  who  was  found  after  death  to  be  the  subject  of  a 
very  remarkable  change  in  the  relative  position  of  the  viscera, — the  stomach 
lying  in  the  thorax,  which  cavity  communicated  with  the  abdomen  by  an 
opening  in  the  diaphragm,  giving  passage  to  the  oesophagus  and  duodenum. 
This  case  was  regarded  by  its  reporters  as  proving  that  vomiting  might  take 
place  by  the  action  of  the  stomach  alone  ;  but  it  can  scarcely  be  held  to  justify 
this  conclusion ;  since,  the  diaphragm  being  entirely  passive,  the  abdominal 
muscles  would  have  the  same  power  of  emptying  the  stomach  as  they  would 
possess  over  the  lungs.  The  conformity  of  the  act  of  vomiting  with  that  of 
expiration,  is  further  shown  by  the  ejection  of  the  contents  of  the  oesophagus, 
which  will  take  place,  when  it  is  distended  by  the  deglutition  of  food  that  can- 
not pass  into  the  stomach,  on  account  of  an  obstruction  at  the  cardia. 


CHAPTER    IV. 

ON  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

I.  Of  Sensation  in  general. 

302.  BY  the  term  Sensation  is  rightly  understood  that  change  in  the  con- 
dition of  the  mind,  by  which  we  become  aware  of  an  impression  made  upon 
some  part  of  the  body  ;  or,  in  a  briefer  form  of  expression,  it  may  be  denned 
to  be  the  consciousness  of  an  impression.  Some  physiologists  have,  it  is  true, 
spoken  of  a  sensation  without  consciousness  ;  but  it  seems  very  desirable  thus 
to  limit  the  term ;  since  the  word  impression  may  be  very  well  applied  to 
designate  the  change  produced  in  the  afferent  nerves  by  an  external  cause 
up  to  the  point  at  which  the  mind  becomes  conscious  of  it.  We  have  seen 
reason  to  believe  that  the  impressions  communicated  to  the  Spinal  Cord  may 
there  excite  motor  actions,  without  occasioning  true  Sensation ;  and  it  would 
seem  to  be  with  the  Brain  only,  that  the  Mind  possesses  the  relation  neces- 
sary for  the  production  of  such  a  'change  in  it.  Hence  the  Brain  is  spoken  of 
as  the  Sensorium.  For  the  reasons  already  given  (§  261),  it  seems  probable 
that  the  ganglia  of  Special  Sensation  share  in  this  function  with  the  Cerebral 
Hemispheres.  The  afferent  nervous  fibres,  which  connect  the  various  parts 
of  the  body  with  the  Brain,  are  termed  sensory.  This  term  has  also  been 
applied  to  those  which  terminate  in  the  Spinal  Cord ;  but  as  the  impressions 
which  these  convey  do  not  produce  sensations,  it  seems  desirable  to  avoid 
thus  designating  them ;  and  the  term  excitor,  proposed  by  Dr.  M.  Hall,  is 
much  preferable.  Every  afferent  spinal  nerve,  therefore,  is  made  up  of  sen- 
sory and  of  excitor  fibres  ;  and  these  may  be  distributed  in  very  different  pro- 
portions to  different  parts.  Of  the  excitor  fibres,  enough  has  been  already 
said.  Those  parts  of  the  body  which  are  endowed  with  sensory  fibres,  and 
impressions  on  which,  therefore,  give  rise  to  sensation,  are  ordinarily  spoken 
of  as  sensible ;  and  different  parts  are  spoken  of  as  sensible  in  different  de- 

*  Dublin  Hospital  Reports,  vol.  v. 


OF  SENSATION  IN  GENERAL.  225 

grees,  according  to  the  strength  of  the  sensation  which  is  produced  by  a  cor- 
responding impression  on  each. 

303.  In  accordance  with  what  was  formerly  stated  (§  118)  of  the  depend- 
ence  of  all  nervous  action  on  the  continuance  of  the  capillary  circulation, 
especially  at  the  extremities  of  the  fibres,  it  is  found  that  the  sensory  nerves 
are  distributed  pretty  much  in  the  same  proportion  as  the  blood-vessels ;  that 
is  to  say,  in  the  non-vascular  tissues, — such  as  the  epidermis,  hair,  nails,  car- 
tilage, and  bony  substance  of  the  teeth,— no  nerves  exist,  and  there  is  an 
entire  absence  of  sensibility  ;  and  in  those  whose  vascularity  is  trifling,  the 
sensibility  is  dull,  as  is  the  case  with  bones,  tendons,  ligaments,  fibrous  mem- 
branes, and  other  parts  whose  functions  are  simply  mechanical,  and  even  with 
serous  and  areolar  membranes.     Many  of  these  textures  are  acutely  sensible, 
however,  under  certain  circumstances  ;  thus,  although  tendons  and  ligaments 
may  be  wounded,  burned,  &c.,  with  little  or  no  consciousness  of  the  injury, 
they  cannot  be  stretched  without  considerable  pain ;  and  the  fibrous,  serous, 
and  areolar  tissues,  when  their  vascularity  is  increased  by  inflammation,  also 
become  extremely  susceptible  of  painful  impressions.     All  very  vascular  parts, 
however,  do  not  possess  acute  sensibility :  the  muscles,  for  instance,  are  fur- 
nished with  a  large  supply  of  blood,  to  enable  them  to  perform  their  peculiar 
function  ;  but  they  are  not  sensible  in  by  any  means  the  same  proportion. 
Even  the  substance  of  the  brain,  and  of  the  nerves  of  special  sensation,  ap- 
pears to  be  destitute  of  this  property ;  and  the  same  may  be  said   of  the  mu- 
cous membranes  lining  the  interior  of  the  several  viscera,  which,  in  the  ordi- 
nary condition,  are  much  less  sensible  than  the  membranes  which  cover  those 
viscera,  although  so  plentifully  supplied  with  blood  for  their  especial  purposes. 
The  most  sensible  of  all  parts  of  the  body  is  the  Skin,  in  which  the  sensory 
nerves  spread  themselves  out  into  a  minute  network  ;  and  even  of  this  tissue, 
the  sensibility  differs  greatly  in  different  parts.     The  organs  of  special  sensa- 
tion are,  by  the  peculiar  character  of  the  nerves  with  which  they  are  supplied, 
rendered  sensible  to  impressions  of  a  particular  kind  :  thus,  the  eye  is  sensible 
to  light,  the  ear  to  sound,  &c. ;  and  whatever  amount  of  ordinary  sensibility 
they  possess,  is  dependent  upon  other  sensory  nerves.     The  eye,  for  example, 
contrary  to  the  usual  notions,  is  a  very  insensible  part  of  the  body,  unless 
affected  with  inflammation ;  for  though  the  mucous  membrane  which  covers 
its  surface,  and  which  is  prolonged  from  the  skin,  is  acutely  sensible  to  some 
kinds  of  impressions,  the  interior  is  by  no  means  so,  as  is  well  known  to  those 
who  have  operated  much  on  the  eye.     And  there  are  many  parts  of  the  body, 
that  are  supplied  with  the  common  sensory  nerves,  which  convey  to  the  mind 
impressions  of  particular  kinds  with  much  greater  readiness  than  they  com- 
municate those  of  a  different  description. 

304.  It  appears,  then»  that  the  vascularity  of  a  part  is  an  essential  condition 
of  its  sensibility  ;  but  it  does  not  follow  that  a  tissue  should  be  peculiarly  sen- 
sible, because  it  is  highly  vascular ;  since  its  large  supply  of  blood  may  be 
required  for  other  purposes.     It  is  not  simple  vascularity,  however,  which  is 
necessary,  but  rather  an  active  capillary  circulation ;  any  cause  which  retards 
this,  deadens  the  sensibility,  as  is  well  seen  in  regard  to  cold  ;  and,  on  the 
other  hand,  an  increase  in  its  energy  produces  a  corresponding  increase  in  the 
sensibility,  as  is  peculiarly  evident  in  the   active  congestion  which  usually 
precedes  inflammation.     Acute  sensibility  to  external  impressions  may  arise, 
however,  not  only  from  abnormal  activity  of  the  circulation  in  the  organ  or 
part  itself,  but  from  the  same  condition  affecting  that  part  of  the  sensorium  in 
which  the  impressions  are  received.     Thus,  in  active  congestion  and  inflam- 
mation of  the  brain,  the  most  ordinary  external  impressions  produce  sensations 
of  an  unbearable  violence ;  and  there  are  some  peculiar  conditions  of  the 
nervous  system,  known  under  the  name  of  hysterical,  in  which  the  patients 


226  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

manifest  the  same  discomfort,  even  when  the  circulation  is  in  a  feeble,  rather 
than  an  excited  state.  It  is  remarkable  that  the  sensibility  of  the  mucous 
membranes  lining  the  internal  organs,  is  less  exalted  by  the  state  of  inflamma- 
tion, than  is  that  of  most  other  parts  ;  and  in  this  arrangement  we  may  trace 
a  wise  and  beneficent  provision  ;  since,  were  it  otherwise,  the  functions  neces- 
sary to  life  could  not  be  performed  without  extreme  distress,  with  a  very  mo- 
derate amount  of  disorder  in  the  viscera.  If  a  joint  is  inflamed,  we  can  give 
it  rest ;  but  to  the  actions  of  the  alimentary  canal  we  can  give  little  voluntary 
respite. 

305.  The  feelings  of  Pain  or  Pleasure,  which  are  connected  with  particular 
sensations,  cannot,  (for  the  most  part  at  least)  be  explained  upon  any  other 
principle  than  that  of  the  necessary  association  of  these  feelings,  by  an  original 
law  of  our  nature,  with  the  sensations  in  question.     As  a  general  rule  it  may 
be  stated,  that  the  violent  excitement  of  any  sensation  is  disagreeable,  even 
when  the  same  sensation  in  a  moderate  degree  may  be  a  source  of  extreme 
pleasure.     This  is  the  case  alike  with  those  impressions  which  are  communi- 
cated through  the  organs  of  sight,  hearing,  smell,  and  taste,  as  with  those  that 
are  received  through  the  nerves  of  common  sensation ;   and  there  can  be  no 
doubt  that  the  final  cause  of  the  association  of  painful  feelings  with  such  violent 
excitement,  is  to  stimulate  the  individual  to  remove  himself  from  what  would 
be  injurious  in  its  effects  upon  the  system.     Thus,  the  pain  resulting  from 
violent  pressure  on  the  cutaneous  surface,  or  from  the  proximity  of  a  heated 
body,  gives  warning  of  the  danger  of  injury,  and  excites  mental  operations 
destined  to  remove  the  part  from  the  influence  of  the  injurious  cause ;  and 
this  is  shown  by  the  fact,  that  loss  of  sensibility  is  frequently  the  indirect  occa- 
sion of  severe  lesions, — the  individual  not  receiving  the  customary  intimation 
that  an  injurious  process  is  taking  place.     Instances  have  occurred,  in  which 
severe  inflammation  of  the  membrane  lining  the  air-passages  has  resulted 
from  the  effects  of  ammoniacal  vapours,  introduced  into  them  during  a  state  of 
syncope, — the  patient  not  receiving  that  notice  of  the  irritation  which  would, 
in  an  active  condition  of  his  nervous  system,  have  prevented  him  from  inhaling 
the  noxious  agent.     It  is  a  general  rule,  with  regard  to  all  sensations,  however, 
that  their  intensity  is  much  affected  by  habit;  being  greatly  diminished  by 
frequent  and  continual  repetition.     This  is  partly  due  to  the  different  degree 
of  attention  which  the  sensations  excite  in  the  mind  ;  but  there  are  many  facts 
which  lead  to  the  conclusion,  that  it  is  chiefly  to  be  attributed  to  a  change  in 
the  degree  in  which,  after  frequent  repetition,  they  impress  the  consciousness 
itself.     Thus,  most  persons  are  readily  awoke  from  a  sound  sleep  by  a  trifling 
noise,  if  the  sound  be  of  a  kind  which  they  are  unaccustomed  to  hear  ;  but 
after  a  few  repetitions,  the  sound  loses  its  effect,  unless  its  intensity  be  increased. 
Of  this,  every  one  has  had  experience,  who  has  occasionally  made  use  of  an 
alarum  to  arouse  him  for  a  few  mornings  in  succession.     It  is  curious  also, 
that  the  feelings  of  pain  or  pleasure,  which  unaccustomed  sensations  excite, 
are  often  exchanged  for  each  other,  when  the  system  is  habituated  to  them ; 
this  is  especially  the  case  in  regard  to  impressions  communicated  through 
the  organs  of  smell  and  taste.     There  are  many  articles  in  common  use  among 
mankind, — such  as  Tobacco,  Fermented  liquors,  &c.,  the  use  of  which  cannot 
be  said  to  produce  a  natural  enjoyment,  since  it  is  at  first  unpleasant  to  most 
persons ;  and  yet  it  first  becomes  tolerable,  then  agreeable  ;    and  at  last  the 
want  of  them  is  felt  as  a  painful  privation,  and  the  stimulus  must  be  applied 
in  an  increasing  degree,  in  order  to  produce  the  usual  effect. 

306.  The  general  law,  that  sensations  are  blunted  by  frequent  repetition, 
may  perhaps  be  connected  with  certain  other  general  facts,  which  lie  under 
the  observation  of  every  one.     It  is  well  known  that  the  vividness  of  sensa- 
tions depends  rather  on  the  degree  of  change  which  they  produce  in  the 


OF  SENSATION  IN  GENERAL.  227 

system  than  on  the  absolute  amount  of  the  impressing  cause  ;  and  this  is  alike 
the  case  with  regard  to  the  special  and  the  ordinary  sensations.  Thus,  our 
sensations  of  heat  and  cold  are  entirely  governed  by  the  previous  condition  of 
the  parts  affected ;  as  is  shown  by  the  well-known  experiment  of  putting  one 
hand  in  hot  water,  the  other  in  cold,  and  then  transferring  both  to  tepid  water, 
which  will  seem  cool  to  one  hand,  and  warm  to  the  other.  Every  one  knows, 
too,  how  much  more  we  are  affected  by  a  warm  day  at  the  commencement  of 
summer,  than  by  an  equally  hot  day  later  in  the  season.  The  same  is  the 
case  in  regard  to  light  and  sound,  smell  and  taste.  A  person  going  out  of  a 
totally  dark  room  into  one  moderately  bright,  is  for  the  time  painfully  impressed 
by  the  light,  but  soon  becomes  habituated  to  it ;  whilst  another,  who  enters  it 
from  a  room  brilliantly  illuminated,  will  consider  it  dark  and  gloomy.  Those 
who  are  constantly  exposed  to  very  loud  noises,  become  almost  unconscious  of 
them,  and  are  even  undisturbed  by  them  in  illness  ;*  and  the  medical  student 
well  knows,  that  even  the  effluvia  of  the  dissecting-room  are  not  perceived, 
when  the  organ  of  smell  is  habituated  to  them ;  although  an  intermission  of 
sufficient  length  would,  in  either  instance,  occasion  a  renewal  of  the  first  un- 
pleasant feelings,  when  the  individual  is  again  subjected  to  the  impression. 

807.  Again,  it  is  a  well-known  fact,  that  impressions  made  upon  the  organs 
of  sense  continue  for  a  time,  after  the  cause  of  the  impression  has  ceased.  It 
is  in  this  manner  that  a  musical  tone,  which  seems  perfectly  continuous,  results 
from  a  series  of  consecutive  vibrations,  following  each  other  with  a  certain 
rapidity :  and  that  a  line  or  circle  of  light  is  produced  by  a  luminous  body 
moving  with  a  certain  velocity.  Now  there  is  reason  to  believe  that  changes, 
of  which  the  effects  thus  transiently  remain  upon  the  nerves  of  sense,  are  more 
permanently  impressed  upon  the  sensorium;  since,  as  formerly  shown  (§  291), 
we  can  only  in  this  manner  account  for  the  phenomena  of  Memory,  and  for  the 
effects  produced  upon  this  power,  by  material  changes  in  the  brain.  Hence 
the  diminution  in  the  force  of  sensations,  which  is  the  consequence  of  their 
habitual  recurrence,  may  be  considered  as  resulting  from  these  two  general 
facts, — the  persistence  of  the  impression  made  by  them  upon  the  sensorium, — 
and  the  consequent  absence  of  a  change  in  its  state,  when  a  sensory  impression 
is  brought  to  it,  which  is  of  the  same  nature  with  one  already  registered  there: 
the  degree  in  which  the  consciousness  is  excited,  being  dependent,  as  just 
stated,  not  upon  the  absolute  degree  of  the  impressing  cause,  but  upon  the 
amount  of  change  which  it  produces  in  the  sensorial  apparatus.  In  this 
respect  there  is  a  perfect  conformity  between  the  law  of  sensation,  and  that  of 
muscular  contraction ;  for  stimuli  which  excite  the  latter,  usually  lose  their 
force  in  proportion  to  the  frequency  of  their  repetition.  Indeed,  both  may  be 
considered  as  results  of  the  more  general  laws  of  vitality;  for  the  actions  of 
other  tissues  follow  the  same  rule,  as  is  shown  by  the  tolerance  that  may  be 
gradually  established  in  the  system  of  medicinal  agents,  poisons,  &c.,  which 
would  have  at  first  produced  the  most  violent  effects,  when  given  in  the  same 
amount. 

308.  It  is  through  the  medium  of  Sensation  that  we  acquire  a  knowledge 
of  the  material  world  around  us  ;  and  that  its  changes  excite  mental  operations 
in  ourselves.  The  various  kinds  or  modes  of  Sensation  excite  in  us  various 
ideas  regarding  the  properties  of  matter ;  and  these  properties  are  known  to 
us  only  through  the  changes  which  they  produce  in  the  several  organs. 
Thus  a  man  totally  blind  from  birth  can  form  no  idea  of  the  nature  of  light  or 
colours ;  nor  could  one  completely  deaf  have  any  just  conception  of  musical 

*  This  fact  is  very  well  known  in  the  manufacturing  districts;  where  it  is  not  at  all 
uncommon  for  a  family  to  live  in  the  immediate  vicinity  of  a  forge-hammer;  and  those 
who  are  accustomed  to  the  noise  are  unable  to  sleep  anywhere  else. 


228  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

tones.  It  is  well  known  that  instances  exist  in  which,  from  some  imperfec- 
tion in  organization,  there  is  an  incapacity  for  distinguishing  colours  or  musical 
tones,  whilst  there  is  no  want  of  sensibility  to  light  or  sound ;  and  that  some 
persons  are  naturally  endowed  with  a  much  greater  range  of  the  sensory 
faculties  than  others  possess.  Hence  it  does  not  seem  at  all  improbable,  that 
there  are  properties  of  matter  of  which  none  of  our  senses  can  take  immediate 
cognizance ;  and  which  other  beings  might  be  formed  to  perceive,  in  the  same 
manner  as  we  are  sensible  to  light,  sound,  &c.  Thus,  it  is  well  known  that 
many  animals  are  affected  by  atmospheric  changes,  in  such  a  manner,  that 
their  actions  are  regarded  by  Man  as  indications  of  the  probable  state  of  the 
weather ;  and  the  same  is  the  case  in  a  less  degree  with  some  of  our  own 
species,  who  are  peculiarly  susceptible  of  the  same  influences.  Now  the 
most  universal  of  all  the  qualities  or  properties  of  matter, — that,  in  fact,  on 
which  our  notion  of  it  is  founded, — is  resistance;  and  it  is  this  quality,  of 
which  the  knowledge  seems  most  universally  diffused  throughout  the  Animal 
kingdom.  In  the  lowest  tribes,  we  find  that  contact  between  their  surface 
and  some  material  body  is  required  to  produce  sensation ;  and  beings  which 
cannot  be  made  conscious,  in  this  manner,  of  the  existence  of  something  ex- 
ternal to  themselves,  do  not  deserve  to  be  ranked  in  the  Animal  kingdom. 
Our  difficulty  lies  (as  heretofore  remarked,  §  113),  in  ascertaining  what  are 
to  be  regarded,  in  such  beings,  as  unequivocal  indications  of  consciousness. 
Those  animals  which  are  fixed  to  one  spot,  can  have  few  other  ideas  of  matter 
than  this  most  general  one  ;  but  in  those  which  have  the  power  of  locomotion, 
the  general  sensibility  of  the  surface  doubtless  communicates  to  them  some 
notion  of  the  character  of  the  body  over  which  they  move,  in  the  same  manner 
as  we  learn  it  by  passing  the  hand  over  its  exterior.  We  shall  presently  see, 
however,  that  the  idea  of  the  shape  of  a  body  which  we  form  from  the  touch, 
results  from  a  very  complex  process ;  which  animals  of  the  lowest  grade  can 
scarcely  be  supposed  to  exercise.  There  can  be  no  doubt  that,  next  to  the 
mere  sense  of  resistance,  sensibility  to  temperature  is  the  most  universally 
diffused  through  the  Animal  kingdom;  and  probably  the  consciousness  of 
luminosity  is  the  next  in  the  extent  of  its  diffusion.  There  is  good  reason  to 
believe,  from  observation  of  their  habits,  that  many  animals  are  susceptible  of 
the  influence,  and  are  directed  by  the  guidance  of  light ;  whilst  their  organs 
are  not  adapted  to  receive  true  visual  impressions,  or  to  form  optical  images  ; 
and  such  would  seem  to  be  the  function  of  the  red  spots,  frequently  seen  on 
prominent  parts  of  Animalcules,  the  lower  Articulata  and  Mollusca,  and  even 
of  some  Radiata.  Wherever  these  are  of  sufficient  size  to  allow  their  struc- 
ture to  be  examined,  they  are  found  to  be  largely  supplied  with  nerves,  but  to 
be  destitute  of  the  peculiar  organization  which  alone  constitutes  a  true  eye. 
The  sense  of  Taste  may  be  considered  as  a  refined  modification  of  that  of 
touch ;  and  it  is  probable  that  this  exists  very  low  down  in  the  animal  scale, 
being  obviously  of  great  importance  in  the  selection  of  food ;  but  the  Anatomist 
has  no  means  of  ascertaining  where  this  refinement  exists,  and  where  it  does 
not ;  since  the  organs  of  taste  and  touch  are  so  similar.  The  sense  of  Hearing 
does  not  seem  to  be  distinctly  present  among  the  Invertebrate  animals,  except 
in  such  as  approach  most  nearly  to  the  Vertebrata;  it  is  not  improbable,  how- 
ever, that  sonorous  vibrations  may  produce  an  effect  upon  the  system  of  those 
animals  which  do  not  receive  them  as  sound  ;  and  this  would  appear,  from  a 
fact  subsequently  to  be  mentioned  (§  320),  to  be  not  improbably  the  case  with 
regard  especially  to  aquatic  animals.  The  sense  of  Smell,  which  is  concerned 
with  one  of  the  least  general  properties  of  matter,  appears  to  be  the  least 
widely  diffused  among  the  whole  ;  being  only  possessed  in  any  high  degree 
by  Vertebrated  animals,  and  being  but  feebly  present  in  a  large  proportion  of 
these. 


OF  SENSATION  IN  GENERAL.  229 

309.  Besides  the  various  kinds  of  sensibility  which  have  been  just  enume- 
rated, there  are  others  which  are  ordinarily  associated  together  along  with 
the  sense  of  material  resistance  (and  its  several  modifications),  and  the  sense 
of  temperature,  under  the  head  of  Common  Sensation ;  but  several  of  them, 
especially  those  which  originate  in  the  body  itself,  can  scarcely  be  regarded 
in  this  light.     Such  are  the  feelings  of  Hunger^and  Thirst;  that  of  Nausea; 
that  of  distress  resulting  from  suspended  aeration  of  the  blood;  that  of  "sink- 
ing at  the  stomach,"  as  it  is  vulgarly  but  expressively  described,  which  results 
from  strong  mental  emotion;  that  of  the  venereal  excitement,  and  perhaps 
some  others.     Now  in  regard  to  all  these,  it  is  impossible  in  the  present  state 
of  our  knowledge  to  say,  whether  their  peculiarity  results  from  the  particular 
constitution  of  the  nerves  that  receive  and  convey  them,  or  only  from  a  modifi- 
cation in  the  impressing  causes,  and  in  the  mode  in  which  they  operate. 
Thus  we  have  no  evidence  that  the  nervous  fibrils,  which  convey  from  the 
lungs  the  sense  of  distress  resulting  from  deficient  aeration,  may  not  be  of  a 
different  character  from  those  which  convey  from  the  surface  of  the  air-pas- 
sages the  sense  of  the  contact  of  a  foreign  body.     But  as  we  know  that  all  the 
trunks,  along  which  these  peculiar  impressions  travel,  do  minister  to  ordinary 
sensation,  whilst  the  nerves  of  truly  special  sensation  are  not  sensible  to  com- 
mon impressions,  it  is  evident  that  the  probability  is  in  favour  of  the  identity 
of  the  fibres  which  minister  to  these  sensations  with  those  of  the  usual  sensory 
character.     For  the  sense  of  temperature,  however,  it  is  not  by  any  means 
certain  that  a  special  set  of  fibres  does  not  exist ;  for  many  cases  are  on  record, 
in  which  it  has  been  lost,  whilst  the  ordinary  sense  of  tact  remained ;  and  it  is 
sometimes  preserved,  when  the  anaesthesia  is  in  other  respects  complete. 

310.  With  regard  to  all  kinds  of  sensation  it  is  to  be  remembered,  that  the 
change  of  which  the  mind  is  informed,  is  not  the  change  at  the  peripheral 
extremities  of  the  nerves,  but  the  change  communicated  to  the  sensorium ; 
hence  it  results,  that  external  agencies  can  give  rise  to  no  kind  of  sensation, 
which  cannot  also  be  produced  by  internal  causes,  exciting  changes  in  the 
condition  of  the  nerves  in  their  course.     This  very  frequently  happens  in 
regard  to  the  senses  of  sight  and  hearing;  flashes  of  light  being  seen,  and 
ringing  sounds  in  the  ears  being  heard,  when  no  external  stimulus  has  pro- 
duced such  impressions.     The  production  of  odorous  and  gustative  sensations 
from  internal  causes,  is  perhaps  less  common ;  but  the  sense  of  nausea  is  more 
frequently  excited  in  this  manner  than  by  the  direct  contact  of  the  nauseating 
substance  with  the  tongue  or  fauces.     The  various  phases  of  common  sen- 
sibility often  originate  thus :  and  it  is  an  additional  evidence  in  favour  of  the 
distinctness  of  the  fibres  which  convey  the  impressions  of  temperature,  that 
these  are  frequently  affected, — a  person  being  sensible  of  heat  or  of  chilli- 
ness in  some  part  of  his  body,  without  any  real  alteration  of  its  temperature, — 
whilst  there  is  no  corresponding  affection  of  the  tactual  sensations.     The  most 
common  of  the  internal  causes  of  these  subjective  sensations  (as  they  have 
been  termed,  in  contradistinction  to  the  objective  which  result  from  a  real 
material  object),  is  congestion  or  inflammation ;  and  it  is  interesting  to  remark 
that  this  cause,  operating  through  each  nerve,  produces  in  the  sensorium  the 
changes  to  which  that  nerve  is  usually  subservient.     Thus,  congestion  in  the 
nerves  of  common  sensation  gives  rise  to  feelings  of  pain  or  uneasiness ;  but 
when  occurring  in  the  retina  and  optic  nerve  it  produces  flashes  of  light ;  and 
in  the  auditory  nerve  it  occasions  a  "noise  in  the  ears."     It  maybe  observed, 
also,  of  some  external  causes,  that  they  may  excite  changes  in  the  sensorium 
through  several  different  channels ;  and  that  in  each  case  the  sensation  is 
characteristic  of  the  particular  nerve  on  which  the  impression  is  made.    Thus 
pressure,  which  produces  through  the  nerves  of  common  sensation  the  feeling 

20 


230  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

of  resistance,  is  well  known  to  occasion,  when  exerted  on  the  eye,  the  sensa- 
tion of  light  and  colours;  and,  when  made4 with  some  violence  on  the  ear,  to 
produce  tinnitus  aurium.  It  is  not  so  easy  to  excite  sensations  of  taste  and 
smell  by  mechanical  irritation;  and  yet,  as  Dr.  Baly*  has  shown,  it  may 
readily  be  accomplished  in  regard  to  the  former.  The  sense  of  nausea  may 
be  easily  produced,  as  is  familiarly  known,  by  mechanical  irritation  of  the 
fauces.  The  stimulus  of  electricity  still  more  completely  possesses  the  power 
of  affecting  all  the  sensory  nerves,  with  the  changes  which  are  peculiar  to 
them ;  for,  by  proper  management,  an  individual  may  be  made  conscious  at 
the  same  time  of  flashes  of  light,  of  distinct  sounds,  of  a  phosphoric  odour,  of 
a  peculiar  taste,  and  of  pricking  sensations,  all  excited  by  the  same  cause,  the 
effects  of  which  are  modified,  according  to  the  respective  peculiarities  of  the 
instruments  through  which  it  operates.  But  although  there  are  some  stimuli 
which  can  produce  sensory  impressions  on  all  the  nerves  of  sensation,  it  will 
be  found  that  those,  to  which  any  one  organ  is  peculiarly  fitted  to  respond, 
produce  little  or  no  effect  upon  the  rest.  Thus  the  ear  cannot  distinguish  the 
slightest  difference  between  a  luminous  and  a  dark  object.  A  tuning-fork, 
which  when  laid  upon  the  ear  whilst  vibrating,  produces  a  distinct  musical 
tone,  excites  no  other  sensation  when  placed  upon  the  eye  than  a  slight  jarring 
feeling.  The  most  delicate  touch  cannot  distinguish  a  substance  which  is 
sweet  to  the  taste,  from  one  which  is  bitter;  nor  can  the  taste  (if  the  commu- 
nication between  the  mouth  and  the  nose  be  cut  off)  perceive  any  thing  peculiar 
in  the  most  strongly-odoriferous  bodies. 

311.  It  may  hence  be  inferred  that  no  nerve  of  special  sensation  can,  by  any 
possibility,  take  on  the  function  of  another.     How  far  the  nerves  of  common 
sensation  can,  under  any  circumstances,  perform  the  offices  usually  delegated 
to  those  of  special  sense,  we  are  not  yet  in  a  condition  to  determine.     Com- 
parative Anatomy  seems  to  show  that,  in  the  lowest  animals  in  which  the 
rudiments  of  eyes  can  be  detected,  there  is  no  distinction  between  the  nerves 
proceeding  to  these  organs,  and  the  rest ;  and  there  would  appear  some  ground 
for  the  belief  that,  as  in  other  cases,  the  special  organs  of  sensibility  are 
gradually  elaborated,  in  ascending  the  Animal  scale,  from  the  more  general 
apparatus,  and  are  not  merely  superadded  to  it.     Hence  we  may  conceive  the 
possibility  (though  there  is  no  proof  of  the  fact)  that  states  of  the  system  might 
occur,  in  which  a  change  in  the  common  sensory  nerves  might  produce  the 
sensation  of  light,  sound,  &c.     But  it  is  quite  impossible  (so  far  at  least  as  our 
present  knowledge  of  physical  phenomena  permits  us  to  decide  upon  the  im- 
possibility of  any  thing)  that  distinct  visual  impressions  should  be  communi- 
cated to  a  nerve,  except  through  the  mediation  of  such  an  optical  instrument 
as  the  eye ;  or  distinct  sonorous  impressions,  except  through  such  an  acoustic 
instrument  as  the  ear.     Hence  we  must  receive  with  the  greatest  caution 
the  wonderful  accounts  of  transference  of  sensation,  many  of  which  have 
undoubtedly  been  the  offspring  of  deception.     Still  it  may  be  objected  that,  as 
we  are  so  totally  destitute  of  real  knowledge  as  to  the  mode  in  which  vision 
is  ordinarily  produced  by  inverted  images  upon  the  retina,  we  have  no  right  to 
assert  that  it  may  not  take  place  in  some  other  way,  and  perhaps  this  objec- 
tion should  lead  us  to  consider  the  phenomenon  rather  as  extremely  improbable, 
than  as  impossible.     But  the  improbability  maybe  compared  to  that  of  a  stone 
ascending  like  a  balloon,  or  a  piece  of  lead  floating  on  the  water ;  for  we  have 
no  more  knowledge  of  the  ultimate  cause  of  that  which  \ve  term  the  force  of 
Gravitation,  than  we  have  of  the  nature  of  Sensation. 

312.  The  peculiar  aptitudes  of  the  different  Sensory  nerves,  to  receive  and 
convey  impressions  of  various  kinds,  must  be  regarded  as  the  result  of  proper- 

*  Translation  of  Mailer's  Physiology,  p.  1062,  note. 


OF  SENSATION  IN  GENERAL.  231 

ties  inherent  in  themselves ;  just  as  we  consider  the  difference  between  the 
afferent  nerves  in  general,  and  the  motor  nerves,  to  be  one  belonging  to  their 
own  constitution.  But  it  is  probable  that  there  are  also  different  localities  in 
the  Sensorium,  in  which  the  changes  to  which  they  give  rise  are  performed. 
This  may  be  judged  of  from  the  fact,  that  the  phenomena  of  subjective  sensa- 
tion frequently  originate  in  peculiar  conditions  of  the  encephalon  itself,  and 
not  in  the  nervous  trunks  or  organs  of  sense ;  thus,  in  dreaming,  we  have 
frequently  very  vivid  pictures  of  external  objects  presented  to  our  minds  ;  and 
we  sometimes  distinctly  hear  voices  and  musical  tones,  or  have  perceptions 
(though  this  is  less  common)  of  tastes  and  odours.  The  phenomena  of  spec- 
tral illusions  are  very  nearly  connected  with  those  of  dreaming ;  both  may  be 
in  some  degree  influenced  by  external  causes,  acting  upon  the  organs  of  sen- 
sation, which  are  misinterpreted  (as  it  were*)  by  the  mind,  owing  to  its  state 
of  imperfect  operation ;  but  both  also  may  entirely  originate  in  the  central 
organs.  There  seems  to  be  no  difference,  in  the  feelings  of  the  individual, 
between  the  sensations  thus  originating,  and  those  which  are  produced  in  the 
usual  manner;  for  we  find  that,  unless  otherwise  convinced  by  their  own 
reason,  persons  who  witness  spectral  illusions  believe  as  firmly  in  the  reality 
of  the  objects  that  come  before  their  minds,  as  if  the  images  of  those  objects 
were  actually  formed  on  their  retina.  This  is  another  proof,  if  any  were 
wanting,  that  the  organ  of  sense,  and  the  nerve  belonging  to  it,  are  but  the 
instruments  by  which  certain  changes  are  produced  in  the  sensorium;  of 
which  changes,  and  not  of  the  immediate  impression  of  the  object,  the  sensa- 
tion really  consists.  It  seems  to  be  by  an  innate  law  of  our  constitution,  that 
these  subjective  sensations,  whether  originating  in  the  central  organs,  or  in 
the  course  of  the  nervous  trunks,  should  be  referred  by  the  mind  to  the  ordi- 
nary situations  of  the  peripheral  terminations  of  those  nerves ;  even  though 
these  should  not  exist,  or  should  be  destitute  of  the  power  of  receiving  impres- 
sions. Thus,  after  amputations,  the  patients  are  for  some  time  affected  with 
sensations  (originating  probably  in  the  cut  extremities  of  the  nerves),  which 
they  refer  to  the  removed  extremities  ;  the  same  has  been  noticed  in  regard  to 
the  eye,  as  well  when  it  has  been  completely  extirpated,  as  when  its  powers 
have  been  destroyed  by  disease.  The  effects  of  the  Taliacotian  operation  also 
exhibit  the  operation  of  this  law  in  a  curious  manner ;  for  until  the  flap  of 
skin,  from  which  the  new  nose  is  formed,  obtains  vascular  and  nervous  con- 
nections in  its  new  situation,  the  sensation  produced  by  touching  it  is  referred 
to  the  forehead.  Another  interesting  illustration  of  it  may  be  obtained  by  the 
following  very  simple  experiment : — if  the  middle  finger  of  either  hand  be 
crossed  behind  the  fore-finger,  so  that  its  extremity  is  on  the  radial  side  of  the 
latter,  and  the  ends  of  the  two  fingers  thus  disposed  be  rolled  over  a  marble, 
pea,  or  other  round  body,  a  sensation  will  be  produced,  which,  if  unconnected 
by  reason,  would  cause  the  mind  to  believe  in  the  existence  of  two  distinct 
bodies ;  this  is  due  to  the  impression  being  made  at  the  same  time  upon  the 
radial  side  of  the  fore-finger,  and  the  ulnar  side  of  the  middle  finger, — two 
joints  which,  in  the  natural  position,  are  at  a  considerable  distance. 

313.  The  acuteness  of  particular  sensations  is  influenced  in  a  remarkable 
degree  by  the  attention  they  receive  from  the  mind.  If  the  mind  be  entirely 
inactive,  as  in  profound  sleep,  no  sensation  whatever  is  produced  by  ordinary 
impressions ;  on  the  other  hand,  when  the  mind  is  from  any  cause  strongly 
directed  upon  them,  impressions  very  feeble  in  themselves  produce  sensations 
of  even  painful  acuteness.  Every  one  knows  how  much  a  slight  itching  of 
some  part  of  the  surface  may  be  magnified,  by  the  direction  of  the  thoughts 
to  it ;  whilst  as  soon  as  they  are  forced  by  some  stronger  impression  into  an- 
other channel,  the  irritation  is  no  longer  felt.  To  the  traveler  in  warm  coun- 
tries, the  shrill  but  feeble  buzz  of  a  single  mosquito,  accidentally  enclosed 


232  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

within  the  netting  that  surrounds  his  bed,  becomes  a  source  of  almost  inexpres- 
sible annoyance,  when  he  is  composing  himself  to  sleep :  and  every  one  is 
aware  how  vividly  other  sounds  are  perceived,  when  they  break  in  upon  the 
stillness  of  the  night,— being  increased  in  strength,  not  only  by  the  contrast, 
but  by  absorbing  the  whole  attention.  An  interesting  experiment  is  mentioned 
by  Miiller,  which  shows  how  completely  the  mind  may  be  unconscious  of  im- 
pressions communicated  to  it  by  one  organ  of  sense,  when  occupied,  even 
without  a  distinct  effort  of  the  will,  by  those  received  through  another.  If  we 
look  at  a  sheet  of  white  paper  through  two  differently-coloured  glasses  at  the 
same  time, — one  being  placed  before  each  eye,  the  resulting  sensation  is  sel- 
dom that  of  a  mixture  of  the  colours  ;  if  the  experiment  be  tried  with  blue  and 
yellow  glasses,  for  example,  we  do  not  see  the  paper  of  an  uniform  green,  but 
the  blue  is  predominant  at  one  moment,  and  the  yellow  at  another,  or  blue 
nebulous  spots  may  present  themselves  on  a  yellow  field,  or  yellow  spots  on  a 
blue  field.  We  perceive,  from  this  experiment,  that  the  attention  may  not  only 
be  directed  to  the  impressions  made  on  either  retina,  to  the  complete  exclusion 
of  those  of  the  other,  but  it  may  be  directed  to  those  made  on  particular  spots 
of  either.  This  may  be  noticed,  again,  in  the  process  by  which  we  make 
ourselves  acquainted  with  a  landscape  or  a  picture  ;  if  our  attention  be  directed 
to  the  whole  field  of  vision  at  once,  we  see  nothing  distinctly ;  and  it  is  only 
by  abstracting  ourselves  from  the  contemplation  of  the  greater"  part  of  it,  and 
by  directing  our  attention  to  smaller  portions  in  succession,  that  we  can  obtain 
a  definite  conception  of  the  details.  The  same  is  the  case  in  regard  to  audi- 
tory impressions ;  and  here  the  power  of  attention  in  causing  one  sensation 
or  series  of  sensations  to  predominate  over  others,  which  are  really  more  in- 
tense, is  often  most  remarkably  manifested.  When  we  are  listening  to  a 
piece  of  music  played  by  a  large  orchestra,  for  example,  we  may  either  attend 
to  the  combined  effect  of  all  the  instruments,  or  we  may  single  out  any  one 
part  in  the  harmony,  and  follow  this  through  all  its  mazes  ;  and  a  person  with 
a  practised  ear  (as  it  is  commonly  but  erroneously  termed,  it  being  not  the  ear 
but  the  mind  that  is  practised),  can  even  distinguish  the  sound  of  the  weakest 
instrument  in  the  whole  band,  and  can  follow  its  strain  through  the  whole 
performance.  This  attention  to  a  single  element  can  only  be  given,  however, 
by  withdrawing  the  mind  from  the  perception  of  the  rest ;  and  a  musician 
who  thus  listens,  will  have  very  little  idea  of  the  rest  of  the  harmonic  parts,  or 
of  the  general  effect.  In  fact,  when  the  mind  is  thus  directed,  by  a  strong 
effort  of  the  will,  into  a  particular  channel,  it  may  be  almost  considered  as  un- 
conscious quoad  any  other  impressions. 

314.  The  effects  of  this  principle  are  manifested  in  regard  to  the  sensations 
which  originate  within  the  system ;  as  well  as  in  respect  to  those  which  are 
excited  by  external  impressions.  Every  one  is  aware  how  difficult  it  is  to 
keep  the  body  perfectly  quiescent,*  especially  when  there  is  a  particular 
motive  for  doing  so,  and  when  the  attention  is  strongly  directed  to  the  object. 
This  is  experienced  even  whilst  a  Photogenic  likeness  is  being  taken,  when 
the  position  is  chosen  by  the  individual,  and  a  support  is  adapted  to  assist 
him  in  retaining  it ;  and  it  is  still  more  strongly  felt  by  the  performers  in  the 
Tableaux  Vivans,  who  cannot  keep  up  the  effort  for  more  than  three  or  four 
minutes.  Now  it  is  well  known  that,  when  the  attention  is  strongly  directed 
to  an  entirely  different  object,  (when  we  are  listening,  for  example,  to  an  elo- 
quent sermon,  or  an  interesting  lecture,)  the  body  may  remain  perfectly 
motionless  for  a  much  longer  period;  the  uneasy  sensations  which  would 
otherwise  have  occasioned  the  individual  to  change  his  position,  not  being  felt : 
but  no  sooner  is  the  discourse  ended  than  a  simultaneous  movement  of  the 

*  Of  course  the  movements  of  respiration  and  winking  are  left  out  of  the  question. 


OF  SENSATION  IN  GENERAL.  233 

whole  audience  takes  place,  every  one  then  becoming  conscious  of  some  discom- 
fort which  he  seeks  to  relieve.  This  is  the  case  also  in  regard  to  the  respi- 
ratory sensation ;  in  general  it  may  be  observed,  that  the  usual  reflex  move- 
ments are  not  enough  for  the  perfect  aeration  of  the  blood,  and  that  a  more 
prolonged  inspiration,  prompted  by  an  uneasy  feeling,  takes  place  at  intervals ; 
but  under  such  circumstances  as  those  just  alluded  to,  this  feeling  is  not  expe- 
rienced until  the  attention  ceases  to  be  engaged  by  a  more  powerful  stimulus, 
and  then  it  manifests  itself  by  the  deep  inspirations  which  accompany,  in 
almost  every  individual,  the  general  movement  of  the  body. 

315.  It  is  curious  that  the  constant  direction  of  the  attention  to  internal  sensa- 
tions of  a  subjective  kind,  should  sometimes  occasion  actual  disorder  of  the 
parts  to  which  these  sensations  are  referred ;  and  yet  this  seems  the  only  way 
of  accounting  for  some  of  the  phenomena  of  disease.  Sometimes  the  cause  of 
the  sensation  may  exist  in  the  trunk  of  the  nerve,  in  some  part  of  its  course ; 
whilst  in  other  instances,  it  may  be  confined  to  the  sensorium.  Pain  of  the 
testicle,  for  example,  may  be  occasioned  by  irritation  having  its  seat  in  the 
lower  part  of  the  spine,  the  organ  itself  being  perfectly  sound ;  yet  if  that  pain 
continue,  it  may  become  diseased.  The  following  are  some  very  interesting 
remarks  on  this  subject,  from  the  able  pen  of  Dr.  Holland.*  "  There  is  cause 
to  believe  the  action  of  the  heart  to  be  quickened  or  otherwise  disturbed,  by 
the  mere  centering  of  consciousness  upon  it,  without  any  emotion  or  anxiety." 
This  is* specially  the  case  where  its  impulses  are  irregular,  or  are  so  loud  as 
to  be  audible.  "  The  same  may  be  said  of  the  parts  concerned  in  respiration. 
If  this  act  be  expressly  made  the  subject  of  consciousness,  it  will  be  felt  to 
undergo  some  change ;  generally  to  be  retarded  at  first,  and  afterwards  quick- 
ened." "  The  act  of  swallowing  is  manifestly  rendered  more  difficult,  by  the 
attention  being  fixed  upon  it ;  and  the  same  cause  will  often  be  found  to  render 
articulation  less  distinct,  especially  when  there  exists  already  some  impediment 
to  the  function.  A  similar  direction  of  consciousness  to  the  region  of  the 
stomach,  creates  in  this  part  a  sense  of  weight,  oppression,  or  other  less  defi- 
nite uneasiness ;  and,  when  the  stomach  is  full,  appears  greatly  to  disturb  the 
due  digestion  of  the  food.  The  state  and  action  of  the  bowels  are  much  influ- 
enced by  the  same  cause."  A  peculiar  sense  of  weight  and  restlessness, 
approaching  to  cramp,  is  felt  in  a  limb,  to  which  the  attention  is  particularly 
directed.  "  The  attention  concentrated,  for  so  by  an  effort  of  will  it  may  be, 
on  the  head  or  sensorium,  gives  certain  feelings  of  tension  and  uneasiness, 
caused  possibly  by  some  change  in  the  circulation  of  the  part ;  though  it  may 
be  an  effect,  however  difficult  to  be  conceived,  on  the  nervous  system  itself. 
Persistence  in  this  effort,  which  is  seldom,  indeed,  possible  beyond  a  short  time 
without  confusion,  produces  results  of  much  more  complex  nature,  and  scarcely 
to  be  defined  by  any  common  terms  of  language."  These  phenomena  have 
an  evident  affinity  with  those  of  several  morbid  conditions.  Thus  the  hypo- 
chondriac patient  "  in  fixing  his  consciousness  with  morbid  intentness  on  cer- 
tain organs,  creates  not  merely  disordered  sensations,  but  often  also  disordered 
actions  in  them.  There  may  be  palpitation  of  the  heart,  hurried  or  choked 
respiration,  flatulence  and  other  distress  of  stomach,  irritation  of  the  bladder; 
all  arising  from  this  morbid  direction  of  attention  to  the  organs  in  question." 
In  hysteria,  again,  "  the  instances  are  frequent,  of  attacks  brought  on  by  the 
mere  expectation  of  them;  or  by  irritation;  or  occasionally  even  a  sort  of 
morbid  solicitation  of  the  organs  to  these  singular  actions."  These  facts  go  a 
long  way  to  explain  the  phenomena  of  Animal  Magnetism,  many  of  which  are 
obviously  to  be  referred  to  the  exaggerated  operation  of  the  same  principle. 

*  Medical  Notes  and  Reflection?,  chap.  v. 
20* 


234 


OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 


We  now  proceed  to  consider  in  more  detail  the  functions  of  the  several  Organs 
of  the  Senses,  and  shall  commence  with  that  of  the  most  general  character. 

II.  Sense  of  Touch. 

316.  By  the  sense  of  Touch,  as  commonly  understood,  is  meant  that  modifi- 
cation of  the  common  sensibility  of  the  body,  of  which  the  cutaneous  surface 
is  the  especial  seat.  It  derives  its  peculiar  powers  simply  from  the  large 
amount  of  sensory  nervous  fibres,  which  are  distributed  in  its  substance ;  and 
especially  through  the  terminations  (or  rather  the  origins)  of  these  in  the 
papilla,  which  are  little  elevations  of  the  surface  of  the  cutis,  easily  percepti- 
ble by  the  aid  of  a  lens,  and  each  chiefly  composed  of  a  vascular  plexus  sur- 
rounding the  extremity  of  the  nervous  fibril.  The  number  of  these  papillae 
within  any  given  area,  pretty  closely  corresponds  with  the  degree  of  sensibility 
of  that  part  of  the  surface ;  thus  we  find  them  most  abundant  on  the  hands, 
especially  towards  the  points  of  the  fingers,  and  on  the  lips  and  tongue.  In 
some  animals,  especially  those  of  the  Feline  tribe,  the  long  vibrisse  (commonly 
termed  whiskers)  evidently  minister  to  sensation ;  and  it  has  been  demon- 
strated that  their  pulps  are  largely  supplied  with  nerves  from  the  fifth  pair. 
Some  interesting  observations  have  been  made  by  Prof.  Weber,  on  the  sensi- 
bility of  different  parts  of  the  skin.  His  mode  of  ascertaining  this,  was  to 
touch  the  surface  with  the  legs  of  a  pair  of  compasses,  the  points  of  which 
were  guarded  with  pieces  of  cork ;  the  eyes  being  closed  at  the  time,  the  legs 
were  approximated  to  each  other,  until  they  were  brought  within  the  smallest 
distance,  at  which  they  could  be  felt  to  be  distinct  from  one  another.  The 
following  are  some  of  the  results  of  the  experiments.  With  the  extremities 
of  the  fingers  and  the  point  of  the  tongue,  the  distance  could  be  distinguished 
most  easily  in  the  longitudinal  direction ;  on  the  dorsum  of  the  tongue,  the 
face,  neck,  and  extremities,  the  distance  could  be  recognized  best  when  the 
arms  were  placed  tranversely. 


Point  of  middle  finger      -       £  of  aline 
Point  of  tongue        -         -       ^  of  a  line 
Palmar  surface  of  third  finger  1  line 
Red  surface  of  lips  -       2  lines 

Palmar  surface  of  middle  finger  2  — 
Dorsal  surface  of  third  finger  3  — 
Tip  of  the  nose  -  -3  — 
Dorsum  and  edge  of  tongue  4  — 
Part  of  the  lips  covered  by  skin  4  — 
Palm  of  hand  -  -  5  — 

Skin  of  cheek    -        -  5    — 

Extremity  of  great  toe  -  5  — 
Hard  palate  -  -  6  — 

Dorsal  surface  of  forefinger  7  — 
Dorsum  of  hand  -  -  8  — 


Mucous  membrane  of  gun's 

Lower  part  of  forehead 

Lower  part  of  occiput 

Back  of  hand 

Neck,  under  lower  jaw 

Vertex 

Skin  over  Patella 

Sacrum 

acromion 

Dorsum  of  foot 
Skin  over  sternum 
Skin  beneath  occiput 
Skin  over  spine,  in  back 
Middle  of  the  arm 
thigh 


9  lines 

10  — 

12  — 

14  — 

15  — 

15  — 

16  — 
1    

18  — 

18  — 

20  — 

24  — 

30  — 

30  — 

30  — 


It  is  curious  that  the  distance  between  the  legs  of  the  compasses  seemed  to  be 
greater  (although  really  so  much  less),  when  it  was  felt  by  the  more  sensitive 
parts,  than  when  it  was  estimated  by  parts  of  less  distinct  sensibility.  As  a 
general  fact,  it  seems  that  the  sensibility  of  the  trunk  is  greater  on  the  median 
line,  both  before  and  behind,  and  less  at  the  sides.  Differences  of  tempera- 
ture, and  the  weight  of  bodies,  were,  according  to  Prof.  Weber's  observations, 
most  accurately  recognized  at  the  parts  which  were  determined  to  be  most 
sensible  by  the  foregoing  method  of  inquiry. 

317.  As  already  stated  (§  308),  the  only  idea  communicated  to  our  minds  by 
the  sense  of  Touch,  when  exercised  in  its  simplest  form,  is  that  of  Resistance ; 
but  when  the  sensory  surface  and  the  substance  touched  are  made  to  change 


SENSE  OF  TOUCH.  235 

their  place  in  regard  to  each  other,  we  obtain  the  additional  notion  of  Exten- 
sion or  Space.  By  the  various  degrees  of  resistance  which  the  sensory  surface 
encounters,  we  estimate  the  hardness  or  softness  of  the  body ;  but  in  this  we 
are  assisted  by  the  muscular  sense  (§  257),  which  makes  us  conscious  of  the 
degree  of  pressure  we  are  employing.  By  the  impressions  made  upon  the' 
papillae,  during  the  movement  of  the  tactile  surface  over  that  which  is  being 
examined,  the  roughness,  smoothness,  or  other  peculiar  characters  of  the  latter 
are  estimated.  Our  knowledge  of  form,  however,  is  a  very  complex  process, 
requiring  not  merely  the  exercise  of  the  sense  of  touch,  but  also  great  atten- 
tion to  the  muscular  sensations.  It  is  chiefly,  as  formerly  remarked,  in  the 
variety  of  movements  of  which  the  hand  of  Man  is  capable,  that  it  is  superior 
to  that  of  any  other  animal ;  and  it  cannot  be  doubted  that  this  affords  a  very 
important  means  of  acquiring  information  in  regard  to  the  external  world,  and 
especially  of  correcting  many  vague  and  fallacious  notions,  which  we  should 
derive  from  the  sense  of  Sight,  if  used  alone.  On  the  other  hand,  it  must  be 
confessed,  that  our  knowledge  would  have  a  very  limited  range,  if  this  sense 
were  the  only  medium  through  which  we  could  acquire  ideas.  It  is  probably 
on  the  sensations  communicated  through  the  touch,  that  the  idea  of  the  mate- 
rial world,  as  something  external  to  ourselves,  chiefly  rests  ;  but  this  idea  is  by 
no  means  a  direct  result  of  these  sensations,  being  rather  an  instinctive  or  intui- 
tive perception  excited  by  them.  Every  person  who  directs  the  least  attention 
to  the  subject  must  perceive,  how  completely  different  are  those  notions  of  the 
primary  or  elementary  properties  of  matter,  which  we  base  upon  the  informa- 
tion thus  communicated  to  us  from  the  sensations  themselves ;  and,  as  Dr. 
Alison  has  justly  remarked,  "a  decisive  proof  of  this  being  the  true  repre- 
sentation of  this  part  of  our  mental  constitution,  is  obtained  by  attending  to  the 
idea  of  extension  or  space  ;  which  is  undoubtedly  formed  during  the  exercise 
of  the  sense  of  touch ;  and  is  no  sooner  formed,  than  it  '  swells  in  the  human 
mind  to  Infinity,'  to  which  certainly  no  human  sensation  can  bear  any  resem- 
blance." 

318.  That  the  conditions  under  which  certain  of  the  modifications  of  com- 
mon sensation  operate,  are  in  some  respects  different  from  those  of  ordinary 
Touch,  is  very  easily  shown.  Thus,  the  feeling  of  tickling  is  excited  most 
readily  in  parts  which  have  the  least  tactual  sensibility, — the  armpits,  flanks, 
and  soles  of  the  feet ;  whilst  in  the  points  of  the  fingers  it  cannot  be  excited. 
Moreover,  the  nipple  is  very  moderately  endowed  with  ordinary  sensibility; 
yet  by  a  particular  kind  of  irritation,  a  very  strong  feeling  may  be  excited 
through  it.  Again,  in  regard  to  temperature,  it  is  remarked  by  Weber  that 
the  left  hand  is  more  sensitive  than  the  right;  although  the  sense  of  touch  is 
undoubtedly  the  most  acute  in  the  latter.  He  states  that,  if  the  two  hands, 
previously  of  the  same  temperature,  be  plunged  into  separate  basins  of  warm 
water,  that  in  which  the  left  hand  is  immersed  will  be  felt  as  the  warmest, 
even  though  its  temperature  is  somewhat  lower  than  that  of  the  other.  In 
regard  to  the  sensations  of  heat  and  cold,  he  points  out  another  curious  fact, — 
that  a  weaker  impression  made  on  a  large  surface,  seems  more  powerful  than 
a  stronger  impression  made  on  a  small  surface ;  thus,  if  the  forefinger  of  one 
hand  be  immersed  in  water  at  104°,  and  the  whole  of  the  other  hand  be 
plunged  in  water  at  102°,  the  cooler  water  will  be  thought  the  warmer;  whence 
the  well-known  fact,  that  water  in  which  a  finger  can  be  held,  will  scald  the 
whole  hand.  Hence  it  also  follows,  that  minute  differences  in  temperature, 
which  are  imperceptible  to  a  single  finger,  are  appreciated  by  plunging  the 
whole  hand  into  the  water ;  in  this  manner,  a  difference  of  one-third  of  a  degree 
may  readily  be  detected,  when  the  same  hand  is  placed  successively  in  two 
vessels.  The  judgment  is  more  accurate,  when  the  temperature  is  not  much 


236  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

above  or  below  the  usual  heat  of  the  body;  just  as  sounds  are  best  discrimi- 
nated, when  neither  very  acute  nor  very  grave. 

319.  The  improvement  in  the  sense  of  Touch,  in  those  persons  whose 
dependence  upon  it  is  increased  by  the  loss  of  other  senses,  is  well  known ; 
this  is  doubtless  to  be  in  part  attributed  (as  already  remarked)  to  the  increased 
attention  which  is  given  to  the  sensations,  and  in  part  to  the  increased  develop- 
ment of  the  organ  itself,  resulting  from  the  frequent  use  of  it.  The  case  of 
Saunderson,  who,  although  he  lost  his  sight  at  two  years  old,  became  Professor 
of  Mathematics  at  Cambridge,  is  well  known ;  amongst  his  most  remarkable 
faculties,  was  that  of  distinguishing  genuine  medals  from  imitations,  which  he 
could  do  more  accurately  than  many  connoisseurs  in  full  possession  of  their 
senses.  The  process  of  the  acquirement  of  the  power  of  recognizing  ele- 
vated characters  by  the  touch,  is  a  remarkable  example  of  this  improbability. 
When  a  blind  person  first  commences  learning  to  read  in  this  manner,  it  is 
necessary  to  use  a  large  type ;  and  every  individual  letter  must  be  felt  for 
some  time  before  a  distinct  idea  of  its  form  is  acquired.  After  a  short  period 
of  diligent  application,  the  individual  becomes  able  to  recognize  the  combina- 
tions of  letters  in  words,  without  forming  a  separate  idea  of  each  letter ;  and 
can  read  line  after  line,  by  passing  the  finger  over  each,  with  considerable 
rapidity.  Now  when  this  power  is  once  thoroughly  acquired,  it  is  found  that 
the  size  of  the  type  may  be  gradually  diminished ;  and  this  seems  to  indicate, 
that  the  sensations  themselves  are  rendered  more  acute,  by  the  frequent  appli- 
cation of  them  in  this  direction.  As  an  instance  of  the  correct  notions  which 
may  be  conveyed  to  the  mind  of  the  forms  and  surfaces  of  a  great  variety  of 
objects,  and  of  the  sufficiency  of  these  notions  for  accurate  comparison,  the 
Author  may  mention  the  case  of  a  blind  friend  of  his  own,  who  has  acquired 
a  very  complete  knowledge  of  Conchology,  both  recent  and  fossil;  and  who  is 
not  only  able  to  recognize  every  one  of  the  numerous  specimens  in  his  own 
Cabinet,  but  to  mention  the  nearest  alliances  of  a  Shell  previously  unknown  to 
him,  when  he  has  thoroughly  examined  it  by  his  touch.  Many  instances  are 
on  record,  of  the  acquirement,  by  the  blind,  of  the  power  of  distinguishing  the 
colours  of  surfaces,  which  were  similar  in  other  respects ;  and,  however  won- 
derful this  may  seem,  it  is  by  no  means  incredible.  For  it  is  to  be  remem- 
bered that  the  difference  of  colour  depends  upon  the  position  and  arrangement 
of  the  particles  composing  the  surface,  which  render  it  capable  of  reflecting 
one  ray  whilst  it  absorbs  all  the  rest;  and  it  is  quite  consistent  with  what  we 
know  from  other  sources,  to  believe  that  the  sense  of  touch  may  become  so 
refined  as  to  communicate  a  perception  of  such  differences. 

320.  The  examples  of  peculiar  acuteness  of  this  sense,  which  we  occasion- 
ally meet  with  among  the  lower  animals,  are  very  interesting,  when  viewed 
in  connection  with  its  improvability  in  Man.  It  was  found  by  Spallanzani, 
that  Bats,  when  deprived  of  sight,  and  (as  far  as  possible)  of  hearing  and 
smelling  also,  still  flew  about  with  equal  certainty  and  safety,  avoiding  every 
obstacle, 'passing  through  passages  only  just  large  enough  to  admit  them,  and 
flying  about  places  previously  unknown,  with  the  most  unerring  accuracy,  and 
without  coming  into  collision  with  the  objects  near  which  they  passed.  He 
also  stretched  threads  in  various  directions  across  the  apartment,  with  the  same 
result.  So  astonished  was  he  at  these  curious  facts,  that  he  was  led  to  attribute 
the  phenomenon  to  the  possession  of  a  sixth  sense,  unknown  to  Man.  Cuvier 
was  the  first  to  appreciate  the  real  value  of  these  experiments,  as  affording  a 
proof  of  the  existence  of  the  most  exquisite  tactile  sensibility,  over  the  whole 
surface  of  the  flying  membrane ;  the  naked  surface  and  delicate  structure  of 
which  appear  well  adapted  to  constitute  the  seat  of  so  important  a  function. 
From  this  view,  therefore,  it  would  appear  that  it  is  by  means  of  the  pulsation 
of  the  wings  on  the  air,  that  the  propinquity  of  solid  bodies  is  perceived, 


SENSE  OF  TASTE.  237 

through  the  manner  in  which  the  air  reacts  on  their  surface.  It  is  curious 
that  the  instance  which  (so  far  as  we  at  present  know)  is  most  analogous  to 
this,  should  be  met  with  among  the  inhabitants  of  the  deep.  It  is  a  fact  well 
known  to  Whale-fishers,  especially  to  those  who  pursue  the  Spermaceti  Whale, 
that  these  animals  have  the  power  of  communicating  with  each  other  at  great 
distances.  It  has  often  been  observed,  for  example,  that,  when  a  straggler  is 
attacked,  at  the  distance  of  several  miles  from  a  shoal,  a  number  of  its  fellows 
bear  down  to  its  assistance,  in  an  almost  incredible  short  space  of  time.  It  can 
scarcely  be  doubted,  then,  that  the  communication  must  be  made  through  the 
medium  of  the  vibrations  of  the  water,  excited  by  the  struggles  of  the  animal, 
or  perhaps  by  some  peculiar  movements  especially  designed  for  this  purpose, 
and  propagated  through  the  fluid  to  the  large  cutaneous  surface  of  the  distant 
Whales;  and  this  idea  is  fully  confirmed  by  the  fact,  that  the  nerves  which 
proceed  to  the  skin,  pass  through  the  inner  layers  of  blubber  with  scarcely 
any  subdivision,  but  spread  out  into  a  network  of  extreme  minuteness,  as  soon 
as  they  arrive  at  the  surface. 

III.  Sense  of  Taste. 

3*21.  That  this  sense  may  be  really  considered  as  a  peculiar  modification  of 
that  of  Touch,  appears  from  several  considerations.  In  the  first  place,  the 
actual  contact  of  the  object  of  sense,  with  the  organ  through  which  the  impres- 
sion is  received,  is  here  necessary ;  and  this  is  the  case  in  regard  to  no  other 
sense.  Moreover  the  intimate  structure  of  the  organ  is  nearly  the  same  in 
both  instances.  Again,  it  appears  from  the  considerations  formerly  alluded  to 
(§  228),  that  there  is  no  special  nerve  of  taste;  the  gustative  impressions  nuulc 
upon  the  front  of  the  tongue  being  conveyed  by  the  lingual  branch  of  the 
fifth  pair;  whilst  those  made  upon  the  back  of  the  organ  are  conveyed  by  the 
glosso-pharyngeal.  The  first  of  these  nerves  also  ministers  to  ordinary  tactile 
sensibility;  the  second  appears  to  convey  the  impressions  which  produce 
nausea.*  The  papillae  of  the  tongue  are  essentially  the  same  in  structure 
with  those  of  the  skin ;  and  although  Anatomists  have  classified  them,  accord- 
ing to  their  differences  of  form  and  situation,  there  is  no  definite  physiological 
evidence  that  they  possess  corresponding  varieties  of  endowment,  although 
this  is  quite  possible.  As  a  general  rule,  it  is  a  necessary  condition  of  the 
sense  of  Taste,  that  the  object  should  either  be  in  a  state  of  solution,  or  should 
be  soluble  in  the  moisture  covering  the  tongue ;  if  this  be  not  the  case,  or  if 
the  tongue  be  dry,  a  simple  feeling  of  contact  is  all  that  is  produced.  As  in 
the  case  of  touch,  the  idea  of  the  character  of  the  sapid  body  is  very  imperfect, 
unless  it  is  made  to  move  over  the  gustative  surface ;  and  thus  the  taste  is  very 
much  heightened  by  the  compression  and  friction  of  the  substance  between 
the  tongue  and  the  palate.  From  all  these  circumstances  it  appears  indis- 
putable, that  a  very  strong  analogy  exists  between  Taste  and  Touch ;  indeed 
it  may  be  questioned  whether  they  are  not  in  reality  more  closely  allied  than 
is  the  sense  of  Temperature  with  that  of  Resistance. 

322.  Although  the  tongue  seems  to  be  the  chief  seat  of  Gustative  sensibility, 
yet  this  is  also  possessed,  though  in  a  less  degree,  by  the  palate.  But  it  is  to 
be  remarked  that  the  sensations  produced  by  most  sapid  substances  are  of  a 
complex  kind ;  and  are  in  great  part  due  to  the  organ  of  Smell.  Of  this  any 
one  may  convince  himself,  by  closing  the  nostrils,  and  inspiring  and  expiring 
through  the  mouth  only,  when  holding  in  the  mouth,  or  even  rubbing  between 

*  Indeed  it  may  be  questioned  whether  the  glosso-pharyngeal  is  really  a  nerve  of  taste 
at  all;  since  the  experiments  which  would  indicate  that  it  is  so,  may  be  explained  upon 
the  supposition  that  nausea,  rather  than  real  gustative  sensibility,  was  induced  by  the 
substances  applied  to  the  tongue  after  division  of  the  lingual  branch  of  the  fifth  pair. 


238  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

the  tongue  and  the  palate,  some  sapid  substance ;  of  which  the  taste  is  then 
scarcely  recognized,  although  it  is  immediately  perceived,  when  its  effluvia 
are  drawn  into  the  nose.  It  is  well  known,  too,  that,  when  the  sensibility  of 
the  Schneiderian  membrane  is  blunted  by  inflammation,  (as  in  an  ordinary  cold 
in  the  head,)  the  power  of  distinguishing  flavours  is  very  much  diminished. 
In  fact  some  physiologists  are  of  opinion  that  all  our  knowledge  of  the  flavour 
of  sapid  substances  is  received  through  the  Smell ;  and  this  is  not  improbably 
true :  but  it  is  to  be  remembered,  that,  besides  flavour,  a  sapid  body  may  excite 
various  other  sensations,  as  those  of  irritation  and  pungency ;  and  of  these,  it 
seems  to  be  the  true  function  of  the  sensory  surface  of  the  mouth  to  take  cog- 
nizance. Such  sensations  are  evidently  not  far  removed  from  those  of  ordi- 
nary touch ;  and  correspond  with  those  which  may  be  excited  in  the  nostrils 
through  the  medium  of  the  Fifth  pair.  Taken  in  its  ordinary  compound 
acceptation,  the  sense  of  Taste  has  for  its  object  to  direct  us  in  the  choice  of 
food,  and  to  excite  the  flow  of  the  mucus  and  saliva,  which  are  destined  to  aid 
in  the  preparation  of  the  food  for  Digestion.  Among  the  lower  Animals,  the 
instinctive  perceptions  connected  with  this  sense  are  much  more  remarkable 
than  our  own;  thus  an  omnivorous  Monkey  will  seldom  touch  fruits  of  a  poi- 
sonous character,  although  their  taste  may  be  agreeable  ;  and  animals,  whose 
diet  is  restricted  to  some  one  kind  of  food,  will  decidedly  reject  all  others.  As 
a  general  rule  it  may  be  stated,  that  substances  of  which  the  taste  is  agreeable 
to  us,  are  useful  in  our  nutrition;  and  vice  versa:  but  there  are  many  signal 
exceptions  to  this, 

323.  Like  other  senses,  that  of  Taste  is  capable  of  being  rendered  more 
acute;  ^education  ;  and  this  on  the  principles  already  laid  down  with  regard 
to  touch.*     The  experienced  wine-taster  can  distinguish  differences  in  age, 
purity,  place  of  growth,  &c.,  between  liquors  that  to  ordinary  judgments  are 
alike ;  and  the  epicure  can  give  an  exact  determination  of  the  spices  that  are 
combined  in  a  particular  sauce,  or  of  the  manner  in  which  the  animal,  on 
whose  flesh  he  is  feeding,  was  killed.     As  in  the  case  of  other  senses,  more- 
over, impressions  made  upon  the  sensory  surface  remain  there  for  a  certain 
period  ;  and  this  period  is  for  the  most  part  longer  than  that  which  is  required 
for  the  departure  of  the  impressions  made  upon  the  eye,  the  ear,  or  the  organ 
of  smell.     Every  one  knows  how  long  the  taste  of  some  powerful  substances 
remains  in  the  mouth ;  and  even  of  those  which  make  less  decided  impres- 
sions, the  sensation  remains  to  such  a  degree,  that  it  is  difficult  to  compare 
them  at  short  intervals.     Hence  if  a  person  be  blindfolded,  and  be  made  to 
taste  substances  of  distinct,  but  not  widely-different  flavours  (such  as  various 
kinds  of  wine  or  of  spirituous  liquors),  one  after  another  in  rapid  succession, 
he  soon  loses  the  power  of  discriminating  between  them.     In  the  same  man- 
ner, the  difficulty  of  administering  very  disagreeable  medicines  may  be  some- 
times got  over,  by  either  previously  giving  a  powerful  aromatic,  or  combining 
the  aromatic  with  the  medicine ;  its  strong  impression  in  both  cases  preventing 
the  unpleasant  taste  from  exciting  nausea. 

IV.  Sense  of  Smell. 

324.  Of  the  nature  of  CEdorous  emanations,  the  Natural  Philosopher  is  so 
completely  ignorant,  that  the  Physiologist  cannot  be  expected  to  give  a  definite 
account  of  the  mode  in  which  they  produce  sensory  impressions.     Although 
it  may  be  surmised  that  they  consist  of  particles  of  extreme  minuteness,  dis- 
solved as  it  were  in  the  air,  and  although  this  idea  seems  to  derive  confirma- 
tion from  the  fact  that  most  odorous  substances  are  volatile,  and  vice  versa, — 
yet  the  most  delicate  experiments  have  failed  to  discover  any  diminution  in 
weight,  in  substances  that  have  been  impregnating  with  their  effluvia  a  large 


SENSE  OF  SMELL.  239 

quantity  oT  air  for  several  years  (§  104,  note) ;  and  there  are  some  volatile 
fluids,  such  as  water,  which  are  entirely  inodorous.  The  Schneiderian  or 
Pituitary  membrane  is  the  seat  of  the  sense  of  smell ;  but  it  is  probable  that 
every  part  of  it  is  not  equally  endowed  with  the  faculty  of  distinguishing 
odours,  which  is  a  very  different  power  from  that  of  becoming  sensible  of  irri- 
tation from  them.  The  Olfactory  nerves  cannot  be  traced  to  the  membrane 
covering  the  middle  and  inferior  spongy  bones,  or  to  that  which  lines  the  dif- 
ferent sinuses,  these  parts  of  the  surface  being  supplied  by  the  fifth  pair  only  ; 
and  it  is  a  matter  of  common  experience,  that  we  cannot  distinguish  faint 
odours,  unless,  by  a  peculiar  inspiratory  effort,  we  draw  the  air  changed  with 
them  to  the  upper  part  of  the  nose.  In  animals  living  in  the  air,  it  is  a  neces- 
sary condition  of  the  exercise  of  the  sense  of  Smell,  that  the  odorous  matter 
should  be  transmitted  by  a  respiratory  current  through  the  nostrils  ;  and  that 
the  membrane  lining  these  should  be  in  a  moist  state.  Hence,  by  breathing 
through  the  mouth,  we  may  avoid  being  affected  by  odours,  even  of  the 
strongest  and  most  disagreeable  kind ;  and  in  the  first  stage  of  a  catarrh, 
when  the  ordinary  mucous  secretion  is  suspended,  the  sense  of  smell  is  blunted 
from  this  cause,  as  it  afterwards  is  from  the  excess  in  the  quantity  of  the  fluid, 
which  prevents  the  odoriferous  effluvia  from  coming  into  immediate  relation 
with  the  sensory  extremities  of  the  nerves.  Hence  we  may  easily  compre- 
hend, that  section  of  the  fifth  pair,  which  exercises  a  considerable  control  over 
the  secretions,  will  greatly  diminish  the  acuteness  of  the  smell ;  and  it  will 
have  the  further  effect  of  preventing  the  reception  of  any  impressions  of  irri- 
tation from  acrid  vapours,  which  are  entirely  different  in  their  character  from 
true  odorous  impressions,  and  which  are  not  transmitted  through  the  olfactory 
nerve  (§  220).  The  nasal' passages  may  indeed  be  considered  as  nerving,  in 
the  air-breathing  Vertebrata,  two  distinct  offices ;  jhey  constitute  the  organ  of 
smell,  through  the  distribution  of  the  olfactory  nerve  upon  a  part  of  their  sur- 
face ;  but  they  also  constitute  the  portals  of  the  respiratory  organs,  having  for 
their  office  to  take  cognizance  of  the  aeriform  matter  which  enters  them,  and 
to  give  warning  of  that  which  would  be  injurious;  this  latter  function  is  per- 
formed by  the  Fifth  pair,  as  by  the  Par  Vagum  in  the  glottis.  It  is  through 
this  nerve,  that  the  act  of  sneezing  is  excitable  :  the  evident  purpose  of  which 
is  the  ejection  of  a  strong  blast  of  air  through  the  nasal  passages,  in  such  a 
manner  as  to  drive  out  any  offending  matter  they  may  contain. 

325.  The  importance  of  the  sense  of  Smell  among  many  of  the  lower  ani- 
mals, in  guiding  them  to  their  food,  or  in  giving  them  warning  of  danger,  and 
also  in  exciting  the  sexual  feelings  is  well  known.  To  Man  its  utility  is  very 
subordinate  under  ordinary  circumstances ;  but  it  may  be  greatly  increased 
when  other  senses  are  deficient.  Thus,  in  the  well-known  case  of  James 
Mitchell,  who  was  deaf,  blind  and:  dumb,  from  his  birth,  it  was  the  principal 
means  of  distinguishing  persons,  and  enabled  him  at  once  to  perceive  the  en- 
trance of  a  stranger.  It  is  recorded  that  a  blind  gentleman,  who  had  an  anti- 
pathy to  cats,  was  possessed  of  a  sensibility  so  acute  in  this  respect,  that  he 
perceived  the  proximity  of  one  that  had  been  accidentally  shut  up  in  a  closet ' 
adjoining  his  room.  Among  Savage  tribes,  whose  senses  are  more  cultivated 
than  those  of  civilized  nations,  more  direct  use  being  made  of  the  powers  of 
observation,  the  scent  is  almost  as  acute  as  in  the  lower  Mammalia;  it  is  as- 
serted by  Humboldt,  that  the  Peruvian  Indians  in  the  middle  of  the  night  can 
thus  distinguish  the  different  races, — whether  European,  American  Indian,  or 
Negro.*  The  agreeable  or  disagreeable  character  assigned  to  particular 

*  The  author  has  been  assured  by  a  competent  witness,  that  a  lad  in  a  state  of  som- 
nambulism had  his  sense  of  Smell  so  remarkably  heightened,  as  to  be  able  to  assign 
(without  the  least  hesitation)  a  glove  placed  in  his  hand~to  its  right  owner,— in  the  midst 
of  about  thirty  persons,  the  boy  himself  being  blindfolded. 


240  X  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

odours,  is  by  no  means  constant  amongst  different  individuals.  Many  of  the 
lower  animals  pass  their  whole  lives  in  the  midst  of  odours,  which  are  to  Man 
(in  his  civilized  condition  at  least)  in  the  highest  degree  revolting ;  and  will 
even  refuse  to  touch  food,  until  it  is  far  advanced  in  putridity.  It  more  fre- 
quently happens  in  regard  to  odours  and  savours,  than  with  respect  to  other 
sensory  impressions,  that  habit  makes  that  agreeable,  and  even  strongly  re- 
lished, which  was  at  first  avoided ;  the  taste  of  the  epicure  for  game  that  has 
acquired  thefumet, — for  olives, — for  assafcetida,  &c.,  are  instances  of  this.  As 
to  the  length  of  time,  during  which  impressions  made  upon  the  organ  of  smell 
remain  u^>on  it,  no  certain  knowledge  can  be  obtained.  It  is  difficult  to  say 
that  the  effluvia  have  been  completely  removed  from  the  nasal  passages  ;  since 
it  is  not  improbable  that  the  odorous  particles  (supposing  such  to  exist)  are 
absorbed  or  dissolved  by  the  mucous  secretion ;  it  is  probably  in  this  manner 
that  we  may  account  for  the  fact,  well  known  to  every  medical  man,  that  the 
cadaverous  odour  is  frequently  experienced  for  days  after  a  post-mortem  ex- 
amination.* 

V.  Sense  of  Vision. 

326.  The  objects  of  this  sense  are  bodies,  which  are  either  in  themselves 
luminous,  or  which  become  so  by  reflecting  the  light  that  proceeds  from  others. 
Whether  their  light  is  transmitted  by  the  actual  emission  of  rays,  or  by  the 
propagation  of  undulations  analogous  to  those  of  sound,  is  a  question  at  present 
keenly  debated  amongst  Natural  Philosophers ;  but  it  is  of  little  consequence 
to  the  Physiologist,  which  is  the  true  solution ;  since  it  is  only  with  the  laws 
which  actually  regulate  the  transmission  of  light,  that  he  is  concerned.     These 
laws  it  may  be  desirable  here  briefly  to  recapitulate. 

327.  Every  point  of  a  luminous  body  sends  off  a  number  of  rays,  which 
diverge  in  every  directidn,  so  as  to  form  a  cone,  of  which  the  luminous  point  is 
the  apex.     So  long  as  these  rays  pass  through  a  medium  of  the  same  density, 
they  proceed  in  straight  lines ;  but,  if  they  enter  a  medium  of  different  density, 
they  are  refracted  or  bent, — towards  the  perpendicular  to  the  surface  at  the 
point  at  which  they  enter,  if  they  pass  from  a  rarer  into  a  denser  medium,— 
and  from  the  perpendicular,  when  they  pass  from  a  denser  medium  into  a 
rarer.     It  is  easily  shown  to  be  a  result  of  this  law,  that,  when  parallel  rays 
passing  through  air  fall  upon  a  convex  surface  of  glass,  they  will  be  made  to 
converge  ;  so  as  to  meet  at  the  opposite  extremity  of  the  diameter  of  the 
circle,  of  which  the  curve  forms  part.     If,  instead  of  continuing  in  the  glass, 
they  pass  out  again,  through  a  second  convex  surface,  of  which  the  direction 
is  the  reverse  of  the  first,  they  will  be  made  to  converge  still  more,  so  as  to 
meet  in  the  centre  of  curvature.     Rays  which  are  not  parallel,  but  which  are 
diverging  from  a  focus,  are  likewise  made  to  converge  to  a  point  or  focus ; 
but  this  point  will  be  more  distant  from  the  lens,  in  proportion  as  the  object 
is  nearer  to  it,  and  the  angle  of  divergence  consequently  greater.     The  rays 
diverging  from  every  point  of  a  luminous  object  are  thus  brought  to  a  corre- 
sponding focus ;  and  the  places  of  all  these  foci  hold  exactly  the  same  relation 
to  each  other,  with  that  of  the  points  from  which  the  rays  diverged ;  so  that 
a  perfect  image  of  the  object  is  formed  upon  a  screen  held  in  the  focus  to  the 
lens.     This  image,  however,  will  be  inverted ;  and  its  size,  in  proportion  to  that 
of  the  object,  will  depend  upon  their  respective  distances  from  the  lens.     If 
their  distances  be  the  same,  their  size  will  also  be  the  same ;  if  the  object  be 
distant,  and  the  image  near,  the  latter  will  be  much  the  smaller ;  and"  vice 
versa. 

*  This  may  partly  be  attributed  also  to  the  effluvia  adhering  to  the  dress.    It  has  been 
remarked  that  dark  cloths  retain  these  more  strongly  than  light. 


SENSE  OF  VISION.  241 

328.  There  are  two  circumstances,  however,  which  interfere  with  the  perfec- 
tion of  an  image  thus  formed  by  a  convex  lens.  The  one  is,  that,  if  the  lens 
constitute  a  large  part  of  the  sphere  from  which  it  is  taken,  the  rays  which 
fall  near  its  margin  are  not  brought  to  a  focus  at  the  same  point  with  those 
which  pass  through  its  centre,  but  at  a  point  nearer  the  lens.  This  difference, 
which  must  obviously  interfere  greatly  with  the  distinctness  of  the  image,  is 
termed  spherical  aberration ;  it  may  be  corrected  by  the  combination  of  two 
or  more  lenses,  of  which  the  curvatures  are  calculated  to  balance  one  another 
in  such  a  manner  that  all  the  rays  shall  be  brought  to  the  same  focus  ;  or  by 
diminishing  the  aperture  of  the  lens  by  means  of  a  stop  or  diaphragm,  in  such 
a  manner  that  only  the  central  part  of  it  shall  be  used.  The  latter  of  these 
methods  is  the  one  employed,  where  the  diminution  in  the  amount  of  light 
transmitted  is  not  attended  with  inconvenience!  The  nearer  the  object  is  to 
the  lens  (and  the  greater,  therefore,  the  angle  of  divergence  of  its  rays),  the 
greater  will  be  the  spherical  aberration,  and  the  more  must  the  aperture  of  the 
diaphragm  be  contracted  in  order  to  counteract  it. — The  other  circumstance 
that  interferes  with  the  distinctness  of  the  image,  is  the  unequal  refrangibility 
of  the  diffefently-coloured  rays,  which  together  make  up  white  or  colourless 
light ;  the  violet  being  more  bent  from  their  course  than  the  blue,  the  blue 
more  than  the  yellow,  and  the  yellow  more  than  the  red  ;  the  consequence  of 
which  will  be,  that  the  violet  rays  are  brought  to  a  focus  much  nearer  to  the 
lens  than  the  blue,  and  the  blue  nearer  than  the  red.  If  a  screen  be  held  to 
receive  the  image,  in  the  focus  of  any  of  the  rays,  the  others  will  make  them- 
selves apparent  as  fringes  round  its  margin.  This  difference  is  termed 
Chromatic  Aberration.  It  is  corrected  in  practice,  by  combining  together 
lenses  of  different  substances,  of  which  the  dispersive  power  (that  is,  the  power 
of  separating  the  coloured  rays)  differs  considerably.  This  is  the  case  with 
flint  and  crown  glass,  for  instance, — the  dispersive  power  of  the  former  being 
much  greater  than  that  of  the  latter,  whilst  its  refractive  power  is  nearly  the 
same :  so  that,  if  a  convex  lens  of  crown  glass  be  united  with  a  concave  of 
flint  whose  curvature  is  much  less,  the  dispersion  of  the  rays  effected  by  the 
former  will  be  counteracted  by  the  latter,  which  diminishes  in  part  only  its 
refractive  power. 

329.  The  Eye  may  be  regarded  as  an  optical  instrument  of  great  perfec- 
tion, adapted  to  produce,  on  the  expanded  surface  of  the  Optic  nerve,  a  com- 
plete image  or  picture  of  luminous  objects  brought  before  it ;  in  which  the 
forms,  colours,  lights  and  shades,  &c.,  of  the  object  are  all  accurately  repre- 
sented. By  the  different  refractive  powers  of  the  transparent  media,  through 
which  the  rays  of  light  pass,  and  by  the  curvatures  given  to  their  respective 
surfaces,  both  the  Spherical  and  Chromatic  aberrations  are  corrected  in  a  degree 
sufficient  for  all  practical  purposes ;  so  that,  in  a  well-formed  eye,  the  picture  is 
quite  free  from  haziness,  and  from  false  colours.  The  power  by  which  it  adapts 
itself  to  variations  in  the  distance  of  the  object, — so  as  to  form  a  distinct  image 
of  it,  whether  it  be  six  inches,  six  yards,  or  six  miles  off, — is  extremely 
remarkable,  and  cannot  be  regarded  as  hitherto  completely  explained.  It  is 
obvious  that,  if  we  fix  upon  any  distance  as  that  for  which  the  eye  is  naturally 
adjusted  (say  12  or  14  inches,  the  distance  at  which  we  ordinarily  read),  the 
frays  proceeding  from  an  object,  placed  nearer  to  the  eye  than  this,  would  not 
be  brought  to  a  focus  upon  the  retina,  but  Avould  converge  towards  a  point  behind 
it;  whilst,  on  the  contrary,  the  rays  from  an  object  at  a  greater  distance  would 
meet  before  they  reached  the  retina,  and  would  have  again  diverged  from  each 
other  when  they  impinge  upon  it;  so  that,  in  either  case,  vision  would  be  indis- 
tinct. Now  two  methods  of  adaptation  suggest  themselves  to  the  Optician. 
Either  he  may  vary  the  distance  between  the  refracting  surface  and  the  screen 
on  which  the  image  is  formed,  in  such  a  manner,  that  the  latter  shall  always 
21 


OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 
Fig.  43. 


A  longitudinal  section  of  the  globe  of  the  Eye;  1,  the  sclerotic,  thicker  behind  than  in  front;  2,  the  cornea, 
received  within  the  anterior  margin  of  the  sclerotic,  and  connected  with  it  by  means  of  ajbeveled  edge;  3, 
the  choroid,  connected  anteriorly  with  (4)  the  ciliary  ligament,  and  (5)  the  ciliary  processes;  6,  the  iris;  7, 
the  pupil ;  8,  the  third  layer  of  the  eye,  the  retina,  terminating  anteriorly  by  an  abrupt  border  at  the  com- 
mencement of  the  ciliary  processes;  9,  the  canal  of  Petit,  which  encircles  the  lens  (12);  the  thin  layer  in 
front  of  this  canal  is  the  zonula  ciliaris,  a  prolongation  of  the  vascular  layer  of  the  retina  to  the  lens' 
10,  the  anterior  chamber  of  the  eye,  containing  the  aqueous  humour;  the  lining  membrane  by  which  the 
humour  is  secreted  is  represented  in  the  diagram;  11,  the  posterior  chamber;  12,  the  lens  more  convex 
behind  than  before,  and  enclosed  in  its  proper  capsule;  13,  the  vitreous  humour  enclosed  in  the  hyaloid 
membrane,  and  in  cells  formed  in  its  interior  by  that  membrane ;  14,  a  tubular  sheath  of  the  hyaloid  mem- 
brane, which  serves  for  the  passage  of  the  artery  of  the  capsule  of  the  lens ;  15,  the  neurilema  of  the  optic 
nerve ;  16,  the  arteria  centralis  retinae,  imbedded  in  its  centre.  • 

be  in  the  focus  of  the  converging  rays ;  or,  the  distance  of  the  screen  remain- 
ing the  same,  he  may  vary  the  convexity  of  his  lens,  in  such  a  manner  as  to 
adapt  it  to  the  distance  of  the  object.  It  is  not  improbable,  that  both  of  these 
methods  are  employed  in  the  eye,  though  no  distinct  evidence  has  been  obtained 
of  the  operation  of  either.  Several  hypotheses  have  been  proposed,  to  account 
for  the  phenomenon ;  it  is  easily  proved  tjiat  no  one  of  them  can  alone  be 
true ;  but  it  cannot  be  readily  shown  that  any  of  them  is  entirely  false :  and  it 
would  not  seem  unlikely,  therefore,  that  all  may  participate,  in  various  degrees, 
in  the  effect.  The  following  are  the  principal  of  these. — 1.  An  alteration  in 
the  form  of  the  globe  of  the  eye  by  the  action  of  the  muscle^,  so  that  its  antero- 
posterior  diameter  may  be  increased  or  diminished.* — 2.  A  change  in  the  con- 
vexity of  the  cornea.  This  might  be  very  well  connected  with  the  last ;  since, 
if  the  globe  were  converted  into  a  spheroid,  of  which  the  antero-posterior 
diameter  would  be  the  longest,  the  curvature  of  the  cornea  would  be  increased ; 
whilst,  if  the  antero-posterior  diameter  were  shortened,  the  curvature  would 
be  diminished. — 3.  Change  of  position  of  the  crystalline  lens,  by  means  of 
the  ciliary  processes. — 4.  Change  of  figure  of  the  lens  itself.  That  one  or 
both  of  the  last  two  are  concerned  in  the  effect,  would  appear  from  the  fact, 
well  known  to  every  Oculist,  that,  after  the  removal  of  a  cataract,  the  power  of 
adapting  the  eye  to  distances  is  greatly  diminished. — 5.  Change  in  the  aper- 
ture of  the  pupil;  the  mode  in  which  this  could  assist  in  accommodating  the 
eye  to  variations  of  distance,  is  not  very  obvious. 

330.  Some  curious  circumstances  relative  to  the  connection  between  the 
optical  adaptation  of  the  eye  to  distances,  and  the  changes  in  the  direction  of 
the  axes  of  the  two  eyes,  have  been  pointed  out  by  Miiller.  When  both  eyes 

*  The  influence  of  the  muscles  in  altering  the  form  of  the  globe  may  be  better  com- 
prehended, now  that  we  know  the  mode  in  which  this  is  kept  in  its  place  in  the  front  of 
the  orbit,  by  a  fascia  passing  behind  it,  and  attached  anteriorly  to  the  lids. 


SENSE  OF  VISION. 

[Fig.  44. 


243 


"'-  -tf 


A  Horizontal  Section  of  the  Eye-Ball;  1,  sclerotic  coat;  2,  sheath  of  the  optic  nerve,  or  canal  of  Fon- 
tana;  3,  circular  venous  sinns  of  the  iris;  4,  proper  substance  of  the  cornea;  5,  arachnoidea  oculi;  6, 
membrane  of  the  anterior  chamber  of  the  aqueous  humour;  of  the  two  dotted  lines  one  points  to  the  sup- 


244  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

posed  membrane  of  Descemet,  the  other  to  the  supposed  continuation  of  that  membrane  over  the  anterior 
surface  of  the  iris;  7,  choroid  coat;  8,  annulus  albidus;  9,  ciliary  ligament;  10,10',  ciliary  body,  consisting 
of  (10')  a  pars  non-fimbriata,  and  (10)  a  pars  fimbriata  formed  by  the  ciliary  process;  11,  ora  serrata  of  the 
ciliary  body  ;  12,  iris;  13,  pupil;  14,  membrane  of  the  pigment;  15,  delicate  membrane  lining  the  posterior 
chamber  of  the  aqueous  humour;  16,  membrane  of  Jacob;  17,  the  optic  nerve  surrounded  by  its  neurilema; 
17',  the  fibres  of  the  optic  nerve  consisting  of  fasciculi  of  primitive  tubules ;  18,  central  artery  of  the 
retina;  19,  papilla  cornica  of  the  optic  nerve  ;  20,  retina;  the  situation  of  its  vascular  layer  is  indicated  by 
a  dotted  line  ;  21,  central  transparent  point  of  the  retina ;  22,  vitreous  humour;  23,  the  hyaloid  membrane ; 
24,  canalis  hyaloideus ;  25,  zonula  ciliaris;  in  the  plate,  none  of  its  fimbriated  part  is  seen,  being  concealed 
by  the  ciliary  processes;  26,  canal  of  Petit;  27,  crystalline  lens;  28,  anterior  wall  of  the  capsule  of  the 
lens;  29,  posterior  wall  of  the  capsule  of  the  lens;  30,  posterior  chamber  of  the  aqueous  humour;  31,  ante- 
rior chamber  of  the  aqueous  humour.] 

are  fixed  upon  an  object,  their  axis  must  converge  (as  formerly  explained, 
§  254)  so  as  to  meet  in  it.  The  nearer  the  object,  the  greater  must  be  the 
degree  of  convergence ;  and  when  the  object  is  brought  within  the  ordinary 
distance  of  distinct  vision,  the  convergence  must  very  rapidly  increase.  Now 
this  is  precisely  what  takes  place,  in  regard  to  alterations  in  the  focus  of  the 
eye;  for  little  change  is  required,  when  the  object  is  made  to  approach  from 
a  considerable  distance  to  a  moderate  distance ;  but,  when  it  is  brought  near 
the  eye,  the  focus  must  be  considerably  lengthened,  or  the  convexity  of  the 
eye  increased,  to  cause  the  rays  to  meet  on  the  retina :  and  hence  it  may  be 
surmised,  that  the  same  cause  is  acting  to  produce  both  changes.  But  that 
the  convergence  of  the  axis  is  not  itself  in  any  way  the  occasion  of  the  altera- 
tion of  the  focus  of  the  eye,  is  shown  by  the  fact,  that  the  adaptation  is  as 
perfect  in  a  person  who  only  possesses  or  uses  one  eye,  as  it  is  when  both  are 
employed;  and  also  by  the  power  which  is  possessed  by  some  persons  of 
altering  the  focus  of  the  eye  by  an  effort  of  the  will,  whilst  the  convergence 
remains  the  same.  In  regard  to  the  adaptation  of  the  eyes  to  varying  distances, 
it  is  further  to  be  remarked,  that,  when  an  object  is  being  viewed  as  near  to 
the  eye  as  it  can  be  distinctly  seen,  the  pupil  contracts  in  a  considerable 
degree.  The  final  cause  of  this  change  is  evidently  to  exclude  the  outer  rays 
of  the  cone  or  pencil,  which,  from  the  large  angle  of  their  divergence,  would 
fall  so  obliquely  on  the  convex  surface  of  the  eye,  as  to  be  much  affected  by 
the  spherical  aberration;  and  to  allow  the  central  rays  only  to  enter  the  eye, 
so  as  to  preserve  the  clearness  of  the  image.  The  channel  through  which  it 
is  effected  is  evidently  the  same  as  that  by  which  the  convergence  of  the  eyes 
is  produced, — namely,  the  inferior  branch  of  the  third  pair  of  nerves  ;  to  the 
action  of  which,  the  sensations  upon  the  retina  form  the  stimulus,  in  the  Same 
manner  as  they  do  to  the  ordinary  variation  in  the  diameter  of  the  pupil  under 
the  influence  of  light. 

331.  The  ordinary  forms  of  defective  vision,  which  are  known  under  the 
names^of  myopia  and  presbyopia,  or  short-sightedness  and  long-sightedness, 
are  entirely  attributable  to  defects  in  the  optical  adaptation  of  the  eye.  In  the 
former,  its  refractive  power  is  too  great;  the  rays  from  objects  at  the  usual 
distance  are  consequently  brought  too  soon  to  a  focus,  so  as  to  cross  one 
another  and  diverge  before  they  fall  upon  the  retina;  whilst  the  eye  is 
adapted  to  bring  to  their  proper  focus  on  the  retina  only  those  rays  which 
were  previously  diverging  at  a  large  angle,  from  an  object  in  its  near  proxi- 
mity. Hence  a  short-sighted  person,  whose  shortest  limit  of  distinct  vision 
is  not  above  half  that  of  a  person  of  ordinary  sight,  can  see  minute  objects 
more  clearly;  his  eyes  having,  in  fact,  the  same  magnifying  power  which 
those  of  the  other  would  possess,  if  aided  by  a  convex-glass  that  would  enable 
him  to  see  the  object  distinctly  at  the  shorter  distance.  But  as  the  myopic 
structure  of  the  eye  incapacitates  its  possessor  from  seeing  objects  clearly,  at 
even  a  moderate  distance,  it  is  desirable,  to  apply  a  correction ;  and  this  is 
done  by  simply  interposing  a  concave  lens,  of  which  the  curvature  is  properly 


SENSE  OF  VISION. 


245 


Fig.  45. 


adapted  to  compensate  for  the  excess  of  that  of  the  organ  itself,  between  the 
object  and  the  eye.  On  the  other  hand,  in  the  presbyopic  eye,  the  curvature 
and  refractive  power  are  not  sufficient  to  bring  to  a  focus  on  the  retina,  rays 
which  were  previously  divergent  in  a  considerable  or  even  in  a  moderate 
degree;  and  indistinct  vision  in  regard  to  all  near  objects  is,  therefore,  a 
necessary  consequence,  whilst  distant  objects  are  well  seen.  This  defect  is 
remedied  by  the  use  of  convex  lenses,  which  make  up  for  the  deficiency  of 
the  curvature.  We  commonly  meet  with  myopia  in  young  persons,  and  with 
presbyopia  in  old ;  but  this  is  by  no  means  the  invariable  rule ;  for  even  aged 
persons  are  sometimes  short-sighted;  and  long-sightedness  is  occasionally  met 
with  amongst  the  young.  In  choosing  spectacles,  for  the  purpose  of  correcting 
the  errors  of  the  eye,  it  is  of  great  consequence  not  to  make  an  over-compen- 
sation ;  for  this  has  a  tendency  to  increase  the  defect,  besides  occasioning 
great  fatigue  in  the  employment  of  the  sight.  It  may  be  easily  found,  when 
a  glass  of  the  right  power  has  been  selected,  by  inquiring  of  the  individual 
whether  it  alters  the  apparent  size  of  the  objects,  or  only  renders  them  distinct. 
If  it  alter  the  size  (increasing  it  if  it  be  a  convex  lens,  and  diminishing  it  if  it 
be  a  concave),  its  curvature  is  too  great;  whilst  if  it  do  not  disperse  the  haze, 
it  is  not  sufficiently  powerful.  In  general  it  is  better  to  employ  a  glass  which 
somewhat  under-compensates  the  eye,  than  one  which  is  of  a  curvature  at  all 
too  high ;  since,  with  the  advance  of  years  in  elderly  persons,  a  progressive 
increase  in  power  is  required ;  and,  as  young  persons  grow  up  to  adult  age, 
they  should  endeavour  to  dispense  with  the  aid  of  spectacles. 

332.  Many  other  interesting  inquiries,  re- 
specting the  action  of  the  eye  as  an  optical 
instrument,  suggest  themselves  to  the  physical 
philosopher ;  but  the  foregoing  are  the  chief  in 
which  the  physiologist  is  concerned ,  and  we 
shall  now  proceed,  therefore,  to  consider  the 
share,  which  the  retina  and  optic  nerve  per- 
form in  the  phenomena  of  vision.  The  Optic 
Nerve,  at  its  entrance  into  the  eye,  divides 
itself  into  numerous  small  fasciculi  of  ultimate 
fibrils ;  and  these  spread  themselves  out,  and 
inosculate  with  each  other  by  an  exchange  of 
fibrils,  so  as  to  form  a  net-like  plexus,  which 
is  the  outer  layer  of  the  true  retina.  From 
this  plexus,  in  which  the  fibres  are  lying  in  the 
a  plane  of  the  surface  of  the  vitreous  humor, 
very  large  number  of  fibrils  arise,  in  a  direction 
perpendicular  to  that  surface,  so  as  all  to  be 
directed  towards  the  centre  of  the  eye.  These 
pass  through  a  delicate  layer  of  cellular  tissue, 
containing  a  minute  plexus  of  blood-vessels ; 
and  from  this  every  fibril  receives  a  sheath, 
which  envelops  its  extremity,  thus  forming 
a  minute  papilla.  The  surface  of  the  retina 
nearest  the  vitreous  humor,  is  entirely  com 
posed  of  these  papillae,  which  are  closely  set 
together ;  a  layer  of  cells  is  interposed  between 
them,  however ;  and  these  cells  are  regarded  Papilla?  of  the  retina  of  the  Frog,  seen 
by  Valentin  as  analogous  to  those  of  ganglionic  from  the  side  ^ur"ed  t(>w*rds  the  vitre' 

J  ,  ,          •»?.  •   ,       j«  r   f  ous  humor;  the  four  hipher   rows  are 

matter;  but  other  Microscopists  dissent  from     geen  sidew'ayg    Magni^ed  300  times 
this  opinion,  considering  them  as   belonging    {After  Treviranus.) 
rather  to  the  vitreous  humor.     In  the  retina  of 

21* 


Part  of  the  retina  of  a  Frog,  seen  from 
the  outer  surface.  Magnified  300  times. 
(After  Treviranus.) 

Fig.  46. 


246 


OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 


[Fig.  47. 


the  Frog,  the  diameter  of  the  ultimate  nervous 
fibres  is  stated  by  Treviranus  at  about  y^Q-th 
of  an  inch  ;  whilst  that  of  the  papillae  is  about 
i th  of  an  inch.  In  Birds  and  Mammalia, 


0 

A  portion  of  the  Retina  of  an  Infant, 
with  its  vessels  injected  and  magnified 
25  diameters.  An  outline  of  the  natural 
size  of  this  piece  is  seen  just  below  the 
main  cut.] 


however,  the  papillas,  as  well  as  the  nervous 
fibrils,  are  much  smaller;  in  the  former  the 
diameter  of  the  papillae  is  stated  at  from  about 
__^.__th  to  fi-3J5otn  °f  an  inch;  in  the  Rabbit 
at  yYQ-oth  of  an  inch ;  and  in  Man  at  from  the 
^^--th  to  grV^h  °f  an  inch.*  An  attempt 
has  been  made  to  show,  that  the  size  of  the 
papillae  determines  that  of  the  smallest  object, 
which  can  be  seen  by  the  unaided  eye  ;  and 
it  is  a  curious  fact,  that  the  calculation  long 
ago  made  by  Smith,  in  regard  to  the  size  of 
the  most  minute  sensitive  point  upon  the  retina, 
founded  upon  the  dimensions  which  the  image 
of  the  minutest  visible  object  will  possess,  co- 
incides exactly  with  the  measurement  of  Weber. 
There  is  no  doubt,  however,  that,  under  favour- 
able circumstances,  the  eye  will  take  cognizance 
of  objects  much  smaller  than  those  on  which 
Smith's  calculation  was  founded.  The  follow- 
ing statements  on  this  interesting  subject  com- 
prehend the  result  of  numerous  inquiries  re- 
cently made  by  Ehrenberg,  with  the  view  of 
establishing  the  limits  of  Human  Vision,  as  a 
datum  from  which  to  calculate  the  ultimate  power  of  the  Microscope.! 

333.  In  opposition  to  the  generally-received  opinion,  Ehrenberg  arrived  at 
the  conclusion  that,  in  regard  to  the  extreme  limits  of  vision,  there  is  little 
difference  amongst  persons  of  ordinarily  good  sight,  whatever  may  be  the  focal 
distance  of  their  eyes.  The  smallest  square  magnitude  usually  visible  to -the 
naked  eye,  either  of  white  particles  on  a  black  ground,  or  of  black  upon  a 
white  or  light-coloured  ground,  is  about  the  4  ^th  of  an  inch.  It  is  possible,  by 
the  greatest  condensation  of  light,  and  excitement  of  the  attention,  to  recognize 
magnitudes  between  the  j^-jth  and  j^th  of  an  inch;  but  without  sharpness 
or  certainty.  Bodies  which  are  smaller  than  these  cannot  be  discerned  with 
the  naked  eye  when  single ;  but  may  be  seen  when  placed  in  a  row.  Parti- 
cles which  powerfully  reflect  light,  however,  may  be  distinctly  seen,  when  not 
half  the  size  of  the  least  of  the  foregoing ;  thus,  gold  dustf  of  the  fineness  of 
of  an  inch,  may  be  discerned  with  the  naked  eye  in  common  daylight, 
e  delicacy  of  vision  is  far  greater  for  lines  than  for  single  articles ;  opaque 
threads  of  T -oVo-tn  °f  an  inch  in  diameter  may  be  discerned  with  the  naked 
eye,  when  held  towards  the  light.  Such  threads  are  about  half  the  diameter 
of  the  Silkworm's  fibre.  It  is  evident,  from  these  facts,  that  the  images  of 
such  particles  formed  upon  the  retina,  must  be  considerably  smaller  than  the 
diameter  of  the  papillae.  Still  it  is  by  no  means  improbable  that,  when  we  are 
looking  at  a  continuous  surface,  the  diameter  of  the  papillae  will  regulate  our 

*  This  is  the  diameter  assigned  by  Weber  to  what  he  terms  the  globules  of  the  Retina; 
there  can  be  little  doubt,  however,  that  these  are  identical  with  the  papillas,  since  the 
latter  are  very  apt  to  separate,  in  eyes  which  are  examined  even  a  short  time  after  death, 
from  the  fibres  beneath. 

j- Taylor's  Scientific  Memoirs,  vol.  i.  p.  576. 

t  Ehrenberg  mentions  that  he  obtained  the  finest  particles  of  gold,  by  scraping  gilt  brass ; 
by  filing  pure  gold  he  always  obtained  much  coarser  particles. 


SENSE  OF  VISION.  247 

power  of  distinguishing  minute  parts  of  that  surface ;  since,  as  Weber  justly 
remarks,  two  impressions  falling  upon  one  of  these  points,  can  scarcely  affect 
the  sensorium  otherwise  than  with  one  sensation.  The  degree  in  which  the 
attention  is  directed  to  them,  has  a  great  influence  on  the  readiness  with  which 
very  minute  objects  can  be  perceived ;  and  Ehrenberg  remarks  that  there  is 
a  much  greater  difference  amongst  individuals  in  this  respect  than  there  is  in 
regard  to  the  absolute  limits  of  vision.  Many  persons  can  distinctly  see  such 
objects,  when  their  situation  is  exactly  pointed  out  to  them,  who  cannot  other- 
wise distinguish  them ;  and  the  same  is  the  case  with  persons  of  acuter  per- 
ception, with  respect  to  objects  at  distances  greater  than  those  at  which  they 
can  see  most  clearly.  "  1  myself,"  says  Ehrenberg,  "  cannot  see  ^yL-^th  of 
an  inch,  black  on  white,  at  twelve  inches  distance ;  but  having  found  it  at 
from  four  to  five  inches  distance,  I  can  remove  it  to  twelve  inches,  and  still  see 
the  object  plainly."  Similar  phenomena  are  well  known  in  regard  to  a  bal- 
loon, or  a  faint  star,  in  a  clear  sky  ;  or  a  ship  in  the  horizon :  we  easily  see 
them  after  they  have  been  pointed  out  to  us ;  but  the  faculty  of  rapidly 
descrying  depends  on  the  habit  of  using  the  eyes  in  search  of  such  objects 
(§  313). 

334.  The  sense  of  Vision  depends,  in  the  first  place,  on  the  transference  to 
our  minds  of  the  picture  which  is  formed  upon  the  retina ;  this  picture  puts 
us  in  possession  of  the  outlines,  lights  and  shades,  colours  and  relative  posi- 
tions of  the  objects  before  us  ;  and  all  the  ideas  respecting  the  real  forms,  dis- 
tances, &c.,  of  bodies,  which  we  found  upon  these  data,  must  be  considered  in 
the  light  of  perceptions  either  instinctive  or  acquired.  Many  of  these  are 
derived  through  the  combination,  in  our  minds,  of  the  visual  sensations,  with 
those  derived  from  the  sense  of  touch.  Thus,  to  take  a  most  simple  illustra- 
tion, the  idea  of  smoothness  is  one  essentially  tactile ;  and  yet  it  constantly 
occurs  to  us  on  looking  at  a  surface  which  reflects  light  in  a  particular  man- 
ner. But  if  it  were  not  for  the  association,  which  experience  leads  us  to 
form,  of  the  connection  between  polish  as  seen  by  the  eye,  and  smoothness  as 
felt  by  the  touch,  we  should  not  be  able  to  determine,  as  we  now  can  do,  the 
existence  of  both  these  qualities,  from  an  impression  communicated  to  us 
through  either  sense  singly.  The  general  fact  that,  in  Man,  the  greater  part 
of  those  notions  of  the  external  wrorld,  by  which  his  actions  in  the  adult  state 
are  guided,  are  acquired  by  the  gradual  association  of  the  sensations  commu- 
nicated by  the  sight  and  by  touch,  is  substantiated  by  amply  sufficient  evidence. 
This  evidence  is  chiefly  derived  -from  observations  made  upon  persons  born 
blind,  to  whom  sight  has  been  communicated  by  an  operation  at  a  period  of 
life  which  enabled  them  to  give  an  accurate  description  of  their  sensations. 
The  case  recorded  by  Cheselden  is  one  of  the  most  interesting  of  these.  The 
youth  (about  12  years  of  age)  for  some  time  after  tolerably  distinct  vision  had 
been  obtained,  saw  every  thing^fotf,  as  in  a  picture  ;  simply  receiving  the  con- 
sciousness of  the  impressions  made  upon  his  retina :  and  it  was  some  time 
before  he  acquired  the  power  of  judging,  by  his  sight,  of  the  real  forms  and 
distances  of  the  objects  around  him.  An  amusing  anecdote  recorded  of  him, 
shows  the  complete  want  of  natural  or  intuitive  connection  which  there  is  in 
Man,  between  the  ideas  formed  through  visual  and  through  tactile  sensations. 
He  was  well  acquainted  with  a  Dog  and  a  Cat  by  feeling;  but  could  not 
remember  their  respective  characters  when  he  saw  them.  One  day,  when 
thus  puzzled,  he  took  up  the  Cat  in  his  arms,  and  felt  her  attentively,  so  as  to 
associate  the  two  sets  of  ideas ;  and  then,  setting  her  down,  said,  "  So,  puss,  I 
shall  know  you  another  time."  A  similar  instance  has  come  under  the 
Author's  own  knowledge ;  but  the  subject  of  it  was  scarcely  old  enough  to 
present  phenomena  so  striking.  One  curious  circumstance  was  remarked  of 
him,  which  fully  confirms  (if  confirmation  were  wanting)  the  view  here  given. 


248  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

For  some  time  after  the  sight  was  tolerably  clear,  the  lad  preferred  finding  his 
way  through  his  father's  house,  to  which  he, had  been  quite  accustomed  when 
blind,  by  touch  rather  than  by  sight, — the  use  of  the  latter  sense  appearing  to 
perplex  rather  than  to  assist  him ;  but,  when  learning  a  new  locality,  he 
employed  his  sight,  and  evidently  perceived  the  increase  of  facility  which  he 
derived  from  it. 

335.  The  question  has  been  proposed,  whether  a  person  born  blind,  who 
was  able  by  the  sense  of  touch  to  distinguish  a  cube  from  a  sphere,  would,  on 
suddenly  obtaining  his  sight,  be  able  to  distinguish  them  by  the  latter  sense. 
This  question  was  answered  by  Locke  in  the  negative ;  and  probably  with 
justice.     It  is  no  real  objection  to  such  a  reply,  that  a  netv-born  animal  seeks 
the  nipple  of  its  mother,  when  informed  of  its  proximity  by  sight ;  for  all  that 
is  indicated  by  this  fact  is,  that  the  sensation  excites  an  intuitive  feeling  of 
desire,  which  gives  rise  to  movements  adapted  to  gratify  it.     Such  instinctive 
actions,  founded  upon  intuitive  perceptions,  are,  as  already  pointed  out,  much 
more  numerous  in  the  lower  animals  than  in  the  higher,  and  in  the  young  of 
the  Human  species  than  in  the  adult  (§  259) ;  and  they  do  not  afford  any  proof 
that  definite  notions,  such  as  we  acquire,  of  the  forms  and  properties  of  exter- 
nal objects,  are  possessed  by  the  animals  which  exhibit  them.     We  shall  now 
examine,  a  little  more  in  detail,  into  the  means  by  which  we  gain  such  notions, 
and  the  data  on  which  they  are  founded. 

336.  The  first  point  to  be  determined,  is  one  which  has  been  a  fruitful 
source  of  discussion, — the  cause  of  erect  vision,  the  picture  upon  the  retina 
being  inverted.     Many  solutions  of  it  have  been  attempted ;  but  they  are  for 
the  most  part  rather  specious  than  really  satisfactory.     That  which  has  been 
of  late  years  the  most  in  vogue,  is  founded  upon  what  was  styled  the  Law  of 
Visible  Direction,  which  has  been  supported  by  Sir  D.  Brewster  and  other 
eminent  Philosophers.     This  law  affirms,  that  every  object  is  seen  in  the 
direction  of  the  perpendicular  to  that  point  of  the  retina,  on  which  its  image 
is  formed ;  or,  in  other  words,  that,  as  all  the  perpendiculars  to  the  several 
points  of  the  inner  surface  of  a  sphere  meet  in  the  centre,  the  line  of  direction 
of  any  object  is  identical  with  the  prolonged  radius  of  the  sphere,  drawn  from 
the  point  at  which  its  image  is  made  upon  the  retina.     Upon  close  examina- 
tion, however,  it  is  found  that  this  law  cannot  be  optically  correct ;  since  the 
lines  of  direction  cross  each  other  at  a  point  much  anterior  to  the  centre  of  the 
globe;  as  may  be  determined  by  drawing  a  diagram  upon  a  large  scale,  and 
laying  down  the  course  of  the  rays  received  by  the  eye,  according  to  the  cur- 
vatures and  refractive  powers  of  its  different  parts/   In  this  manner  it  has 
been  determined  by  Volkmann,  that  the  lines  of  direction  cross  each  other  in 
a  point  a  little  behind  the  crystalline  lens;  and  that  they  will  thus  fall  at  such 
different  angles  on  different  points  of  the  retina,  that  no  general  law  can  be 
laid  down  respecting  them.     It  may  be  questioned,  moreover,  whether  any 
such  law  would  afford  any  assistance  in  explaining  the  phenomenon;  since, 
after  all,  it  is  requisite  to  assume  an  intuitive  applicatjon  of  it,  in  supposing 
the  mind  to  derive  its  ideas  of  the  relative  situations  of  objects,  from  the 
imagined  line  of  direction £-A  much  simpler  and  more,  direct  explanation 
may  be  given.     We  must  remember  that— which  we  have  had  occasion  to 
notice  in  regard  to  all  the  other  senses, — the  broad  line  of  distinction  between 
the  sensation  and  the  perception  or  elementary  notion;  and  this  is  still  more 
clearly  shown  by  the  complete  absence  of  any  relation,  but  such  as  experience  ' 
develops,  between  the   perceptions   derived   through   the   sight   and  those 
acquired  from  the  touch.     Hence  there  is  no  more  difficulty  in  understanding 
that  an  inverted  picture  upon  the  retina  should  convey  to  us  a  notion  of  the 
external  world,  which  harmonizes  with  that  acquired  through  the  sense  of 
touch,  than  there  is  in  comprehending  the  formation  of  any  of  those  intuitive 


SENSE  OF  VISION.  249 

perceptions  of  animals  which  are  so  much  more  removed  from  the  teachings 
of  our  own  experience  (§  290).  1  It  is  justly  remarked  by  Miiller  that,  "  if  we 
do  see  objects  inverted  [or  rather,  if  the  picture  on  the  retina  is  inverted]  the 
only  proof  we  can  possibly  have  of  it,  is  that  afforded  by  the  study  of  the  laws 
of  Optics ;  and,  if  every  thing  is  seen  reversed,  the  relative  position  of  the 
objects  remains  unchanged.  Hence  it  is,  also,  that  no  discordance  arises 
between  the  sensations  of  inverted  vision  and  those  of  touch,  which  perceives 
every  thing  in  its  erect  position ;  for  the  images  of  all  objects,  even  of  our 
own  limbs,  on  the  retina,  are  equally  inverted,  and  therefore  maintain  the 
same  relative  position.  Even  the  image  of  our  hand,  when  used  in  touch,  is 
inverted."  From  what  has  been  stated,  it  would  appear  quite  conceivable, 
that  a  person  just  endowed  with  sight,  should  not  at  first  know  by  his  visual 
powers,  whether  a  pyramid  placed  before  his  eyes  is  the  same  body,  and  in 
the  same  position,  as  one  with  which  he  has  become  acquainted  by  the  touch ; 
and,  if  this  be  admitted,  the  inference  necessarily  follows,  that  the  notion  of 
erectness,  which  we  form  by  the  combined  use  of  our  eyes  and  our  hands,  is 
really  the  product  of  experience  in  ourselves,  whilst  it  is  probably  innate  or 
intuitional  in  the  lower  animals. 

337.  The  cause  of  single  vision  with  the  two  eyes  has,  in  like  manner,  been 
the  subject  of  much  discussion;  since  the  mode  in  which  we  are  affected!  by 
the  two  simultaneous  impressions,  is  quite  different  from  that  in  which  we 
derive  our  knowledge  of  external  things  through  the  other  senses.  Some  have 
even  asserted,  that  we  do  not  really  employ  both  eyes  simultaneously,  but 
that  the  mind  is  affected  by  the  image  communicated  by  one  only ;  and  this 
idea  might  seem  to  be  confirmed  by  the  fact  heretofore  mentioned  (§  313) 
respecting  the  alternate  use  of  the  two  eyes,  when  they  are  looking  through 
two  differently-coloured  media.  But  it  is  easily  disproved  in  other  ways.  It 
will  presently  be  shown,  that  all  our  estimates  of  the  forms  of  bodies  depend 
on  the  combination  by  the  mind  of  the  images  simultaneously  transmitted  by 
the  two  eyes  ;  and  our  knowledge  of  distances  is  in  great  part  obtained  in  like 
manner.  /  The  condition  of  Single  Vision  has  been  already  stated  (§  253)  to 
be  probably  this, — that  the  two  images  of  the  object  should  be  formed  on  parts 
of  the  two  retina?  which  are  accustomed  to  act  in  concert ;  and  reasons  were 
given  for  the  belief,  that  habit  is  the  chief  means  by  which  this  conformity  is 
produced.  ;  There  can  be  no  doubt,  however,  that  double  images  are  continu- 
ally being  conveyed  to  our  minds ;'  but  that,  from  their  want  of  force  and  dis- 
tinctness, and  from  the  attention  being  fixed  on  something  else,  we  do  not  take 
cognizance  of  them.  This  may  be  sho\vn  by  a  very  simple  experiment.  If 
two  fingers  be  held  up  before  the  eyes,  one  in  front  of  the  other,  and  vision  be 
directed  to  the  more  distant,  so  that  it  is  seen  singly,  the  nearer  will  appear 
double ;  while,  if  the  nearer  one  be  regarded  more  particularly,  so  as  to  appear 
single,  the  more  distant  will  be  seen  double.  A  little  consideration  will  show, 
therefore,  that  our  minds  must  be  continually  affected  with  sensations  which 
cannot  be  united  into  the  idea  of  a  single  image  ;  since,  whenever  we  direct 
the  axes  of  our  eyes  towards  any  object,  every  thing  else  will  be  represented 
to  us  as  double  ;  but  we  do  not  ordinarily  perceive  this,  from  our  minds  being 
fixed  upon  a  clear  and  distinct  image,  and  disregarding,  therefore,  the  vague 
undefined  images  formed  by  objects  at  a  different  focus.  Of  this  it  is  very 
easy  to  convince  one's  self.  It  is,  moreover,  evident  from  this  experiment,  that 
double  vision  cannot  result  from  want  of  symmetry  in  the  position  of  the 
images  upon  the  retina,  to  which  some  have  attributed  it;  for  it  answers 
equally  well,  if  the  line  of  the  two  fingers  be  precisely  in  front  of  the  nose, 
so  that  the  inclination  of  both  eyes  towards  either  object  is  equal;  the  position 
of  the  images  of  the  second  object  must  then  be  at  the  same  distance  on  each 
side  from  the  central  line  of  the  retina,  and  yet  they  are  represented  to  the 


250  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

mind  as  double.  It  is,  moreover,  easily  shown  that,  in  the  lower  animals  whose 
orbits  are  not  directed  forwards  as  in  us,  but  sideways  in  a  greater  or  less 
degree,  whenever  an  object  is  so  situated  as  to  be  seen  by  both  eyes,  the  points 
of  the  two  retinae  on  which  its  images  are  formed,  must  be  very  far  from  possess- 
ing this  symmetry. 

338.  Many  attempts  have  been  made  to  explain  the  phenomena  of  single 
vision,  by  the  peculiar  decussation  of  the  optic  nerves ;  and  an   interesting 
correspondence  between  the  varieties  in  the  degree  of  decussation,  and  the 
position  of  the  eyes,  in  several  animals,  has  been  pointed  out  by  Mr.  Solly 
and  Mr.  Mayo.     It  is  stated  by  Mr.  Mayo  that  the  Optic  nerve  in  Man  con- 
sists of  three  tracts;  of  which  the  internal  one  is  strictly  commissural,  con- 
necting together  the  two  retinae  anteriorly,  and  the  two  optic  ganglia  posteri- 
orly; the  middle  tract  decussates,  and  is  believed  by  Mr.  M.  to  supply  that 
part  of  the  retina  which  lies  on  the  inner  side  of  each  ball,  between  its  ante- 
rior border  and  the  insertion  of  the  optic  nerve ;  whilst  the  external  tract  does 
not  decussate,  but  passes  on  to  supply  the  exterior  portion  of  the  retina  on  the 
same  side.     Thus  the  right  optic  nerve  supplies  the  right  side  of  each  ball ; 
whilst  the  left  supplies  the  left  side.     On  the  other  hand,  in  most  of  the  Osse- 
ous Fishes,  the  decussation  is  complete ;  each  nerve  passing  entirely  to  the 
eye  of  the  opposite  side.     From  these  and  other  data,  it  has  been  concluded, 
that  each  nerve  is  used  in  looking  towards  the  opposite  side.     This  is  evidently 
true  of  the  Osseous  Fishes,  whose  two  eyes,  being  directed  sideways,  have 
two  entirely  different  spheres  of  vision.      And  it  is -also  true  of  Man,  if  Mr. 
M.'s  account  of  the  distribution  of  the  nerve  be  correct ;  since,  when  we  look 
at  an  object  held  directly  in  front  of  the  face,  at  the  level  of  the  eyes,  and  at 
the  nearest  point  for  distinct  vision,  almost  the  whole  of  that  portion  of  the 
right  retina,  which  lies  to  the  outside  of  the  entrance  of  the  optic  nerve,  is 
directed  to  the  left ;  and  the  exactly  different,  complementary,  or  inner  portion 
of  the  left  retina,  which  is  supplied  by  the  same  nerve,  is  likewise  directed  to 
the  left.     On  this  supposition,  all  the  rays  entering  the  two  eyes  from  any  one 
point,  will  be  brought  to  a  focus  on  fibrils  belonging  to  the  same  nerve ;  though 
these  are  in  Man,  as  in  other  animals  whose  spheres  of  vision  are  nearly  or 
partly  coincident,  distributed  to  distinct  visual  organs.*     It  is  obvious,  how- 
ever, that  this  or  any  similar  explanation  must  be  insufficient  to  explain  the 
phenomenon  of  single  vision ;  since  the  images  formed  upon  the  two  retinae 
are  necessarily  different,  and  must  be  combined  or  harmonized  by  an  act  of 
the  mind,  as  will  be  shown  in  the  succeeding  paragraphs. 

339.  We  shall  next  consider  the  mode  in  which  our  notion  of  the  solid 
forms  and  relative  projection  of  objects  is  acquired ;  on  which  great  light  has 

recently  been  thrown  by  the  interesting  experiments  of  Mr.  Wheatstone.t  It 
is  perfectly  evident,  both  from  reason  and  experience,  that  the  flat  picture 
upon  the  retina,  which  is  the  only  object  of  our  sensation,  could  not  itself 
convey  to  our  minds  any  notion  but  that  of  a  corresponding  plane  surface. 
In  fact,  any  notion  of  solidity  which  might  be  formed  by  a  person  who  had 
never  had  the  use  of  more  than  one  eye,  would  entirely  depend  upon  the 
combination  of  his  visual  and  tactile  sensations.  This  idea  is  fully  confirmed 
by  the  case  already  referred  to,  as  recorded  by  Cheselden.  The  first  visual 

*  The  late  Dr.  Wollaston  was  subject  to  a  curious  affection  of  vision,  which  consisted 
m  his  not  being  able  to  see  more  than  half  of  an  object,— the  loss  being  sometimes  on 
one  side,  and  sometimes  on  the  other.  The  Author  has  met  with  several  cases  of  this 
disorder,  which  has  been  termed  hemiopia.  Dr.  W.  thought  that  they  might  be  explained 
by  the  decussation  of  the  optic  nerve;  but  Mr.  Mayo  states  that  he  has  known  instances 
of  a  parallel  affection,  involving  alternately  the  centre  and  the  circumference  of  the  retina, 
and  therefore  not  attributable  to  any  such  structural  arrangement. 

f  Philosophical  Transactions,  1838. 


SENSE  OF  VISION.  251 

idea  formed  by  the  youth  was,  that  the  objects  around  him  formed  a  flat  sur- 
face, which  touched  his  eyes,  as  they  had  previously  been  in  contact  with  his 
hands  ;  and  after  this  notion  had  been  corrected,  through  the  education  of  his 
sight  by  his  touch,  he  fell  into  the  converse  error  of  supposing  that  a  picture, 
which  was  shown  to  him,  was  the  object  itself  represented  in  relief  on  a  small 
scale.  But  where  both  eyes  are  employed,  it  has  been  ascertained  by  Mr. 
Wheatstone  that  they  concur  in  exciting  the  perception  of  solidity  or  pro- 
jection, which  arises  from  the  combination  of  two  different  images  in  the 
mind.  It  is  easily  shown  that  any  near  object  is  seen  in  two  different  modes 
by  the  two  eyes.  Thus,  let  the  reader  hold  up  a  thin  book,  in  such  a  manner 
that  its  back  shall  be  exactly  in  front  of  his  nose,  and  at  a  moderate  distance 
from  it ;  he  will  observe,  by  closing  first  one  eye  and  then  the  other,  that  his 
perspective  view  of  it  (or  the  manner  in  which  he  would  represent  it  on  a 
plane  surfabe)  is  very  different,  according  to  the  eye  with  which  he  sees  it. 
With  the  right  eye  he  will  see  its  right  side,  very  much  foreshortened ;  with 
the  left,  he  will  gain  a  corresponding  view  of  the  left  side ;  and  the  apparent 
angles,  and  the  lengths  of  the  different  lines  will  be  found  to  be  very  different 
in  the  two  views.  On  looking  at  either  of  these  views  singly,  no  other  notion 
of  solidity  can  be  acquired  from  it  than  that  to  which  the  mind  is  conducted 
by  the  association  of  such  a  view  with  the  touch  of  the  object  it  represents. 
But  it  is  capable  of  proof,  that  the  mental  association  of  the  two  different 
pictures  upon  the  retinae  does  of  itself  give  rise  to  the  idea  of  solidity.  This 
proof  is  afforded  by  Mr.  Wheatstone's  ingenious  instrument,  the  Stereoscope. 
340.  The  Stereoscope  essentially  consists  of  two  plane  mirrors,  inclined 
with  their  backs  to  one  another  at  an  angle  of  90°.  If  two  perspective  draw- 
ings of  any  solid  object,  as  seen  at  a  given  distance  with  the  two  eyes  respect- 
ively, be  placed  before  these  mirrors,  in  such  a  manner  that  their  images 
shall  be  made  to  fall  upon  the  corresponding  parts  of  the  two  retinae,  in 
the  same  manner  as  the  two  images  formed  by  the  solid  object  itself  would 
have  done,  the  mind  will  perceive,  not  a  single  representation  of  the  object, 
nor  a  confused  union  of  the  two,  but  a  body  projecting  in  relief, — the  exact 
counterpart  of  that  from  which  the  drawings  were  made.  Mr.  Wheatstone 
further  shows,  by  means  of  the  Stereoscope,  that  similar  images,  differing  to  a 
certain  extent  in  magnitude,  when  presented  to  the  corresponding  parts  of  the 
two  retinae,  give  rise  to  the  perception  of  a  single  object,  intermediate  in  size 
between  the  two  monocular  pictures.  Were  it  not  for  this,  objects  would 
appear  single  only  when  at  an  equal  distance  from  both  eyes,  so  that  their 
pictures  upon  the  retina  are  of  the  same  size  ;  which  will  only  happen  when 
they  are  directly  in  front  of  the  median  line  of  the  face.  Again,  if  pictures 
of  dissimilar  objects  be  simultaneously  presented  to  the  two  eyes,  the  conse- 
quence will  be  similar  to  that  which  is  experienced  when  the  rays  come  to 
the  eye  through  two « differently-coloured  media; — the  two  images  do  not 
coalesce,  nor  do  they  appear  permanently  superposed  upon  one  another ;  but 
at  one  time  one  image  predominates  to  the  exclusion  of  the  other,  and  then 
the  other  is  seen  alone  ;  and  it  is  only  at  the  moment  of  change  that  the  two 
seem  to  be  intermingled.  It  does  not  appear  to  be  in  the  power  of  the  will, 
Mr.  Wheatstone  remarks,  to  determine  the  appearance  of  either ;  but,  if  one 
picture  be  more  illuminated  than  the  other,  it  will  be  seen  during  a  larger 
proportion  of  the  time.  :Many  other  curious  experiments  with  this  simple 
instrument  are  related  by  Mr.  Wheatstone ;  and  they  all  go  to  confirm  the 
general  conclusion,  that  the  combination  of  the  images  furnished  by  the  two 
eyes  is  a  mental  act,  resulting  from  an  inherent  law  of  our  psychical  constitu- 
tion ;  and  that  our  perceptions  of  the  solidity  and  projection  of  objects,  near 
enough  to  be  seen  in  different  views  with  the  two  eyes,  result  from  this  cause. 
In  regard  to  distant  objects,  however,  the  difference  in  the  images  formed  by 


252  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

the  two  eyes  is  so  slight,  that  it  cannot  aid  in  the  determination ;  and  hence 
it  is,  that,\vhilst  we  have  no  difficulty  in  distinguishing  a  picture,  however 
well  painted,  from  a  solid  object,  when  placed  near  our  eyes,  (since  the  idea 
which  might  be  suggested  by  the  image  formed  on  one  eye,  will  then  be 
corrected  by  the  other,)  we  are  very  liable  to  be  misled  by  a  delineation,  in 
which  the  perspective,  light  and  shade,  &c.,  are  faithfully  depicted,  if  we  are 
placed  at  a  distance  from  it,  and  are  prevented  from  perceiving  that  it  is  but  a 
picture.  In  this  case,  however,  a  slight  movement  of  the  head  is  sufficient  to 
undeceive  us ;  since  by  this  movement  a  great  change  would  be  occasioned 
in  the  perspective  view  of  the  object,  supposing  it  to  possess  an  uneven  sur- 
face ;  whilst  it  scarcely  affects  the  image  formed  by  a  picture.  In  the  same 
manner,  a  person  who  only  possesses  one  eye,  obtains,  by  a  slight  motion  of 
his  head,  the  same  idea  of  the  form  of  a  body  which  another  would  acquire 
by  the  simultaneous  use  of  his  two  eyes. 

341.  The  appreciation  of  the  distance  of  objects  may  be   easily  shown  to 
be  principally  derived  from  the  association,  in  the  mind,  of  visual  and  tactual 
sensations  assisted,  in  regard  to   near  objects,  by  the  muscular  sensations 
derived  from  the  convergence  of  the  eyes.     Thus,  an  infant,  or  a  person  who 
has  but  recently  acquired  sight,  evidently  forms  very  imperfect  ideas  regard- 
ing the  distance  of  objects ;  and  it  is  only  after  long  experience  that  a  correct 
notion  is  formed.     The  assistance  which  is  given  by  the  joint  use  of  both 
eyes,  is  evident  from  the  fact  that,  if  we  close  one  eye,  we  are  unable  to  exe- 
cute with  certainty  many  actions  which  require  a  precise  appreciation  of  the 
distance  of  near  objects, — such  as  threading  a  needle,  or  snuffing  a  candle. 
In  regard  to  distant  objects,  our  judgment  is  chiefly  founded  upon  their  appa- 
rent size,  if  their  actual  size  be  known  to  us ;  but  if  this  is  not  the  case,  and 
if  we  are  so  situated  that  we  cannot  judge  of  the  intervening  space,  we  prin- 
cipally form  our  estimate  from  the  greater  or  less  distinctness  of  their  colour 
and  outline.     Hence  this  estimate  is  liable  to  be  greatly  affected  by  varying 
states  of  the  atmosphere ;  as  is  well  known  to  every  one  who  has  visited 
warmer  latitudes.     The  extreme  clearness  of  the  air  sometimes  brings  into  an 
apparently  near  proximity  a  hill  that  rises  beyond  some  neighbouring  ridge 
(the  intervening  space  being  hidden,  so  as  not  to  afford  any  datum  for  the  esti- 
mate of  the  distance  of  the  remote  hill) ;  and  which,  by  a  slight  haziness,  is 
carried  to  three  or  four  times  the  degree  of  apparent  remoteness.     It  is  pro- 
bable that,  in  the  lower  animals,  the  perception  of  distance  is  much  more 
intuitive  than  it  is  in  ourselves. 

342.  Our  estimate  of  the  real  size  of  an  object  is  manifestly  connected  Avith 
that  of  its  distance.     The  apparent  size  is  dependent  upon  the  angle  at  which 
its  rays  diverge,  to  impinge  upon  the  cornea ;  this  angle  increases  with  the 
proximity,  and  diminishes  with  the  remoteness  of  the  object.     Our  estimate 
of  the  comparative  size  of  near  objects,  of  whose  distances  we  can  become 
aware  by  the  inclination  of  the  optic  axes,  is  much  more  correct  than  that 
which  we  form  when  one  or  both  are  far  removed ;  since,  when  we  are  uncer- 
tain as  to  its  distance,  we  cannot  form  a  judgment  of  the  real  size  of  a  body 
from  the  angle  at  which  its  rays  diverge.     Hence  our  estimate  of  the  size  of 
objects,  even  moderately  distant,  is  much  influenced  by  states  of  the  atmo- 
sphere.    Thus,  if  we  walk  across  a  common  in  a  fog,  a  child  approaching  us 
appears  to  have  the  size  of  a  man,  and  a  man  seems  like  a  giant ;  since  the 
indistinctness  of  the  outline  excites  in  the  mind  the  idea  of  distance ;  and  an 
object  seen  under  a  given  visual  angle  at  a  distance,  must  of  necessity  be 
much  larger  than  one  of  which  the  apparent  size  is  the  same,  but  which  is 
much  nearer.     The  want  of  innate  power  in  Man  to  form  a  true  conception  of 
either  size  or  distance,  is  well  shown  by  the  effect  produced  on  the  mind  unpre- 
pared for  such  delusions,  by  a  skilfully-painted  picture ;  the  view  of  which  is 


SENSE  OF  VISION.  253 

/ 

so  contrived,  that  its  distance  from  the  eye  cannot  be  estimated  in  the  ordinary 
manner;  the  objects  it  represents  are  invested  by  the  mind  with  their  real 
sizes  and  respective  distances,  as  if  their  real  image  was  formed  upon  the 
retina.* 

343.  From  all  these  considerations,  we  are  led  to  perceive  the  truth  of  the 
quaint  observation  made  by  Dr.  Brown, — that  "  vision  is,  in  fact,  the  art  of 
seeing  things  which  are  invisible  ;"  that  is,  of  acquiring  information  by  means 
of  the  eye,  which  is  neither  contained  in  the  sensations  of  sight  themselves 
nor  logically  deducible  from  the  intimations  which  those  sensations  really  con- 
vey.    We  cannot  too  constantly  bear  in  mind,  in  treating  of  this  subject,  that 
we  do  not  take  cognizance  by  our  optic  nerves,  as  we  do  by  the  nerves  of 
touch,  of  material  bodies  themselves,  but  of  the  pictures  or  images  formed  by 
those  objects  ;  and  whatever  be  the  notions  suggested  by  the  picture,  that  can 
never  be  transformed  into  any  thing  else.     These  notions  appear  to  be,  in  the 
lower  animals,  entirely  of  an  intuitional  or  instinctive  character ;  in  Man  they 
are  so  in  a  much  less  degree ;  and  although  it  is  impossible  to  come  to  a  pre- 
cise conclusion  on  the  subject,  from  the  want  of  sufficient  data,  it  is  indubita- 
ble that  a  large  part  of  the  knowledge  of  the  external  world,  which  he  derives 
in  the  adult  condition  from  the  use  of  his  eyes  alone,  is  really  dependent  upon 
the  early  education  of  his  perceptive  powers,  in  which  process  the  sensations 
conveyed  by  different  organs  are  brought  to  bear  upon  one  another. 

344.  The  persistence,  during  a  certain  interval,  of  impressions  made  upon 
the  retina,  gives  rise  to  a  number  of  curious  visual  phenomena.     The  pro- 
longation of  the  impression  will  be  governed,  in  part,  by  its  previous  duration. 
Thus,  when  we  rapidly  move  an  ignited  point  through  a  circle,  the  impression 
itself  is  momentary,  and  remains  but  for  a  short  time  ;  whilst,  if  we  have  been 
for  some  time  looking  at  a  window,  and  then  close  our  eyes,  the  impression  of 
the  dark  bars  traversing  the  illuminated  space  is  preserved  for  several  seconds. 
Such  phenomena  can  here  only  be  briefly  adverted  to.     One  of  these  is  the 
combination,  into  one  image,  of  two  or  more  objects  presented  to  the  eye  in 
successive  movements :  but  these  must  be  of  a  kind  which  can  be  united ; 
otherwise  a  confused  picture  is  produced.     Thus  in  a  little  toy,  called  the 
Thaumatrope,  which  was  introduced  some  years  ago,  the  two  objects  were 
painted  on  the  opposite  sides  of  a  card, — a  bird,  for  instance,  on  one,  and  a 
cage  in  the  other ;  and,  when  the  card  was  made  (by  twisting  a  pair  of  strings) 
to  revolve  about  one  of  its  diameters,  in  such  a  manner  as  to  be  alternately 
presenting  the  two  sides  to  the  eye  at  minute  intervals,  the  two  pictures  were 
blended,  the  bird  being  seen  in  the  cage.     A  far  more  curious  illusion,  how- 
ever, was  that  first  brought  into  notice  by  Mr.  Faraday ;  who  showed  that,  if 
two  toothed  wheels,  placed  one  behind  the  other,  be  made  to  revolve  with 
equal  velocity,  a  stationary  spectrum  will  be  seen ;  whilst  if  one  be  made  to 
revolve  more  rapidly  than  the  other,  or  the  number  of  teeth  be  different,  the 
spectrum  also  will  revolve.     The  same  takes  place  when  a  single  wheel  is 
made  to  revolve  before  a  mirror;  the  wheel  and  its  image  answering  the  pur- 
pose of  the  two  wheels  in  the  former  case.     On  this  principle  a  number  of 
very  ingenious  toys  have  been  constructed ;  in  some  of  these,  the  same  figure 
or  object  is  seen  in  a  variety  of  positions ;  and  the  impressions  of  these,  pass- 
ing rapidly  before  the  eye,  give  rise  by  their  combinations  to  the  idea  that 
the  object  is  itself  moving  through  these  positions.     Similar  illusions  may  be 
produced  in  regard  to  colour. 

345.  When  the  Retina  has  been  exposed  for  some  time  to  a  strong  impres- 

*  This  delusion  has  been  extremely  complete,  in  some  of  those  who  have  seen  the 
panoramic  view  of  London  in  the  Coliseum.    A  lively  and  interesting  account  of  it  is 
given  in  the  Journal  of  the  Parsee  Shipbuilders,  who  recently  visited  England. 
22 


254  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

sion  of  some  particular  kind,  it  seems  less  susceptible  of  feebler  impressions 
of  the  same  kind.  Thus,  if  we  look  at  any  Brightly  luminous  object,  and  then 
turn  our  eyes  on  a  sheet  of  white  paper,  we  shall  perceive  a  dark  spot  upon 
it ;  the  portion  of  the  retina  which  had  been  affected  by  the  bright  image  not 
being  able  to  receive  an  impression  from  the  fainter  rays  reflected  by  the 
paper.  The  dark  spectrum  does  not  at  once  disappear,  but  assumes  different 
colours  in  succession, — these  being  expressions  of  the  states  through  which 
the  retina  passes,  in  its  transition  to  the  natural  condition.  If  the  eye  has 
received  a  strong  impression  from  a  coloured  object,  the  spectrum  exhibits  the 
complementary  colour  ;*  thus,  if  the  eye  be  fixed  for  any  length  of  time  upon 
a  bright  red  spot  on  a  white  ground,  and  be  then  suddenly  turned  so  as  to  rest 
upon  the  white  surface,  we  see  a  spectrum  of  a  green  colour.  The  same  expla- 
nation applies  to  the  curious  phenomenon  of  coloured  shadows.  It  may  not  un- 
frequently  be  observed  at  sunset,  that  when  the  light  of  the  sun  acquires  a  bright 
orange  colour  from  the  clouds  through  which  it  passes,  the  shadows  cast  by  it 
have  a  blue  tint.  Again,  in  a  room  with  red  curtains,  the  light  which  passes 
through  these  produces'  green  shadows.  In  both  instances,  a  strong  impres- 
sion of  one  colour  is  made  on  the  general  surface  of  the  retina ;  and  at  any 
particular  spots,  therefore,  at  which  the  light  is  colourless  but  very  faint,  that 
colour  is  not  perceived,  its  complement  only  being  visible.  The  correctness 
of  this  explanation  is  proved  by  the  fact  that,  if  the  shadow  be  viewed  through 
a  tube,  in  such  a  manner  that  the  coloured  ground  is  excluded,  it  seems  like 
an  ordinary  shadow.  It  is  not  unlikely  that,  as  Miiller  suggests,  the  pre- 
dominant action  of  one  colour  on  the  retina  disturbs  (as  it  were)  the  equili- 
brium of  its  condition,  and  excites  in  it  a  tendency  to  the  development  of  a 
state  corresponding  to  that  which  is  produced  by  the  impression  of  the  com- 
plementary colour ;  for  the  latter  is,  according  to  him,  perceived  even  where 
it  does  not  exist ; — as  when  the  eye,  after  receiving  a  strong  impression  from 
a  coloured  spot,  and  directed  upon  a  completely  dark  surface  or  into  a  dark 
cavity,  still  perceives  the  spectrum. — Upon  these  properties  of  the  eye  are 
founded  the  laws  of  harmonious  colouring,  which  have  an  obvious  analogy 
with  those  of  musical  harmony.  All  complementary  colours  have  an  agree- 
able effect  when  judiciously  disposed  in  combination ;  and  all  bright  colours 
which  are  not  complementary  have  a  disagreeable  effect  if  they  are  predomi- 
nant :  this  is  especially  the  case  in  regard  to  the  simple  colours,  strong  com- 
binations of  any  two  of  which,  without  any  colour  that  is  complimentary  to 
either  of  them,  are  extremely  offensive.  Painters,  who  are  ignorant  of  these 
laws,  introduce  a  large  quantity  of  dull  gray  into  their  pictures,  in  order  to 
diminish  the  glaring  effects  which  they  would  otherwise  produce ;  but  this 
benefit  is  obtained  by  a  sacrifice  of  the  vividness  and  force,  which  may  be 
secured  in  combination  with  the  richest  harmony,  by  a  proper  attention  to 
physiological  principles. 

346.  Some  persons,  who  can  perfectly  distinguish  forms,  are  deficient, 
through  some  original  •peculiarity  in  the  constitution  of  the  retina,  in  the 
power  of  discriminating  colours.  This  is  most  commonly  seen  in  regard  to 
the  complementary  colours,  especially  red  and  green  ;  such  persons  not  being 
able  to  perceive  cherries  amidst  the  leaves  on  a  tree,  except  by  the  difference 
oi  their  form.  Several  distinct  varieties  of  this  affection  may  be  distinguished, 
however ;  and  these  have  been  classified  by  Leebeck.t 

*  By  the  complementary  colour  is  meant  that  which  would  be  required  to  make  white 
or  colour  ess  light,  when  mixed  with  the  original.  As  red,  blue  and  yellow  are  the  pri- 
mary or  elementary  colours,  red  is  the  complement  of  green  (which  is  composed  of  yel- 
low and  blue);  blue  is  the  complement  of  orange  (red  and  yellow);  and  yellow  of  purple 
(red  and  blue)  ;  and  vice  versa  in  all  instances 

f  Mailer's  Physiology,  p.  1213. 


SENSE  OF  HEARING.  255 

347.  Amongst  other  curious  phenomena  of  Vision,  is  the  vanishing  of 
images  which  fall  at  the  entrance  of  the  optic  nerve ;  as  is  shown  in  the  fol- 
lowing experiment.     Let  two  black  spots  be  made  upon  a  piece  of  paper, 
about  four  or  five  inches  apart ;  then  let  the  left  eye  be  closed,  and  the  right 
eye  be  strongly  fixed  upon  the  left-hand  spot.     If  the  paper  be  then  moved 
backwards  and  forwards,  so  as  to  change  its  distance  from  the  eye,  a  point 
will  be  found  at  which  the  right-hand  spot  is  no  longer  visible ;  though  it  is 
clearly  seen  when  the  paper  is  brought  nearer  or  removed  further.     In  this 
position  of  the  eye  and  object,  the  rays  from  the  right-hand  spot  cross  to  the 
nasal  side  of  the  globe,  and  fall  upon  the  point  of  the  retina,  which  has  just 
been  mentioned.    The  phenomenon  is  not  confined  to  that  spot,  however;  nor 
is  it  correct  to  say,  as  is  sometimes  done,  that  the  retina  is  not  sensible  to  light 
at  that  point ;  since,  if  such  were  the  case,  we  should  see  a  dark  spot  in  our 
field  of  view,  whenever  we  use  only  one  eye.     The  fact  is,  that  a  similar  phe- 
nomenon may  occur  under  somewhat  different  conditions,  in  any  division  of 
the  retina,  especially  in  its  lateral  parts.     Thus,  if  we  fix  the  eye  for  some 
time,  until  it  is  fatigued,  upon  a  strip  of  coloured  paper  lying  upon  a  white 
surface,  the  image  of  the  coloured  object  will  in  a  short  time  disappear,  and 
the  white  surface  will  be  seen  in  its  place ;  the  disappearance  of  the  image, 
however,  is  only  of  a  few  seconds'  duration.     The  truth  seems  to  be,  that 
there  is  a  tendency  in  the  retina,  to  the  propagation,  over  neighbouring  parts, 
of  impressions  which  occupy  a  large  proportion  of  its  surface ;  and  that  this 
tendency  is  the  strongest  around  the  point  at  which  the  optic  nerve  enters,  so 
that  the  state  of  this  part  will  generally  become  similar  to  that  of  the  surround- 
ing portion  of  the  retina.     Hence,  when  we  are  using  one  eye  only,  we  do 
not  perceive  any  dark  spot  in  the  field,  but  only  a  certain  degree  of  indistinct- 
ness in  a  portion  of  the  image. 

348.  Under  particular  circumstances,  we  may  receive  a  visual  representa- 
tion of  the  retina  itself;  as  is  shown  by  the  experiment  of  Purkinje.     "  If,  in 
a  room  otherwise  dark,  a  lighted  candle  be  moved  to  and  fro,  or  in  a  circle,  at 
a  distance  of  six  inches  before  the  eyes,  we  perceive,  after  a  short  time,  a  dark 
arborescent  figure  ramifying  over  the  whole  field  of  vision ;  this  appearance 
is  produced  by  the  vasa  centralia  distributed  over  the  retina,  or  by  the  parts 
of  the  retina  covered  by  those  vessels.     There  are,  properly  speaking,  two 
arborescent  figures,  the  trunks  of  which  are  not  coincident,  but  on  the  con- 
trary arise  in  the  right  and  left  divisions  of  the  field,  and  immediately  take 
opposite  directions.     One  trunk  belongs  to  each  eye,  but  their  branches  inter- 
sect each  other  in  the  common  field  of  vision.     The  explanation  of  this  phe- 
nomenon is  as  follows : — By  the  movement  of  the  candle  to  and  fro,  the  light 
is  made  to  act  on  the  whole  extent  of  the  retina,  and  all  the  parts  of  the  mem- 
brane which  are  not  immediately  covered  by  the  vasa  centralia  are  feebly 
illuminated ;  those  parts,  on  the  contrary,  which  are  covered  with  those  ves- 
sels, cannot  be  acted  on  by  the  light,  and  are  perceived,  therefore,  as  dark 
arborescent  figures.     These  figures  appear  to  lie  before  the  eye,  and  to  be 
suspended  in  the  field  of  vision."*     We  have  thus  another  demonstration  of 
the  fact  that,  in  ordinary  vision,  the  immediate  object  of  our  sensation  is  a 
certain  condition  of  the  retina,  which  is  excited  by  the  formation  of  a  luminous 
image. 

VI.  Sense  of  Hearing. 

349.  In  the  Ear,  as  in  the  Eye,  the  impressions  made  upon  the  sensory 
nerve  are  not  at  once  made  by  the  body  which  originates  the  sensation;  but 
they  are  propagated  to  it,  through  a  medium  capable  of  transmitting  them. 

*  Mailer's  Physiology,  p.  1163. 


256  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

Here  too,  therefore,  we  take  cognizance  by  the  mind,  not  of  the  sonorous 
object,  but  of  the  condition  of  the  auditory  nerve ;  and  all  the  ideas  we  form 
of  sounds,  as  to  their  nature,  intensity,  direction,  &c.,  must  be  based  upon  the 
changes  which  they  produce  in  it.  The  complex  contrivances  which  we 
meet  with  in  the  organ  of  hearing  among  higher  animals,  are  evidently 
intended  to  give  them  greater  power  of  discriminating  sounds  than  is  pos- 
sessed by  the  lower  tribes ;  in  which  last  it  is  reduced  to  a  form  so  simple, 
that  it  may  be  questioned  whether  they  can  be  said  to  possess  an  organ  of 
hearing,  if  by  this  term  we  imply  any  thing  more  than  the  mere  consciousness 
of  sonorous  vibrations.  There  is  a  considerable  difference,  however,  between 
the  Eye  and  the  Ear,  in  regard  to  the  special  purposes  for  which  they  are 
respectively  adapted.  In  the  former  we  have  seen  that  the  whole  object  of 
the  instrument  was  to  direct  the  rays  of  light  received  by  it,  in  such  a  manner 
as  to  occasion  them  to  fall  upon  the  expansion  of  the  optic  nerve  in  a  similar 
relative  position,  and  with  corresponding  proportional  intensity  to  that  which 
they  possessed  when  issuing  from  the  object.  We  have  no  reason  to  believe 
any  thing  of  this  kind  to  be  the  purpose  of  the  Ear;  indeed  it  would  be  incon- 
sistent with  the  laws  of  the  propagation  of  sound.  Sonorous  vibrations  having 
the  most  various  directions,  and  the  most  equal  rate  of  succession,  are  trans- 
mitted by  all  media  without  modification,  however  numerous  their  lines  of 
intersection;  and  wherever  these  undulations  fall  upon  the  auditory  nerve, 
they  must  cause  the  sensation  of  corresponding  sounds.  Still  it  is  probable 
that  some  portions  of  the  complex  organ  of  hearing,  in  Man  and  in  the  higher 
animals,  are  more  adapted  than  others  to  receive  impressions  of  a  particular 
character;  and  that  thus  we  may  be  especially  informed  of  the  direction  of  a 
sound  by  one  part  of  the  organ,  of  its  musical  tone  by  another,  and  of  some 
other  of  its  qualities  by  a  third.  In  our  inquiries  into  this  ill-understood  sub- 
ject, we  shall  commence  with  a  brief  survey  of  the  comparative  structure  of 
the  organ. 

350.  The  essential  part  of  an  Organ  of  Hearing  being  obviously  a  nerve, 
endowed  with  the  peculiar  property  of  receiving  and  transmitting  sonorous 
undulations,  it  is  by  no  means  indispensable  that  a  special  provision  should 
be  made  for  this  purpose ;  since  the  Auditory  nerve,  if  merely  in  contact 
with  the  solid  parts  of  the  head,  will  be  affected  by  the  vibrations,  in  which 
it  is  continually  participating.  Hence  we  must  not  imagine  the  sense  to  be 
absent,  wherever  we  cannot  discover  a  special  organ.  It  is  among  the  highest 
only  of  the  Invertebrate  animals,  that  any  such  special  organ  presents  itself; 
and  then  only  in  a  very  simple  form.  Thus  in  the  Crustacea  and  Cephalopoda, 
the  ear  consists  of  a  small  cavity  excavated  in  the  solid  frame-work  of  the 
head ;  this  cavity  is  lined  with  a  membrane,  on  which  the  nerve  is  distributed ; 
and  it  is  filled  with  a  watery  fluid.  In  some  instances,  the  cavity  is  com- 
pletely shut  in  by  its  solid  walls ;  and  the  sonorous  vibrations  can  then  only  be 
communicated  through  these  :  but  in  the  higher  forms  of  this  apparatus,  there 
is  a  small  aperture  covered  with  a  membrane,  upon  which  the  external  me- 
dium can  at  once  act.  In  tracing  this  most  simple  into  the  more  complex 
forms,  it  is  at  once  seen,  that  the  cavity  corresponds  with  the  vestibule  of  the 
ear  of  higher  animals,  and  its  opening  with  thefenestra  ovalis.  In  the  lowest 
Cyclostome  Fishes,  the  organ  is  but  little  more  complicated ;  from  the  vestibule 
proceeds  a  single  annular  passage,  which  may  be  considered  as  a  semicircular 
canal ;  and  the  auditory  nerve  is  distributed  minutely  upon  its  lining  mem- 
brane, as  upon  that  of  the  vestibule  itself.  In  species  a  little  higher  in  the 
scale,  two  such  canals  exist;  these  are  present  in  the  Lamprey.  And  in  all  the 
rest  of  the  class,  three  semicircular  canals  are  found,  holding  the  same  direc- 
tion in  regard  to  each  other  as  they  do  in  Man.  Within  the  vestibular  sac  of 
Fishes  are  found  calcareous  concretions,  which  are  pulverulent  in  the  Carti- 


SENSE  OF  HEARING. 


257 


laginous,  but  hard  and  stony  in  the  Osseous  tribes;  to  these  the  name  of  Oto- 
lithes  has  been  given.  Some  rudiments  of  a  tympanic  cavity  may  be  found 
in  Fishes;  but  there  is  no  vestige  of  a  cochlea;  in  several  tribes,  the  organ 
of  hearing  possesses  a  peculiar  connection  with  the  air-bladder,  which  appears 
to  be  a  foreshadowing  of  the  Eustachian  tube  of  higher  classes. 

351.  In  the  true  Reptiles,  a  considerable  advance  is  constantly  to  be  found 
in  the  character  of  the  Ear;  a  tympanic  cavity  being  added,  with  a  drum  and 
a  chain  of  bones ;  and  a  rudiment  of  the  cochlea  being  generally  discoverable. 
Among  the  Amphibia,  however,  which  are  in  so  many  respects  intermediate 

[Fig.  48. 


An  imaginary  figure  or  plan  of  the  Cochlea;  this  figure  is  designed  to  show  how  the  twoscalaeof  the  coch- 
lea communicate  in  its  summit ;  the  parietes  of  the  scala  vestibuli  are  supposed  to  be  removed ;  1.  1,  the 
osseous  portion  of  the  lamina  spiralis;  its  small  end  is  the  hamulus  cochleae;  2,  2,  the  dark  ground  here 
represents  the  membranous  portion  of  the  cochlea  or  the  zona  membranacea;  3,  the  commencement  of  the 
scala  tympani ;  4,  its  external  edge;  5,  its  internal  edge ;  6  corresponds  to  the  modiolus  around  which  the 
lamina  spiralis  is  wound ;  7,  its  summit;  8,  the  point  of  communication  9f  the  two  scalae.] 

[Fig.  49. 


A  view  of  the  axis  of  the  Cochlea  and  the  Lamina  Spiralis,  showing  the  arrangement  of  the  three  Zones 
the  osseous  zone  and  the  membrane  of  the  vestibule  have  been  removed;  1,  the  natural  size  of  the  pans; 
the  other  figure  is  greatly  magnified;  2,  trunk  of  the  auditory  nerve ;  3,  the  distribution  of  its  filaments  in 
the  zona  ossca;  4,  the  nervous  anastomosis  of  the  zona  vesicularis;  5,  the  zona  membranacea ;  6,  the 
osseous  tissue  of  the  modiolus ;  7,  the  opening  between  the  two  scalce.l 

22* 


258  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

between  the  true  Reptiles  and  Fishes,  there  is  a  remarkable  variation  in  this 
respect — some  having  a  tympanum,  and  some  being  completely  destitute  of 
it.  Wherever  a  tympanic  cavity  distinctly  exists,  there  is  an  Eustachian  tube 
connecting  it  with  the  fauces.  This  cavity,  in  the  true  Reptiles,  not  only 
possesses  the  fenestra  ovalis  (or  opening  into  the  vestibule)  but  the  fenestra 
rotunda  (or  opening  into  the  cochlea).  The  membrana  tympani  is  usually 
visible  externally ;  but  it  is  sometimes  covered  by  the  skin. — In  Birds,  the 
structure  of  the  ear  is  essentially  the  same,  as  in  the  higher  Reptiles.  A  dis- 
tinct cochlea  exists,  though  its  form  is  not  spiral  but  nearly  straight :  of  its 
character,  however,  there  can  be  no  doubt ;  a  division  into  two  passages,  by  a 
membranous  partition  on  which  the  nerve  is  spread  out,  being  evident.  More- 
over, the  tympanum  communicates  with  cavities  in  the  cranial  bones,  which 
are  thus  filled  with  air;  and  these,  by  increasing  the  extent  of  surface,  pro- 
duce a  more  powerful  resonance.  There  is  no  external  ear,  except  in  a  few 
species  of  nocturnal  Birds. — In  Mammalia,  the  organ  of  hearing  is  usually 
formed  upon  the  same  plan  as  it  presents  in  Man ;  in  the  Monotremata,  how- 
ever, it  more  approaches  that  of  Birds.  The  cochlea  of  the  Mammalia  in 
general  is  a  spiral,  forming  about  two  turns  and  a  half;  the  partition  which 
divides  its  canal  is  partly  osseous,  partly  membranous ;  and  its  two  passages 
communicate  with  the  tympanic  cavity  and  the  vestibule  respectively.  The 
cavity  of  the  tympanum  is  very  large  in  some  species,  extending  even  into 
the  contiguous  bones.  All  the  Mammalia,  except  the  aquatic  tribes,  have 
an  external  ear ;  and  this  is  sometimes  of  an  enormous  size  in  proportion  to 
the  dimensions  of  the  body,  as  it  is  in  the  Bats.  The  labyrinth  of  the  higher 
Vertebrata  contains  no  otolithes. 


The  Cochlea  divided  parallel  with  its  axis,  through  the  centre  of  the  Modiolus;  after  Breschet;  1,  the 
modiolus;  2,  the  infundibulum  in  which  the  modiolus  terminates;  3,  3,  the  cochlear  nerve,  sending  its  fila- 
ments through  the  centre  of  the  modiolus ;  4,  4,  the  scala  tympani  of  the  first  turn  of  the  cochlea;  5,  5,  the 
scala  vestibula  of  the  first  turn;  6,  section  of  the  lamina  spiralis,  its  zonula  ossea;  one  of  the  filaments  of 
the  cochlear  nerve  is  seen  passing  between  the  two  layers  of  the  lamina  spiralis  to  be  distributed  upon  the 
membrane  which  invests  the  lamina;  7,  the  membranous  portion  of  the  lamina  spiralis ;  8,  loops  formed  by 
the  filaments  of  the  cochlear  nerve ;  9,  9,  scala  tympani  of  the  second  turn  of  the  cochlea;  10, 10,  scala 
vesubula  of  the  second  turn;  the  septum  between  the  two  is  the  lamina  spiralis;  11,  the  scala  tympani  of 
he  rema.nmg  half  turn;  12,  the  remaining  half  turn  of  the  scala  vestibula;  the  dome  placed  over  this  half 
turn  is  the  cupola:  13,  the  lamina  of  bone  which  forms  the  floor  of  the  scala  vestibula  curving  spirally 
round  to  constitute  the  infundibulum  (2) ;  14,  the  helicotrema  through  which  a  bristle  is  passed;  its  lower 
extremity  issues  from  the  scala  tympani  of  the  middle  turn  of  the  cochlea. 

352.  The  ultimate  terminations  of  the  fibres  of  the  auditory  nerve  in  minute 
papillae  are  best  seen  in  the  lamina  spiralis  of  the  cochlea,  and  its  membranous 
prolongation.  Much  diversity  exists,  however,  as  to  the  interpretation  of  the 
appearances  there  seen;  some  observers  affirming  that  there  are  no  free  or 
papillary  terminations,  and  that  the  nervous  fibres  all  return  by  loops;  whilst 


SENSE  OF  HEARING. 


259 


Fig.  51, 


[Fig.  52. 


Papillre  of  the  Auditory  Nerve,  on  a 
Segment  of  the  Spiral  Lamina  of  the 
Cochlea  of  a  young  Mouse ;  the  lower 
portion  is  the  osseous,  and  the  higher  the 
membranous  part  of  the  lamina.  Mag- 
nified 300  times.  After  Treviranus. 


The  Auditory  Nerve  taken  out  of  the  Cochlea;  1, 1, 1,  the 
trunk  of  the  nerve  ;  2,  2,  its  filaments  in  the  zona  ossea  of  the 
lamina  spiralis;  3,  3,  its  anastomoses  in  the  zona  vesicularis.] 

[Fig.  53. 


A  highly  magnified  view  of  a  small  piece  of  the  Lamina  Spiralis,  showing  the  globular  structure  of  the 
Nerves,  and  the  manner  in  which  they  leave  their  Neurilema  as  they  anastomose;  the  natural  size  of 
the  piece  is  seen  on  the  side  of  the  figure;  1,  portion  of  the  auditory  nerve;  2,  2,  osseous  canals  in  the  zona 
ossea  of  the  lamina  spiralis;  3,  3,  anastomoses  in  the  zona  mollis ;  4, 4,  the  neurilema  leaving  the  nervous 
loops  and  interlocking  to  form  the  layer  of  the  zona  membranacea.] 

others  state  that  the  papillae  are  clearly  to  be  distinguished.  The  fact  appears 
to  be  that,  as  in  the  retina,  the  fibres  do  form  a  minute  plexus ;  but  that  fibres 
are  connected  with  this,  which  end,  or  rather  commence,  in  papillae.  The 
auditory  nerve  is  also  very  minutely  distributed  on  the  membrane  lining  the 
vestibule  and  semicircular  canals  ;  and  in  the  ampullae  or  dilated  extremities 
of  the  latter,  there  are  little  projections  of  this  membrane  internally,  which 
are  largely  supplied  with  nerves. 

353.  In  order  to  gain  any  definite  idea  of  the  uses  of  different  parts  of 
the  Ear,  it  is  necessary  to  bear  in  mind,  that  sounds  may  be  propagated 
amongst  solid  or  fluid  bodies  in 'three  ways, — by  reciprocation,  by  resonance, 
and  by  conduction. — 1.  Vibrations  of  reciprocation  are  excited  in  a  sounding 
body,  when  it  is  capable  of  yielding  a  musical  tone  of  definite  pitch,  and 


200 


OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 
[Fig.  54. 


The  soft  parts  of  the  Vestibule  taken  out  of  their  bony  case,  so  as  to  show  the  distribution  of  the  Nerves 
in  the  Ampullae;  1,  the  superior  semicircular  membranous  canal  or  tube;  2,  the  external  semicircular 
tube;  3,  the  inferior  semicircular  tube;  4,  the  tube  of  union  of  the  superior  and  inferior  canals;  5,  the 
sacculus  ellipticus;  6,  the  sacculus  sphericus;  7,  the  portio  dura  nerve;  8,  the  anterior  fasciculus  of  the 
auditory  nerve;  9,  the  nerve  to  the  sacculus  sphericus;  10, 10,  the  nervous  fasciculi  to  the  superior  and 
external  ampullne;  11,  the  nerve  to  the  sacculus  elliplicus;  12,  the  posterior  fasciculus  of  the  auditory 
nerve,  furnishing  13,  the  filaments  of  the  sacculus  sphericus,  and  14,  the  filaments  of  the  cochlea,  cut  off.] 

[Fig.  55. 


The  Ampulla  of  the  External  Semicircular  Membranous  Canal,  showjng  the  mode  of  termination  of  its 
Nerve.] 

another  body  of  the  same  pitch  is  made  to  sound  near  it.  Thus  if  two  strings 
of  the  same  length  and  tension  be  placed  alongside  of  each  other,  and  one  of 
them  be  sounded  with  a  violin-bow,  the  other  will  be  thrown  into  reciprocal 
vibration ;  or  if  the  same  tone  be  produced  near  the  string  in  any  other  man- 
ner, as  by  a  flute,  or  a  tuning-fork,  the  same  effect  will  result.— 2.  Vibrations 
of  resonance  are  of  somewhat  the  same  character  ;  but  they  occur  when  a 
sounding  body  is  placed  in  connection  with  any  other,  of  whi^n'one  or  more 


SENSE  OF  HEARING.  261 

Fig.  56. 


The  labyrinth  of  the  Left  Ear,  laid  open  in  order  to  show  its  cavities  and  the  Membranous  Labyrinth  ; 
after  Breschet;  1,  the  cavity  of  the  vestibule,  opened  from  its  anterior  aspect  in  order  to  show  the  three-cor- 
nered form  of  its  interior,  and  the  membranous  labyrinth  which  it  contains;  the  figure  rests  upon  the  com- 
mon saccule  of  the  membranous  labyrinth  —  the  sacculus  communis  ;  2,  the  ampulla  of  the  superior  or  per- 
pendicular semicircular  canal,  receiving  a  nervous  fasciculus  from  the  superior  bronch  of  the  vestibular 
nerve;  3,  4,  the  superior  or  perpendicular  canal  with  its  contained  membranous  canal;  5,  the  ampulla  of 
the  inferior  or  horizontal  semicircular  canal,  receiving  a  nervous  fasciculus  from  the  superior  branch  of 
the  vestibular  nerve;  6,  the  termination  of  the  membranous  canal  of  the  horizontal  semicircular  canal  in 
the  sacculus  communis;  7.  the  ampulla  of  the  middle  or  oblique  semicircular  canal,  receiving  a  nervous 
fasciculus  from  the  inferior  branch  of  the  vestibular  nerve;  8,  the  oblique  semicircular  canal  with  its 
membranous  canal;  9,  the  common  canal,  resulting  from  the  union  of  the  perpendicular  with  the  oblique 
semicircular  canal;  10,  the  membranous  common  canal  terminating  in  the  sacculus  communis;  11,  the 
otoconite  of  the  sacculus  communis  seen  through  the  membranous  parietes  of  that  sac  ;  a  nervous  fasci- 
culus from  the  inferior  branch  of  the  vestibular  nerve  is  seen  to  be  distributed  to  the  sacculus  communis 
near  to  the  otoconite;  the  extremity  of  the  sacculus  above  the  otoconite  is  lodged  in  the  superior  ventricle 
of  the  vestibule,  and  that  below  it  in  the  inferior  ventricle  ;  12,  the  sacculus  proprius  situated  in  the  ante- 
rior ventricle;  its  otoconite  is  seen  through  its  membranous  parietes,  and  a  nervous  fasciculus  derived 
from  the  middle  branch  of  the  vestibular  nerve,  is  distributed  to  it;  the  spaces  around  the  membranous 
labyrinth  are  occupied  by  the  aqua  labyrinth!;  13,  the  first  turn  of  the  cochlea;  the  figure  is  situated  in  the 
scala  tympani;  14,  the  extremity  of  the  scala  tympani  corresponding  with  the  fenestra  rotunda;  15,  the 
lamina  spiralis;  the  figure  is  situated  in  the  scala  vestibuli  ;  16,  the  opening  of  the  scala  vestibuli  into  the 
vestibule;  17,  the  second  turn  of  the  cochlea;  the  figure  is  placed  upon  the  lamina  spiralis,  and,  therefore, 
in  the  scala  vestibuli,  the  scala  tympani  being  beneath  the  lamina;  18,  the  remaining  half  turn  of  the 
cochlea;  the  figure  is  placed  in  the  scala  tympaui;  19,  the  lamina  spiralis  terminating  in  a  falciform  ex- 
tremity ;  the  dark  space  included  within  the  falciform  curve  of  the  extremity  of  the  lamina  spiralis  is  the 
helicotrema  ;  20,  the  infundibulum. 

parts  may  be  thrown  into  reciprocal  vibration,  even  though  the  tone  of  the 
whole  be  different,  or  it  be  not  capable  of  producing  a  definite  tone  at  all. 
This  is  the  case,  for  example,  when  a  tuning-fork  in  vibration  is  placed  upon 
a  sound-board  ;  for  even  though  the  whole  board  have  no  definite  fundamental 
note,*  it^tt  divide  itself  into  a  number  of  parts,  which  will  reciprocate  the 


*  The  fundamental  note  of  &  body  is  the  lowest  tone  which  it  will  yield,  when  the  whole 
of  it  is  in  vibraftj^  together.  By  dividing  the  body  into  two  or  more  distinct  parts,  it 
may  be  made  to^pre  a  great  variety  of  sounds.  Thus,  if  a  stretched  string  be  divided 
by  a  bridge  into  two  equal  parts,  each  will  sound  the  octave  of  the  fundamental  note,  or 
the  8th  note  above  it.  If  it  be  divided  into  three  parts,  each  will  give  the  12th  above  the  fun- 
damental note  ;  if  into  four,  the  15th  or  double  octave  will  be  heard  ;  if  into  five,  the  17th  ; 
if  into  six,  the  19th;  if  into  seven,  the  20£  (flat  seventh  above  the  second  octave);  if  into 
eight,  the  22dor  triple  octave.  A  string  forcibly  set  in  vibration  has  a  tendency  to  sound 
these  harmonics  with  the  fundamental  note,  by  spontaneous  division  into  several  distinct 
segments  of  vibration  ;  as  may  be  easily  made  evident,  by  striking  one  of  the  lower  keys 
of  the  piano,  and  listening  to  the  sounds  heard  whilst  the  fundamental  note  is  dying  away. 


262  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

original  sound,  so  as  greatly  to  increase  its  intensity ;  and  the  same  sound- 
board will  act  equally  well  for  tuning-forl^s  of  several  different  degrees  of 
pitch.  When  a  smaller  body  is  used  for  resonance,  however,  it  is  essential 
that  there  should  be  a  relation  between  its  fundamental  note  and  that  of  the 
sonorous  body;  otherwise  no  distinct  resonance  is  produced.  Thus,  if  a 
tunino-fork  in  vibration  be  held  over  a  column  of  air  in  a  tube,  of  such  a 
length  that  the  same  note  would  be  given  by  its  vibration,  its  sound  will  be 
reciprocated.  And  if  it  be  held  over  a  pipe,  the  column  of  air  in  which  is  a 
multiple  of  this,  the  column  will  divide  itself  into  that  number  of  shorter  parts 
each  of  which  will  reciprocate  the  original  sound,  and  the  total  action  will  be 
one  of  resonance.  But  if  the  length  of  the  pipe  bear  no  such  correspondence 
with  the  note  sounded  by  the  tuning-fork,  no  resonance  is  given  by  the  column 
of  air  it  contains. — 3.  Vibrations  of  conduction  are  the  only  ones  by  which 
sounds  can  strictly  be  said  to  be  propagated.  These  are  distinguishable  into 
various  kinds,  into  which  it  is  not  requisite  here  to  inquire.  It  should  be 
remarked,  however,  that  all  media,  fluid,  liquid,  or  solid,  are  capable  of  trans- 
mitting sound  in  this  manner, — a  vacuum  being  the  only  space  through  which 
it  cannot  pass.  The  transmission  is  usually  much  more  rapid  through  solid 
bodies  than  through  liquid ;  and  through  liquid  than  through  gaseous.  The 
greatest  diminution  in  the  intensity  of  sound  is  usually  perceived,  when  a 
change  takes  place  in  the  medium  through  which  it  is  propagated,  especially 
from  the  aeriform  to  the  liquid. 

354.  The  detailed  application  of  these  principles  has  been  most  elaborately 
worked  out  by  Miiller;  and  the  following  statement  of  what  may  be  regarded 
as  the  present  condition  of  our  knowledge  of  the  subject,  is  little  more  than  an 
abstract  o£  his  results.  Considering  it  desirable,  in  the  first  place,  to  establish 
the  conditions  under  which  those  animals  hear,  that  are  constantly  immersed 
in  water,  he  made  a  series  of  experiments,  from  which  he  draws  the  following 
conclusions : — i.  Sonorous  vibrations,  excited  in  water,  are  imparted  with  con- 
siderable intensity  to  solid  bodies. — n.  Sonorous  vibrations  of  solid  bodies  are 
communicated  with  greater  intensity  to  other  solid  bodies  brought  in  contact 
with  them  than  to  water ;  but  with  much  greater  intensity  to  water  than  to 
atmospheric  air. — in.  Sonorous  vibrations  are  communicated  from  air  to  water 
with  great  difficulty, — with  very  much  greater  difficulty  than  they  are  pro- 
pagated from  one  part  of  the  air  to  another ;  but  their  transition  from  air  to 
water  is  much  facilitated  by  the  intervention  of  a  membrane  extended  between 
them. — iv.  Sonorous  vibrations  are  not  only  imparted  from  water  to  solid 
bodies  with  definite  surfaces,  which  are  in  contact  with  the  water,  but  are  also 
returned  with  increased  intensity  by  these  bodies  to  the  water ;  so  that  the 
sound  is  heard  loudly  in  the  vicinity  of  those  bodies,  in  situations  where,  if  it 
had  its  origin  in  the  conducting  power  of  the  water  alone,  it  would  be  faint. — 
v.  Sonorous  undulations,  propagated  through  water,  are  partially  reflected  by 
the  surfaces  of  solid  bodies. — vi.  Thin  membranes  conduct  sound  in  water 
without  any  loss  of  its  intensity,  whether  they  be  tense  or  lax. — From  m.,  iv., 
and  vi.,  we  learn  the  mode  in  which  the  sound  is  conducted  to  the  ear,  in 
aquatic  animals  not  breathing  atmospheric  air.  The  labyrinth  of  such  is 
either  entirely  enclosed  within  the  bones  of  the  head,  as  in  the  Cephalopoda, 
and  in  the  Cyclostome  and  Osseous  Fishes  ;  or,  its  cavity  being  prolonged  to 
the  surface  of  the  body,  it  is  there  brought  into  communication  with  the  con- 
ducting medium,  by  means  of  a  membrane, — besides  receiving  the  vibrations 
through  the  medium  of  the  solids  of  the  body,  as  is  the  case  in  Cartilaginous 
Fishes  and  Crustacea.  It  would  seem  as  if,  in  the  Osseous  Fishes,  the  reso- 
nance of  the  cranial  bones,  in  which  the  labyrinth  is  imkrdded,  were  sufficient 
to  give  the  requisite  increase  of  intensity  to  the  sound ;  whilst  in  the  Cartila- 
ginous orders,  the  softness  of  these  bones  renders  some  other  means  necessary. 


SENSE  OF  HEARING.  263 

In  addition  to  this,  we  find  in  many  Fishes  a  communication  with  the  air- 
bladder  ;  which,  indeed,  seems  to  have  in  these  but  little  other  use.  The 
mode  in  which  this  increases  by  resonance  the  intensity  of  the  sounds,  will 
appear  from  the  following  experimental  conclusions. — vn.  When  sonorous 
vibrations  are  communicated  from  water  to  air  enclosed  in  membranes  or  solid 
bodies,  a  considerable  increase  in  the  intensity  of  the  sound  is  produced,  by 
the  resonance  of  the  air  thus  circumscribed.— vm.  A  body  of  air  enclosed  in 
a  membrane,  and  surrounded  by  water,  also  increases  the  intensity  of  the 
sound  by  resonance,  when  the  sonorous  undulations  are  communicated  to  it  by 
a  solid  body.  From  these  observations  it  .may  be  concluded,  that  the  air- 
bladder  of  Fishes,  in  addition  to  other  uses,  serves  the  purpose  of  increasing 
by  resonance  the  intensity  of  the  sonorous  undulations,  communicated  from 
the  water  to  the  body  of  the  Fish.  Moreover,  as  the  conducting  and  resonant 
power  of  the  air  in  the  air-bladder  is  greater  in  proportion  to  its  density,  the 
influence  of  this  organ  on  the  perception  of  sounds  will,  of  course,  be  greater 
in  deep  waters,  where  the  pressure  upon  it  is  considerably  increased. 

355.  Most  animals  living  in  air,  are  provided  with  an  opening  into  the  ves- 
tibule, covered  by  a  thin  membrane ;  and,  in  the  majority  of  cases,  with  the 
tympanic  apparatus  also.     The  following  experimental  results  bear  upon  the 
manner  in  which  the  Ear  of  such  animals  is  affected  by  sound. — ix.  Sonorous 
undulations,  in  passing  from  air  directly  into  water,  suffer  a  considerable  dimi- 
nution in  their  strength;  while,  on  the  contrary,  if  a  tense  membrane  exists 
between  the  air  and  the  water,  the  sonorous  undulations  are  communicated 
from  the  former  to  the  latter  medium  with  great  intensity. — x.  The  sonorous 
vibrations  are  also  communicated,  without  any  perceptible  loss  of  intensity, 
from  the  air  to  the  water;  when,  to  the  membrane  forming  the  medium  of 
communication,  there  is  attached  a  short  solid  body,  which  occupies  the  greater 
part  of  its  surface,  and  is  alone  in  contact  with  the  water. — xi.    A  small  solid 
body,  fixed  in  an  opening  by  means  of  a  border  of  membrane,  so  as  to  be 
movable,  communicates  sonorous  vibrations  from  air  on  one  side  to  water  or 
the  fluid  of  the  labyrinth  on  the  other,  much  better  than  solid  media  not  so 
constructed.     But  the  propagation  of  sound  to  the  fluid  is  rendered  much 
more  perfect,  if  the  solid  conductor,  thus  occupying  the  opening,  is  by  its  other 
end  fixed  to  the  middle  of  the  tense  membrane,  which  has  atmospheric  air  on 
both  sides. — The  fact  stated  in  ix.  is  evidently  one  of  great  importance  in  the 
physiology  of  hearing ; .  and  fully  explains  the  nature  of  the  process  in  those 
animals  which  receive  the  sonorous  vibrations  through  air,  but  which  have  no 
tympanic  apparatus.     In  x.  we   have  the  elucidation  of  the  action  of  the 
fenestra  ovalis,  and  of  the  movable  plate  of  the  stapes  which  occupies  it,  in 
animals  living  in  air  but  destitute  of  tympanic  apparatus ;  this  is  naturally  the 
case  in  many  Amphibia ;  and  it  may  happen  as  the  result  of  disease  in  the 
human  subject.     In  xi.  we  have  a  very  interesting  demonstration  of  the  pur- 
pose and  action  of  the  tympanum,  in  the  more  perfect  forms  of  the  auditory 
apparatus.     We  are  now  prepared  to  inquire,  in  somewhat  more  of  detail,  into 
the  action  of  the  different  parts  of  this  apparatus;  and  it  will  be  better  to  com- 
mence with  that  of  the  Internal  Ear,  the  accessory  organs  being  afterwards 
considered. 

356.  The  object  of  the  Membrana  Tympani  is  evidently  to  receive  the 
sonorous  undulations  from  the  air,  in  such  a  manner  as  to  be  thrown  by  them 
into  a  reciprocal  vibration,  which  is  to  be  communicated  to  the  chain  of  bones. 
This  membrane  is,  in  its  usual  state,  rather  lax  than  tense  ;  and  this  laxity  is 
found  by  experiment  to  be,  for  a  small  membrane,  the  best  condition  for  the 
propagation  of  ordinary  sounds.     This  is  easily  rendered  sensible  in  one's 
own  person ;  for  an  increased  tension  may  be  given  to  the  membrana  tym- 
pani,  either  by  holding  the  breath  and  forcing  air  into  the  Eustachian  tube, 


264  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

so  as  to  distend  it  from  within,  or  Ipy  exhausting  the  cavity  so  as  to  cause 
the  external  air  to  make  increased  pressure  upon  it.  In  either  case  the 
hearing  is  found  immediately  to  become  indistinct.  It  is  observed,  however, 
that  grave  and  acute  sounds  are  not  equally  affected  by  this  action ;  for  the 
experimenter  renders  himself  deaf  to  grave  sounds,  whilst  acute  sounds  are 
heard  even  more  distinctly  than  before.  This  fact  is  easily  understood,  by 
referring  to  the  laws  of  Acoustics  already  mentioned.  The  greater  the  tension 
to  which  the  membrana  tympani  is  subjected,  the  more  acute  will  be  its  fun- 
damental tone ;  and  as  no  proper  reciprocation  can  take  place  in  it,  to  any 
sound  lower  than  its  fundamental  tone,  its  power  of  repeating  perfectly  the 
vibrations  proper  to  the  deeper  notes  will  diminish.  The  nearer  a  sound 
approaches  to  the  fundamental  note  proper  to  the  tense  membrane,  the  more 
distinctly  will  it  be  heard.  On  the  other  hand,  when  the  membrane  is  in  its 
natural  lax  condition,  its  fundamental  note  is  very  low,  and  it  is  capable  of 
repeating  a  much  greater  variety  of  sounds  ;  for,  when  it  receives  undulations 
of  a  higher  tone  than  those  to  which  the  whole  membrane  would  reciprocate, 
it  divides  itself  into  distinct  segments  of  vibration,  which  are  separated  by  lines 
of  rest ;  and  every  one  of  these  reciprocates  the  sound,*  at  the  same  time 
rendering  it  more  intense  by  multiplication.  These  facts  enable  us  to  under- 
stand the  influence  of  the  tensor  tympani  muscle,  in  modifying  the  tension  of 
the  membrane,  and  thus  causing  it  to  vibrate  in  reciprocation  to  sounds  having 
a  great  variety  of  fundamental  notes.  Moreover,  the  fact  that  some  persons 
are  deaf  to  grave  sounds,  whilst  they  readily  hear  the  more  acute,  is  thus 
accounted  for.  The  tensor  tympani,  like  the  iris,  is  probably  excited  to  opera- 
tion by  a  reflex  action ;  and  it  is  by  no  means  improbable  that  one  of  its  func- 
tions may  be  to  prevent  the  internal  ear  from  being  too  violently  affected  by 
loud  sounds,  by  putting  the  membrana  tympani  into  such  a  state  of  tension  as 
not  readily  to  reciprocate  them. 

357.  The  uses  of  the  Tympanic  cavity  are  very  obvious.  One  of  its  pur- 
poses is  to  render  the  vibrations  of  the  membrane  quite  free ;  and  the  other, 
to  isolate  the  chain  of  bones  in  such  a  manner  as  to  prevent  their  vibrations 
from  being  weakened  by  diffusion  through  the  surrounding  solid  parts.  As 
to  the  objects  of  the  Eustachian  tube,  however,  opinions  have  been  much 
divided.  From  the  experiments  of  Miiller,  it  appears  that  it  does  not  increase 
the  intensity  of  sound,  but  that  it  prevents  a  certain  degree  of  dulness  which 
would  attend  it  if  the  cavity  of  the  tympanum  were  completely  closed  ;  of 
this  dulness  we  are  conscious,  when  any  tumefaction  of  the  fauces  causes  an 
occlusion  of  the  extremity  of  the  tube.  It  has  been  supposed  that,  among 
other  uses,  this  canal  serves  for  the  conduction  of  the  speaker's  voice  to  his 
ears ;  but  this  is  certainly  not  the  case  in  any  considerable  degree ;  for,  when 
the  Eustachian  tubes  are  obstructed  by  disease,  the  patient  hears  his  own 
voice  well,  though  other  sounds  are  indistinct ;  and  it  is  easily  shown,  that  its 
transmission  is  chiefly  accomplished  in  other  ways.  The  common  idea  is, 
that  it  serves  the  same  purpose  with  the  hole  in  an  ordinary  drum ;  the  effect 
of  which  js  generally  supposed  to  be,  the  removal  of  the  impediment  to  the 
vibrations*  of  the  membrane,  that  would  be  offered  by  the  complete  enclosure 
of  the  air  within.  It  does  not  appear,  however,  that  any  such  impediment  is 
really  offered ;  and  the  effect  of  the  hole  in  the  drum  seems  rather  to  be  the 

*  This  is  very  easily  proved  by  experiments  on  a  membrane  stretched  over  a  resonant 
cavity;  if  light  sand  be  strewed  upon  it,  and  a  strong  musical  tone  be  produced  in  its 
vicinity,  the  membrane  will  immediately  be  set  in  vibration,  not  as  a  whole  (unless  its 
fundamental  note  be  in  unison  with  that  sounded),  but  in  distinct  segments,  of  which 
every  one  reciprocates  the  sound;  from  the  vibrating  parts,  the  sand  will  be  violently 
thrown  off;  but  it  will  settle  on  the  intermediate  lines  of  rest,  forming  a  variety  of  curious 
figures,  which  are  known  as  the  nodal  lines. 


SENSE  OF  HEARING.  265 

communication,  to  the  ear  of  the  auditor,  of  the  sonorous  vibrations  of  the 
contained  air ;  which  are  thus  transmitted  directly  through  the  atmosphere, 
instead  of  being  weakened  by  transmission  through  the  walls  of  the  instru- 
ment. Hence  there  is  no  real  analogy  in  the  two  cases.  The  principal  object 
of  the  Eustachian  tube  (which  is  always  found  where  there  is  a  tympanic 
cavity)  seems  to  be  the  maintenance  of  the  equilibrium  between  the  air  within 
the  tympanum  and  the  external  air ;  so  as  to  prevent  inordinate  tension  of  the 
membrana  tympani,  which  would  be  produced  by  too  great  or  too  little  pres- 
sure on  either  side,  and  the  effect  of  which  would  be  imperfection  of  hearing. 
It  also  has  the  office  of  conveying  away  mucus  secreted  in  the  cavity  of  the 
tympanum,  by  means  of  cilia  vibrating  on  its  lining  membrane  ;  and  the  deaf- 
ness, consequent  on  occlusion  of  this  tube,  is  in  part  explicable  by  the  accu- 
mulation which  will  then  take  place  in  the  tympanum. 

858.  From  what  has  been  stated,  it  is  evident  that  sonorous  undulations 
taking  place  in  the  air,  will  be  propagated  to  the  fluid  contained  in  the  laby- 
rinth,—through  the  tympanum,  the  chain  of  bones,  and' the  membrane  of  the 
fenestra  ovalis  to  which  the  stapes  is  attached, — without  any  loss,  but  rather 
an  increase  of  intensity.  Why  water  should  be  chosen  as  the  medium  through 
which  the  impression  is  to  be  made  upon  the  nerve,  it  is  impossible  for  us  to 
say  with  any  thing  like  certainty,  in  our  present  state  of  ignorance  as  to  the 
physical  character  of  that  impression.  But,  the  problem  being  to  communi- 
cate to  water  the  sonorous  undulations  of  air,  the  experimental  results  already 
detailed  satisfactorily  prove,  that, — whilst  this  may  be  accomplished,  in  a 
degree  sufficient  for  the  wants  of  the  inferior  animals,  by  the  simple  interposi- 
tion of  a  tense  membrane  between  the  air  and  the  fluid,— the  tympanic  appa- 

[Fig.  57. 


A  view  of  the  labyrinth  of  the  Left  Side,  laid  open  in  its  whole  extent  so  as  to  show  its  Structure; 
these  figures  are  all  magnified ;  1,  the  thickness  of  the  outer  covering  of  the  cochlea;  2,  2,  the  scala  vesti- 
buli  or  upper  layer  of  the  lamina  spiralis;  3, 3,  the  scala  tympani  or  lower  layer  of  the  lamina  spiralis; 
4,  the  hamulus  cochlese ;  5,  centre  of  the  infundibulum ;  6,  the  foramen  rotundum  communicating  with  the 
tympanum;  7,  the  thickness  of  the  outer  layer  of  the  vestibule;  8,  the  foramen  rotundum;  9,  the  fenestra 
ovalis;  10,  the  orifice  of  the  aqueduct  of  the  vestibule  ;  11,  the  inferior  semicircular  canal;  12,  the  superior 
semicircular  canal;  13,  the  external  semicircular  canal;  14,  the  ampulla  of  the  inferior  canal;  15,  the  am- 
pulla of  the  superior  canal ;  16,  the  common  orifice  of  the  superior  and  inferior  canals ;  17,  the  ampulla  of 
the  external  canal.] 

23 


266  OF  SENSATION,  AND  THE  ORGANS  OF  THE  SENSES. 

ratus  of  the  higher  classes  is  most  admirably  adapted  for  this  purpose.  The 
fenestra  ovalis  is  not,  however,  the  only  cjiannel  of  communication  between 
the  tympanum  and  the  labyrinth;  for  there  is,  in  most  animals,  a  second  aper- 
ture, the  fenestra  rotunda,  leading  into  the  cochlea,  and  simply  covered  with 
a  membrane.  It  is  generally  supposed  that,  the  labyrinth  being  filled  with  a 
nearly  incompressible  fluid,  this  second  aperture  is  necessary  to  allow  of  the 
free  vibration  of  that  fluid, — the  membrane  of  the  fenestra  rotunda  being  made 
to  bulge  out,  as  that  of  the  fenestra  ovalis  is  pushed  in.  It  may,  however,  be 
easily  shown  by  experiment,  as  well  as  by  reference  to  comparative  anatomy, 
that  no  such  contrivance  is  necessary ;  for  sonorous  undulations  may  be  excited 
in  a  non-elastic  fluid,  completely  enclosed  within  solid  walls  at  every  part, 
except  where  these  are  replaced  by  the  membrane  through  which  the  vibra- 
tions are  propagated;  and  this  is  precisely  the  condition,  not  only  of  the 
Invertebrated  animals,  but  even  of  Frogs  ;  in  which  last  a  tympanic  apparatus 
exists,  without  a  second  orifice  into  the  labyrinth.  Moreover  it  is  certain,  that 
the  vibrations  of  the  air  in  the  cavity  of  the  tympanum,  must  of  themselves 
act  upon  the  membrane  of  the  fenestra  rotunda;  and  this  is  perhaps  the  most 
direct  manner  in  which  the  fluid  in  the  cochlea  will  be  affected ;  although  it 
will  ultimately  be  thrown  into  much  more  powerful  action,  by  the  transmission 
of  vibrations  from  the  vestibule.  For  it  has  been  satisfactorily  determined  by 
experiment  (xn.),  that  vibrations  are  transmitted  with  very  much  greater 
intensity  to  water,  when  a  tense  membrane,  and  a  chain  of  insulated  solid 
bodies,  capable  of  free  movement,  are  successively  the  conducting  media,  than 
when  the  media  of  communication  between  the  vibrating  air  and  the  water 
are  the  same  tense  membrane,  air,  and  a  second  membrane : — or,  to  apply  this 
fact  to  the  organ  of  hearing,  the  same  vibrations  of  the  air  act  upon  the  fluid 
of  the  labyrinth  with  much  greater  intensity,  through  the  medium  of  the  chain 
of  auditory  bones  and  the  fenestra  ovalis,  than  through  the  medium  of  the  air 
of  the  tympanum  and  the  membrane  closing  the  fenestra  rotunda. — The 
fenestra  rotunda  is  not  to  be  considered  as  having  any  peculiar  relation  with 
the  cochlea;  since,  in  the  Turtle  tribe,  the  former  exists  without  the  latter. 

359.  In  regard  to  the  functions  of  particular  parts  of  the  labyrinth,  no  cer- 
tainty can  be  said  to  exist.  From  the  experimental  results  already  stated,  it 
appears  likely  that,  the  greater  the  extension  of  the  cavity  into  the  dense  sub- 
stance of  the  bone,  the  greater  will  be  the  resonance  communicated  to  the 
fluid,  and  thence  transmitted  to  the  nerves  exposed  to  its  influence. — It  is 
commonly  supposed  that  the  Semicircular  Canals  have  for  their  peculiar 
function,  the  reception  of  the  impressions  by  which  we  distinguish  the  direc- 
tion of  sounds  ;  and  it  is  certainly  a  powerful  argument  in  support  of  this  view, 
that,  in  almost  every  instance  in  which  these  parts  exist  at  all,  they  hold  the 
same  relative  position  to  each  other  as  in  Man,  their  three  planes  being  nearly 
at  right  angles  to  one  another.  The  idea,  however,  must  be  regarded  as  a 
mere  speculation,  the  value  of  which  cannot  be  decided  without  an  increased 
knowledge  of  the  laws,  according  to  which  sonorous  vibrations  are  transmitted. 
Regarding  the  special  function  of  the  Cochlea,  there  is  precisely  the  same 
uncertainty.  This  part  of  the  organ  is  peculiar  in  one  respect, — that  the 
expansion  of  the  auditory  nerve  is  here  spread  out  (upon  the  lamina  spiralis) 
in  closer  proximity  with  the  bone  itself,  than  it  is  in  any  other  part  of  the 
labyrinth ;  so  that  the  vibrations  of  the  bone  will  be  more  directly  communi- 
cated to  the  nerve.  It  is  not  easy  to  see,  however,  what  can  be  the  peculiar 
object  of  this  disposition,  in  regard  to  the  function  of  hearing.  By  M.  Duges 
it  is  surmised,  that  by  the  cochlea  we  are  especially  enabled  to  estimate  the 
pitch  of  sounds,  particularly  of  the  voice  ;  and  he  adduces,  in  support  of  this 
idea,  the  fact,  that  the  development  of  the  cochlea  follows  a  very  similar 
proportion  with  the  compass  of  the  voice.  This  is  much  the  greatest  in  the 


SENSE  OF  HEARING. 


267 


Mammalia ;  less  in  Birds ;  and  in  Reptiles,  which  have  little  true  vocal  power, 
the  cochlea  is  reduced  to  its  lowest  form,  disappearing  entirely  in  the  Amphibia. 
That  there  should  be  an  acoustic  relation  between  the  voice  and  ear  of  each 
species  of  animals,  cannot  be  regarded  as  improbable ;  but  the  speculation  of 
M.  Duges  can  at  present  only  be  received  as  a  stimulus  to  further  inquiry. 

360.  We  have  now  to  consider  the  functions  of  the  accessory  parts, — the 
External  Ear,  and  the  Meatus.     The  Cartilage  of  the  external  ear  may  propa- 


[Fig.  58. 


[Fig.  5U. 


A  view  of  the  Left  Ear  in  its  natural  state  ;  1, 2,  An  anterior  view  of  the  External  Ear,  as  well 

the  origin  and  termination  of  the  helix;  3,  the  as  of  the  Meatus  Auditorius,  Labyrinth,  &c.;  l,the 

anti-helix;  4,  the  anti-tragus;  5,  the  tragus;  6,  the  opening  into  the  ear  at  the  bottom  of  the  concha,; 

lobus  of  the  external  ear;  7,  points  to  the%capha  2,  the  meatus  auditorius  externus  or  cartilaginous 

and  is  on  the  front  and  top  of  the  pinna;  8,  the  canal;  3,  the  membrana  tympani  stretching  upon 

concha;  9,  the  meatus  auditorius  externus.]  its  ring;  4,  the  malleus;  5,  the  stapes;  6,  the  laby- 
rinth.] 

gate  sonorous  vibrations  in  two  ways, — by  reflection  and  by  conduction.  In 
reflection,  the  concha  is  the  most  important  part,  since  it  directs  the  reflected 
undulations  towards  the  tragus,  whence  they  are  thrown  into  the  auditory 
passage.  The  other  inequalities  of  the  external  ear  cannot  promote  hearing 
by  reflection ;  and  the  purpose  of  the  extension  of  its  cartilage  is  evidently  to 
receive  the  sonorous  vibrations  from  the  air,  and  to  conduct  them  to  its  point 
of  attachment.  In  this  point  of  view,  the  inequalities  become  of  importance ; 
for  those  elevations  and  depressions  upon  which  the  undulations  fall  perpen- 
dicularly, will  be  affected  by  them  in  the  most  intense  degree ;  and  in  conse- 
quence of  the  varied  form  and  position  of  these  inequalities,  sonorous  undula- 
tions, in  whatever  direction  they  may  come,  must  fall  advantageously  upon 
some  of  them. — The  functions  of  the  Meatus  appear  to  be  threefold.  The 
sonorous  undulations  entering  from  the  atmosphere  are  propagated  directly, 
without  dispersion,  to  the  membrana  tympani : — the  sonorous  undulations 
received  on  the  external  ear,  are  conveyed  along  the  walls  of  the  meatus  to  the 
membrana  tympani : — the  air  which  it  contains,  like  all  insulated  masses  of 
air,  increases  the  intensity  of  sounds  by  resonance.  That,  in  ordinary  hearing, 
the  direct  transmission  of  atmospheric  vibrations  to  the  membrana  tympani,  is 
the  principal  means  of  exciting  the  reciprocal  vibrations  of  the  latter,  is  suffi- 
ciently evident ;  the  undulations  which  directly  enter  the  passage,  will  pass 
straight  on  to  the  membrane ;  whilst  those  that  enter  obliquely  will  be  reflected 


268  OF  SENSATION,  AND  THE  ORGANS  OF  THE.  SENSES. 

from  side  to  side,  and  at  last  will  fall  obliquely  on  the  membrane,  thus  perhaps 
contributing  to  the  notion  of  direction.  The  power  of  the  lining  of  the  meatus 
to  conduct  sound  from  the  external  ear,  is  made  evident  by  the  fact,  that,  when 
both  ears  are  closely  stopped,  the  sound  of  a  pipe  having  its  lower  extremity 
covered  by  a  membrane,  is  heard  more  distinctly,  when  it  is  applied  to  the 
cartilage  of  the  external  ear  itself,  than  when  it  is  placed  in  contact  with  the 
surface  of  the  head.  The  resonant  action  of  the  air  in  the  tube  is  easily 
demonstrated,  by  lengthening  the  passage  by  the  introduction  of  another  tube  ; 
the  intensity  of  external  sounds,  and  also  that  of  the  individual's  own  voice,  as 
heard  by  himself,  are  then  much  increased. 

361.  'Many  facts  prove,  however,  that  the  fluid  of  the  labyrinth  may  be 
thrown  into  vibration  in  other  ways  than  by  the  tympanic  apparatus.     Thus 
in  Osseous  Fishes,  it  is  only  by  the  vibrations  transmitted  through  the  bones 
of  the  head  that  hearing  can  take  place.     There  are  many  persons,  again, 
who  can  distinctly  hear  sounds  which  are  thus  transmitted  to  them  ;  although, 
through  some  imperfection  of  the  tympanic  apparatus,  they  are  almost  insensible 
to  those  which  they  receive  in  the  ordinary  way.     It  is  evident,  where  this  is 
the  case,  that  the  nerve  must  be  in  a  state  fully  capable  of  functional  activity  ; 
and,  on  the  other  hand,  where  sounds  cannot  thus  be  perceived,  there  will  be 
good  reason  to  believe  that  the  nerve  is  diseased. 

362.  A  single  impulse  communicated  to  the  Auditory  nerve,  in  any  of  the 
foregoing  modes,  seems  to  be  sufficient  to  excite  the  momentary  sensation  of 
sound;  but  most  frequently  a  series  of  such  impulses  is  concerned,  there 
being  but  few  sounds  which  do  not  partake,  in  a  greater  or  less  degree,  of  the 
character  of  a  tone.     Any  continuous  sound  or  tone  is  dependent  upon  a  suc- 
cession of  such  impulses  ;  and  its  acuteness  or  depth  is  governed  by  the  rapidity 
with  which  they  succeed  one  another.     It  is  not   difficult  to  ascertain  by 
experiment,  what  number  of  such  impulses  or  undulations  are  required  to 
give  every  tone  which  the  ear  can  appreciate.     Thus,  if  a  circular  plate,  with 
a  number  of  apertures  at  regular  intervals,  be  made  to  revolve  over  the  top  of 
a  pipe  through  which  air  is  propelled,  a  succession  of  short  puffs  will  be 
allowed  to  issue  from  this ;  and,  if  the  revolution  is  sufficiently  rapid,  these 
impulses  will  unite  into  a  definite  tone.     In  the  same  manner,  if  a  spring  be 
fixed  near  the  edge  of  a  revolving  toothed  wheel,  in  such  a  manner  as  to  be 
caught  by  every  tooth  as  it  passes,  a  succession  of  clicks  will  be  heard ;  and 
these  too,  if  the  revolution  of  the  wheel  be  sufficiently  rapid,  will  produce  a 
tone.     The  number  of  apertures  in  the  plate  which  pass  the  orifice  of  the  pipe 
in  a  given  time,  or  the  number  of  teeth  which  pass  the  spring  being  known, 
it  is  easy  to  see  that  this  must  be  the  number  of  impulses  required  to  produce 
the  given  tone.     Each  impulse  produces  a  double  vibration, — forwards  and 
backwards  ;*  hence  the  number  of  impulses  is  always  half  that  of  the  single 
vibrations.     The  maximum  and  minimum  of  the  intervals  of  successive  pulses, 
still  appreciable  by  the  ear  as  determinate  sounds,  have  also  been  determined 
by  M.  Savart  more  satisfactorily  and  more  accurately  than  had  previously 
been  done.     If  their  intensity  is  great,  sounds  are  still  audible  which  result 
from  the  succession  of  24,000  impulses  in  a  second  ;  and  this,  probably,  is  not 
the  extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear.     From  some 
observations  of  Dr.  Wollaston's,  it  seems  probable  that  the  ears  'of  different 
individuals  are  differently  constituted  in  this  respect, — some  not  being  able  to 
hear  very  acute  tones  produced  by  Insects,  or.  even  Birds,  which  are  distinctly 
audible  to  others.     Again,  the  sound  resulting  fr«n  16  impulses  per. second, 
is  not,  as  has  been  usually  supposed,  the  lowest  appreciable  note  ;  on  the  con- 
trary, M.  Savart  has  succeeded  in  rendering  tones  distinguishable,  which  were 

*This  is  seen  when  a  string  is  put  in  vibration,  by  pulling  it  out  of  the  straight  line. 


SENSE  OF  HEARING.  269 

produced  by  only  7  or  8  impulses  in  a  second ;  and  continuous  sounds  of  a 
still  deeper  tone  could  be  heard,  if  the  individual  pulses  were  sufficiently 
prolonged.  In  regard,  however,  to  the  precise  time  during  which  a  sonorous 
impression  remains  upon  the  ear,  it  is  difficult  to  procure  exact  information, 
since  it  departs  more  gradually  than  do  visual  impressions  from  the  eye.  This 
is  certain,  however, — that  it  is  much  longer  than  the  interval  between  the 
successive  pulses  in  the  production  of  tones  ;  since  it  was  found  by  M.  Savart, 
that  one  or  even  several  teeth  might  be  removed  from  the  toothed  wheel, 
without  a  perceptible  break  in  its  sound, — showing  that,  when  the  tone  was 
once  established,  the  impression  of  it  remained  during  an  intermission  of  some 
length. 

363.  The  Ear  may,  like  the  Eye,  vary  considerably,  as  regards  general 
acuteness,  amongst  different  individuals ;  and  its  power  may  be  much  increased 
by  practice.     A  part  of  this  increase  depends,  however,  as  in  other  instances, 
upon  the  greater  attention  which  its  fainter  indications  receive ;  but  a  part, 
also,  upon  an  increased  use  of  the  organ.     The  power  of  hearing  very  faint 
sounds  is  as  different  from  the  power  of  distinguishing  musical  tones,  as  the 
power  of  discerning  very  minute  objects,  or  of  seeing  with  very  faint  degrees 
of  light,  is  from  that  of  distinguishing  colours.     Many  persons  are  altogether 
destitute  of  what  is  termed  a  musical  ear ;  whilst  others  are  endowed  with  it 
in  a  degree,  which  is  a  source  of  great  discomfort  to  them,  since  every  dis- 
cordant sound  is  a  positive  torment.     The  power  of  distinguishing  the  direc- 
tion of  sounds  appears  to  be,  in  Man  at  least,  for  the  most  part  acquired  by 
habit.     It  is  some  time  before  the  infant  seems  to  know  any  thing  of  the  direc- 
tion of  noises  which  attract  his  attention.     Now  although  there  can  be  no 
question  that  this  perception  is  acquired  by  attention  to  certain  variations  in 
the  impression  made  upon  the  nerve,  through  the  medium  either  of  the  tym- 
panic apparatus  or  of  the  bones  of  the  head,  yet  it  is  equally  evident  that 
there  can  be  nothing  in  these  variations  themselves  adequate  to  excite  the 
idea,  and  that  it  must  therefore  be  either  intuitive  or  acquired  by  habit.     This 
is  a  consideration  of  some  importance,  in  regard  to  the  similar  question  as  to 
the  sense  of  Visual  direction.     In  some  cases  we  are  probably  assisted  by  the 
relative  intensity  of  the  sensations,  communicated  by  the  two  ears  respectively. 
The  idea  of  the  distance  of  the  sonorous  body  is  another  acquired  perception, 
depending  principally  upon  the  loudness  or  faintness  of  the  sound,  when  we 
have  no  other  indications  to  guide  us.     In  this  respect  there  is  a  great  simi- 
larity between  the  perception  of  distance  of  an  object,  through  the  Eye,  by 
its  size,  and  through  ^he  Ear  by  the  intensity  of  its  sound.     When  we  know 
the  size  of  the  object,  or  are  acquainted  with  the  usual  intensity  of  its  sound, 
we  can  judge  of  its  distance  ;  and  vice  versa,  when  we  know  its  distance,  we 
can  at  once  form  an  idea  of  its  real  from  its  apparent  size,  and  of  its  real 
Strength  of  tone  from  that  which  affects  our  ears.     In  this  manner,  the  mind 
may  be  affected  with  corresponding  deceptions  through  both  senses ;  thus,  in 
the  Phantasmagoria,  the  figure  is  gradually  diminished  while  its  distance  re- 
mains the  same,  and  it  appears  to  the  spectators  to  recede, — the  illusion  being 
more  complete,  if  its  brightness  be  at  the  same  time  diminished ;  and  the 
effect  of  a  distant  full  military  band  gradually  approaching,  may  be  alike  given 
by  a  corresponding  crescendo  of  concealed  instruments.     It  is  upon  the  com- 
plete imitation  of  the  conditions,  which  govern  our  ideas  of  the  intensity  and 
direction,  as  well  as  of  the  character,  of  sounds,  that  the  deceptions  of  the 
Ventriloquist  are  founded. 

364.  Some  facts  of  much  interest  have  lately  been  ascertained,  in  regard 
to  an  occasional  variation  in  the  rapidity  of  the  perception  of  sensory  impres- 
sions, received  through  the  Eye  and  through  the  Ear.     These  facts  are  the 
result  of  comparisons  made  amongst  different  astronomical  observers,  who  may 

23* 


270  OF  MUSCULAR  CONTRACTILITY. 

be  watching  the  same  visual  phenomena,  and  timing  their  observations  by 
the  same  clock ;  for  it  has  been  remarked,  that  some  persons  see  the  same 
phenomenon,  a  third  or  even  half  of  a  second  earlier  than  others.  There  is  no 
reason  to  suppose  from  this,  however,  that  there  is  any  difference  in  the  rate 
of  transmission  of  the  sensory  impressions  in  the  two  nerves.  The  fact  seems 
rather  to  be,  that  the  sensorium  does  not  readily  perceive  two  different  impres- 
sions with  equal  distinctness ;  and  that,  when  several  impressions  are  made 
on  the  nerves  at  the  same  time,  the  mind  takes  cognizance  of  one  only,  or 
perceives  them  in  succession.  When,  therefore,  both  sight  and  hearing  are 
directed  simultaneously  to  one  object,  the  communication  of  the  impression 
through  one  sense  will  necessarily  precede  that  made  by  the  other.  The 
interval  between  the' two  sensations  is  greater  in  some  persons  than  in  others ; 
for  some  can  receive  and  be  conscious  of  many  impressions,  seemingly  at  the 
same  moment ;  whilst  in  others  a  perceptible  space  must  elapse. 

365.  Amongst  other  important  offices  of  the  power  of  Hearing,  is  that  of 
supplying  the  sensations  by  which  the  Voice  is  regulated.  It  is  well  known 
that  those  who  are  born  entirely  deaf,  are  also  dumb, — that  is,  destitute  of  the 
power  of  forming  articulate  sounds ;  even  though  not  the  least  defect  exist  in 
their  organs  of  voice.  Hence  it  appears  that  the  vocal  muscles  can  only  be 
guided  in  their  actijn  by  the  sensations  received  through  the  Ears,  in  the 
same  manner  as  other  muscles  are  guided  by  the  sensations  received  through 
themselves  (§  399).  On  this  point,  more  will  be  said  hereafter  (§  413). 


CHAPTER    V. 

OF  MUSCULAR  CONTRACTILITY. 

I.  Of  Contractility  in  general. 

366.  THE  Nervous  System  has  no  power  of  occasioning  movement  in  any 
part  of  the  body,  save  by  exciting  to  contraction  certain  structures,  to  which 
the  term  Muscular  is  given.  That  one  tissue  should  possess  within  itself  the 
property  of  contractility  on  the  application  of  a  stimulus,  is  no  more  wonderful 
than  that  another  should  be  capable  of  conveying  sensory  or  motor  influences, 
or  another  of  separating  a  peculiar  secretion  from  the  blood.  Such  contrac- 
tile tissues  are  found  in  Vegetables  as  well  as  in  Animals ;  and  instances  of 
their  operation  have  been  already  referred  to  (§  13).  The  only  essential 
difference  between  the  contractility*  of  Muscular  Fibre,  and  that  of  the  cells 
of  the  Sensitive  Plant,  is  that  the  former  can  be  excited  by  the  stimulus  of 
innervation,  as  well  as  by  those  of  a  physical  or  chemical  nature,  which  will  act 
upon  the  latter.  Muscular  structure,  as  heretofore  remarked,  is  employed  in 

*  The  peculiar  operation  of  this  property  in  Muscular  Fibre,  the  ordinary  contraction 
of  which  alternates  with  relaxation,  has  occasioned  the  distinctive  term  Irritability  to  be 
applied  to  it.  This  term  has  been  employed,  however,  in  so  many  different  'senses 
(being,  by  some  Physiologists,  used  almost  synonymously  with  the  more  general  one  of 
Vitality),  that  it  seems  desirable  to  avoid  adopting  it  for  such  a  purpose. 


MUSCLES  OF  ANIMAL  LIFE.  271 

the  Animal  body,  not  only  as  the  instrument  of  the  operation  of  the  Nervous 
System  upon  the  external  world, — in  which  respect  alone  its  action  can  be 
said  to  form  part  of  the  Functions  of  Animal  Life, — but  also  to  execute  many 
of  those  interior  movements  which  the  peculiar  conditions  of  Animal  existence 
require  for  its  own  maintenance,  such  as  the  propulsion  of  the  food  along  the 
alimentary  canal,  and  that  of  the  blood  through  the  vascular  system.  The 
muscles  concerned,  however,  in  these  operations,  which  are  so  immediately 
connected  with  the  maintenance  of  the  Organic  functions,  differ  essentially 
from  those  strictly  forming  part  of  the  apparatus  of  Animal  life,  both  in  their 
own  structure,  and  in  the  manner  in  which  their  contractility  is  called  into 
operation.  The  former  are  (like  the  contractile  tissues  of  Plants)  much  more 
susceptible  than  the  latter,  of  being  excited  to  action  by  a  stimulus  immediately 
applied  to  themselves,  and  are  with  difficulty  shown  to  be  in  any  degree 
under  the  influence  of  nerves  (§  201) ;  whilst  the  latter  are  readily  thrown 
into  violent  contraction,  by  a  stimulus  conveyed  to  them  through  the  nervous 
system.  Hence  a  physiological  distinction  may  be  made,  between  these  two 
groups  of  muscles ;  which  is  fully  borne  out  by  differences  in  the  structure 
and  arrangement  of  their  component  parts.  By  some,  the  two  classes  have 
been  spoken  of  as  those  of  Involuntary  and  Voluntary  Muscles ;  but  this 
distinction  is  not  correct ;  since  every  muscle  ordinarily  termed  voluntary,  is 
susceptible  of  being  called  into  action  involuntarily.  It  is  better  to  found  the 
distinction  upon  their  nearer  or  more  remote  concern-  in  the  functions  of  Or- 
ganic Life  :  those  which  are  immediately  involved  in  their  maintenance,  and 
over  which  the  will  can  never  exert  any  influence, — the  Heart,  and  Muscular 
coat  of  the  Intestinal  Canal,  for  instance, — being  designated  as  the  Muscular 
System  of  Organic  Life  ;  and  those  which  can  be  employed  by  the  Nervous 
System  to  execute  the  commands  of  the  Will,  being  included  in  the  Muscular 
System  of  Animal  life.  The  structure  peculiar  to  the  latter  will  first  be  de- 
scribed ;  as  it  is  evidently  that  which  is  most  characteristic  of  Muscle. 

II.  Muscles  of  Animal  Life. 

367.  When  we  examine  an  ordinary  Muscle  (from  one  of  the  extremities,  for 
example),  with  the  naked  eye,  we  observe  that  it  presents  a  fibrous  appearance ; 
and  that  the  fibres  are  arranged  with  great  regularity  in  the  direction  in  which 
the  muscle  is  to  act.  Upon  further  examination  it  is  found,  that  these  fibres 
are  united  together  in  fasciculi  or  bundles  of  larger  or  smaller  size,  by  means 
of  areolar  tissue ;  ana  when  the  Microscope  is  applied  to  the  smallest  fibre 
which  can  be  seen  with  the  naked  eye,  it  is  seen  itself  to  consist  of  a  fascicu- 
lus, composed  of  a  number  of  cylindrical  fibres  lying  in  a  parallel  direction, 
and  closely  bound  together.  These  pri- 
mitive fibres  present  two  sets  of  markings  Fig.  60. 
or  striae  ;  one  set  longitudinal, — the  other 
transverse  or  annular.  By  more  closely 
examining  these  fibres,  when  separated 
from  each  other,  it  is  frequently  seen  that 
each  may  be  resolved  into  fibrillg,  by 
the  splitting  of  its  contents  in  a  longi- 
tudinal direction,  as  shown  in  Fig.  60. 
These  fibrillae  have  a  peculiar  beaded  ap- 
pearance, which  will  be  presently  noticed 
more  particularly.  It  not  unfrequentlv 
happens,  however,  that  when  a  fibre  is 

,  the  fibres  se 

drawn  apart,  its  contents  separate  in  the     bundles  of  fibriiUe. 
direction  of  the  transverse  striae;  forming  a 


272 


OF  MUSCULAR  CONTRACTILITY, 

Fig.  61. 


Portion  of  Human  Muscular  Fibre,  separating  into  disks,  by  cleavage  in  direction  of  transverse  Striae. 
After  Bowman. 

series  of  discs,  as  shown  in  Fig.  61  [and  Fig.  62].  This  cleavage  is  just  as 
natural  as  the  former,  though  less  frequent ;  and  it  leads  us  to  a  view  of  the 
composition  of  Muscular  Fibre,  somewhat  different  from  the  one  commonly 
adopted.  To  use  the  words  of  Mr.  Bowman,*  it  would  be  as  proper  to  say, 
"that  the  fibre  is  a  pile  of  discs,  as  that  it  is. a  bundle  of  fibrillx;  but  in  fact 
it  is  neither  the  one  nor  the  other,  but  a  mass  in  whose  structure  there  is  an 
intimation  of  the  existence  of  both,  and  a  tendency  to  cleave  in  the  two  direc- 
tions. If  there  were  a  general  disintegration  along  all  the  lines  in  both  direc- 
tions, there  would  result  a  series  of  particles,  which  may  be  termed  primitive 
particles  or  sarcous  elements,  the  union  of  which  constitutes  the  mass  of  the 


[Fig.  62. 


7      8 


Fragments  of  Striped  Elementary  Fibres,  showing  a  cleavage  in  opposite  directions ;  magnified  300  dia- 
meters; 1,  longitudinal  cleavage ;  the  longitudinal  and  transverse  lines  are  both  seen;  some  longitudinal 
lines  are  darker  and  wider  than  the  rest,  and  are  not  continuous  from  end  to  end ;  this  results  from  par- 
tial separation  of  the  fibrillae;  6,  fibrillee.  separated  from  one  another  by  violence  at  the  broken  end  of  the 
fibre,  and  marked  by  transverse  lines  equal  in  width  to  those  on  the  fibre;  7,  &  represent  two  appear- 
ances commonly  presented  by  the  separated  single  fibrillae,  (more  highly  magnified;)  at  7  the  borders  and 
transverse  lines  are  all  perfectly  rectilinear,  and  the  included  spaces  perfectly  rectangular;  at  8  the 
borders  are  scalloped,  the  spaces  bead-like;  when  most  distinct  and  definite,  the  fibrilla  presents  the  former 
of  these  appearances:  2,  transverse  cleavage;  the  longitudinal  lines  are  scarcely  visible ;  3,  incomplete 
fracture  following  the  opposite  surfaces  of  a  disc,  which  stretches  across  the  interval  and  retains  the  two 
fragments  in  connection  ;  the  edge  and  surface  of  this  disc  are  seen  to  be  minutely  granular,  the  granules 
corresponding  in  size  to  the  thickness  of  the  disc,  and  to  the  distance  between  the  faint  longitudinal  lines; 
4,  another  disc  nearly  detached;  5,  detached  disc  more  highly  magnified,  showing  the  sarcous  elements.] 

*  See  Bowman  on  the  Minute  Structure  and  Movements  of  Voluntary  Muscle,  in 
Phil.  Trans.  1840.  His  description  is  here  followed  by  the  Author,  as  that  most  gene- 
rally»received  amongst  Physiologists.  An  entirely  different  account,  however,  has  been 
given  by  Dr.  Barry  (Phil.  Trans.  1842).  The  Author  cannot  satisfy  himself,  that  either 
of  these  explains  all  the  appearances  which  are  presented  by  this  interesting  object. 


MUSCLES  OF  ANIMAL  LIFE.  273 

fibre.  These  elementary  particles  are  arranged  and  united  together  in  the  two 
directions.  All  the  resulting  discs  as  well  as  fibrillse  are  equal  to  one  another 
in  size,  and  contain  an  equal  number  of  particles.  The  same  particles  compose* 
both.  To  detach  an  entire  fibrilla,  is  to  abstract  a  particle  of  every  disc;  and 
vice  versa.1'' 

368.  The  elements  of  Muscular  Fibre  are  bound  together,  in  the  perfect 
condition  of  the  fibre,  by  a  very  delicate  tubular  sheath,  which  seems  to 
answer  to  the  tube  of  nervous  fibre.     This  cannot  always  be  readily  brought 
into  view ;  but  it  is  occasionally  seen  with  great  distinctness :  thus,  when  the 
two  ends  of  a  fibre  are  drawn  apart,  its 

contents  will  sometimes  separate  with-  Fig.  63. 

out  the  rupture  of  the  sheath,  which 

then  becomes  evident;  and  this,  during 

the  act  of  contraction,  may  sometimes 

be  observed  to  rise  up  in  wrinkles  upon 

the  surface  of  the  fibre,  as  spen  in  Fig. 

66.     This  sheath  is  quite  distinct  from 

the   areolar   tissue,  which   binds   the 

,.       .1?  i     •     i  Fibre  of  Human  Muscle  broken  across;  the  frag- 

fibres  mtO   fasciculi;    and    it   has   been      menta  connected  by  the  uiitorn  sarcolemma.  After 

termed,  for  the  sake  of  distinction,  the  Bowman. 
Sarcolemma.  Its  existence  may  be  de- 
monstrated in  any  muscular  fibre,  by  subjecting  it  to  the  action  of  fluids,  which 
occasion  a  swelling  of  its  contents ;  this  is  especially  the  effect  of  acids  and 
alkalies,  and  may  be  well  produced  by  the  citric  and  tartaric  acids,  and  by 
potash.  For  a  time,  the  Sarcolemma  yields  to  the  distension  which  takes 
place  from  within ;  but  at  last  it  bursts  at  particular  points,  and  a  sort  of  hernia 
of  its  contents  takes  place,  making  the  existence  of  a  perfect  envelop  in  all 
other  parts  quite  evident.  This  membrane  is  itself  perfectly  transparent,  and 
has  nothing  to  do  with  the  production  of  either  the  longitudinal  or  the  trans- 
verse stria3.  There  is  no  reason  to  believe  that  it  is  perforated  either  by 
nerves  or  by  capillary  vessels;  in  fact  it  seems  to  be  an  effectual  barrier 
between  the  real  elements  of  Muscular  structure,  and  the  surrounding  parts. 
That  it  has  no  share  in  the  contraction  of  the  fibre,  is  evident  from  the  fact 
just  mentioned,  respecting  the  condition  which  it  occasionally  presents  when 
the  fibre  is  much  shortened. 

369.  Muscular  Fibres  are  commonly  described  as  cylindrical ;  but  there  is 
reason  to  believe  that  they  are  rather  of  a  polygonal  form,  than  sides  being 
flattened  against  those  of  adjoining  fibres.     In  some  instances  the  angles  are 
sharp  and  decided;  in  others  they  are  rounded  off,  so  as  to  leave  spaces 
between  the  contiguous  fibres  for  the  passage  of  vessels.     In  Insects,  the  fibres 
often  present  the  form  of  flattened  bands.     Their  size  varies  considerably  in 
different  classes  of  animals ;  and  even  in  the  same  animal,  and  the  same  mus- 
cle.    The  following  table  gives  illustrations  of  these  varieties;  the  extremes 
are  those  met  with  by  Mr.  Bowman  himself;  but  other  observers  speak  of 
dimensions  more  widely  separated. 

Fractions  of  an  inch. 


BIRDS 


Mole 
Mouse 
Owl    - 
Chaffinch 
Heron 


274 


OF  MUSCULAR  CONTRACTILITY. 


REPTILES 

FISH 
INSECTS 


Frog 

Lizard 

Boa    - 

Skate 

Cod    - 

Sprat 

Staghorn  Beetle 

Blue-bottle  Fly 


to  ik 
<U 
to  jiff 

t0  & 
t0  *V 
t0  20<J 

to 


It  is  interesting  to  remark,  upon  this  table,  that  the  Muscular  Fibre  of  Reptiles 
and  Fishes  is  upon  the  whole  much  larger  than  that  of  other  Vertebrata,  and 
that  its  dimensions  present  the  greatest  extremes  of  variation ;  whilst  in  Birds 
it  is  much  smaller  than  in  all  other  Vertebrata,  and  its  dimensions  are  also  less 
variable.  Further,  the  size  of  the  fibres  bears  no  proportion  to  that  of  the 
animal;  for  we  observe  that  in  the  Chaffinch  they  are  larger  than  in  the  Owl, 
in  the  Cat  larger  than  in  the  Horse,  and  in  the  Frog  often  larger  than  in  the 
Boa.  Moreover  in  Insects,  the  diameter  of  the  fibres  is  even  greater  than  it 
is  in  Mammalia.  Some  difference  of  opinion  exists  as  to  whether  the  arrange- 
ment of  the  fibrillae  within  the  sarcolemma  is  such  as  to  form  a  hollow  or  a 
solid  bundle.  It  frequently  happens  that,  when  a  fibre  is  torn  across,  the 
appearance  of  the  brush-like  tuft  of  fibrillas  at  the  broken  extremity  is  such  as 
to  indicate  that  they  form  a  hollow  cylinder ;  but  this  may  be  accounted  for 
by  the  fact  that  the  outer  layer  of  fibrillae  is  evidently  adherent  in  some  degree 
to  the  Sarcolemma,  and  will  consequently  be  extended  with  it,  at  the  moment 
of  its  rupture,  beyond  the  deeper  layers.  The  appearance  presented  by  trans- 
verse sections  shows,  that  the  bundle  of  fibrillae  contains  no  central  cavity ;  the 
extremities  of  the  cut  fibrillae,  however,  cannot  always  be  distinguished  in 
Mammalia,  in  consequence,  as  it  would  seem,  of  their  close  and  intimate  lateral 
union ;  but  they  are  very  evident  in  Birds,  Reptiles  and  Fishes  (Fig.  64). 
The  addition  of  an  acid  increases  the  distinctness  of  the  fibrillae,  by  widening 
the  interstices  between  them. 

Fig.  64. 


Transverse  Section  of  Muscular  Fibres  from  Pectoral  Muscle  of  Teal:  showing  the  irregular  form  of  the 
fibres,  and  the  aggregation  of  circular  particles,  with  which  they  are  completely  filled.    After  Bowman. 

370.  When  the  fibrillae  are  separately  examined,  they  are  found  to  present 
an  alternation  of  dark  and  light  spaces ;  and  these  points  are  capable  of  being 


MUSCLES  OF  ANIMAL  LIFE.  275 

reversed  by  an  alteration  of  the  focus  of  the  microscope ;  so  that  the  appear- 
ance is  evidently  due  to  the  mode  in  which  the  light  passing  through  them  is 
refracted,  and  not  to  any  difference  of  colour  in  the  two  series  of  points.  It  is 
in  fact  precisely  that  which  is  given  by  a  glass  rod  with  beaded  enlargements, 
when  held  to  the  light ;  the  beads  will  appear  bright,  and  the  intervening 
spaces  dark.  When  the  fibrillae  are  separately  examined,  however,  under  the 
highest  magnifying  power,  and  the  most  perfect  definition,  it  is  perceived  that 
they  are  perfectly  cylindrical ;  and  that  the  dark  spaces  are  slender  lines,  run- 
ning directly  across  them.  Hence  the  beaded  appearance  must  be  regarded 
as  an  optical  illusion ;  the  light  points  being  the  centres  of  highly-refracting 
particles,  which  act  as  lenses ;  and  the  dark  lines  the  intervals  between  them, 
formed  of  a  less  powerfully  refracting  substance.  The  size  of  the  ultimate 
fibrils  is  stated  by  Wagner  to  be  nearly  the  same  in  all  Vertebrata,  as  well  as 
in  Insects,  and  in  the  Craw-fish ;  its  usual  extremes  being  from  about  ¥Jj F  to 
TT&T*  °f  an  i*10*1 '  but  Muller  has  observed  them  in  the  Frog  to  be  .sometimes 
as  much  as  jg^j  of  an  inch,  and  in  the  Parrot  to  be  4-^3-5  of  an  inch  in 
diameter.  Taking  the  average  stated  by  Wagner,  and  comparing  it  with  the 
average  dimensions  of  the  fibre  in  the  Human  Species,  which  is  estimated  by 
Mr.  Bowman  at  about  TT^-  of  an  inch,  each  Muscular  fibre  in  Man  may  be 
regarded  as  composed  of  from  five  to  eight  hundred  fibrillae.  The  transverse 
strise,  which  are  peculiarly  characteristic  of  the  Muscular  Fibre  of  Animal 
life,  have  been  supposed,  by  several  observers,  to  be  due  to  the  pressure  of 
circular  bands  or  girths,  surrounding  the  fibrillce  ;  and  some  have  even  imagined 
that  they  might  be  attributed  to  a  continuous  spiral  coil.  The  existence  of 
such  bands,  is  not,  however,  indicated  in  any  other  way.  As  already  stated, 
the  fibrillae  are  only  bound  together  by  the  Sarcolemma  or  enveloping  tube ; 
and  this  is  composed  of  a  simple  transparent  membrane,  destitute  of  any  ap- 
pearance of  bands.  The  spaces  between  the  light  and  dark  striae  on  the  fibre, 
exactly  correspond  with  those  between  the  light  and  dark  points  in  individual 
fibrillae ;  and  this  is  the  case  in  all  conditions  of  the  muscle ;  so  that  it  cannot 
be  doubted,  that  the  appearance  must  be  the  result 
of  the  same  cause  in  each  condition.  The  average  Fig.  65. 

distance  of  the  striae  in  the  muscular  fibre  of  differ- 
ent animals,  is  very  nearly  uniform ;  as  will  be  seen 
from 'the  following  table.  Between  the  extremes, 


**•• 
however,  there  is  considerable  variation;  and  this 

will  be  presently  shown  to  depend  upon  the  condi- 
tion of  the  muscle  at  the  time  of  examination.  The  Fragment  of  Muscular  Fibre 
distance  is  not  only  often  different  in  the  same  mus-  from  macerated  Heart  of  Ox> 
cle  and  the  same  fasciculus,  but  even  in  the  same  'bowing  S£t?£S£  7 

~,          .        ,.~,  r   •       -I  i         mi        n  tlie  aggregation  or  bead-like  n- 

fibre  m  different  parts  of  its  length.     The  figures     brilte.   After  Bowman, 
indicate  the  number  of  striae  in  TTJ!jr3.  of  an  inch. 

Maximum.  Minimum.  Mean. 

Human  15-0                6-0  9-4 

Other  Mammalia  15-0                 6-7  10-9 

Birds  14-0                7-0  10-4 

Reptiles  20-0  •  6-7  11-5 

Fish  18-0                7-5  11-1 

Insects  16-0                4-5  9-5 

The  extremes  in  the  same  specimen,  however,  were  in  no  instance  so  widely 
apart  as  the  table  indicates  for  the  Class ;  the  greatest  proportion  between  the 
maximum  and  minimum  being,  except  in  Insects,  as  2  to  1. 

371;  The  general  opinion  as  to  the  disposition  of  the  fibres  during  the  con- 


276  OF  MUSCULAR  CONTRACTILITY. 

traction  of  muscle,  has  been  that  of  Prevost  and  Dumas,  who  stated  that  they 
are  thrown  into  a  sinuous  or  zigzag  flexure.  Recent  observations,  however, 
have  fully  demonstrated  the  incorrectness  of  this  view ;  the  improbability  of 
which  might  have  been  suspected  from  the  consideration  that  fibres  in  this 
state  of  flexure  could  not  be  imagined  to  be  exerting  any  force  of  traction.* 
Prof.  Owen  has  noticed  that,-  in  the  contracted  state  of  the  very  transparent 
muscles  of  some  Entozoa,  each  separate  fibre,  which  may  be  seen  with  great 
distinctness,  presents  a  knot  or  swelling  in  the  middle,  besides  being  generally 
thickened ;  but  that  it  is  simply  shortened  without  falling  out  of  the  straight 
line.  Dr.  A.  Thomson  remarked  the  same  thing  in  the  Frog;  single  fibres, 
whilst  continuing  in  contraction,  being  simply  shortened,  without  falling  into 
zigzag  line ;  and  he  was  led  to  suspect,  from  this  and  other  circumstances, 
that  the  zigzag  arrangement  was  not  produced  until  the  act  of  contraction  had 
ceased.  The  recent  inquiries  of  Mr.  Bowman  have  proved  most  satisfactorily, 
that,  in  a  state  of  contraction,  there  is  an  approximation  of  the  transverse 
strise,  and  a  general  shortening  of  the  fibre ;  and  that  its  diameter  is  at  the 
same  time  increased ;  but  that  it  is  never  thrown  out  of  the  straight  line,  except 
when  it  has  ceased  to  contract,  and  its  two  extremities  are  still  held  in  proxi- 
mity by  the  contraction  of  other  fibres.  The  whole  process  may  be  distinctly 
seen  under  the  Microscope  in  a  single  fibre  isolated  from  the  rest ;  it  is,  of 
course,  desirable  to  select  the  specimen  from  those  animals  in  which  the  con- 
tractility of  the  Muscle  is  retained  for  the  longest  period  after  death, — which 
is  particularly  the  case  in  Reptiles  among  Vertebrata,  and  in  most  Invertebrata 
(Mr.  Bowman  particularly  recommends' the  Crab  and  Lobster) ;  but  the  change 
has  been  fully  proved  to  differ  in  no  essential  degree,  in  the  warm-blooded 
Vertebrata.  The  contraction  usually  commences  at  the  extremities  of  the 
fibre ;  but  it  frequently  occurs  also  at  one  or  more  intermediate  points.  The 
first  appearance  is  a  spot  more  opaque  than  the  rest,  caused  by  the  approxi- 
mation of  a  few  of  the  segments  of  some  of  the  fibrillse:  this  spot  usually 
extends  in  a  short  time  through  the  whole  diameter  of  the  fibre,  and  the 
shading,  caused  by  the  approximation  of  the  transverse  striaB,  increases  in 
intensity.  The  strise  are  found  to  be  two,  three,  or  even  four  times  as  nume- 
rous in  the  contracted  as  in  the  uncontracted  part,  and  are  also  proportionally 
narrower  and  more  delicate.  The  line  of  demarkation  between  the  contracted 
and  uncontracted  portions  is  well  defined ;  but,  as  the  process  goes  on;  fresh 
striae  are  absorbed  (aS-it  were)  from  the  latter  into  the  former.  The  contracted 
parts  augment  in  thickness;  but  not  in  a  degree  commensurate  with  its 
diminished  length ;  so  that  its  solid  parts  lie  in  smaller  compass  than  before, — 
the  fluid  which  previously  intervened  between  them,  being  -pressed  out  in 
bullse  under  the  sarcolemma  (Fig.  66).  The  force  with  which  the  elements 

Fig.  66. 


Muscular  Fibre  of  Dytiscus,  contracted  in  the  centre ;  the  stria;  approximated ;  the  breadth  of  the  fibre 
increased ;  and  the  sarcolemma  raised  in  bullee  on  its  surface.  After  Bowman. 

*  By  Prevost  and  Dumas  it  was  imagined  that  the  muscular  fibres  themselves  were 
passive  agents  in  contraction;  and  that  the  real  power  was  given  by  an  attractive  force, 
analogous  to  or  identical  with  that  of  electricity,  existing  between  the  nervous  fibres, 
which  were  stated  by  them  to  be  disposed  in  parallel  rows,  transversely  to  the  direction 
of  the  muscle.  Other  Physiologists,  however,  have  shown  that  this  was  a  hasty  assump- 
tion ;  and  it  is  completely  disproved  by  the  numerous  facts  which  prove  that  muscular 
contractility  does  not  depend  on  nervous  agency  (§§  380—385). 


MUSCLES  OF  ANIMAL  LIFE. 


277 


Muscular  fibre  of  Skate,  in  a  state  of 
rest  (1),  and  in  three  different  stages  of 
contraction  (2,  3,  4).  After  Bowman. 


of  the  fibre  thus  tend  to  approximate  -is  Fig.  67. 

evidently  considerable  ;  for  if  the  two  ex- 
tremities be  held  apart,  the  fibre  is  not 
unfrequently  ruptured.  This  corresponds 
with  the  appearances  found  in  the  muscles 
of  persons  who  have  died  from  tetanus ; 
for  in  the  ruptured  fibres  of  those  muscles, 
which  had  been  the  subjects  of  the  spas- 
modic action,  the  striae  have  been  observed 
to  approximate  so  closely  as  to  be  scarcely 
distinguishable.  When  the  contraction  is 
not  very  decided,  the  dark  and  elevated 
spot  appears  to  play  like  a  wave  along  the 
fibre,  before  it  involves  the  whole  diameter 
in  any  part ;  and  even  when  considerable 
traction  is  being  exercised,  there  is  con- 
tinual interchange  in  the  elements  by 
which  it  is  effected, — the  disks  at  one  end 
of  the  contracted  part  receding  from  each 
other,  whilst  at  the  other  end  new  disks 
are  being  received  into  it. 

372.  The  foregoing  description  is  chiefly 
derived  from  the  appearances-  presented  by 
muscular  fibre,  when  spontaneously  pass- 
ing into  that  state  of  contraction  which  is 
termed  the  rigor  mortis ;  and  it  has  not 
been  fully  demonstrated  that  the  pheno- 
mena of  contraction,  excited  by  the  agency 
of  the  nerves,  are  precisely  similar.  Mr.  Bowman  has  remarked,  however,  that 
stimuli  of  various  kinds,  directly  applied  to  them,  produce  corresponding  effects, 
although,  in  the  case  of  galvanism,  the  change  is  too  rapid  for  its  steps  to  be 
followed ;  and  that,  from  the  appearances  presented  by  muscles  which  have 
been  affected  with  tetanic  spasms,  the  contraction  produced  by  nervous  agency 
may  be  inferred  to  correspond  in  character.  It  now  remains,  therefore,  to 
inquire  what  is  the  cause  of  the  zigzag  arrangement  which  is  often  seen  in 
the  fibres.  This  may  be  easily  produced  by  approximating  the  ends  of  a 
fasciculus,  after  the  irritability  of  its  fibres  has  ceased ;  and  it  would  not  seem 
unlikely  that  the  passage  of  vessels  or  nerves  should  determine  the  points;  at 
which  the  flexures  take  place.  Hence  it  appears  that  the  sinuous  or  zigzag 
arrangement  is  that  into  which  fibres  are  naturally  thrown,  if,  on  elongation 
following  contraction,  they  are  not  at  once  stretched  by  antagonist  muscles.-— 
Many  facts  support  the  opinion,  which  has  long  been  held  by  several  physi- 
ologists, that,  when  an  entire  muscle  is  contracting,  all  its  fasciculi  are  not  in 
contraction  at  once  ;  but  that  there  is  a  continual  interchange  in  the  parts  by 
which  the  tension  is  effected ;  some  relaxing,  whilst  others  are  shortening. 
When  the  ear  is  applied  to  a  muscle  in  vigorous  action,  an  exceedingly  rapid, 
faint,  silvery  vibration  is  heard  ;  which  seems  to  be  attributable  to  this  constant 
movement  in  its  substance.  Now,  on  examining  a  muscle,  of  which  some 
fasciculi  present  the  zigzag  arrangement,  others  will  be  seen  (if  the  two  ex- 
tremities have  not  been  purposely  approximated)  to  be  quite  straight,  and  in 
a  state  of  contraction ;  and  it  thence  appears,  that  the  former  appearance  is 
presented  by  bundles  of  fibres,  which  have  either  not  yet  entered  into  con- 
traction, or  which  have  relaxed  after  undergoing  it,  but  of  which  the  extremi- 
ties are  still  approximated  by  the  agency  of  other  contracting  fibres.  From 
the  fact  that  a  single  muscular  fibre,  isolated  from  all  other  tissues,  can  pass 
24 


278 


OF  MUSCULAR  CONTRACTILITY. 


into  a  state  of  complete  contraction,  when  subjected  to  excitement  of  some 
kind,  the  very  important  inference  may  be  drawn, — that  the  property  of 
contractility  is  inherent  in  the  tissue  itself,  and  is  not  dependent  (as  some 
physiologists  have  supposed)  upon  nervous  agency,  though  usually  called 
into  action  by  it  in  the  living  body.  This  inference  will  be  shown  to  be  fully 
borne  out  by  physiological  facts.  The  result  of  various  experiments  made  for 
the  purpose,  leads  to  the  conclusion,  that  the  total  bulk  of  a  muscle  in  con- 
traction is  not  less  than  when  it  is  in  a  relaxed  state  ;  or  that  the  difference,  if 
any  exist,  is  extremely  trifling. 

373.  All  muscular  fibres  are  attached  at  their  extremities  to  tissues  of  the 
ordinary  fibrous  character ;  and  most  commonly  to  that  which  is  known  as 
tendinous  structure.  The  component  fibres  of  this  are  arranged,  with  great 
regularity,  parallel  to  each  other ;  and  they  are  attached  to  the  end  of  the 
sarcolemma,  which  terminates  abruptly ;  so  that  the  muscular  fibre  does  not 
taper  to  a  point,  as  some  have  supposed.  The  line  of  demarkation  between 
the  muscular  and  tendinous  structure,  is  always  very  distinct  (Fig.  68). 

Fig.  68. 


Attachment  of  Tendon  to  Muscular  Fibre,  in  Skate.    After  Bowman. 

374.  The  Sarcolemma  of  the  Muscle,  like  the  tube  of  the  Nerve  (§  110), 
appears  to  be  the  part  first  formed  ;  being  distinctly  visible  long  before  any 

[Fig.  69. 


Stages  of  the  development  of  striped  Muscular  Fibre ;  1,  arrangement  of  the  primitive  cells  in  a  linear 
series,— after  Schwann;  2,  the  cells  united;  the  nuclei  separated,  and  some  broken  up;  longitudinal  lines 
becoming  apparent.— from  a  foetal  calf  three  inches  long;  3,  4,  transverse  stripes  apparent;  in  3,  the  nuclei 
are  internal,  and  bulge  the  fibre  ;  in  4,  they  are  prominent  on  the  surface, — from  a  fcetal  calf  of  two  months 
old;  5,  transverse  stripes,  fully  formed  and  dark;  nuclei  disappearing  from  view,— from  the  human  infant 
at  birth;  6,  elementary  fibre  from  the  adult,  treated  with  acid,  showing  the  nuclei,— magnified  about  300 
diameters, — after  Bowman.] 


MUSCLES  OF  ORGANIC  LIFE. 


279 


traces  of  fibrillse  can  be  observed  in  it.  This  tube  takes  its  origin,  like  the 
ducts  of  Plants,  in  cells  laid  end  to  end,  the  cavities  of  which  coalesce,  by  the 
disappearance  of  the  partitions,  at  a  subsequent  period  ;  and  the  nuclei  of 
these  original  cells  may  be  distinctly  seen,  for  some  time  after  the  appearance 
of  the  striae,  which  indicate  the  formation  of  the  fibrillae  in  their  interior.  In 
an  early  stage  of  the  development  of  the  fibres,  indeed,  these  bodies  project 
considerably  from  their  sides  :  in  this  respect  as  well  as  in  others,  there  is  a 
close  correspondence  between  the  temporary  character  of  the  Muscular  fibre 
of  Animal  life,  and  the  permanent  condition  of  that  of  Organic  life.  In  the 
fully-formed  muscle  of  Animal  life,  they  are  not  perceptible,  except  when  a 
peculiar  method  has  been  adopted  for  bringing  them  into  view.  This  method 
consists  in  treating  the  fibre  with  weak  acids,  which  render  the  nuclei  more 
opaque,  whilst  the  surrounding  structure  becomes  more  transparent.  They 
are  usually  numerous  in  proportion  to  the  size  of  the  fibre ;  when  the  fibre  is 
small,  as  in  Birds  or  Mammalia,  they  lie  at  or  near  its  surface  ;  but  in  those  of 
greater  bulk,  as  in  Fishes  and  Reptiles,  they  are  intermingled  with  the  fibrillae 
through  the  whole  thickness  of  the  fibre,  and  are  brought  into  view  by  a 
transverse  section.  It  would  seem  probable  that  these  bodies  are  continually 
exercising  their  functions, — that  of  giving  origin  to  new  cells,  and  thence  to 
new  muscular  tissue  ;  since  their  amount  is  far  greater  in  the  adult  than  in 
the  fetus,  their  number  relatively  to  the  bulk  of  the  fasciculi  (which  is  in  the 
fetus  about  one-third  of  that  of  the  adult)  being  nearly  the  same  at  the  two 
periods.  In  the  Larvae  of  several  Insects,  perfect  and  imperfect  fibres  may 
often  be  found  lying  side  by  side. 

III.  Muscles  of  Organic  Life. 

375.  The  Muscular  fibre  of  Organic  life  is  very  different  from  that  which 
has  been  thus  fully  described.  It  consists  of  a  series  of  tubes  which  do  not 
present  transverse  striae,  and  in  which  the  longitudinal  striae  are  very  faint ; 
these  tubes  are  usually  much  flattened,  and  cannot  be  shown  to  contain  dis- 
tinct fibrillae.  Their  size  is  usually  muchness  than  that  of  the  fibres  of  Animal 
life  ;  but,  owing  to  the  extreme  variation  in  the  flattening  which  they  undergo, 
it  is  difficult  to  make  a  precise  estimate  of  their  dimensions.  Those  of  the 
alimentary  canal  of  Man  are  stated  by  Dr.  Baly  to  measure  from  about  ^  iVo 
to  ??Tj-o  part  of  an  inch.  They  sometimes  present  markings,  which  indicate 

[Fig.  70. 


Another  view  of  the  stages  of  development  of  Muscular  Fibre;  1,  a  muscular  fibre  of  animal  life  enclosed 
in  its  sheath  or  myolemma;  2,  an  ultimate  fibril  of  the  same;  3,  a  more  highly  magnified  view  of  1, 
showing  the  true  nature  of  the  longitudinal  striae,  as  well  as  the  mode  of  formation  of  the  transverse  striae  ; 
the  myolemma  is  here  so  thin  as  to  permit  the  ultimate  fibrils  to  be  seen  through  it;  4,  a  muscular  fibre  of 
Organic  Life  with  two  of  its  nuclei;  taken  from  the  urinary  bladder,  and  magnified  600  diameters;  5, 
muscular  fibre  of  organic  life  from  the  stomach,  magnified  the  same.] 


280  OF  MUSCULAR  CONTRACTILITY. 

a  granular  arrangement  in  their  interior ;  and  these  markings  have  occasion- 
ally a  degree  of  regularity  which  approaches  that  of  the  stria?  on  the  Muscular 
Fibre  of  Animal  life.  In  most  instances,  the  nuclei  of  the  cells  in  which  they 
originate,  are  very  perceptible ;  and  from  their  similarity  to  the  imperfectly 
formed  fibres  of  Animal  life,  it  would  seem  that  they  are  rather  to  be  com- 
pared with  these  than  with  their  fibrillaz,  to  which  some  have  considered  them 
analogous.  These  fibres  are,  like  those  of  the  other  muscles,  arranged  in  a 
parallel  manner  into  bands  or  fasciculi ;  but  these  fasciculi  are  generally  inter- 
woven into  a  network,  not  having  any  fixed  points  of  attachment,  but  contract- 
ing against  each  other.  This  kind  of  structure  is  that  which  forms  the  muscular 
coat  of  the  oesophagus,  stomach,  [Fig.  70,  (4  and  5,)]  intestinal  tube,  bladder, 
and  pregnant  uterus ;  it  is  found,  also,  in  no  inconsiderable  amount,  in  the 
trachea  and  bronchial  tubes.  The  pharyngeal  muscles,  however,  belong  to  the 
former  system.*  The  fibres  of  the  Uterus  somewhat  differ  in  aspect  from  those 
of  other  parts ;  being  much  broader  at  their  centre,  and  tapering  off  at  their 
extremities  into  what  appear  to  be  cylindrical  parts.  In  the  Heart,  both  the 
striated  and  non-striated  muscular  fibres  are  found  ;  and  this  accords  with  the 
structure  of  the  organ,  which  affords  some  fixed  points,  whilst  much  of  its 
action  resembles  (except  in  its  greater  degree  of  vigour)  that  of  the  muscular 
coat  of  the  intestines.  It  is  a  curious  and  interesting  fact,  that  in  Articulata, 
whose  animal  life  is  so  predominant  (§  22),  the  Animal  muscular  fibre  is 
formed  as  perfectly  as  in  the  highest  Vertebrata ;  whilst  in  Mollusca,  whose 
character  is  exactly  the  reverse  (§  28),  scarcely  any  striated  fibres  can  be 
detected. — It  seems  probable  that  the  contractility  possessed  by  the  skin 
(which  gives  rise  to  the  state  termed  culis  anserina,  under  the  influence  of 
cold,  or  of  depressing  mental  emotions),  and  that  which  is  peculiar  to  the 
Dartos  (by  which  the  scrotum  is  thrown  into  wrinkles),  are  alike  due  to  the 
action  of  fibres  of  this  description,  intermingled  with  the  other  fibrous  tissues 
of  which  these  parts  are  chiefly  composed.  The  middle  coat  of  the  Arteries 
will  be  hereafter  shown  to  have  a  strong  analogy  to  this  form  of  muscular 
tissue,  both  in  structure  and  properties  (Chap.  ix). 

• 

IV.  Properties  of  Muscular  Fibre. 

376.  Muscles  may  be  thrown  into  contraction,  so  long  as  they  preserve 
their  vitality,  by  stimuli  applied  to  themselves.  Mechanical  and  chemical 
influences,  cold,  heat,  and  electricity,  produce  this  effect.  They  do  not  lose 
their  vitality  immediately  on  the  general  death  of  the  system,  which  must  be 
considered  as  taking  place  when  the  circulation  ceases  without  a  power  of 
renewal ;  in  cold-blooded  animals  it  is  retained  much  longer  after  this  period 
than  in  the  higher  Vertebrata,  in  some  of  which  it  disappears  within  an  hour. 
From  experiments  on  the  bodies  of  executed  criminals,  who  were  previously 
in  good  health,  Nysten  ascertained  that  in  the  Human  subject,  the  contractility 
of  the  several  muscular  structures  departs  in  the  following  time  and  order. — 
The  left  ventricle  of  the  heart  first ;  the  intestinal  canal  at  the  end  of  45  or  55 
minutes ;  the  urinary  bladder  nearly  at  the  same  time ;  the  right  ventricle 
after  the  lapse  of  an  hour ;  the  oesophagus  at  the  expiration  of  an  hour  and  a 
half;  the  iris  a  quarter  of  an  hour  later ;  the  muscles  of  Animal  life  somewhat 
later ;  and  lastly,  the  auricles  of  the  heart,  especially  the  right,  which  in  one 
instance  contracted  under  the  influence  of  galvanism  16|  hours  after  death. 
The  muscles  of  young  animals  generally  retain  their  contractility  for  a  longer 

*  The  distinctness  between  the  two  is  remarkably  shown  in  bodies  infested  with  the 
Trichina  spiralis,  which,  whilst  it  profusely  infests  the  foraier,  is  seldom  or  never  found 
in  the  latter;  so  that  there  is  a  definite  line  of  demarkation,  even  in  closely  contiguous 
parts,  such  as  at  the  lower  edge  of  the  inferior  constrictor  of  the  pharynx. 


PROPERTIES  OF  MUSCULAR  FIBRE.  281 

time  than  those  of  adults ;  on  the  other  hand,  those  of  Birds  lose  their  con- 
tractility sooner  than  those  of  Mammalia.  Hence,  as  a  general  rule,  the  dura- 
tion of  the  contractility  is  inversely  to  the  amount  of  respiration.  Muscular 
contractility  is  deadened  by  many  substances,  especially  by  those  which  have 
a  narcotic  or  sedative  action  on  the  nervous  s^tem.  In  carbonic  acid  gas, 
hydrogen,  carbonic  oxide,  or  sulphurous  acid  gas,  muscles  contract  very  feebly, 
or  not  at  all,  when  stimulated ;  whilst  in  oxygen  they  retain  their  contractility 
longer  than  usual.  Narcotic  substances,  such  as  a  watery  solution  of  opium, 
when  applied  directly  to  the  muscles,  have  an  immediate  and  powerful  effect 
in  diminishing  or  even  destroying  their  contractility ;  this  effect  is  also  pro- 
duced, though  in  a  less  powerful  degree,  by  injecting  these  substances  into 
the  blood.  In  the  same  manner,  venous  blood,  charged  with  carbonic  acid, 
and  deficient  in  oxygen,  has  the  effect  of  a  poison  upon  muscles  ;  diminishing 
their  contractility,  when  it  continues  to  circulate  through  them,  to  such  a 
degree,  that  they  sometimes  lose  it  almost  as  soon  as  the  circulation  ceases,  as 
is  seen  in  those  who  have  died  from  gradual  and  therefore  prolonged  Asphyxia. 
The  unfavourable  influence  of  venous  blood  is  also  shown  in  the  Morbus 
Cceruleus ;  patients  affected  with  which  are  incapable  of  any  considerable 
muscular  exertion.  Most  of  the  stimuli  which  occasion  muscular  contraction, 
when  directly  applied  to  their  fibres,  operate  also  when  applied  to  their  motor 
nerves ;  but  the  same  does  not  hold  good  in  regard  to  those  agents  which 
diminish  contractility.  It  is  a  fact  of  some  importance,  in  relation  to  the  dis- 
puted question  of  the  connection  of  muscular  contractility  with  the  nervous 
system,  that  when,  by  the  application  of  narcotic  substances  to  the  nerves, 
their  vital  properties  are  destroyed,  the  contractility  of  the  muscle  may  remain 
for  some  time  longer ;  and  the  latter  must,  therefore,  be  independent  of  the 
former.  Hence  we  should  conclude,  that  contractility  must  be  a  property 
really  inherent  in  Muscular  tissue,  which  may  be  called  into  action  by  various 
stimuli,  and  which  may  be  weakened  by  various  depressing  agents,  applied 
to  itself ;  and  that  the  nerves  have  the  power  of  conveying  the  stimuli,  which 
call  the  property  into  action,  but  have  little  or  no  other  influence  on  it. 

377.  It  seems  to  be  a  general  law  of  Muscular  Contraction,  that  it  shall  alter- 
nate with  relaxation  at  no  long  intervals.  This  is  most  evident  in  the  action 
of  the  Heart,  and  in  the  peristaltic  movements  of  the  Alimentary  canal.  In  these 
parts,  the  whole  or  a  large  part  of  the  fibres  seem  to  contract  together,  and  then 
shortly  to  relax ;  but  this  is  probably  no  less  true,  as  has  been  just  shown,  of 
the  individual  fibres  of  those  muscles  which  are  kept  in  a  state  of  contraction 
by  an  effort  of  the  will ;  since  none  of  them  appear  to  remain  in  a  contracted 
state  for  any  length  of  time. — The  peculiar  contractility  of  Muscular  tissue, 
like  the  vital  properties  of  other  parts,  is  diminished  by  want  of  action ;  and 
in  this,  as  in  other  cases,  it  is  quite  clear  that  the  cause  of  its  loss  is  to  be 
found  in  the  alteration  of  the  nutritive  processes,  which  results  from  the  ces- 
sation of  the  usual  operations  of  the  part  (§  221).  In  persons  whose  lower 
extremities  have,  from  any  cause,  been  long  disused,  not  only  does  the  bulk  of 
the  muscles  much  diminish,  but  their  characteristic  structure  in  great  part 
disappears,  degenerating  into  fat  mixed  with  ordinary  fibrous  tissue.  On  the 
other  hand,  a  frequently-renewed  exercise  of  muscular  contractility  increases 
the  power,  by  stimulating  the  increased  nutrition  of  the  muscles,  which  be- 
come more  developed,  and  consequently  more  powerful;  this  is  welt  seen  in 
the  arms  of  the  Smith  or  Waterman,  and  in  the  legs  of  the  Opera-dancer. 
But  the  exercise  must  not  be  too  constant ;  for  it  appears  to  be  during  the 
intervals  of  rest,  that  the  increased  nutrition  chiefly  takes  place ;  and  if  the 
action  have  been  of  a  violent  character,  the  contractility  of  the  muscle  is  for  a 
time  exhausted,  and  can  only  be  restored  by  an  interval  of  inactivity. — A  great 
variety  of  evidence  has  been,  for  some  time,  conducting  physiologists  to  the 

24* 


282 


OF  MUSCULAR  CONTRACTILITY. 


opinion,  that  every  act  of  Muscular  contraction  necessarily  involves  the  death 
and  disintegration  of  a  certain  amount  of  Muscular  Tissue  (§  77) ;  and  it  has 
been  recently  argued  by  Liebig,  that  this  disintegration,  resulting  from  the 
action  of  Oxygen  upon  the  elements  of  which  the  tissue  is  composed,  is  the 
real  source  of  the  mechanical  power ; — by  setting  at  liberty  (so  to  speak)  the 
Vital  Force,  which  was  previously  employed,  in  a  latent  manner,  in  holding 
together  the  components  of  the  structure.  Certain  it  is,  that  the  amount  of 
Muscular  power  exercised  by  an  animal,  bears  a  very  close  correspondence 
(other  things  being  equal),  on  the  one  hand  to  the  measure  of  oxygen  intro- 
duced into  the  system  by  the  lungs,  and  on  the  other  to  the  amount  of  those 
excretions,  which  seem  especially  produced  by  this  metamorphosis  :  and  this 
is  true,  as  a  general  fact,  whether  we  compare  together  different  animals,  or 
different  states  of  the  same  animal  (See  Chap.  vm.  Sect.  i). 

378.  The  effects  of  stimuli  locally  applied  to  portions  of  the  Muscles  of 
Animal  Life,  are  very  different  from  those  which  result  from  their  application 
to  the  muscles  of  Organic  life.     If,  for  example,  we  irritate  mechanically  a 
portion  of  the  Biceps,  the  fasiculus  of  fibres  which  is  touched  will  contract, 
but  the  surrounding  parts  will  be  unaffected,  and  the  contracted  fasciculus 
will  soon  relax ;  in  fact,  the  only  way  to  call  the  whole  muscle  into  contrac- 
tion at  once,  is  to  stimulate  it  through  its  nerves.     On  the  other  hand,  if  we 
apply  a  similar  irritation  to  the  intestinal  canal,  when  in  a  state  of  equal  con- 
tractility, the   fasciculus  which  is  stimulated   shortens  in  a  much  greater 
degree ;  and  propagates  its  action  in  a  wave-like  manner  to  other  bundles  of 
fibres;   so  that  successive  contractions   and   relaxations   may  be  produced, 
through  a  considerable  part  of  the  canal,  by  a  single  prick  with  the  point  of  a 
scalpel ;  but  the  contractions  into  which  these  same  fibres  are  thrown,  by  irri- 
tating their  nerves,  are  for  the  most  part  feeble  and  undecided  (§  200).     It  is, 
indeed,  a  curious  fact,  corroborative  of  what  has  been  just  said  of  the  influence 
of  narcotics,  that  the  ganglionic  nerves  lose  their  power  of  exciting  these 
muscles   to   contraction,  when  themselves  irritated,  much  sooner  than  the 
muscles  lose  their  power  of  contraction,  when  directly  stimulated. 

379.  There  can  be  no  doubt  that  it  is  through  the  motor  or  efferent  nerves, 
that  contraction  is  ordinarily  excited  in  the  muscles  of  the  first  class,  in  the 
living  body ;  and  these  nerves  may,  as  formerly  shown,  convey  the  influence 
of  volition,  of  emotional  or  instinctive  operations  of  mind,  or  of  the  reflex 
action  of  the  Spinal  Cord.     As  the  effect  produced  upon  the  muscle  is  in  all 
instances  similar,  there  can  be  little  doubt  that  the  stimulus  actually  commu- 

Fig.  71. 


Form  of  the  terminating  loops  of  the  Nerves  in  the  Muscles.    After  Burdach. 


PROPERTIES  OF  MUSCULAR  FIBRE.  283 

nicated  by  the  nerve  is  of  the  same  character,  whatever  may  have  been  its 
source.  The  motor  nerves  cannot  be  properly  said  to  terminate  in  the 
muscles  ;  for  the  trunks  form  a  kind  of  network  in  their  substance,  the  fibres 
which  they  send  off  returning  again  to  themselves,  by  loops,  or  to  other  trunks. 
In  what  manner  the  stimulus  is  conveyed  and  communicated,  can  only  be  at 
present  a  matter  of  speculation.  That  the  influence  is  of  an  electrical  kind, 
has  been  supposed  by  some  ;  principally  on  account  of  the  similarity  between 
the  muscular  contractions,  excited  by  galvanism  transmitted  through  the 
nerves,  and  those  ordinarily  produced  by  voluntary  direction.  But  it  is  to  be 
remembered  that  other  agents,  both  physical  and  chemical,  may  produce  the 
same  effect ;  and  there  are  objections,  which  at  present  appear  insuperable,  to 
the  belief  that  nervous  influence  and  electricity  are  identical,  whatever  may 
be  the  analogy  in  their  mode  of  operation.  The  muscles  of  the  second  class 
appear  to  be,  in  the  living  body,  much  seldomer  called  into  contraction  through 
their  nerves,  than  they  are  by  stimuli  applied  directly  to  themselves.  The 
will  has  no  power  over  them ;  and  they  would  seem  to  be  rather  affected  by 
those  emotional  conditions  of  mind  which  volition  cannot  imitate.  This 
influence  is  continually  experienced  in  the  action  of  the  heart,  and  probably 
also  affects  the  movements  of  the  intestinal  tube. 

380.  The  continual  and  evident  influence  of  the  Nervous  System  upon 
Muscular  Contractility,  has  led  many  physiologists  to  the  belief,  that  the  latter 
is  dependent  upon  the  agency  of  the  former.     Two  views  upon  this  question 
have  been  commonly  taught,  to  both  of  which  it  seems  necessary  to  devote  a 
brief  consideration.     The  first  of  these  is,  that  Muscular  contractility  is  de- 
rived from  some  influence  or  energy  communicated  from  the  Brain  or  Spinal 
Cord.     This  opinion  is  evidently  analogous  to  that  which  attributes  the  vital 
properties  of  other  parts  to  the  Nervous  System  alone ;  and  it  is  open  to  the 
same  objection,  in  limine,  which  has  been  applied  to  the  latter, — the  improba- 
bility that  any  one  of  the  solid  textures  of  the  living  body  should  have  for  its 
office  to  give  to  any  other  the  pow-er  of  performing  any  vital  action.     More- 
over, it  is  inconsistent  with  the  fact  that,  in  Vegetables,  tissues  endowed  with 
a  high  degree  of  contractility  exist,  and  manifest  their  property  when  a  stimulus 
is  directly  applied  to  themselves ;  which,  nevertheless,  can  have  no  depend- 
ence whatever  upon  a  nervous  system.     In  the  lower  classes  of  Animals,  too, 
there  is  good  reason  to  believe  that  the  property  is  much  more  universally 
diffused   through   their  tissues  than  nervous  agency  can  be.      Again,  the 
action  of  the  heart  may  be  kept  up,  in  the  highest  animals,  by  taking  care 
that  the  current  of  the  circulation  be  not  interrupted,  for  a  long  time  after 
the  removal  of  the  brain  and  spinal  cord ;  it  may  even  continue  when  com- 
pletely separated  from  the  body,  which  shows  that  the  ganglionic  system 
cannot  supply  any  influence  necessary  to  it ;  and  there  are  many  instances  in 
which  the  human  foetus  has  come  to  its  full  size,  so  that  its  heart  must  have 
regularly  acted,  without  the  existence  of  a  brain  or  spinal  cord.     Further,  the 
irritability  of  muscles  of  the  first  class  continues  for  a  long  time  after  their 
nerves  are  divided,  and  may  be  called  into  action  by  stimuli  directly  applied 
to  the  parts  themselves,  or  to  their  nerves  below  the  section,  so  long  as  their 
nutrition  is  unimpaired. 

381.  The  loss  of  the  irritability  of  Muscles,  within  a  few  weeks  after  the 
section  of  their  nerves, — on  which  great  stress  has  been  laid  by  Miiller  in 
support  of  a  modified  form  of  the  above  doctrine,  (it  being  maintained  by  this 
distinguished  physiologist,  that,  if  muscular  irritability  is  not  dependent  on  the 
Brain  and  Spinal  Cord,  they  supply  some  influence  essential  to  its  exercise,) 
— is  clearly  due  to  the  alteration  in  their  nutrition,  consequent  upon  their 
disuse.     This  has  been  recently  proved  to  demonstration,  by  the  very  inge- 


284  OF  MUSCULAR  CONTRACTILITY. 

nious  experiments  of  Dr.  J.  Reid.*  "  The  spinal  nerves  were  cut  across,  as 
*they  lie  in  the  lower  part  of  the  spinal  canal,  in  four  frogs  ;  and  both  posterior 
extremities  were  thus  insulated  from  their  nervous  connections  with  the  spinal 
cord.  The  muscles  of  one  of  the  paralyzed  limbs  were  daily  exercised  by  a 
weak  galvanic  battery ;  while  those  of  the  other  limb  were  allowed  to  remain 
quiescent.  This  was  continued  for  two  months  ;  and  at  the  end  of  that  time, 
the  muscles  of  the  exercised  limb  retained  their  original  size  and  firmness  and 
contracted  vigorously,  while  those  of  the  quiescent  limb  had  shrunk  to  at  least 
one-half  of  their  former  bulk,  and  presented  a  marked  contrast  with  those  of 
the  exercised  limb.  The  muscles  of  the  quiescent  limb  still  retained  their 
contractility,  even  at  the  end  of  two  months  :  but  there  can  be  little  doubt  that, 
from  their  imperfect  nutrition,  and  the  progressing  changes  in  their  physical 
structure,  this  would  in  no  long  time  have  disappeared,  had  circumstances 
permitted  the  prolongation  of  the  experiment. "t  This  experiment  satisfactorily 
explains  the  fact  observed  by  Dr.  M.'Hall,  and  heretofore  adverted  to,  (§§  177, 
208,)  that  in  cases  in  which  the  cause  of  the  paralysis  is  situated  in  the  Brain, 
and  in  which  the  Spinal  Cord  and  its  nerves  are  unaffected,  the  irritability 
of  the  muscles  of  the  paralyzed  part  is  not  destroyed  even  after  a  considerable 
lapse  of  time.  For,  if  the  capability  of  performing  reflex  actions  still  exist, 
on  the  part  of  the  nervous  system,  it  is  manifest  that  the  muscles  will  be  con- 
tinually excited  to  action  through  this  channel ;  and  that  their  nutrition  and 
vital  properties  will  thereby  be  preserved,  as  they  were  in  Dr.  Reid's  experi- 
ments by  the  artificial  excitement  of  galvanism.  Hence  Dr.  M.  Hall's  opinion, 
that  the  property  of  Muscular  contractility  is  derived  from  the  Spinal  Cord 
is  no  more  tenable  than  that  which  locates  it  in  the  Brain. 

382.  The  loss  of  contractility  from  section  of  the  nerves,  takes  place  more 
speedily  in  warm-blooded  Vertebrata,  all  whose  vital  operations  are  performed 
with  a  much  greater  activity  than  in  Reptiles  and  other  cold-blooded  animals. 
Dr.  Reid  found  that,  in  a  Rabbit,  a  portion  of  whose  sciatic  nerve  had  been 
removed  on  one  side,  the  muscles  of  that  leg  were  but  very  feebly  excited  to 
contraction  by  Galvanism,  after  the  lapse  of  seven  weeks.     The  change  in 
their  nutrition  was  evident  to  the  eye,  and  was  made  equally  apparent  by  the 
balance.     The  muscles  of  the  paralyzed  limb  were  much  smaller,  paler  and 
softer  than  the  corresponding  muscles  of  the  opposite  leg ;  and  they  scarcely 
weighed  more  than  half, — being  only  170  grains,  whilst  the  others  were  327 
grains.     It  was  found,  also,  that  a  perceptible  difference  existed  in  the  size  of 
the  bones  of  the  leg,  even  after  so  short  an  interval  had  elapsed ;  the  tibia  and 
fibula  of  the  paralyzed  limb  weighing  only  81  grains,  whilst  those  of  the  sound 
limb  weighed  89  grains.     On  examining  the  muscular  fibres  with  the  micro- 
scope, it  was  found  that  those  of  the  paralyzed  leg  were  considerably  smaller 
than  those  of  the  sound  limb,  and  presented  a  somewhat  shriveled  appearance ; 
and  that  the  longitudinal  and  transverse  striae  were  much  less  distinct. 

383.  Another  equally  satisfactory  proof,  that  the  loss  of  Contractility,  which 
follows  the  severance  of  the  connection  between  the  Nervous  centres  and  the 
Muscle,  is  not  immediately  due  to  the  interruption  of  any  influence  communi- 
cated by  the  former,  has  been  given  by  the  experiments  of  Dr.  J.  Reid.     It 

*  Edinburgh  Monthly  Journal  of  Medical  Science,  May,  1841. 

f  A  fact  of  an  exactly  parallel  character  has  fallen  under  the  Author's  observation,  in 
a  case  ol  Hysteric  Paraplegia,  in  which  one  leg  was  occasionally  affected  with  severe 
cramps.  The  muscles  of  this  leg  suffered  much  less  diminution  of  size  and  firmness 
than  those  of  the  other;  so  that  there  was  a  difference  of  more  than  an  inch  in  the  cir- 
cumference of  the  limbs.  But  since  the  paraplegia  has  been  partially  recovered  from, 
some  degree  of  voluntary  power  having  been  established  in  both  limbs,  and  the  muscles 
of  both  having  been  exercised  in  the  same  degree,  they  have  greatly  improved  in' size 
and  firmness,  and  there  is  now  little  or  no  perceptible  difference  between  them. 


PROPERTIES  OF  MUSCULAR  FIBRE.  285 

was  asserted  by  Mr.  Earle  (and  the  statement  has  been  repeated  by  Mil  Her) 
that,  if  the  irritability  of  a  muscle,  whose  nerves  have  been  divided,  be 
exhausted  by  repeated  stimulation,  it  cannot  be  recovered.  Dr.  J.  Reid  has 
shown,  however,  that  the  means  employed  by  Mr.  E.  to  exhaust  the  irrita- 
bility were  such  as  would  probably  induce  an  inflammatory  condition  of  the 
muscles,  and  would  thereby  interfere  with  the  nutritive  processes,  which 
would  be  necessary  to  re-establish  the  irritability  during  the  state  of  subse- 
quent quiescence.  And  he  has  further  proved,  that  if  the  contractility  be 
exhausted  by  means  which  have  no  such  unfavourable  tendency,  and  the 
other  conditions  favour  the  normal  performance  of  the  nutrient  processes,  the 
irritability  is  restored,  and  remains  for  some  time.  His  first  experiments  were 
on  cold-blooded  animals,  and  they  would  in  themselves  be  sufficiently  satisfac- 
tory ;  but  he  has  since  repeated  them  in  the  Rabbit,  and  established  the  fact 
beyond  all  doubt.*  "  The  sciatic  nerve  was  divided  in  the  Rabbit,  and  a  por- 
tion of  it  removed.  One  wire  from  two  galvanic  batteries,  consisting  of  thirty 
pairs  of  plates,  was  applied  over  the  course  of  the  nerve  ;  and  the  other  wire 
was  applied  over  the  foot,  which  was  kept  moist,  until  the  muscles  had  ceased 
to  contract.  Three  days  after  this,  a  weaker  battery  was  used,  and  the  mus- 
cles of  the  limb  had  recovered  their  contractility,  and  contracted  powerfully. 
The  more  powerful  battery  was  used  as  before,  until  the  muscles  had  ceased 
to  respond  to  the  excitement ;  and  three  days  after  this,  they  had  again  recov- 
ered their  contractility."  It  seems  scarcely  possible  to  draw  any  other  infer- 
ence from  these  experiments  than  that  Contractility  is  a  property  inherent  in 
Muscular  tissue,  and  that  the  agency  of  the  Nervous  system  upon  it  is  merely 
to  call  it  into  active  operation. 

384.  The  second  doctrine  above  referred  to  (§  380),  as  having  been  taught 
by  some  physiologists,  is  that  Muscles,  though  not  dependent  on  nerves  for 
vital  power,  are  yet  dependent  upon  them  for  the  exercise  of  that  power, — 
all  stimuli,  which  excite  muscles  to  contraction,  operating  first  on  the  nervous 
filaments  which  enter  muscles,  and  through  them  on  the  muscular  fibres. 
The  facts  which  have  been  already  stated,  in  regard  to  the  ordinary  action  of 
the  Muscles  of  Organic  life,  furnish  a  sufficient  answer  to  this  hypothesis.     It 
is  with  great  difficulty  that  these  can  be  made  to  display  their  irritability,  by 
any  stimuli  applied  to  their  nerves ;  whilst  they  manifest  it  strongly,  when 
the  stimulus  is  directly  applied  to  themselves.    Even  in  the  Muscles  of  Animal 
life,  individual  fasciculi  may  be  thrown  into  action  in  the  same  manner; 
although  the  entire  mass  cannot  be  put  into  combined  operation,  except  by  a 
stimulus  simultaneously  communicated  to  the  whole,  which  the  nerve  affords 
the  readiest  means  of  effecting.     Perhaps  the  most  satisfactory  disproof  of  it, 
however,  is  to  be  found  in  the  observation  of  Mr.  Bowman,  already  cited 
(§  371),  that  a  single  fibre,  completely  isolated  from  all  its  connections,  may 
be  seen  with  the  microscope  to  pass  into  a  state  of  contraction,  under  the  influ- 
ence of  direct  irritation.     Further,  it  has  been  experimentally  ascertained, 
that  there  are  some  chemical  stimuli,  which  will  produce  the  contraction  of 
muscles  when  directly  applied  to  them,  but  of  which  the  influence  cannot  be 
transmitted  through  the  nerves ;  this  is  especially  the  case  with  regard  to 
acids. 

385.  When  all  these  considerations  are  allowed  their  due  weight,  we  can 
scarcely  do  otherwise  than  acquiesce  fully  in  the  doctrine  of  Haller,  which 
involves  no  hypothesis,  and  which  is  perfectly  conformable  to  the  analogy  of 
other  departments  of  Physiology.     He  regarded  every  part  of  the  body  which 
is  endowed  with  Irritability,  as  possessing  that  property  in  and  by  itself;  but 
considered  that  the  property  is  subjected  to  excitement  and  control  from  the 

*  Loc.  cit. 


286  OF  MUSCULAR  CONTRACTILITY. 

Nervous  System,  the  agency  of  which  is  one  of  the  stimuli  that  can  call  it 
into  operation. — It  may  be  desirable  briefly  to  recapitulate  the  facts  by  which 
this  doqtrine  is  supported.  1 .  The  existence  in  Vegetables  of  irritable  tissues, 
which  are  excited  to  contraction  by  stimuli  directly  applied  to  themselves,  and 
can  be  in  no  way  dependent  upon,  or  influenced  by,  a  Nervous  system.  2.  The 
existence  in  Animals  of  a  form  of  Muscular  tissue,  which  is  especially  con- 
nected with  the  maintenance  of  the  Organic  functions,  and  which  is  much 
more  readily  excited  to  action  by  direct  stimulation  than  it  is  by  nervous 
agency.  3.  The  fact  that,  by  the  agency  of  these,  the  organic  functions  may 
go  on  (as  long  as  their  other  requisite  conditions  are  supplied)  after  the  removal 
of  the  nervous  centres,  and  when  none  were  ever  present ;  rendering  it  next 
to  certain,  that  their  ordinary  operations  are  not  dependent  upon  any  stimuli 
received  through  the  nerves,  but  upon  those  directly  applied  to  themselves. 
4.  The  persistence  of  irritability  in  muscles,  for  some  time  after  the  nerves 
have  ceased  to  be  able  to  convey  to  them  the  effects  of  stimuli ;  this  is  con- 
stantly seen  in  regard  to  the  Sympathetic  system  of  nerves,  and  the  muscles 
of  Organic  life  upon  which  they  operate;  and  it  may  also  be  shown  to  occur 
with  respect  to  the  Cerebro-Spinal  system,  and  the  muscles  of  Animal  life,  by 
the  agency  of  narcotics.  5.  The  persistence  of  irritability  in  the  muscles, 
after  their  complete  isolation  from  the  nervous  centres,  so  long  as  their  nutri- 
tion is  unimpaired;  and  the  effects  of  frequent  exercise,  in  preventing  the 
impairment  of  the  nutrition  and  the  loss  of  irritability.  6.  The  recovery  of 
the  irritability  of  muscles,  when  isolated  from  the  nervous  centres,  after  it  has 
been  exhausted  by  repeated  stimulation ;  this  also  depends  upon  the  healthy 
performance  of  the  nutritive  actions.  7.  The  contraction  of  muscular  fibre 
under  the  microscope,  when  completely  isolated  from  all  other  tissues. — In 
the  words  of  Dr.  Alison,  then,  "  the  only  ascertained  final  cause  of  all  endow- 
ments bestowed  on  Nerves  in  relation  to  Muscles,  in  the  living  body,  appears 
to  b.e,  not  to  make  Muscles  irritable,  but  to  subject  their  irritability,  in  different 
ways,  to  the  dominion  of  the  acts  and  feelings  of  the  Mind," — to  its  volitions, 
emotions,  and  instinctive  determinations. 

386.  There  can  be  no  doubt,  however,  that  the  Nervous  System  is  capable 
of  exerting  an  influence  upon  the  property  itself ;  for  we  find  that  sudden  and 
severe  injuries  of  the  Nervous  Centres  have  power  to  impair,  directly  and 
instantaneously,  or  even  to  destroy  the  Contractility  of  the  whole  Muscular 
System ;  so  that  death  immediately  results,  and  no  irritability  subsequently 
remains.  It  is  in  this  manner,  that  the  sudden  destruction  of  the  Brain  and 
Spinal  Cord,  especially  of  the  latter,  occasions  the  immediate  cessation  of  the 
heart's  action  ;  though  they  may  be  gradually  removed,  without  any  consider- 
able effect  upon  it.  Severe  concussion  has  the  same  effect ;  hence  the  Syn- 
cope which  immediately  displays  itself.  It  is  sometimes  an  important  question 
in  Forensic  Medicine,  whether  an  individual,  who  has  died  from  the  effects  of 
a  blow  upon  the  head,  could  have  moved  from  the  place  where  the  blow  was 
inflicted.  If  there  be  found,  as  is  frequently  the  case,  no  sensible  disorgan- 
ization of  the  Brain,  the  death  must  be  attributed  to  the  concussion,  and  must 
have  been  in  that  case  immediate.  If,  on  the  other  hand,  effusion  of  blood 
has  taken  place  within  the  cranium  to  any  considerable  extent,  it  is  probable 
that  the  first  effects  of  the  blow  were  in  some  degree  recovered  from,  and  that 
the  circulation  was  re-established.— It  is  not  essential,  however,  that  the  im- 
pression should  be  primarily  made  upon  the  Cerebro-Spinal  system.  The 
well-known  fact  of  sudden  death  not  unfrequently  resulting  from  a  blow  on 
the  stomach,  especially  after  a  full  meal,  without  any  perceptible  lesion  of  the 
viscera,  clearly  indicates  that  an  impression  upon  the  widely-spread  coeliac 
plexus  of  Sympathetic  nerves  (which  will  be  much  more  extensively  commu- 
nicated to  them,  when  the  stomach  is  full,  than  when  it  is  empty),  may  cause 


PROPERTIES  OF  MUSCULAR  FIBRE.  287 

the  immediate  cessation  of  the  heart's  action,  in  the  same  manner  as  a  violent 
injury  of  the  Brain  or  Spinal  Cord.  Now  it  is  interesting  to  remark  that,  in 
all  these  cases,  the  whole  vitality  of  the  system  appears  to  be  destroyed  at 
once  ;  for  the  processes  which  would  otherwise  succeed  the  injury,  and  which, 
after  other  kinds  of  death  less  sudden  in  their  character,  produce  evident 
changes  in  the  part  of  the  surface  that  has  immediately  received  it,  are  here 
entirely  prevented.  An  instance  is  on  record,  in  which  a  criminal  under 
sentence  of  death  determined  to  anticipate  the  law  by  self-destruction.  Having 
no  other  means  of  accomplishing  his  purpose,  he  stooped  his  head  and  ran 
violently  against  the  wall  of  his  cell ;  he  immediately  fell  dead  ;  and  no  mark 
of  contusion  showed  itself  on  his  forehead.  The  same  absence  of  the  usual 
results  is  to  be  noticed,  in  the  case  of  blows  on  the  stomach.  Yet  it  is  well 
known,  that  many  of  the  ordinary  vital  processes  will  take  place  in  the  injured 
parts,  after  death  of  a  more  lingering  nature  ;  the  vitality  of  the  individual 
organs  not  being  destroyed,  immediately  on  the  severance  of  the  chain  which 
binds  together  the  different  functions. 

387.  The  influence  of  severe  impressions  on  the  Nervous  System  in  dimi- 
nishing, where  it  does  not  altogether  destroy,  Muscular  Contractility,  is  well 
seen  in  the  effect  of  severe  injuries  affecting  vital  organs,  or  extending  over  a 
large  part  of  the  surface,  in  depressing  the  heart's  action.     This  is  a  well- 
known  result  of  severe  burns,  especially  in  children,  whose  nervous  system  is 
more  susceptible  of  such  impressions  than  that  of  the  adult ;  also  of  the  rupture 
of  the  alimentary  canal,  of  the  bladder  or  uterus  ;  and  of  the  shattering  of  one 
of  the  extremities,  by  violence  affecting  a  large  part  of  their  substance.     In 
all  these  cases,  the  sufferer  is  in  the  same  condition  with  one  who  has  received 
a  severe  blow  on  the  head,  that  does  not  quite  stun  him;  the  shock  mime* 
diately  diminishes  the  muscular  contractility  of  the  whole  system ;  and  its 
influence  on  the  heart,  which  of  course  manifests  itself  most  conspicuously, 
produces  a  degree  of  depression,  which  is  frequently  never  recovered  from, 
and  which  at  any  rate  renders  necessary  the  employment  of  stimulants,  for 
the  purpose  of  counteracting  this  very  dangerous  effect.*     Excessive  mental 
emotion,  of  a  kind  not  in  itself  depressing,  may  occasion  the  sudden  cessation 
of  the  heart's  action,  and  a  general  loss  of  muscular  contractility ;  and  it  is 
well  known  that  muscular  power  is  greatly  diminished  by  emotions  which 
produce  no  other  direct  action. 

388.  There  is  no  evidence  that  Muscular  Irritability  can  be  increased  by 
any  cause  operating  through  the  nervous  system.     It  is  quite  true  that,  under 
the  stimulus  of  alcohol,  nitrous  oxide,  &c.,  or  of  some  purely  mental  excite- 
ment, individuals  can  perform  actions  requiring  a  degree  of  strength,  which 
they  cannot  exert  under  any  other  circumstances.      But  it  does  not  hence 
follow,  that  the  irritability  is  increased ;  since  the  energy  of  the  action  may 
be  due  solely  to  the  power  of  the  stimulus,  by  which  it  is  excited.     It  is  well 
known  that  stimulating   agents,  which  thus  temporarily  increase  Muscular 
power,  primarily  excite  the  nervous  system ;  as  is  shown  by  the  increased 
mental  activity,  which  results  from  the  moderate  use  of  alcohol,  nitrous  oxide, 
opium,  &c. ;  and  it  does  not  seem  necessary,  therefore,  to  go  further  in  search 

*  The  large  quantity  of  stimulus  which  can  be  borne  even  by  children,  suffering  under 
severe  burns,  is  very  extraordinary.  There  can  be  no  doubt  that  many  lives  have  been 
saved  by  the  judicious  administration  of  them,  to  an  amount  which  would,  a  priori,  have 
been  judged  in  itself  fatal ;  but  that. many  more  have  been  sacrificed  to  neglect,  even  on 
the  part  of  those  whose  duty  it  is  to  watch  the  indications  with  the  closest  attention.  The 
Author's,  observation  leads  him  to  believe,  that  Hospital-Nurses  very  commonly  make 
up  their  minds  that  children,  who  have  met  with  severe  burns,  must  die  ;  and  that,  unless 
closely  watched,  they  neglect  the  means  of  which  Science  and  Experience  alike  dictate 
the  free  employment. 


288  OF  MUSCULAR  CONTRACTILITY. 

of  an  explanation  of  their  effect  on  muscular  action.  It  is  worthy  of  remark, 
that  whilst  the  influence  of  general  depressing  causes  acting  through  the 
Nervous  System,  is  primarily  manifested  on  the  muscles  of  Organic  life,  that 
of  stimulants  chiefly  shows  itself  in  the  muscles  subjected  to  the  will. 

389.  The  last  general  question  now  to  be  considered  regarding  Muscular 
Contractility,  is  that  which  relates  to  the  Rigor  Mortis.     The  temporary  stif- 
fening of  the  body  after  death,  from  a  general  contraction  of  its  muscles,  is  a 
phenomenon  which  is  rarely  absent ;  though  it  may  be  so  slight,  and  may  last 
for  so  short  a  time,  as  to  escape  observation.     The  period  which  elapses  before 
its  commencement,  is  as  variable  as  its  duration  ;  and  both  appear  to  be  in  some 
degree  dependent  upon  the  vital  condition  of  the  body  at  the  time  of  death. 
When  the  fatal  termination  has  supervened  on  slow  and  wasting  disease,  occa- 
sioning great  general  depression  of  the  vital  powers,  the  rigidity  usually 
develops  itself  very  early,  and  lasts  for  a  short  time.     In  diseases  which  pow- 
erfully affect  the  nervous  energy,  such  as  Typhus,  this  is  the  case ;  even 
though  they  have  not  been  of  long  duration.     Thus,  after  death  from  Typhus, 
the  limbs  have  been  sometimes  known  to  stiffen  within  15  or  20  minutest    The 
same  is  observed  in  infants  and  in  old  people.     On  the  other  hand,  where  the 
general  energy  has  been  retained  up  to  a  short  period  before  death,  the  rigidity 
is  much  later  in  coming  on,  and  lasts  longer ;  this  happens,  for  example,  in 
many  cases  of  Asphyxia  and  Poisoning,  in  which  it  has  been  said  not  to  occur 
at  all.     The  commencement  of  the  rigidity,  however,  is  not  usually  prolonged 
much  beyond  seven  hours ;  but  twenty  or  even  thirty  hours  may  elapse  before 
it  shows  itself.     Its  general  duration  is  from  twenty-four  to  thirty-six  hours ; 
but  it  may  pass  off  much  more  rapidly,  or  it  may  be  prolonged  through  seve- 
ral days.     An  attempt  has  been  made  to  connect  it  with  the  lowering  of  the 
temperature  of  the  dead  body ;  but  with  this  it  does  not  seem  to  have  any  rela- 
tion.    It  occurs  in  cold-blooded  Vertebrata,  and  even  in  Invertebrata,  as  well 
as  in  warm-blooded  animals;  and  it  has  frequently  been  noticed  to  commence 
in  the  latter  Jong  before  the  heat  has  entirely  departed  from  the  body.    Moreover, 
it  appears  first  upon  the  trunk,  which  is  the  region  last  deserted  by  the  caloric. 
It  first  affects  the  neck  and  lower  jaw,  and  seems  gradually  to  travel  down- 
wards; but,  according  to  some  observers,  the  lower  extremities  are  stiffened 
before  the  upper.     In  its  departure,  which  is  immediately  followed  by  decom- 
position, the  same  order  is  observed.     It  affects  all  the  muscles  nearly  alike  ; 
but  the  flexors  are  usually  more  contracted  than  the  extensors,  so  that  the 
fingers  are  somewhat  flexed  on  the  palm,  and  the  forearm  on  the  arm;  and  the 
lower  jaw,  if  previously  drooping,  is  commonly  drawn  firmly  against  the  upper. 
It  is  remarkable  that  it  is  equally  intense  in  muscles  which  have  been  para- 
lyzed by  Hemiplegia,  provided  that  no  considerable  change  has  taken  place 
in  their  nutrition. 

390.  The  Muscular  contraction  which  gives  rise  to  the  Rigor  Mortis,  appears 
to  be  of  the  same  kind  with  that  which  takes  place  under  the  influence  of 
nervous  agency,  though  differing  as  to  its  conditions.  When  very  strong,  it 
renders  the  muscles  prominent,  as  in  voluntary  contraction;  and  the  compara- 
tive observations  of  Mr.  Bowman,  upon  the  state  of  muscular  fibre  passing 
into  this  condition,  and  upon  that  which  presented  various  degrees  of  contrac- 
tion from  ordinary  causes,  leave  no  doubt  as  to  their  correspondence.  It  is  to 
be  remarked,  however,  that  the  tendency  of  the  muscle  to  contract  upon  the 
ordinary  stimuli,  appears  to  be  almost  invariably  lost,  or  greatly  diminished, 
before  the  rigor  mortis  commences.  This  statement  holds  good  in  regard  to 
animals  of  different  classes,  as  well  as  with  respect  to  Man  under  various  con- 
Ihus,  in  Birds  whose  muscles  most  speedily  lose  their  contractility, 
the  cadaveric  rigidity  is  most  quickly  exhibited;  whilst  in  Reptiles  it  is  much 
longer  m  commencing,  the  irritability  of  the  muscles  being  more  persistent. 


PROPERTIES  OF  MUSCULAR  FIBRE.  289 

An  attempt  has  been  made  to  show  a  correspondence^  between  the  rigor 
mortis  and  the  coagulation  of  the  blood  in  the  vessels ;  and  there  is  certainly 
evidence  enough  to  make  it  appear  that  some  analogy  exists  between  these 
two  actions,  though  they  are  far  from  being  identical.  After  those  forms  of 
death,  in  which  the  blood  does  not  coagulate,  or  coagulates  feebly,  the  rigidity 
commonly  manifests  itself  least ;  but  this  is  by  no  means  an  invariable  rule. 
It  seems  probable  that,  as  the  coagulation  of  the  blood  will  be  shown  to  be  the 
last  act  of  its  vitality,  so  the  stiffening  of  the  muscles  is  the  expiring  effort  of 
theirs.  The  property  to  which  it  is  due,  however,  would  appear  to  be  of  a 
different  character  from  ordinary  irritability.  This  may  be  inferred  from  the 
fact,  that  the  rigidity  does  not  ordinarily  come  on  until  after  the  contractility 
has  departed — sometimes  for  a  considerable  period ;  and  also  from  the  circum- 
stance, observable  in  most  cases  of  Asphyxia,  that  the  rigidity  is  very  decided 
and  prolonged,  whilst  the  contractility  is  speedily  lost.  This  property,  to 
which  the  name  of  Tonicity  has  been  given,  is  probably  the  same  as  that 
which  partly  occasions  the  retraction  of  the  muscle  when  divided  during  life ; 
the  degree  of  this  retraction  being  much  greater  than  that  seen  in  a  muscle 
which  has  been  for  some  time  dead.  Moreover,  this  kind  of  tonic  contraction 
is  more  directly  excited  by  heat  than  that  which  results  from  ordinary  con- 
tractility ;  and  it  is  not  excited  by  galvanism  or  mechanical  irritation,  which  so 
powerfully  act  on  the  latter.  It  is  interesting,  moreover,  to  remark,  that  the 
state  of  habitual  preponderance  during  sleep,  of  the  flexor  over  the  extensor 
muscles  (which  last  are  the  stronger),  is  explicable  by  attributing  it  to  the 
same  property ;  the  manifestations  of  which  thus  correspond,  whether  the  con- 
tractility of  the  muscles  be  in  a  dormant  or  unexcited  state,  or  whether  it  have 
altogether  departed  from  the  tissue. 

391.  It  is  necessary  to  bear  in  mind,  when  the  phenomena  of  cadaveric 
rigidity  are  brought  into  question  in  juridical  investigations,  that  a  state  at 
first  sight  corresponding  to  it  may  supervene  immediately  upon  death,  from 
some  peculiar  condition  of  the  nervous  and  muscular  systems  at  the  moment. 
This  has  been  observed  in  some  cases  of  Asphyxia ;  but  chiefly  when  death 
has  resulted  from  apoplexy  following  chronic  ramollissement  of  the  brain  or 
spinal  cord.  This  contraction,  which  is  obviously  of  a  tetanic  character, 
ceases  after  a  few  hours,  and  is  then  succeeded  by  a  state  of  flexibility,  after 
which  the  ordinary  rigidity  supervenes.  The  following  case  illustrates  the 
nature  of  the  inquiries,  to  which  this  condition  may  give  rise.*  The  body  of 
a  man  was  found1  in  a  ditch,  with  the  trunk  and  limbs  in  such  a  relative  posi- 
tion, as  could  only  be  maintained  by  the  stiffness  of  the  articulations.  This 
stiffness  must  have  come  on  at  the  very  moment  when  the  body  took  that  posi- 
tion ;  unless  it  could  be  imagined  that  the  body  had  been  supported  by  the 
alleged  murderers,  until  the  joints  were  locked  by  cadaveric  stiffness.  A 
post-mortem  explanation  showed,  that  there  was  no  necessity  for  this  supposi- 
tion,— obviously  a  very  improbable  one  in  itself;  by  affording  sufficient  evi- 
dence that  apoplexy,  resulting  from  chronic  disease,  was  the  cause  of  death. 
A  case  occurred  a  few  years  since  in  Scotland,  in  which  the  same  plea  was 
raised.  The  body  was  found  in  a  position  in  which  it  could  have  only  been 
retained  by  rigidity  of  the  joints  ;  and  it  was  pleaded,  on  the  part  of  the  pri- 
soner, that  death  had  been  natural,  and  had  resulted  from  fracture  of  the  pro- 
cessus  dentatus,  causing  sudden  pressure  upon  the  spinal  cord,  whence  the 
spasmodic  rigidity  would  naturally  result.  Proof  was  deficient,  however,  as 
to  the  existence  of  this  lesion  before  death  ;  and  the  position  of  the  body  rather 
resembled  that  into  which  it  might  have  been  forced  during  the  rigidity,  than 
that  in  which  it  would  probably  have  been  at  the  moment  of  death.  There 

*  Annales  d'Hygiene,  torn.  vii. 
25 


290  OF  MUSCULAR  CONTRACTILITY. 

were  also  marks  of  violence,  and  many  other  suspicious  circumstances ;  but 
the  prisoner  Avas  acquitted,  chiefly  from  want  of  evidence  against  him.  What 
seemed  to  indicate  that  the  rigidity  was  of  the  ordinary  cadaveric  nature,  was, 
that  there  was  no  evidence  of  the  body  having  become  flexible  and  again 
stiffened ;  as  it  would  probably  have  done,  had  the  rigidity  been  of  the  spas- 
modic character. 

V.  Energy  and  Rapidity  of  Muscular  Contraction. 

392.  There  can  be  no  question  that,  in  the  living  body,  the  energy  of  Mus- 
cular contraction  is  determined  (other  things  being  equal),  by  the  supply  of 
arterial  blood,  which  the  muscle  receives.  It  is  well  known  that,  when  a 
ligature  is  applied  to  a  large  arterial  trunk  in  the  Human  subject,  there  is  not 
only  a  deficiency  of  sensibility  in  the  surface,  but  also  a  partial  or  complete 
suspension  of  muscular  power,  until  the  collateral  circulation  is  established. 
It  is  evident,  however,  that  a  portion  of  this  effect  is  to  be  ascribed  to  the 
interruption  in  the  functions  of  the  nervous  trunks,  which  is  due  to  the  same 
cause ;  since  muscles,  taken  from  the  human  body,  after  the  circulation  has 
entirely  ceased,  retain  their  contractility  for  some  time.  The  influence  of  this 
supply  of  arterial  blood  is  twofold ; — it  supplies  the  materials  for  the  nutrition 
of  the  tissue  ; — and  it  furnishes  (what  is  perhaps  more  immediately  necessary) 
the  supply  of  oxygen  required  for  that  metamorphosis  of  the  tissue  which  is 
probably  an  essential  condition  of  the  generation  of  its  contractile  force  (§  377). 
As  this  oxygen  is  taken  in  through  the  lungs,  and  as  the  greater  part  of  it  is 
thrown  off — when  united  with  carbon  into  carbonic  acid,  by  the  same  channel, 
we  should  expect  to  find  a  very  close  correspondence  between  the  amount  of 
muscular  power  developed  in  an  animal,  and  the  quantity  of  oxygen  consumed 
in  its  Respiration :  and  this  is  in  reality  the  case.  We  find,  for  example,  that 
in  Birds  and  Insects,  whose  respiration  is  the  highest,  the  muscular  power  is 
greater  in  proportion  to  their  size  than  in  any  other  animals.  In  the  Mam- 
malia, and  certain  Fishes  that  might  be  almost  called  warm-blooded,  it  is  only 
in  a  degree  inferior.  But  in  the  cold-blooded  reptiles,  Fishes  and  Mollusca, 
the  muscular  power  is  comparatively  feeble ;  though  even  here  we  trace  gra- 
dations, which  accord  well  with  the  relative  quantities  of  oxygen  consumed. 
But  in  proportion  to  the  feebleness  of  the  power,  do  we  usually  find  its  dura- 
tion greater  (§  376) ;  so  that  it  is  not  so  immediately  dependent  upon  the 
supply  of  oxygen,  in  cold-blooded,  as  in  warm-blooded  animals.  Thus,  it  is 
found  that  Frogs  are  still  capable  of  voluntary  movement,  after  the  heart  has 
been  cut  out ;  they  can  move  limbs  which  are  connected  with  the  trunk  by 
.  the  nerves  alone  :  and  that  this  power  is  not  altogether  due  to  the  blood  which 
may  remain  in  the  capillary  vessels,  is  shown  by  the  experiment  of  Miiller, 
who  found  the  muscles  still  contractile,  after  he  had  expelled  all  the  blood,  by 
forcing  a  current  of  water  into  an  artery,  until  it  escaped  from  the  divided 
veins.  It  seems  probable  that  the  Muscles  of  Organic  life  are  less  dependent 
upon  a  supply  of  arterialized  blood,  than  are  those  of  Animal  life ;  for  the 
Heart  will  continue  to  contract,  when  the  blood  in  its  vessels  is  entirely  venous, 
and  when  the  circulation  in  it  has  come  to  a  stand.  Still  the  dependence  of 
its  action  upon  a  constant  supply  of  arterial  blood,  is  very  close ;  and  in  all 
animals,  however  different  the  plans  of  their  circulation,  we  find  a  provision 
for  this  supply,  by  a  special  arrangement  of  the  coronary  arteries.*  That  the 
heart's  action  comes  to  an  end  much  sooner,  after  the  destruction  of  animal 
life  by  pithing,  when  the  coronary  arteries  have  been  tied,  than  when  they 
are  left  untouched,  has  been  proved  by  the  experiments  of  Mr.  Erichsen.t 

*  Dr.  M.  Hall's  Gulstonian  Lectures,  pp.  23,  24. 
f  Medical  Gazette,  July  8,  1842. 


ENERGY  AND  RAPIDITY  OF  MUSCULAR  CONTRACTION.  291 

In  an  animal  that  has  been  pithed,  but  whose  heart  has  been  left  intact,  arti- 
ficial respiration  will  easily  keep  up  its  action  for  an  hour,  or  an  hour  and  a 
half.  But  when  the  coronary  arteries  were  tied,  a  mean  of  six  experiments 
give  a  duration,  for  the  ventricular  action,  of  only  23£  minutes  after  the  liga- 
tures were  applied,  and  32£  after  the  pithing;  and  in  no  instance  was  it 
prolonged  more  than  31  minutes  after  the  application  of  the  ligature,  or  37 
minutes  after  the  pithing.  On  the  other  hand,  when  the  aorta  was  tied,  so 
that  the  coronary  arteries  were  distended  with  blood,  the  circulation  being 
carried  on  through  them  alone,  the  right  ventricle  continued  to  act  up  to  the 
82d  minute. 

393.  There  is  a  remarkable  difference  in  the  degree  of  irritability  in  the 
two  sides  of  the  heart,  to  which  Dr.  M.  Hall  has  directed  attention.     In  the 
warm-blooded  Vertebrata,  the  right  side  of  the  heart  will  act  on  the  stimulus 
of  venous  blood  ;  whilst  the  left  side  requires  the  stimulus  of  arterial.     In 
Fishes,  on  the  other  hand,  whose  heart  corresponds  to  the  right  side  only  of 
that  of  Man,  the  whole  is  put  in  action  by  venous  blood.     In  Reptiles,  one 
auricle  is  sufficiently  stimulated  by  venous  blood,  whilst  the  other  requires 
arterial ;  and  the  ventricle  is  excited  to  action  by  a  mixed  fluid.     In  all  these 
cases,  there  must  be  a  marked  difference  in  the  properties  of  the  several  parts ; 
some  being  sufficiently  affected  by  a  stimulus,  which  is  totally  inoperative  on 
others.     This  is  still  more  remarkably  exemplified  by  the  fact,  that  the  mus- 
cular fibre  of  Frogs  would  be  thrown  into  a  state  of  permanent  and  rigid 
contraction  (through  the  powerful  operation  of  its  property  of  Tonicity),  by 
the  stimulus  of  a  fluid  no  hotter  than  the  blood  which  ordinarily  bathes  the 
muscles  of  Birds.    Now  in  those  warm-blooded  animals  which  pass  the  winter 
in  a  state  of  torpidity,  the  respiration  is  very  slow  and  imperfect,  and  the  blood 
is  very  imperfectly  arterialized.     There  must,  therefore,  be  a  change  in  the 
properties  of  the  left  ventricle,  by  which  it  becomes  capable  of  action  on  a 
more  feeble  stimulus,  thus  resembling  the  ventricle  of  Reptiles.    This  change 
Dr.  M.  Hall  designates  as  an  increase  of  Irritability  ;  considering  that,  if  mus- 
cular action  be  excited  by  a  more  feeble  stimulus,  the  property  to  which  that 
action  is  due,  must  be  itself  more  exalted.     Physiologists  have  been  so  long 
accustomed,  however,  to  consider  the  irritability  of  the  muscles  in  warm-blooded 
animals  as  greater  than  that  of  cold-blooded,  on  account  of  the  greater  energy 
and  rapidity  of  their  contractions  when  excited,  that  it  seems  undesirable  to 
modify  the  term  in  the  manner  proposed  by  Dr.  Hall.    No  one  will  assert  that 
the  vitality  of  the  Muscle  is  exalted,  when  it  is  reduced  to  the  condition  of  that 
of  the  Reptile ;  and,  as  Irritability  is  strictly  a  vital  property,  it  cannot  be 
correctly  spoken  of  in  that  manner.     The  general  principle,  however,  laid 
down  by  Dr.  M.  Hall, — that  the  facility  with  whic.h  the  muscular  system  may 
be  excited  to  contraction,  or,  in  other  words,  the  feebleness  of  the  stimulus 
required  for  the  purpose,  is  inversely  as  the  respiration  of  the  animal, — is,  no 
doubt,  generally  correct. 

394.  A  curious  question  has  been  lately  raised,  the  decision  on  which  is  of 
some  importance  in  our  determination  of  the  nature  of  the  force  by  which  the 
contraction  of  muscles  is  occasioned.  This  isy — whether  the  power  of  a  muscle 
is  greater  or  less  at  different  degrees  of  contraction,  the  same  stimulus  being 
applied.     This  seems  to  have  been  determined  by  the  ingeniously-devised 
experiments  of  Schwann.*     He  contrived  an  apparatus,  which  should  accu- 
rately measure  the  length  of  the  muscle,  and  at  the  same  time,  the  weight 
which  it  would  balance  by  its  contraction.     Having  caused  the  muscle  of  a 
frog  to  shorten  to  its  extreme  point,  by  the  stimulus  of  galvanism  applied  to 
the  nerve,  so  that  no  further  stimulation  could  lift  a  weight  placed  in  the 

*  MQller's  Physiology,  p.  903. 


292  OF  MUSCULAR  CONTRACTILITY. 

opposite  scale,  he  allowed  the  muscle  to  relax  until  it  was  extended  to  a  certain 
point,  and  then  ascertained  the  weight  which  would  balance  its  power.  The 
same  was  several  times  repeated,  as  in  the  following  manner.  The  length  of 
the  muscle  in  its  extreme  state  of  contraction,  at  which  no  additional  force 
could  be  exerted  by  it,  being  represented  by  14,  it  was  found  that,  when  it 
had  been  extended  to  17,  it  would  balance  a  weight  of  60 ;  when  its  length 
increased  to  19-6,  it  would  balance  a  weight  of  120 ;  and  at  22-5,  it  would 
balance  180.  In  another  experiment,  the  muscle  at  13-5,  balanced  0;  at 
18-8,  it  balanced  100;  and  at  23-4,  it  balanced  200.  Hence  it  appears  that 
an  uniform  increase  of  force  corresponds  with  a  nearly  uniform  increase  in  the 
length  of  the  muscle  ;  or,  in  other  words,  that  when  the  muscle  is  nearly  at 
its  full  length,  its  contractile  power  is  the  greatest.  In  later  experiments  upon 
the  same  muscle,  this  uniform  ratio  seemed  to  be  departed  from ;  but  by  com- 
paring the  results  in  a  considerable  number  of  instances,  it  was  constantly 
found  that  in  those  experiments  which  were  performed  the  soonest  after  the 
preparation  of  the  frog,  and  in  which,  therefore,  the  normal  conditions  of  the 
system  were  the  least  disturbed,  the  ratio  was  very  closely  maintained.  It 
has  been  hence  inferred  by  Miiller,  that  the  power  which  causes  the  contrac- 
tion of  a  Muscle  must  be  very  different  in  its  character,  from  any  of  the  forces 
of  attraction  known  to  us ;  since  these  all  increase  in  energy  as  the  attracted 
parts  approach  each  other,  in  the  inverse  ratio  of  the  square  of  the  distance ; 
so  that  the  power  of  a  Muscle,  if  operated  on  by  any  of  these,  ought  to  increase, 
instead  of  regularly  diminishing,  with  its  degree  of  contraction.  But  it  is  to 
be  remembered  that,  as  the  observations  of  Mr.  Bowman  have  clearly  shown, 
there  must  be  a  considerable  displacement  of  the  constituents  of  every  fibre 
during  contraction  (371) ;  so  that  it  is  easy  to  understand  that  the  greater  the 
contraction,  the  more  difficult  must  any  further  contraction  become.  If,  be- 
tween a  magnet  and  a  piece  of  iron  attracted  by  it,  there  were  interposed  a 
spongy  elastic  tissue,  the  iron  would  cease  to  approach  the  magnet  at  a  point, 
at  which  the  attraction  of  the  magnet  would  be  balanced  by  the  force  needed 
to  compress  still  further  the  intermediate  substance. 

VI.  Applications  of  Muscular  Power. 

395.  The  energy  of  Muscular  contraction  is  of  course  to  be  most  remark- 
ably observed  in  those  instances  in  which  the  continual  exercise  of  particular 
parts  has  occasioned  an  increased  determination  of  blood  towards  them,  and 
in  consequence  a  permanent  augmentation  in  their  bulk.  This  has  been  the 
case,  for  example,  with  persons  who  have  gained  their  livelihood  by  exhibit- 
ing feats  of  strength.  Much  will,  of  course,  depend  on  the  mechanically 
advantageous  application  of  muscular  power ;  and  in  this  manner  effects  may 
be  produced,  even  by  persons  of  ordinary  strength,  which  would  not  have  been 
thought  credible.  In  lifting  a  heavy  weight  in  each  hand,  for  example,  a 
person  who  keeps  his  back  perfectly  rigid,  so  as  to  throw  the  pressure  verti- 
cally upon  the  pelvis,  and  only  uses  the  powerful  extensors  of  the  thigh  and 
calf,  by  straightening  the  knees  (previously  somewhat  flexed),  and  bringing 
the  leg  to  a  right  angle  with  the  foot,  will  have  a  great  advantage  over  one 
who  uses  his  lumbar  muscles  for  the  purpose.  A  still  greater  advantage  will 
be  gained,  by  throwing  the  weight  more  directly  upon  the  loins,  by  means  of 
a  sort  of  girdle,  shaped  so  as  to  rest  upon  the  top  of  the  sacrum  and  the  ridges 
of  the  ilia ;  and  by  pressing  with  the  hands  upon  a  frame,  so  arranged  as  to- 
bring  the  muscles  of  the  arms  to  the  assistance  of  those  of  the  legs ;  in  this 
manner,  a  single  man  of  ordinary  strength  may  raise  a  weight  of  2000  Ibs. ; 
whilst  few  who  are  unaccustomed  to  such  exertions,  can  lift  more  than  300 
Ibs.  in  the  ordinary  mode.  A  man  of  great  natural  strength,  however,  has 
been  known  to  lift  800  Ibs.  with  his  hands :  and  the  same  individual 


APPLICATIONS  OF  MUSCULAR  POWER.  293 

performed  several  other  curious  feats  of  strength,  which  seem  deserving 
of  being  here  noticed.  "1.  By  the  strength  of  his  fingers,  he  rolled  up 
a  very  large  and  strong  pewter  dish.  2.  He  hroke  several  short  and 
strong  pieces  of  tobacco-pipe,  with  the  force  of  his  middle  finger,  having 
laid  them  on  the  first  and  third  finger.  3.  Having  thrust  in  under  his 
garter  the  bowl  of  a  strong  tobacco-pipe,  his  legs  being  bent,  he  broke  it 
to  pieces  by  the  tendons  of  his  hams,  without  altering  the  bending  of  the 
knee.  4.  He  broke  such  another  bowl  between  his  fist  and  second  fingers, 
by  pressing  them  together  sideways.  5.  He  lifted  a  table  six  feet  long,  which 
had  half  a  hundred-weight  hanging  at  the  end  of  it,  with  his  teeth,  and  held 
it  in  that  position  for  a  considerable  time.  It  is  true,  the  feet  of  the  table 
rested  against  his  knees ;  but,  as  the  length  of  the  table  was  much  greater 
than  its  height,  that  performance  required  a  great  strength  to  be  exerted  by 
the  muscles  of  his  loins,  neck  and  jaws.  6.  He  took  an  iron  kitchen  poker, 
about  a  yard  long,  and  three  inches  in  circumference,  and,  holding  it  in  his 
right  hand,  he  struck  it  on  his  bare  left  arm  between  the  elbow  and  the  wrist, 
till  he  bent  the  poker  nearly  to  a  right  angle.  7.  He  took  such  another  poker, 
and,  holding  the  ends  of  it  in  his  hands,  and  the  middle  of  it  against  the  back 
of  his  neck,  he  brought  both  ends  of  it  together  before  him ;  and,  what  was 
yet  more  difficult,  he  pulled  it  straight  again."*  Haller  mentions  an  instance 
of  a  man,  who  could  raise  a  weight  of  300  Ibs.,  by  the  action  of  the  elevator 
muscles  of  his  jaw ;  and  that  of  a  slender  girl,  affected  with  tetanic  spasm,  in 
whom  the  extensor  muscles  of  the  back,  in  the  state  of  tonic  contraction  or 
opisthotonos,  resisted  a  weight  of  800  Ibs.,  laid  on  the  abdomen  with  the  absurd 
intention  of  straightening  the  body.  It  is  to  be  recollected,  that  the  mechani- 
cal application  of  the  power  developed  by  muscular  contraction,  to  the  move- 
ment of  the  body,  is  very  commonly  disadvantageous  as  regards  force;  being 
designed  to  cause  the  part  moved  to  pass  over  a  much  greater  space  than  that 
through  which  the  muscle  contracts.  Thus  the  temporal  muscle  is  attached 
to  the  lower  jaw  at  about  one-third  of  the  distance  between  the  condyle  and 
the  incisors  ;  so  that  a  shortening  of  the  muscle  to  the  amount  of  half  an  inch, 
will  draw  up  the  front  of  the  jaw  through  an  inch  and  a  half;  but  a  power  of 
900  Ibs.  applied  by  the  muscle,  would  be  required  to  raise  300  Ibs.  bearing  on 
the  incisors.  In  the  case  of  the  forearm  and  leg,  the  disproportion  is  much 
greater ;  the  points  of  attachment  of  the  muscles,  by  which  the  knee  and 
elbow-joints  are  flexed  and  extended,  being  much  closer  to  the  fulcrum,  in 
comparison  with  the  distance  of  the  points  on  which  the  resistance  bears. 

396.  The  energy  of  muscular  contraction  appears  to  be  greater  in  Insects, 
in  proportion  to  their  size,  than  it  is  in  any  other  animals.     Thus  a  Flea  has 
been  known  to  leap  60  times  its  own  length,  and  to  move  as  many  times  its 
own  weight.     The  short-limbed  Beetles,  however,  which  inhabit  the  ground, 
manifest  the  greatest  degree  of  muscular  power.     The  Lucanus  cervus  (Stag 
Beetle)  has  been  known  to  gnaw  a  hole  of  an  inch  diameter,  in  the  side  of  an 
iron  canister  in  which  it  had  been  confined.     The   Geotrupes  stercorarius 
(Dung  or  shard-borne  Beetle)  can  support  uninjured,  and  even  elevate,  a 
weight  equal  to  at  least  500  times  that  of  its  body.     And  a  small  Carabus  has 
been  seen  to  draw  a  weight  of  85  grains  (about  24  times  that  of  its  body)  up 
a  plane  of  25°  ;  and  a  weight  of  125  grains  (36  times  that  of  its  body)  up  a 
plane  of  5° ;  and  in  both  these  instances  the  friction  was  considerable,  the 
weights  being  simply  laid  upon  a  piece  of  paper,  to  which  the  insect  was 
attached  by  a  string. 

397.  The  rapidity  of  the  changes  of  position  of  the  component  particles 
of  muscular  fibres,  may,  as  Dr.  Alison  justly  remarks,t  be  estimated,  though 

*  Desaguliers'  Philosophy,  vol.  ii. 

f  Cyclopaedia  of  Anatomy  and  Physiology,  Art.  Contractility. 
25* 


294  OF  MUSCULAR  CONTRACTILITY. 

it  can  hardly  be  conceived,  from  various  well-known  facts.  The  pulsations 
of  the  heart  can  sometimes  be  distinctly  numbered  in  children,  at  more  than 
200  in  the  minute  ;  and  as  each  contraction  of  the  ventricles  occupies  only 
one-third  of  the  time  of  the  -whole  pulsation,  it  must  be  accomplished  in  ff|¥th 
of  a  minute,  or  TVth  of  a  second.  Again,  it  is  certain  that,  by  the  movements 
of  the  tongue  and  other  organs  of  speech,  1500  letters  can  be  distinctly  pro- 
nounced by  some  persons  in  a  minute  :  each  of  these  must  require  a  sepa- 
rate contraction  of  muscular  fibres  ;  and  the  production  and  cessation  of  each 
of  the  sounds,  implies  that  each  separate  contraction  must  be  followed  by  a 
relaxation  of  equal  length  ;  each  contraction,  therefore,  must  have  been  effected 
in  —  Votn  Part  of  a  minute,  or  in  the  T\>th  of  a  second.  Haller  calculated 
that,  in  the  limbs  of  a  dog  at  full  speed,  muscular  contractions  must  take  place 
in  less  than  the  o^th  of  a  second,  for  many  minutes  at  least  in  succession.  — 
All  these  instances,  however,  are  thrown  into  the  shade  by  those  which  may 
be  drawn  from  the  class  of  Insects.  The  rapidity  of  the  vibrations  of  the 
wings  may  be  estimated  from  the  musical  tone  which  they  produce  ;  it  being 
easily  ascertained,  by  experiments,  what  number  of  vibrations  are  required  to 
produce  any  note  in  the  scale.  From  these  data,  it  appears  to  be  the  neces- 
sary result  that  the  wings  of  many  Insects  strike  the  air  many  hundred,  or 
even  many  thousand  times  in  every  second.—  The  minute  precision  with 
which  the  degree  of  muscular  contraction  can  be  adapted  to  the  designed 
effect,  is  in  no  instance  more  remarkable  than  in  the  Glottis.  The  musical 
pitch  of  the  tones  produced  by  it,  is  regulated  by  the  degree  of  tension  of  the 
chordae  vocales,  which  are  possessed  of  a  very  considerable  degree  of  elasti- 
city (§  402).  According  to  the  observations  of  Miiller,*the  average  length  of 
these,  in  the  male,  in  a  state  of  repose,  is  about  /^hs  °f  an  inc^  5  whilst,  in 
the  state  of  greatest  tension  it  is  about  T9^otns  5  tne  difference  being  therefore 
or  one-fifth  of  an  inch  :  in  the  female  glottis,  the  average  dimensions 


are  about  yVVtns'  anc^  T6o3otns  respectively  ;  the  difference  being  thus  about 
one-eighth  of  an  inch.  Now  the  natural  compass  of  the  voice,  in  most  per- 
sons who  have  cultivated  the  vocal  organ,  may  be  stated  at  about  two  octaves, 
or  24  semitones.  Within  each  semitone,  a  singer  of  ordinary  capability  could 
produce  at  least  ten  distinct  intervals  ;  so  that  of  the  total  number,  240  is  a 
very  moderate  estimate.  There  must,  therefore,  be  at  least  240  different 
states  of  tension  of  the  vocal  cords,  every  one  of  which  is  producible  by  the 
will,  without  any  previous  trial  ;  and  the  whole  variation  in  the  length  of  the 
cords  being  not  more  than  one-fifth  of  an  inch,  even  in  man,  the  variation 
required  to  pass  from  one  interval  to  another,  will  not  be  more  than  one-twelve 
hundredth  of  an  inch.  And  yet  this  estimate  is  much  below  that  which 
might  be  truly  made  from  the  performances  of  a  practised  vocalist.! 

398.  Of  the  different  associations  of  muscular  actions  which  are  employed 
for  various  purposes  in  the  living  body,  it  would  be  out  of  place  here  to  speak  ; 
since  these  associations  depend  upon  the  nervous  rather  than  upon  the  mus- 
cular system  ;  and  the  most  important  of  them  have  already  been  considered 
in  detail.  It  may  be  mentioned,  however,  that  the  aptitude  which  is  acquired 
by  practice,  for  the  performance  of  particular  actions,  that  were  at  first  ac- 
complished with  difficulty,  seems  to  result  as  much  from  a  change,  which  the 
continual  repetition  of  them  occasions  in  the  muscle,  as  in  the  habit  which  the 
nervous  system  acquires,  of  exciting  their  performance.  Thus  almost  every 

*  Physiology,  p.  1018. 

f  It  is  said  that  the  celebrated  Mad.  Mara  was  able  to  sound  100  different  intervals  be- 
tween each  tone.  The  compass  of  her  voice  was  at  least  three  octaves,  or  22  tones  ;  so  that 
ihe  total  number  of  intervals  was  2200,  all  comprised  within  an  extreme  variation  of  one- 
eighth  of  an  inch  ;  so  that  it  might  be  said  that  she  was  able  to  determine  the  contractions 
of  her  vocal  muscles  to  the  seventeen-thousandth  of  an  inch. 


SENSIBILITY  OF  MUSCLES.  295 

person  learning  to  play  on  a  musical  instrument,  finds  a  difficulty  in  causing 
the  two  shorter  fingers  to  move  independently  of  each  other  and  of  the  rest ; 
this  is  particularly  the  case  in  regard  to  the  ring-finger.  Any  one  may  satisfy 
himself  of  the  difficulty,  by  laying  the  palm  of  the  hand  fiat  on  a  table,  and 
raising  one  finger  after  the  other,  when  it  will  be  found,  that  the  ring-finger 
cannot  be  lifted  without  disturbing  the  rest — evidently  from  the  difficulty  of 
detaching  the  action  of  that  portion  of  the  extensor  communis  digitorum,  by 
which  the  movement  is  produced,  from  that  of  the  remainder  of  the  muscle. 
Yet  to  the  practised  musician,  the  command  of  the  will  over  all  the  fingers 
becomes  nearly  alike ;  and  it  can  scarcely  be  doubted,  that  some  change  takes 
place  in  the  structure  of  the  muscle,  which  favours  the  isolated  operation  of 
its  several  divisions. 

f    VII.  Sensibility  of  Muscles. 

399.  Muscles  are  much  less  sensible  to  external  impressions  than  many 
other  parts  of  the  body ;  this  is  seen  in  amputations,  in  which  the  severest 
pain  caused  by  the  section  is  that  of  the  incision  through  the  skin.     It  is  well 
known  that  a  needle  passed  through  the  skin  may  be  carried  into  the  sub- 
stance of  a  muscle  with  scarcely  any  further  pain ;    and  the  heart  laid  bare 
has  been  observed  to  possess  but  a  very  slight  degree  of  sensibility.     This  is 
easily  accounted  for  by  our  knowledge  of  the  distribution  of  the  nerves  ;  for 
although  every  principal  trunk  may  contain  motor  and  sensory  nerves  in 
equal  proportion,  we  know  that  in  its  various  subdivisions  these  may  be  very 
unequally  distributed.     Thus,  in  the  third  division  of  the  Fifth  pair,  it  has 
been  ascertained  that  the  fibres  from  the  motor  root  chiefly  pass  into  the  mus- 
cular branches,  whilst  those  of  the  sensory  root  predominate  in  those  supplying 
the  surface ;  and  in  the  Par  Vagum,  a  difference  in  the  endowments  of  the 
several  branches  has  been  equally  substantiated.     Again,  in  the  Orbit  we  find 
some  muscles  supplied  by  nerves  which  are  exclusively  motor,  and  scarcely 
receiving  any  sensory  branches  from  the  Fifth  pair.     Knowing  as  we  do, 
that  the  general  surface  of  the  body  would  not  derive  any  advantage  from 
receiving  the  motor  division  of  the  Spinal  nerves,  and  must,  on  the  contrary, 
be  largely  supplied  from  the  sensory,  it  cannot  be  doubted  that,  with  regard 
to  the  subjacent  muscles,  the  case  is  entirely  the  reverse. 

400.  Muscles  are  endowed,  however,  with  the  power  of  originating  sensa- 
tions indicative  of  their  ow^n  condition;  and  these  sensations  differ  so  far  from 
those  conveyed  by  the  usual  sensory  organs,  that  it  has  been  proposed  to 
designate  the  channel  through  which  they  are  received  by  a  peculiar  name, 
the  Muscular  Sense.     It  may  be  questioned,  however,  whether  this  is  de- 
sirable.   The  property  by  which  we  estimate  the  force  with  which  muscles  are 
contracting, — which  enables  us  to  compare  different  degrees  of  weight  and 
resistance,  and  to  acquire  a  knowledge  of  the  distances  and  relative  positions 
of  bodies  brought  in  contact  with  the  surface, — appears  to  be  the  same  with 
that  by  which  we  become  conscious  of  fatigue  from  continued  muscular 
action,  and  experience  pain  \vhen  the  muscles  are  spasmodically  contracted,  as 
in  ordinary  cramp.     Of  the  importance  of  this  sense  in  guiding  and  regulating 
muscular  contraction,  instances  have  already  been  given  (§  257).     It  is,  in 
addition,  one  of  the  principal  means  by  which  we  acquire  our  notions  of  the 
external  world.     All  our  ideas  offeree  and  of  resistance  are  derived  from  it. 
When  we  put  our  muscles  in  action  to  raise  a  weight,  or  to  push  from  us  an 
obstacle,  we  should  have  no  idea  without  this  sense  of  the  effort  required;  and 
it  is  obvious  on  a  little  consideration  that  no  accounts  of  any  natural  forces 
(such  as  that  of  Gravitation,  Magnetic  Attraction,  &c.)  could  convey  a  distinct 
idea  to  our  minds,  were  it  not  for  our  means  of  estimating  them  by  the  same 


296  OF  THE  VOICE  AND  SPEECH. 

method.  It  is  by  the  sensibility  of  the  muscles  that  we  become  conscious  of 
the  existence  and  direction  of  motion,  to  which  the  whole  body  is  being  pas- 
sively subjected.  When  sitting  upright  in  a  carriage,  which  is  suddenly 
drawn  forwards,  we  are  thrown  in  the  contrary  direction ;  and  it  is  only  by 
a  certain  muscular  effort  that  we  can  regain  our  position.  After  some  little 
time,  however,  we  become  so  habituated  to  the  sensation  which  this  occasions, 
that  we  are  unconscious  of  it,  except  by  a  certain  degree  of  fatigue  which 
results  if  it  be  greatly  prolonged.  But,  when  the  motion  suddenly  ceases,  we 
are  thrown  forwards,  showing  that  the  effort  itself-  had  continued ;  and  not 
unfrequently  the  feeling  motion  is  then  experienced  for  a  few  seconds,  as  if 
the  sensation  remained,  and  were  more  perceptible  when  the  cause  of  it  had 
ceased. 


CHAPTER    VI. 

OF    THE    VOICE    AND   SPEECH. 

I.  The  Larynx,  and  its  Actions. 

401.  The  sounds  produced  by  the  organ  of  Voice  constitute  the  most 
important  means  of  communication  'between  Man  and  his  fellows ;   and  the 
power  of  speech  has,  therefore,  a  primary  influence,  as  well  on  his  physical 
condition,  as  on  the  development  of  his  mental  faculties.     Hence,  although  it 
only  depends  on  one  particular  application  of  muscular  force,  comparable  to 
that  by  which  other  volitional  or  emotional  movements  are  effected,  it  seems 
right  in  treating  of  the  Physiology  of  Man,  to  make  it  an  object  of  special 
consideration.     In  order  to  understand  the  nature  of  the  Organ  of  Voice  as  a 
generator  of  Sound,  it  is  requisite  to  inquire,  in  the  first  instance,  into  the 
sources  from  which  sounds  at  all  corresponding  to  the  human  voice  are  else- 
where obtained.     It  is  necessary  to  bear  in   mind  that  Vocal  Sounds  and 
Speech,  or  Articulate  Language,  are  two  things  entirely  different ;  and  that  the 
former  may  be  produced  in  great"  perfection  where  there  is  no  capability  for 
the  latter.     Hence  we  should  at  once  infer  that  the  instrument  for  the  pro- 
duction of  Vocal  Sounds  was  distinct  from  that  by  which  these  sounds  are 
modified  into  articulat  espeech ;  and  this  we  easily  discover  to  be  the  case, 
the  Voice  being  unquestionably  produced  in  the  Larynx  whilst  the  modifica- 
tions of  it,  by  which  language  is  formed,  are  effected  for  the  most  part  in  the 
Oral  cavity.     The  structure  and  functions  of  the  former,  then,  first  claim  our 
attention. 

402.  It  will  be  remembered  that  the  Windpipe  is  surmounted  by  a  stout 
bony  annulus,  termed  the  Cricoid  cartilage,  which  serves  as  a  foundation  for 
the  superjacent  mechanism.     This  is  embraced  (as  it  were)  by  the  Thyroid, 
which  is  articulated  to  its  sides  by  its  lower  horns,  round  the  extremities  of 
which  it  may  be  regarded  as  turning,  as  on  a  pivot.     In  this  manner  the  lower 
front  border  of  the  thyroid  cartilage,  which  is  ordinarily  separated  by  small 
intervals  from  the  upper  margin  of  the  thyroid,  may  be  made  to  approach  it  or 
recede  from  it ;  as  any  one  may  easily  ascertain,  by  placing  his  finger  against 
the  little  depression  which  may  be  readily  felt  externally,  and  observing  its 


THE  LARYNX,  AND  ITS  ACTIONS. 

[Fig,  72. 


297 


A  front  view  of  the  Thyroid  Cartilage;  1,  left 
half  of  the  cartilage ;  2,  anterior  projecting  angle ; 
3,  superior  margin ;  4,  its  notch ,  5,  inferior  mar- 
gin; 6,  6,  cornu  majus  of  each  "half;  7,  7,  cornu 
minus  of  each  half. 


A  front  view  of  the  Cricoid  Cartilage ;  1,  its 
internal  face ;  2,  the  cavity  of  the  larynx  as 
formed  by  this  cartilage ;  3,  its  inferior  surface ; 
4,  the  little  head  or  convexity  for  articulating 
with  the  arytenoids;  5,  ihe  surface  of  the  supe- 
rior edge  for  the  attachment  of  the  lateral  crico- 
arytenoid  muscles.] 


Fig.  73. 


External  and  sectional  views  of  the  Larynx,  after  Willis ;  A  n  B,  the  cricoid  cartilage ;  E  c  G,  the  thyroid 
cartilage;  G,  its  upper  horn ;  c,  its  lower  horn,  where  it  is  articulated  with  the  cricoid;  F,  the  arytenoid 
cartilage;  E  F,  the  vocal  ligament;  A  K,  crico-thyroideus  muscle;  F  e  m,  thyro-arytenoideus  muscle;  x.  e, 
crico-arytenoideus  lateralis ;  s,  transverse  section  of  arytenoideus  transversus ;  m  n,  space  between  thyroid 
and  crycoid;  B  L,  projection  of  axis  of  articulation  of  arytenoid  with  thyroid. 

changes  of  size,  whilst  a  range  of  different  tones  is  sounded:  it  will  then  be 
observed  that,  the  higher  the  note,  the  more  the  two  cartilages  are  made  to 
approximate, — whilst  they  separate  in  proportion  to  the  depth  of  the  tones.* 

*  In  making;  this  observation,  it  is  necessary  to  put  out  of  view  the  general  movement 
of  the  larynx  itself,  which  the  finger  must  be  made  to  follow  up  and  down. 


298 


OF  THE  VOICE  AND  SPEECH. 


Upon  the  upper  surface  of  the  back  of  the  cricoid,  are  seated  the  two  small 
Arytenoid  cartilages  ;  these  are  fixed  in  one  direction  by  a  bundle  of  strong 

[Fig.  74. 


A  posterior  view  of  the  left  Arytenoid  Carti- 
lages ;  1,  its  posterior  face ;  2,  the  summit ;  3,  the 
base  and  cavity  for  articulating  with  the  cricoid 
cartilage ;  4,  its  external  angle ;  5,  its  internal 
angle. 


An  anterior  view  of  the  left  Arytenoid  Carti- 
lages ;  1,  its  anterior  face.  The  other  references 
as  in  the  accompanying  figure.] 


ligaments,  which  tie  them  to  the  back  of  the  cricoid ;  but  they  have  some 
power  of  moving  in  other  directions  upon  a  kind  of  articulating  surface.  The 
direction  of  the  surface,  and  the  mode  in  which  these  cartilages  are  otherwise 
attached,  cause  their  movement  to  be  a  sort  of  rotation  in  a  plane,  which  is 


Fig.  75. 


Bird's-eye  view  of  Larynx  from  above,  after 
Willis;  G  E  H,  the  thyroid  cartilage,  embracing 
the  ring  of  the  cricoid  r  u  x  to,  and  turning  upon 
the  axis  x  z,  which  passes  through  the  lower 
horns,  c,  Fig.  73;  N  F,  N  F,  the  aryterioid  carti- 
lages, connected  by  the  arytenoideus  transversus; 
T  v,  T  v,  the  vocal  ligaments ;  NX,  the  right  crico- 
arytenoideus  lateralis  (the  left  being  removed) ; 
v  kf,  the  left  thyro-arytenoideus,  (the  right  being 
removed) ;  N  /,  N  I,  the  crico-arytenoidei  postici ; 
B  B,  the  crico-arytenoid  ligaments. 


[Fig.  76. 


A  vertical  section  of  the  Larynx  to  show  its 
internal  surface ;  1,  section  of  the  root  of  the 
tongue;  2,  os  hyoides;  3-,  the  muciparous  gland 
of  the  epiglottis ;  4,  top  of  the  epiglottis  cartilage ; 
5,  a  section  of  its  anterior  face ;  6,  a  fold  of  mu- 
cous membrane  from  the  arytenoids  to  the  epi- 
glottis; 7,  superior  vocal  ligament;  8,  section  of 
thyroid  cartilage ;  9,  ventricle  of  Galen  or  Mor- 
gagni;  10,  lower  vocal  ligament;  11,  arytenoid 
cartilages;  12,  inside  of  the  cricoid  cartilage  ;  13, 
its  posterior  portion ;  14,  lining  membranes  of  the 
trachea;  15,  end  of  the  cornu  majus  of  the  os 
hyoides ;  16,  cornu  majus  of  the  thyroid  cartilage ; 
17,  mucous  membrane  of  the  pharynx ;  IS,  oeso- 
phagus ;  19,  thyroid  gland.] 


THE  LARYNX,  AND  ITS  ACTIONS.  299 

nearly  horizontal,  but  partly  downwards ;  so  that  their  vertical  planes  may  be 
made  to  separate  from  each  other,  and  at  the  same  time  to  assume  a  slanting 
position.  This  change  of  place  will  be  better  understood,  when  the  action  of 
the  muscles  is  described.  To  the  summit  of  the  arytenoid  cartilages  are 
attached  the  chordae  vocctles,  or  Vocal  Ligaments,  which  stretch  across  to  the 
front  of  the  thyroid  cartilage ;  and  it  is  upon  the  condition  and  relative  situation  of 
these  ligaments  that  their  action  depends.  It  is  evident  that  they  may  be  ren- 
dered more  or  less  tense  by  the  movement  of  the  thyroid  cartilage  just  described, 
being  tightened  by  the  depression  of  its  front  upon  the  cricoid  cartilage,  and 
slackened  by  its  elevation.  On  the  other  hand,  they  may  be  brought  into  more 
or  less  close  apposition,  by  the  movement  of  the  arytenoid  cartilages ;  being 
made  to  approximate  closely,  or  to  recede  in  such  a  manner  as  to  cause  the 
rima  glottidis  to  assume  the  form  of  a  narrow  V,  by  the  revolution  of  these 
cartilages.  We  shall  now  inquire  into  the  actions  of  the  muscles  upon  the 
several  parts  of  this  apparatus;  and  first  into  those  of  the  larynx  alone. 

403.  The  depression  of  the  front  of  the  Thyroid  cartilage,  and  the  conse- 
quent tension  of  the  vocal  ligaments,  are  occasioned  by  the  conjoint  action  of 
the  Crico-thyroidei  on  both  sides  ;  and  the  chief  antagonists  to  these  are  the 
Thyro-ctrytenoidei,  which  draw  the  front  of  the  Thyroid  back  towards  the 
Arytenoid  cartilages,  and  thus  relax  the  vocal  ligaments.  These  two  pairs 
of  muscles  may  be  regarded  as  the  principal  governors  of  the  pitch  of  the 
notes,  which,  as  we  shall  hereafter  see,  is  almost  entirely  regulated  by  the 
tension  of  the  ligaments ;  their  action  is  assisted,  however,  by  that  of  other 
muscles  presently  to  be  mentioned. — The  Arytenoid  cartilages  are  made  to 
diverge  from  each  other,  by  means  of  the  Crico-arytenoideus  posticus  of  each 
side,  which  proceeds  from  their  outer  corner,  and  turns  somewhat  around  the 
edge  of  the  Cricoid,  to  be  attached  to  the  lower  part  of  its  back ;  its  action  is 
to  draw  the  outer  corner  backwards  and  downwards,  so  that  the  points  to  which 
the  vocal  ligaments  are  attached,  are  separated  from  one  another,  and  the  rima 
glottidis  is  thrown  open.  This  will  be  at  once  seen  from  the  subjoined  dia- 
gram, in  which  the  direction  of  traction  of  the  several  muscles  is  laid  down. — 
The  action  of  this  muscle  is  partly  "antagonized  by  that  of  the  Crico-arytenoi- 

Fig.  77. 


Part  of  Fig.  75  enlarged,  to  show  the  direction  of  the  muscular  forces,  which  act  on  the  Arytenoid  Car- 
tilage ;  Q  N  v  s,  the  right  arytenoid  cartilage;  T  v,  its  vocal  ligament;  B  R  s,  bundle  of  ligaments  uniting  it 
to  cricoid ;  c  p,  projection  of  its  axis  of  articulation;  h  g,  direction  of  the  action  of  the  thyro-arytenoideus ; 
N  x,  direction  of  crico-arytenoideus  lateralis;  N  w,  direction  of  crico-arytenoideus  posticus;  N  T,  direction 
of  arytenoideus  transversus,  After  Willis. 


300  OF  THE  VOICE  AND  SPEECH. 

deus  lateralis,  which  runs  forwards  and  downwards  from  the  outer  corner  of 
the  Arytenoid  cartilage  ;  and  its  action,  with  that  of  its  fellow,  will  be  to  bring 
the  anterior  points  of  the  Arytenoid  cartilages  into  the  same  straight  line,  at 
the  same  time  depressing  them,  and  thus  to  close  the  Glottis.  This  muscle  is 
assisted  by  the  Arytenoideus  transversus,  which  connects  the  posterior  faces 
of  the  Arytenoid  cartilages,  and  which,  by  its  contraction,  will  draw  them  to- 
gether. By  the  conjoint  action,  therefore,  of  the  Crico-arytenoideus  lateralis, 
and  of  the  Arytenoideus  transversus,  the  whole  of  the  adjacent  faces  of  the 
Arytenoid  cartilages  will  be  pressed  together;  and  the  points  to  which  the 
vocal  ligaments  are  attached  will  be  depressed. — But  if  the  Arytenoideus  be 
put  in  action  in  conjunction  with  the  Crico-arytenoidei  postici,  the  tendency 
of  the  latter  to  separate  the  Arytenoid  cartilages  being  antagonized  by  the 
former,  its  backward  action  only  will  be  exerted ;  and  thus  it  may  be  caused 
to  aid  the  Crico-thyroideus  in  rendering  tense  the  vocal  ligaments.  This  action 
will  be  further  assisted  by  the  Sterno-thyroideus,  which  tends  to  depress  the 
Thyroid  cartilage,  by  pulling  from  a  fixed  point  below  ;*  and  the  Thyro-hyoi- 
deus  will  be  the  antagonist  of  this,  when  it  acts  from  a  fixed  point  above,  the 
Os  Hyoides  being  secured  by  the  opposing  contraction  of  several  other  mus- 
cles.— The  respective  actions  of  these  muscles  will  be  best  comprehended  by 
the  following  table. 

Govern  the  Pitch  of  the  Notes. 

^  CDenress  the  front  of  the  Thyroid  cartilage  on  the 

>  C  CRICO-THYROIDEI  |  ....  3  Cricoid,  and  stretch  the  vocal  ligaments;  assisted 
S^STERXO-IHYROIDEI  3  £  by  the  Arytenoideus  and  Crico-arytenoidei  postici. 

("Elevate  the  front  of  the  Thyroid  cartilage,  and  draw 
I  )  THTRO  HY™iOII)EI  }'")     il  towards  lhe  Arytenoids,  relaxing  the  vocal  liga- 

Govern  the  Aperture  of  the  Glottis. 
l> 
5.     CHICO-ARYTENOIDEI  POSTICI '.  . .  . .  Open  the  Glottis. 

§  C  CRICO-ABYTENOIDEI  LATEBALES?  .  .  C  Press  together  the  inner  edges  of  the  Ary- 
5T  £  ABYTENOIDECS  J  "  "  C  tenoid  cartilages,  and  close  the  Glottis. 

F 

404.  The  muscles  which  stretch  or  relax  the  Vocal  ligaments,  are  entirely 
concerned  in  the  production  of  Voice ;  those  which  govern  the  aperture  of  the 
Glottis  have  important  functions  in  connection  with  the  Respiratory  actions  in 
general,  and  stand  as  guards  (so  to  speak)  at  the  entrance  to  the  lungs.  Their 
separate  actions  are  easily  made  evident.  We  can  close  the  aperture  of  the 
Glottis,  by  an  exertion  of  the  will,  either  during  inspiration  or  expiration ;  and 
it  is  a  kind  of  spasmodic  movement  of  this  sort,  which  is  concerned  in  the  acts 
of  Coughing  and  Sneezing  (§  189),  as  well  as  in  the  more  prolonged  impedi- 
ments to  the  ingress  and  egress  of  air,  which  have  been  already  noticed  as 
resulting  from  disordered  states  of  the  Nervous  system  (§  300).  A  slight 
examination  of  the  recent  Larynx  is  sufficient  to  make  it  evident  that,  when 
once  the  borders  of  the  Rima  Glottidis  are  brought  together  by  muscular 
action,  the  effect  of  strong  aerial  pressure  on  either  side, — whether  produced 
by  an  expulsory  blast  from  below,  or  by  a  strong  inspiratory  effort,  occasioning 
a  partial  vacuum  below,  and  consequently  an  increased  pressure  above, — will 

*  This  is  not  usually  reckoned  as  one  of  the  principal  muscles  concerned  in  regulating 
the  voice  ;  but  that  it  is  so,  any  one  may  convince  himself  by  placing  his  finger  just  above 
the  sternum,  whilst  he  is  sounding  high  notes;  a  strong  feeling  of  muscular  tension  is 
then  at  once  perceived. 


THE  LARYNX,  AND  ITS  ACTIONS.  301 

P 

be  to  force  them  into  closer  apposition.  With  this  action,  th^u,  the  muscles 
which  regulate  the  tension  of  the  vocal  ligaments  have  nothing  to  do.  In  the 
ordinary  condition  of  rest,  it  seems  probable  that  the  Ary  enoid  cartilages  are 
considerably  separated  from  each  other ;  so  as  to  cause  a  wide  opening  to 
intervene  between  their  inner  faces,  and  between  the  vocal  ligaments,  through 
which  the  air  freely  passes ;  and  the  vocal  ligaments  are  at  the  same  time  in 
a  state  of  complete  relaxation.  In  order  to  produce  a  vocal  sound,  it  is  not 
sufficient  to  put  the  ligaments  into  a  state  of  tension ;  they  must  also  be  brought 
nearer  to  each  other.  That  the  aperture  of  the  Glottis  is  greatly  narrowed 
during  the  production  of  sounds,  is  easily  made  evident  to  one's  self,  by  com- 
paring the  time  occupied  by  an  ordinary  expiration  with  that  required  for  the 
passage  of  the  same  quantity  of  air  during  the  sustenance  of  a  vocal  tone. 
Further,  the  size  of  the  aperture  is  made  to  vary  in  accordance  with  the  note 
which  is  being  produced ;  of  this,  too,  any  one  may  convince  himself,  by  noting 
the  time  during  which  he  can  hold  out  a  low  and  a  high  note ;  from  which  it 
will  appear,  that  the  aperture  of  the  Glottis  is  so  much  narrowed  in  producing 
a  high  note,  as  to  permit  a  much  less  rapid  passage  of  air  than  is  allowed 
when  a  low  one  is  sounded.  This  adjustment  of  the  aperture  to  the  tension 
of  the  Vocal  Ligaments,  is  a  necessary  condition  for  the  production  of  a  clear 
and  definite  tone.  It  further  appears  that,  in  the  narrowing  of  the  Glottis 
which  is  requisite  to  bring  the  vocal  ligaments  into  the  necessary  approxima- 
tion, the  upper  points  of  the  Arytenoid  cartilages  are  caused  to  approximate, 
not  only  by  being  made  to  rotate  horizontally  towards  each  other,  but  also  by 
a  degree  of  elevation ;  so  that  the  inner  faces  of  the  Vocal  Ligaments  are 
brought  into  parallelism  with  each  other, — a  condition  which  may  be  ex- 
perimentally shown  to  be  necessary  for  their  being  thrown  into  sonorous 
vibration. 

405.  We  have  now  to  inquire  what  is  the  operation  of  the  Vocal  Ligaments 
in  the  production  of  sounds;  and  in  order  to  comprehend  this,  it  is  necessary 
to  advert  to  the  conditions  under  which  tones  are  produced,  by  instruments  of 
various  descriptions,  having  some  analogy  with  the  Larynx.  These  are  chiefly 
of  three  kinds, — strings,  flute-pipes,  and  reeds  or  tongues.  The  Vocal  Liga- 
ments were  long  ago  compared  by  Ferrein  to  vibrating  Strings ;  and  at  first 
sight  there  might  seem  a  considerable  analogy,  the  sounds  produced  by  both 
being  elevated  by  increased  tension.  This  resemblance  disappears,  however, 
on  more  accurate  comparison ;  for  it  may  be  easily  ascertained  by  experiment, 
that  no  string  so  short  as  the  vocal  ligaments  could  give  a  clear  tone  at  all  to 
be  compared  in  depth  with  that  of  the  lowest  notes  of  the  human  voice ;  and 
also,  that  the  scale  of  changes  produced  by  increased  tension  is  fundamentally 
different.  When  strings  of  the  same  length,  but  of  different  tension,  are  made 
the  subject  of  comparison,  it  is  found  that  the  number  of  vibrations  is  in  pro- 
portion to  the  square  roots  of  the  extending  forces.  Thus,  if  a  string  extended 
by  a  given  weight  produce  a  certain  note,  a  string  extended  by  four  times  that 
weight  will  give  a  note,  in  which  the  vibrations  are  twice  as  rapid, — and  this 
will  be  the  octave  of  the  other.  If  nine  times  the  original  weight  be  employed, 
the  vibrations  will  be  three  times  as  rapid  as  those  of  the  fundamental  note, 
producing  the  twelfth  above  it.  Now  by  fixing  the  larynx  in  such  a  manner 
that  the  vocal  ligaments  can  be  extended  by  a  known  weight,  Miiller  has 
ascertained  that  the  sounds  produced  by  a  variation  of  the  extending  force 
will  not  follow  the  same  ratio ;  and  therefore  the  condition  of  these  ligaments 
cannot  be  simply  that  of  vibrating  cords.  Further,  a  cord  of  certain  length, 
which  is  adapted  to  give  out  a  clear  and  distinct  note,  equal  in  depth  to  tfce 
lowest  of  the  human  voice,  may  be  made  by  increased  tension  to  produce  all 
the  superior  notes,  which,  in  stringed  instruments,  are  ordinarily  obtained  by 
26 


302  OF  THE  VOICE  AND  SPEECH. 

t 

shortening  the  strings.*  But  it  does  not  follow  that  a  short  string,  which, 
with  moderate  tension,  naturally  produces  a  high  note,  should  be  able,  by  a 
diminution  of  the  tension,  to  give  out  a  deep  one ;  for,  although  this  might  be 
theoretically  possible,  yet  it  cannot  be  accomplished  in  practice ;  since  the 
vibrations  become  irregular  on  account  of  the  diminished  elasticity .t  These 
considerations  are  in  themselves  sufficient  to  destroy  the  supposed  analogy; 
and  to  prove  that  the  Chordse  Vocales  cannot  be  reduced  to  the  same  category 
with  vibrating  strings. 

406.  The  next  kind  of  instrument,  with  which  some  analogy  might  be  sus- 
pected, is  the  Flute-pipe,  in  which  the  sound  is  produced  by  the  vibration  of 
an  elastic  column  of  air  contained  in  the  tube ;  and  the  pitch  of  the  note  is 
determined  almost  entirely  by  the  length  of  the  column,  although  slightly 
modified  by  its  diameter,  and  by  the  nature  of  the  embouchure  or  mouth  from 
which  it  issues.    This  is  exemplified  in  the  German  Flute,  and  in  the  English 
Flute  or  Flageolet ;  in  both  of  which  instruments,  the  acting  length  of  the 
pipe  is  determined,  by  the  interval  between  the  embouchure  and  the  nearest 
of  the  side  apertures ;  by  opening  or  closing  which,  therefore,  a  modification 
of  the  tone  is  produced.     In  the  Organ,  of  which  the  greater  number  of  pipes 
are  constructed  upon  this  plan,  there  is  a  distinct  pipe  for  every  note ;  and 
their  length  increases  in  a  regular  scale.     It  is,  in  fact,  with  flute-pipes  as 
with  strings, — that  a  diminution  in  length  causes  an  increase  in  the  number 
of  vibrations,  in  an  inverse  proportion ;  so  that  of  two  pipes,  one  half  being 
the  length  of  the  other,  the  shorter  will  give  a  tone  which  is  the  octave  above 
the  other,  the  vibrations  of  its  column  of- air  being  twice  as  rapid.     Now  there 
is  nothing  in  the  form  or  dimensions  of  the  column  of  air  between  the  larynx 
and  the  mouth,  which  can  be  conceived  to  render  it  at  all  capable  of  such 
vibrations  as  are  required  to  produce  the  tones  of  the  Human  voice  ;  though 
there  is  some  doubt  whether  it  is  not  the  agent  in  the  musical  tones  of  some 
Birds.     The  length  of  an  open  pipe  necessary  to  give  the  lowest  G  of  the 
ordinary  bass  voice,  is  nearly  six  feet;  and  the  conditions  necessary  to  produce 
the  higher  notes  from  it,  are  by  no  means  those  which  we  find  to  exist  in  the 
process  of  modulating  the  human  voice. 

407.  We  now  come  to  the  third  class  of  instruments,  in  which  sound  is  pro- 
duced by  the  vibration  of  Reeds  or  Tongues ;  these  may  either  possess  elasticity 
in  themselves,  or  be  made  by  elastic  tension.     The  reeds  of  the  Mouth-^Eoli- 
na,  Accordion,  Seraphine,  &c.,  are  examples  of  instruments  of  this  character, 
in  which  the  lamina  vibrates  freely  in  a  sort  of  frame  that  allows  the  air  to  pass 
out  on  all  sides  of  it  through  a  narrow  channel,  thus  increasing  the  strength 
of  the  blast ;  whilst  in  the  Hautboy,  Bassoon,  &c.,  and  in  Organ-pipes  of  similar 
construction,  the  reed  is  attached  to  one  end  of  a  pipe.     In  the  former  kind, 
the  sound  is  produced  by  the  vibration  of  the  tongue  alone,  and  is  regulated 
entirely  by  its  length  and  elasticity;  whilst  in  the  latter,  its  pitch  is  dependent 
upon  this  conjointly  with  the  length  of  the  tube,  the  column  of  air  contained 
in  which  is  thrown  into  simultaneous  vibration.     Some  interesting  researches 
on  the  effect  produced  on  the  pitch  of  a  sound  given  by  a  reed,  through  the 
union  of  it  with  a  tube,  have  been  made  by  M.  W.  Weber;  and,  as  they  are 
important  in  furnishing  data,  by  which  the  real  nature  of  the  vocal  organ 

*  Thus  in  the  Piano-forte,  where  there  are  strings  for  each  note,  a  gradual  shortening 
is  seen  from  the  lowest  to  the  highest;  and  in  the  Violin  the  change  of  tone  is  produced 
by  stopping  the  strings  with  the  finger,  so  as  to  diminish  their  acting  length. 

f  Thus  it  would  be  impossible  to  produce  good  Bass  notes  on  the  strings  of  a  Violin, 
by  diminishing  their  tension ;  the  length  afforded  by  the  Violoncello  or  Double  Bass  is 
requisite.  The  striking  difference  between  the  tone  of  the  Bass  strings  in  the  Grand 
Piano-forte  and  the  small  upright  Piccolo,  is  another  exemplification  of  the  same  princi- 
ple ;  being  chiefly  due  to  the  length  and  tension  of  the  former,  as  contrasted  with  the 
shortness  and  slackness  of  the  latter. 


THE  LARYNX,  AND  ITS  ACTIONS. 


303 


may  be  determined,  their  chief  results  will  be  here  given. — I.  The  pitch 
of  a  reed  may  be  lowered,  but  cannot  be  raised,  by  joining  it  to  a  tube. 
II.  The  sinking  of  the  pitch  of  the  reed  thus  produced,  is  at  the  utmost  not 
more  than  an  octave.  III.  The  fundamental  note  of  the  reed  thus  lowered, 
may  be  raised  again  to  its  original  pitch,  by  a  further  lengthening  of  the 
tube ;  and  by  a  further  increase,  is  again  lowered.  IV.  The  length  of 
tube  necessary  to  lower  the  pitch  of  the  instrument  to  any  given  point, 
depends  on  the  relation  which  exists  between  the  frequency  of  the  vibra- 
tions of  the  tongue  of  the  reed,  and  those  of  the  column  of  air  in  the  tube, 
each  taken  separately. — From  these  data,  and  from  those  of  the  preceding 
paragraph,  it  follows  that,  if  a  wind-instrument  can,  by  the  prolongation  of  its 
tube,  be  made  to  yield  tones  of  any  depth  in  proportion  to  the  length  of  the 
tube,  it  must  be  regarded  as  a  flute-pipe  ;  whilst,  if  its  pitch  can  only  be  lowered 
an  octave  or  less  (the  embouchure  remaining  the  same)  by  lengthening  the 
tube,  we  may  be  certain  that  it  is  a  reed  instrument.  The  latter  proves  to 
be  the  case  in  regard  to  the  Larynx. 

408.  Between  the  action  of  the  Chordae  Vocales,  however,  and  that  of  an 
ordinary  Reed,  there  appears  to  be  a  marked  difference  ;  but  this  difference  is 
really  by  no  means  considerable.  In  a  reed,  elasticity  is  a  property  of  the 
tongue  itself,  when  fixed  at  one  end,  the  other  vibrating  freely  ;  but  by  a  mem- 
branous lima,  fixed  in  the  same  manner,  no  tone  would  be  produced.  If  such 
a  lamina,  however,  be  made  elastic  by  a  moderate  degree  of  tension,  and  be 
fixed  in  such  a  manner  as  to  be  advantageously  acted  on  by  a  current  of  air, 
it  will  give  a  distinct  tone.  It  is  observed  by  Miiller,  that  membranous  tongues 
made  elastic  by  tension,  may  have  either  of  three  different  forms.  I.  That  of 
a  band  extended  by  a  cord,  and  included  between  two  firm  plates,  so  that  there 
is  a  cleft  for  the  passage  of  air  on  each  side  of  the  tongue.  II.  The  elastic 
membrane  may  be  stretched  over  the  half  or  any  portion  of  the  end  of  a  short 
tube,  the  other  part  being  occupied  by  a  solid  plate,  between  which  and  the 
elastic  membrane  a  narrow  fissure  is  left.  III.  Two  elastic  membranes  may 
be  extended  across  the  mouth  of  a  short  tube,  each  covering  a  portion  of  the 
opening,  and  having  a  chink  left  open  between  them. — This  last  is  evidently 
the  form  most  allied  to  the  Human  Glottis;  but  it  may  be  made  to  approximate 
still  more  closely,  by  prolonging  the 


membranes  in  a  direction  parallel  to 
that  of  the  current  of  air,  so  that  not 
merely  their  edges,  but  their  whole 
planes  shall  be  thrown  into  vibration. 
Upon  this  principle,  a  kind  of  arti- 
ficial Glottis  has  been  constructed  by 
Mr.  Willis ;  the  conditions  of  action 
and  the  effects  of  which  are  so  nearly 
allied  to  that  of  the  real  instrument, 
that  the  similar  character  of  the  two 
can  scarcely  be  doubted.  The  fol- 
lowing is  his  description  of  it.  "  Let 
a  wooden  pipe  be  prepared  of  the 
form  of  Fig.  78,  having  a  foot  C  like 
that  of  an  organ-pipe,  and  an  upper 
opening,  long  and  narrow,  as  at  B, 
with  a  point  A  rising  at  one  end  of 
it.  If  a  piece  of  leather,  or  still 
better,  of  sheet  India  Rubber,  be 
doubled  round  this  point,  and  se- 
cured by  being  bound  round  the 


Fig.  78. 


Fig.  79. 


Artificial  Larynx.    After  Willis. 


304  OF  THE  VOICE  AND  SPEECH. 

pipe  at  D  with  strong  thread,  as  in  Fig.  79,  it  will  give  us  an  artificial  glottis 
with  its  upper  edges  G  H,  which  may  be  made  to  vibrate  or  not,  at  pleasure, 
by  inclining  the  planes  of  the  edges.  A  couple  of  pieces  of  cork  may  be 
glued  to  the  corners,  to  make  them  more  manageable.  From  this  machine, 
various  notes  may  be  obtained  by  stretching  the  edges  in  the  direction  of  their 
length  G  H ;  the  notes  rising  in  pitch  with  the  increased  tension,  although  the 
length  of  the  vibrating  edge  is  increased.  It  is  true  that  a  scale  of  notes  equal 
in  extent  to  that  of  the  human  voice  cannot  be  obtained  from  edges  of  leather  ; 
but  this  scale  is  much  greater  in  India  Rubber  than  in  leather ;  and  the  elas- 
ticity of  them  both  is  so  much  inferior  to  that  of  the  vocal  ligaments,  that  we 
may  readily  infer  that  the  great  scale  of  the  latter  is  due  to  its  greater  elastic 
powers."  By  other  experimenters,  the  tissue  forming  the  middle  coat  of  the 
arteries  has  been  used  for  this  purpose,  in  the  moist  state,  with  great  success ; 
with  this,  the  tissue  of  the  vocal  ligaments  is  nearly  identical.  It  is  worthy  of 
remark,  that  in  all  such  experiments,  it  is  found  that  the  two  membranes  may 
be  thrown  into  vibration,  when  inclined  towards  each  other  in  various  degrees, 
or  even  when  they  are  in  the  same  plane,  and  their  edges  only  approximate ; 
but  that  the  least  inclination  from  each  other  (which  is  the  position  the  vocal 
ligaments  have  during  the  ordinary  state  of  the  glottis,  §  404),  completely  pre- 
vents any  sonorous  vibrations  from  being  produced. 

409.  The  pitch  of  the  note  produced  by  membranous  tongues,  may  be 
affected  in  several  ways.    Thus,  an  increase  in  the  strength  of  the  blast,  which 
has  little  influence  on  metallic  reeds,  raises  their  pitch  very  considerably ;  and 
in  this  manner  the  note  of  a  membranous  reed  may  be  raised  by  semitones  to 
as  much  as  a  fifth  above  the  fundamental.     The  addition  of  a  pipe  has  nearly 
the  same  effect  on  their  pitch  as  on  that  of  metallic  reeds  ;  but  it  cannot  easily 
be  determined  with  the  same  precision.     The  effect  of  the  junction  of  a  pipe 
with  a  double  membranous  tongue,  is  well  shown  in  the  Trumpet,  Horn,  and 
other  instruments,  which  require  the  vibration  of  the  lips,  as  w^ell  as  a  blast 
of  air,  for  the  production  of  their  sound,  having  no  reed  of  their  own.     By 
some,  these  instruments  have  been  classed  with  Flute-pipes ;  but  the  condi- 
tions of  their  action  are  entirely  different.     The  mouth-piece  of  the  horn  or 
trumpet  is  incapable  of  yielding  any  tone,  when  a  current  of  air  is  merely 
blown  through  it ;  and  the  lips  are  necessary  to  convert  it  into  a  musical  reed, 
being  rendered  tense  by  the  contraction  of  their  sphincter,  partly  antagonized 
by  the  slightly  dilating  action  of  other  muscles.     The  variation  of  the  tension 
of  the  lips  is  effected  by  muscular  effort ;  and  several  different  notes  may  be 
produced  with  a  pipe  of  the  same  length ;  but  there  is  a  certain  length  of  the 
column  of  air,  which  is  the  one  best  adapted  for  each  tone  ;  and  different  in- 
struments possess  various  contrivances  for  changing  this.    It  has  been  recently 
ascertained,  that  the  length  of  the  pipe  prefixed  to  the  reed  has  also  a  consider- 
able influence  on  its  tone,  rendering  it  deeper  in  proportion  as  it  is  prolonged, 
down  to  nearly  the  octave  of  the  fundamental  note ;  but  the  pitch  then  sud- 
denly rises  again,  as  in  the  case  of  the  tube  placed  beyond  the  reed.     The 
researches  of  Miiller,  however,  have  not  succeeded  in  establishing  any  very 
definite  relation  between  the  length  of  the  two  tubes,  in  regard  to  their  influence 
on  the  pitch  of  the  reed  placed  between  them. 

410.  From  the  foregoing  statements  it  appears,  that  the  true  theory  of  the 
Voice  may  now  be  considered  as  well  established,  in  regard  to  this  essential 
particular, — that  the  sound  is  the  result  of  the  vibrations  of  the  vocal  ligaments, 
which  take  place  according  to   the  same  laws  with  those  of  metallic  or  other 
elastic  tongues ;  and  that  the  pitch  of  the  notes  is  chiefly  governed  by  the  ten- 
sion of  these  laminae.     With  respect,  however,  to  the  modifications  of  these 
tones,  induced  by  the  shape  of  the  air-passages,  both  above  and  below  the 
larynx,  by  the  force  of  the  blast,  and  by  other  concurrent  circumstances,  little 


THE  LARYNX,  AND  ITS  ACTIONS.  305 

is  certainly  known.  Hence  it  is,  that  on  the  theory  of  the  production  of  what 
are  called  falsetto  notes,  there  is  much  difference  of  opinion  amongst  Physio- 
logists. Some  have  contended,  that  these  tones  are  produced  by  the  vibration 
of  the  vocal  ligaments  along  only  a  part  of  their  length ;  but  this  is  certainly 
untrue.  By  Muller  it  is  believed,  that  in  the  falsetto  notes  merely  the  thin 
border  of  the  glottis  vibrates,  so  that  the  fissure  remains  distinctly  visible; 
whilst  in  the  production  of  the  ordinary  vocal  tones,  the  whole  breadth  of  the 
vocal  ligaments  is  thrown  into  strong  vibrations,  which  traverse  a  wider  sphere, 
so  that  a  confused  motion  is  seen  in  the  lips  of  the  glottis,  rendering  its  fissure 
obscure.  That  the  tension  of  the  vocal  cords  is  not  diminished  (as  it  ought 
to  be  if  only  a  part  of  their  length  were  being  used),  but  is  progressively  in- 
creased, as  we  pass  from  the  ordinary  to  the  falsetto  scale,  any  one  may  convince 
himself,  by  placing  his  finger  on  the  interval  between  the  thyroid  and  cricoid 
cartilages,  as  formerly  described  (§  402).* — A  very  important  adjunct  to  the 
production  of  the  higher  notes,  has  been  pointed  out  by  Muller,  as  being  afforded 
by  the  modification  in  the  space  included  between  the  two  sides  of  the  thyroid 
cartilage,  which  is  effected  by  the  thyro-arytenoidei.  He  had  experimentally 
ascertained,  that  the  introduction  of  a  hollow  plug  into  the  upper  end  of  the 
pipe  beneath  his  artificial  larynx  (and  therefore  just  below  the  reed),  by  dimin- 
ishing its  aperture,  produced  a  considerable  elevation  of  the  tone.  The  action 
may  be  imitated  in  the  human  larynx,  when  made  the  subject  of  experiment, 
by  compressing  the  thyroid  cartilage  laterally  ;  and  in  this  manner,  the  natural 
voice  could  be  made  to  extend  through  a  range  that  could  otherwise  be  only 
reached  by  a  falsetto. 

411.  The  strength  of  the  tone  produced  in  the  larynx  is  much  increased 
by  the  resonance  of  the  elastic  tissue,  which  it  contains  in  various  other 
parts;  but  still  more,  perhaps,  by  that  produced  by  the  air  in  the  trachea, 
bronchi,  and  pulmonary  cells.  This  comes  to  be  of  great  importance  in  the 
phenomena  of  auscultation.  The  aerial  resonance  is  loudest,  where  any  large 
body  of  air  is  collected  together,  as  in  the  trachea,  the  larger  bronchi,  an 
emphysematous  dilatation,  or  a  cavity  resulting  from  tubercular  softening.  On 
the  other  hand,  solidification  of  the  pulmonary  tissue  will  produce  a  resonance 
of  a  somewhat  different  kind.  The  influence  of  the  prefixed  and  superadded 
tubes  in  modifying  the  tones  produced  by  the  Human  larynx,  has  been  found 
by  Prof.  Muller  not  to  be  at  all  comparable  to  that  which  they  exercised  over 
the  artificial  larynx;  the  reason  of  which  difference  does  not  seem  very 
apparent.  It  appears,  however,  that  there  is  a  certain  length  of  the  prefixed 
tube,  as  there  is  a  certain  distance  of  the  vibrating  laminae,  and  a  certain 
length  or  form  of  the  tube  above,  which  is  most  favourable  to  the  production 
of  each  note ;  and  the  downward  movement  of  the  whole  vocal  organ,  which 
takes  place  when  we  are  sounding  deep  notes,  and  its  rise  during  the  eleva- 
tion of  the  tones,  have  been  supposed  to  have  the  purpose  of  making  this 
adjustment  in  the  length  of  the  trachea;  but  this  requires  the  supposition  that 
the  real  length  of  the  trachea  is  shortened  whilst  it  appears  extended,  for 
which  there  seems  no  foundation.  It  is  considered  by  Mr.  Wheatstone,  that 
the  column  of  air  in  the  trachea  may  divide  itself  into  harmonic  lengths,  and 
may  produce  a  reciprocation  of  the  tone  given  by  the  vocal  ligaments  (§  353) ; 
and  in  this  manner  he  considers  that  the  falsetto  notes  are  to  be  explained.  It 

*  That  the  falsetto  voice  differs  in  some  essential  particular  from  the  natural,  is  evident 
from  this, — that  many  persons  who  possess  a  considerable  range  of  both,  are  yet  unable 
to  unite  them,  so  as  to  sing  through  the  whole  scale  without  a  marked  interruption.  Thus 
a  gentleman  of  the  Author's  acquaintance  has  a  bass  voice,  ranging  from  the  lowest  E  oi 
the  Square  Piano  to  the  second  D  above;  and  a  falsetto  ranging  from  the  A  below  this  to 
the  E  of  the  octave  above,  so  as  to  give  a  compass  of  three  octaves  on  the  whole ;  yet 
the  two  registers  cannot  be  smoothly  blended. 

26* 


306  OF  THE  VOICE  AND  SPEECH. 

may  be  added,  that  the  partial  closing  of  the  epiglottis  seems  to  assist  in  the 
production  of  deep  notes,  just  as  the  partial  covering  of  the  top  of  a  short  pipe 
fixed  to  a  reed  will  lower  its  tone ;  and  that  something  of  this  kind  takes 
place  during  natural  vocalization,  would  appear,  from  the  retraction  and 
depression  of  the  tongue  which  accompany  the  lowering  of  the  front  of  the 
head,  when  the  very  lowest  notes  are  being  sounded.  The  arches  of  the 
palate  and  uvula  become  contracted  during  the  formation  of  the  higher  tones; 
but  no  difference  can  be  perceived  in  their  state,  whether  these  tones  be  falsetto 
or  not ;  hence  it  would  appear,  that  they  have  no  concern  in  this  peculiarity ; 
and  the  purpose  of  their  increased  tension  is  probably  to  maintain  their  power 
of  resonance.  The  experiments  of  Savart  have  shown  that  a  cavity  which 
only  responds  to  a  shrill  note  when  its  walls  are  firm  and  dry,  may  be  made 
to  afford  a  great  variety  of  lower  tones,  when  its  walls  are  moistened  and 
relaxed  in  various  degrees.  This  observation  may  probably  be  applied  also 
to  the  trachea. 

412.  These  and  numerous  other  muscular  actions  which  are  employed  in 
the  production  and  regulation  of  the  voice,  are  effected  by  an  impulse  which 
can  scarcely  be  termed  Voluntary,  and  the  nature  of  which  is  a  curious  sub- 
ject for  inquiry.  It  may  be  safely  affirmed  that  the  production  of  sounds  is  in 
itself  an  Instinctive  action ;  although  the  combination  of  these,  whether  into 
music  or  articulate  language,  is  a  matter  of  acquirement.  Now  it  might  be 
supposed  that  the  Will  has  sufficient  power  over  the  vocal  muscles,  to  put 
them  into  any  state  requisite  for  its  purposes,  without  any  further  condition  ; 
but  a  little  self-experiment  will  prove  that  this  is  not  the  case.  No  definite 
tone  can  be  produced  by  a  Voluntary  effort,  unless  that  tone  be  present  to  the 
mind,  during  however  momentary  an  interval,  either  as  immediately  conveyed 
to  it  by  an  act  of  Sensation,  recalled  by  an  act  of  Conception,  or  anticipated  by 
an  effort  of  the  Imagination.  When  thus  present,  the  Will  can  enable  the 
muscles  to  assume  the  condition  requisite  to  produce  it ;  but  under  no  other 
circumstances  does  this  happen,  except  by  a  particular  mode  of  discipline 
presently  to  be  adverted  to.  The  action  itself,  therefore,  must  be  reduced  to 
the  class  of  consensual  movements ;  and  we  must  suppose  that  the  Will  is 
exercised  in  preparing  the  conditions  requisite  for  it,  rather  than  in  directly 
exciting  it. — That  those  who  are  unfortunately  labouring  under  congenital 
deafness,  are  thence  debarred  from  learning  the  use  of  Voice  in  the  ordinary 
manner,  is  well  known ;  the  consensual  action  cannot  be  excited,  either  through 
sensations  of  the  present,  or  conceptions  of  the  past ;  and  the  imagination  is 
entirely  destitute  of  power  to  suggest  that  which  has  been  in  no  shape  expe- 
rienced. But  such  persons  may  be  taught  to  speak  in  an  imperfect  manner, 
by  causing  them  to  imitate  particular  muscular  movements,  which  they  may 
be  made  to  see ;  and  it  is  evident,  that  they  must  be  guided  in  the  imitation 
and  ordinary  performance  of  those  movements,  by  the  common  muscular  sen- 
sations which  accompany  them,  and  not  by  the  sensations  conveyed  through 
the  Auditory  nerve,  which  are  ordinarily  by  far  the  most  precise  guides. 
Many  instances,  indeed,  are  on  record,  in  which  persons  entirely  deaf  were 
enabled  to  carry  on  a  conversation  in  the  regular  way ;  judging  of  what  was 
said,  by  the  movements  of  the  lips  and  tongue,  which  they  had  learned  to 
connect  with  particular  syllables ;  and  regulating  their  own  voices  in  reply, 
by  their  voluntary  power,  guided  by  muscular  sensation.* 

[In  the  foregoing  account  of  the  Physiology  of  Voice,  the  Author  has  been  chiefly 
guided  by  the  excellent  paper  by  Mr.  Willis  in  "the  transactions  of  the  Cambridge  Philo- 
sophical Society,  vol.  iv.,  and  by  the  elaborate  investigations  of  Mailer  and  his  coadju- 
tors, as  detailed  in  the  Fourth  Book  of  his  Physiology.] 

*  See  Johnstone  on  Sensation,  p.  128. 


OF  ARTICULATE  SOUNDS.  307 


II.  Of  Articulate  Sounds. 

413.  The  larynx,  as  now  described,  is  capable  of  producing  those  tones  of 
which  Voice   fundamentally  consists,  and  the   sequence  of  which  becomes 
Music  :  but  Speech  consists  in  the  modification  of  the  laryngeal  tones,  by  other 
organs  intervening  between  the  Glottis  and  the  Os  Externum  ;  so  as  to  produce 
those  articulate  sounds  of  which  Language  is  formed.     It  cannot  be  questioned 
that  Music  has  its  language  ;  and  that  it  is  susceptible  of  expressing  the 
emotional  states  of  the  mind,  among  those  at  least  who  have  been  accustomed 
to  associate  these  with  its  varied  modes,  to  even  a  higher  degree  than  articu- 
late speech.     But  it  is  incapable  of  addressing  the  intellect,  by  conveying 
definite  ideas  of  objects,  properties,  actions,  &c.,  in  any  other  way  than  by  a 
kind  of  imitation,  which  may  be  compared  to  the  signs  used  in  hieroglyphic 
writing.     These  ideas  it  is  the  peculiar  province  of  articulate  language  to 
convey ;  and  we  find  that  the  vocal  organ  is  adapted  to  form  a  large  number 
of  simple  sounds,  which  may  be  readily  combined  into  groups,  forming  words. 
The  number  of  combinations  which  can  be  thus  produced  is  so  inexhaustible, 
that  every  language  has  its  own  peculiar  series ;  no  difficulty  being  found  in 
forming  new  ones  to  express  new  ideas.  There  is  considerable  diversity  in  differ- 
ent languages,  even  with  regard  to  the  use  of  the  simplest  of  these  combinations ; 
some  of  them  are  more  easy  of  formation  than  others,  and  these  accordingly 
enter  into  the  composition  of  all  languages  ;  whilst  of  the  more  difficult  ones, 
some  are  employed  in  one  language,  some  in  another, — no  one  language  pos- 
sessing them  all.    Without  entering  into  any  detailed  account  of  the  mechanism 
required  to  produce  each  of  these  simple  sounds,  a  few  general  considerations 
will  be  offered  in  'regard  to  the  classification  of  them ;  and  the  peculiar  defect 
of  Articulation,  termed  Stammering,  will  be  briefly  treated  of. 

414.  Vocal  sounds  are  divided  into  Vowels  and  Consonants ;  and  the  dis- 
tinctive characters  of  these  are  usually  considered  to  be,  that  the  Vowels  are 
produced  by  the  Voice  alone,  whilst  the  sound  of  the  Consonants  is  formed  by 
some  kind  of  interruption  to  the  voice,  so  that  they  cannot  be  properly  ex- 
pressed, unless  conjoined  with  a  vowel.     The  distinction  may  be  more  cor- 
rectly laid  down,  however,  in  this  manner ;  the  Vowel  sounds  are  continuous 
tones,  modified  by  the  form  of  the  aperture  through  which  they  pass  out ; 
whilst  in  sounding  Consonants,  the  breath  suffers  a  more  or  less  complete  in- 
terruption in  its  passage  through  parts  anterior  to  the  larynx.     Hence  the 
really  simple  Vowel  sounds  are  capable  of  prolongation  during  any  time  that 
the  breath  can  sustain  them ;  this  is  not  the  case,  however,  with  the  real 
Diphthongal  sounds  (of  which  it  will  presently  appear  that  the  English  i  is 
one) ;  whilst  it  is  true  of  some  Consonants.     It  seems  to  have  been  forgotten 
by  many  of  those  who  have  written  upon  this  subject,  that  the  laryngeal  voice 
is  not  essential  to  the  formation  of  either  vowels  or  consonants ;  for  all  may  be 
sounded  in  a  whisper.     It  is  very  evident,  therefore,  that  the  larynx  is  not 
primarily  concerned  in  their  production ;  and  this  has  been  fully  established 
by  the  following  experiment.     A  flexible  tube- was  introduced  by  M.  Deleau 
through  his  nostril  into  the  pharynx,  and  air  was  impelled  by  it  into  the 
fauces ;  then,  closing  the  larynx,  he  threw  the  fauces  into  the  different  posi- 
tions requisite  for  producing  articulate  sounds,  when  the  air  impelled  through 
the  tube  became  an  audible  whisper.     The  experiment  was  repeated,  with 
this  variation,— -that  laryngeal  sound^  were  allowed  to  pass  into  the  fauces ; 
and  each  articulated  letter  was  then  heard  double,  in  a  proper  voice  and  in  a 
whisper. 

415.  That  the  Vowels  are  produced  by  simple  modifications  in  the  form  of 
the  external  passages,  is  easily  proved,  both  by  observation  and  by  imitative 


308  OF  THE  VOICE  AND  SPEECH. 

experiment.  When  the  mouth  is  opened  wide,  the  tongue  depressed,  and  the 
velum  palati  elevated,  so  as  to  give  the  freest  possible  exit  to  the  voice,  the 
vowel  a  in  its  broadest  form  (as  in  ab)  is  sounded.*  On  the  other  hand,  if 
the  oral  aperture  be  contracted,  the  tongue  being  still  depressed,  the  sound  oo 
(the  continental  u)  is  produced.  If  attention  be  paid  to  the  state  of  the  buccal 
cavity,  during  the  pronunciation  of  the  different  vowel  sounds,  it  will  be  found 
to  undergo  a  great  variety  of  modifications,  arising  from  varieties  of  position 
of  the  tono-ue,  the  cheeks,  the  lips,  and  velum  palati.  The  position  of  the 
tongue  is,  indeed,  one  of  the  primary  conditions  of  the  variation  of  the  sound ; 
for  it  may  be  easily  ascertained  that,  by  peculiar  inflexions  of  this  organ,  a 
great  diversity  of  vowel  sounds  may  be  produced,  the  other  parts  remaining 
the  same.  Still  there  is  a  certain  position  of  all  the  parts,  which  is  most 
favourable  to  the  formation  of  each  of  these  sounds;  but  this  could  not  be 
expressed  without  a  lengthened  description.  The  following  table,  slightly 
altered  from  that  of  Kempelen,  expresses  the  relative  dimensions  of  the  buccal 
cavity  and  of  the  oral  orifice,  for  some  of  the  principal  of  these ;  the  number 
5  expressing  the  largest  size,  and  the  others  in  like  proportion : — 

Vowel.  Sound.  Size  of  oral  opening.  Size  of  buccal  cavity. 

a  as  in  ah  5  5 

a  as  in  name  4  2 

e  as  in  theme  '3  1 

o  as  in  cold  2  4 

oo  as  in  cool  1  5 

These  are  the  sounds  of  the  five  vowels,  a,  e,  i,  o,  u,  in  most  Continental  lan- 
guages ;  and  it  cannot  but  be  admitted  that  the  arrangement  is  a  much  more 
natural  one  than  that  of  our  own  vowel  series.  The  English  a  has  three 
distinct  sounds  capable  of  prolongation  ;t — the  true  broad  a  of  ah,  slightly 
modified  in/«r  ;  the  a  of  fate,  corresponding  to  the  e  of  French ;  and  the  a  of 
fall,  which  should  be  really  represented  by  au.  This  last  is  a  simple  sound 
though  commonly  reckoned  as  a  diphthong.  In  Kempelen's  scale,  the  oral 
orifice  required  to  produce  it  would  be  about  3,  and  the  size  of  the  buccal 
cavity  4.J  On  the  other  hand,  the  sound  of  the  English  i  cannot,  like  that  of 
a  true  vowel,  be  prolonged  ad  libitum;  it  is  in  fact  a  sort  of  Diphthong,  result- 
ing from  the  transition  from  a  peculiar  indefinite  murmur  to  the  sound  of  e, 
which  takes  its  place  when  we  attempt  to  continue  it.  The  sound  oy  or  oi, 
as  in  oil,  is  a  good  example  of  the  true  diphthong ;  being  produced  by  the 
transition  from  au  to  e.  In  the  same  manner,  the  diphthong  ou,  which  is  the 
same  with  ow  in  owl,  is  produced  in  the  rapid  transition  from  the  broad  a  of 
ah,  to  the  oo  of  cool. — Much  discussion  has  taken  place  as  to  the  true  charac- 
ter of  y,  when  it  commences  a  word,  as  in  yet,  yawl,  &c. ;  some  having  main- 
tained that  it  is  a  consonant,  (for  the  very  unsatisfactory  reason,  that  we  are  in 
the  habit  of  employing  a  rather  than  an,  when  we  desire  to  prefix  the  indefi- 

*  This  sound  of  the  vowel  a  is  scarcely  used  in  our  language,  though  very  common 
in  most  of  the  continental  tongues;  the  nearest  approach  to  it  in  the  English  is  the  a  in 
far :  but  this  is  a  very  perceptible  modification,  tending  towards  au. 

j-  The  short  vowel  sounds,  as  a  in  fat,  e  in  met,  o  in  pot,  &c.,  are  not  capable  of  pro- 
longation. 

+  The  mode  of  making  a  determination  of  this  kind  may  here  be  given,  for  the  sake  of 
example.  If  the  broad  a  be  sounded,  the  mou.th  and  fauces  being  opened  wide,  and  we 
contract  the  oral  orifice  by  degrees,  at  the  same  time  slightly  elevating  the  point  of  the 
tongue,  we  gradually  come  to  the  sound  of  «u;  by  still  further  contracting  the  orifice, 
and  again  depressing  the  tongue,  \ve  form  oo.  On  the  other  hand,  in  sounding  e,  the 
tongue  is  raised  nearly  to  the  roof  of  the  mouth;  if  it  be  depressed,  without  the  position 
of  the  lips  being  altered,  au  is  given. 


OF  ARTICULATE  SOUNDS.  309 

nite  article  to  such  words,)  whilst  others  regard  it  as  a  peculiar  vowel.  A 
slight  attention  to  the  position  of  the  vocal  organs  during  its  pronunciation, 
makes  it  very  clear,  that  its  sound  in  such  words  really  corresponds  with  that 
of  the  long  (English)  e ;  the  pronunciation  of  the  word  yawl  being  the  same 
as  that  of  eaul,  when  the  first  sound  is  not  prolonged,  but  rapidly  transformed 
into  the  second.— The  sound  of  the  letter  w,  moreover,  is  really  of  the  vowel 
character,  being  formed  in  the  rapid  transition  from  oo  to  the  succeeding 
vowel;  thus  wall  might  be  spelt  ooall.  Many  similar  difficulties  might  be 
removed,  and  the  conformity  between  spoken  and  written  language  might  be 
greatly  increased  (so  as  to  render  far  more  easy  the  acquirement  of  the  former 
from  the  latter),  by  due  attention  to  the  state  of  the  vocal  organs  in  the  pro- 
duction of  the  simple  sounds. 

416.  It  is  not  very  difficult  to  produce  a  tolerably  good  artificial  imitation 
of  the  Vowel  sounds.     This  was  accomplished  by  Kempelen,  by  means  of  an 
India-rubber  ball,  with  an  orifice  at  each  end,  of  which  the  lower  one  was 
attached  to  a  reed;  by  modifying  the  form  of  the  ball,  the  different  vowels 
could  be  sounded  during  the  action  of  the  reed.     He  also  employed  a  short 
funnel-like  tube,  and  obtained  the  different  sounds  by  covering  its  wide  open- 
ing to  a  greater  or  less  extent.     This  last  experiment  has  been  repeated  by 
Mr.  Willis ;  who  has  also  found  that  the  vowel  sounds  might  be  imitated,  by 
drawing  out  a  long  straight  tube  from  the  reed.     In  this  experiment  he  arrived 
at  a  curious  result:— with  a  tube  of  a  certain  length,  the  series  of  vowels, 
i,  e,  a,  0,  u,  was  obtained,  by  gradually  drawing  it  out;  but,  if  the  length  was 
increased  to  a  certain  point,  a  further  gradual  increase  would  produce  the 
same  sequence  in  an  inverted  order,  u,  o,  «,  e,  i;  a  still  further  increase  would 
produce  a  return  to  the  first  scale,  and  so  on.     When  the  pitch  of  the  reed 
was  high,  and  the  pipe  short,  it  was  found  that  the  vowels  o  and  u  could  not 
be  distinctly  formed, — the  proper  tone  being  injured  by  the  elongation  of  the 
pipe  necessary  to  produce  them ;  and  this,  Mr.  Willis  remarks,  is  exactly  the 
case  with  the  Human  voice,  most  singers  being  unable  to  pronounce  u  and  o 
upon  their  highest  notes. 

417.  The  most  natural  primary  division  of  the  Consonants  is  into  those 
which  require  a  total  stoppage  of  the  breath  at  the  moment  previous  to  their 
being  pronounced,  and  which,  therefore,  cannot  be  prolonged ;  and  those  in 
pronouncing  which  the  interruption  is  partial,  and  which  can,  like  the  vowel 
sounds,  be  prolonged  ad  libitum.     The  former  have  received  the  designation 
of  explosive;  and  the  latter  of  continuous. — In  pronouncing  the  explosive  con- 
sonants, the  posterior  nares  are  completely  closed,  so  that  the  exit  of  air  through 
the  nose  is  altogether  prevented ;  and  the  current  may  be  checked  in  the 
mouth  in  three  ways, — by  the  approximation  of  the  lips, — by  the  approxima- 
tion of  the  point  of  the  tongue  to  the  front  of  the  palate, — and  by  the  approxi- 
mation of  the  middle  of  the  tongue  to  the  arch  of  the  palate.     In  the  first  of 
these  modes,  we  pronounce  the  letters  b,  and  p;  in  the  second,  </,  and  t;  in 
the  third,  the  hard  g,  and  k.     The  difference  between  &,  </,  and  g,  on  the  one 
hand,  and  jo,  £,  and  k,*  on  the  other,  seems  to  depend  on  this ; — that  in  the 
former  group  the  approximating  surfaces  are  larger,  and  the  breath  is  sent 
through  them  more  strongly  at  the  moment  of  opening,  than  in  the  latter.— 
The  continuous  consonants  may  be  again  subdivided,  according  to  the  degree 
of  freedom  with  which  the  air  is  allowed  to  make  its  exit,  and  the  compression 
which  it  consequently  experiences.      1.    The  first  class  includes  those  in 
which  no  passage  of  air  takes  place  through  the  nose,  and  in  which  the  parts 
of  the  mouth  that  produce  the  sound  are  nearly  approximated  together,  so  that 

*  For  the  sake  of  proper  comparison,  this  letter  should  be  sounded  not  as  kay  but 
as  key. 


310  OF  THE  VOICE  AND  SPEECH. 

the  compression  is  considerable.  This  is  the  case  with  v  and  /,  which  are 
produced  by  approximating  the  upper  incisors  to  the  lower  lip ;  and  which 
stand  in  nearly  the  same  relation  to  each  other  as  that  which  exists  between 
d  and  £,  or  b  and  p.  The  sibilant  sounds,  z  and  s,  stand  in  nearly  the  same 
relation  to  each  other ;  they  are  produced  by  the  passage  of  air  between  the 
point  of  the  tongue  and  the  front  of  the  palate,  the  teeth  being  at  the  same 
time  nearly  closed.  The  simple  sound  sh  is  formed  by  narrowing  the  channel 
between  the  dorsum  of  the  tongue  and  the  palate ;  the  former  being  elevated 
towards  the  latter,  through  a  considerable  part  of  its  length.  If,  in  sounding 
s,  we  raise  the  point  of  the  tongue  a  very  little,  so  as  to  touch  the  palate,  the 
sound  of  t  is  evolved ;  and  in  the  same  manner  d  is  produced  from  z.  This 
class  also  includes  the  th;  which,  being  a  perfectly  simple  sound,  ought  to  be 
expressed  by  a  single  letter,  as  in  Greek ;  instead  of  by  two,  of  which  the 
combination  does  not  really  produce  any  thing  like  it.  For  producing  this 
sound,  the  point  of  the  tongue  is  applied  to  the  back  of  the  incisors,  or  to  the 
front  of  the  palate,  as  in  sounding  t;*  but,  whilst  there  is  complete  contact  of 
the  tip,  the  air  is  allowed  to  pass  out  around  it.  2.  In  the  second  class  of 
continuous  consonants,  including  the  letters  m,  n,  /,  and  r,  the  nostrils  are  not 
closed;  and  the  air  thus  undergoes  very  little  compression,  even  though  the 
passage  of  air  through  the  oral  cavity  is  almost  or  completely  checked.  In 
pronouncing  m  and  n,  the  breath  passes  through  the  nose  alone ;  and  the  dif- 
ference of  the  sound  of  these  two  letters,  must  be  due  to  the  variation  in  the 
form  of  the  cavity  of  the  mouth,  which  acts  by  resonance.  The  letter  m  is  a 
labial,  like  b;  and  the  only  difference  between  the  two  is,  that  in  the  former 
the  nasal  passage  is  open,  whilst  the  mouth  remains  closed;  whilst  in  the 
latter,  the  nose  is  entirely  closed,  and  the  sound  is  formed  at  the  moment  of 
opening  the  mouth.  The  same  correspondence  exists  between  n  and  t,  or  n 
and  g  (the  particular  part  of  the  tongue  approximated  to  the  palate  not  being 
of  much  consequence  in  the  pronunciation  of  n) ;  and  hence  it  is  that  the 
transition  from  n  to  t,  or  from  n  to  g,  is  so  easy,  that  the  combinations  nt  and 
ng  are  found  abundantly  in  most  languages.  The  sound  of  /  is  produced,  by 
bringing  the  tip  of  the  tongue  into  contact  with  the  palate,  and  allowing  the 
air  to  escape  around  it,  at  the  same  time  that  a  vocal  tone  is  generated  in  the 
larynx;  it  differs,  therefore,  from  th  in  the  position  at  which  the  obstruction  is 
interposed,  as  well  as  in  the  slight  degree  of  the  compression  of  the  air  which 
it  involves.  The  sound  of  the  letter  r  depends  on  an  absolute  vibration  of  the 
point  of  the  tongue,  in  a  narrow  current  of  air  forced  between  the  tongue  itself 
and  the  palate.  3.  The  sounds  of  the  third  class  are  scarcely  to  be  termed 
consonants,  since  they  are  merely  aspirations  caused  by  an  increased  force  of 
breath.  These  are  A,  and  the  c/it  of  most  foreign  languages  (the  Greek  *). 
The  first  is  a  simple  aspiration ;  the  second,  an  aspiration  modified  by  the  ele- 
vation of  the  tongue,  causing  a  slight  obstruction  to  the  passage  of  air,  and  an 
increased  resonance  in  the  back  of  the  mouth.  This  sound  would  become 
either  g  or  A;,  if  the  tongue,  whilst  it  is  being  produced,  were  carried  up  to 
touch  the  palate 4 

418.  These  distinctions  come  to  be  of  much  importance,  when  we  apply 
ourselves  to  the  treatment  of  defects  of  articulation.  Great  as  is  the  number 
of  muscles  employed  in  the  production  of  definite  vocal  sounds,  the  number 
is  much  greater  for  those  of  articulate  language  ;  and  the  varieties  of  combi- 

*  Hence  it  is  easy  to  understand  the  substitution  of  t  or  d,  for  the  English  th,  by 
foreigners. 

f  The  English  ch  is  merely  a  combination  of  t  with  sh;  thus  chime  might  be  spelt 
tshime. 

t  The  general  classification  prqposed  by  Dr.  M.  Hall  is  here  adopted,  with  some  modi- 
fication as  to  the  details. 


OF  ARTICULATE  SOUNDS.  311 

nation,  which  we  are  continually  forming  unconsciously  to  ourselves,  would 
not  be  suspected,  without  a  minute  analysis  of  the  separate  actions.  Thus,  in 
uttering  the  explosive  sounds,  we  check  the  passage  of  air  through  the  pos- 
terior nares,  in  the  very  act  of  articulating  the  letter ;  and  yet  this  important 
movement  commonly  passes  unobserved.  We  must  regard  the  power  of  form- 
ing the  several  articulate  sounds  which  have  been  adverted  to,  and  their  sim- 
ple combinations,  as  so  far  resulting  from  intuition,  that  it  can  in  general  be 
more  readily  acquired  by  early  practice  than  other  actions  of  the  same  com- 
plexity ;  so  that  we  may  consider  these  movements  as  having  somewhat  of  the 
same  consensual  character  as  that  which  has  been  attributed  to  the  purely 
vocalizing  actions  (§412).  But  there  is  in  many  individuals  a  deficiency  of 
the  power  of  rightly  combining  them,  from  which  Stammering  and  other  im- 
perfections result.  Many  theories  regarding  the  nature  of  stammering  have 
been  proposed ;  and  there  can  be  little  doubt,  that  the  impediment  may  be 
attributed  to  a  great  variety  of  exciting  causes.  A  disordered  action  of  the 
nervous  centres  must,  however,  be  regarded  as  the  proximate  cause  ;  though 
this  may  be  (to  use  the  language  of  Dr.  M.  Hall)  either  of  centric  or  of  excen- 
tric  origin, — that  is,  it  may  result  from  a  morbid  condition  of  the  ganglionic 
centre,  or  from  an  undue  excitement  conveyed  through  its  afferent  nerves. — 
When  of  centric  origin  (and  this  is  probably  the  qiost  general  case),  the  phe- 
nomena of  Stammering  and  Chorea  have  a  close  analogy  to  each  other;  in 
fact,  stammering  is  frequently  one  of  the  modes  in  which  the  disordered  con- 
dition of  the  nervous  system  in  Chorea  manifests  itself.  It  is  in  the  pronunci- 
ation of  the  consonants  of  the  explosive  class,  that  the  stammerer  experiences 
the  greatest  difficulty.  The  total  interruption  to  the  breath  which  they  occa- 
sion, frequently  becomes  quite  spasmodic;  and  the  whole  frame  is  thrown  into 
the  most  distressing  semi-convulsive  movement,  until  relieved  by  expiration.* 
In  the  pronunciation  of  the  continuous  consonants  of  the  first  class,  the  stam- 
merer usually  prolongs  them,  by  a  spasmodic  continuance  of  the  same  action ; 
and  there  is,  in  consequence,  an  impeded,  but  not  a  suspended  respiration. 
The  same  is  the  case  with  the  /  and  r  in  the  second  class.  In  pronouncing 
the  m  and  n,  on  the  other  hand,  as  well  as  the  aspirates  and  vowels,  it  is  some- 
times observed  that  the  stammerer  prolongs  the  sound,  by  a  full  and  exhaust- 
ing expiration.  In  all  these  cases,  then,  it  seems  as  if  the  muscular  sense, 
resulting  from  each  particular  combination  of  actions,  became  the  stimulus  to 
the  involuntary  prolongation  of  that  action.  In  some  instances  it  is  possible, 
that  the  defect  may  result  from  malformation  of  the  parts  about  the  fauces, 
producing  an  abnormal  stimulus  of  this  kind,  in  some  particular  positions  of 
the  organ ;  and  such  cases  may  be  really  benefited  by  an  operation  for  the 
removal  of  these  parts.  But  the  effect  of  the  operation  is  evidently  for  the 
most  part  upon  the  Nervous  System  ;  and  it  coincides  with  what  may  be 
frequently  observed,— that  the  stammering  is  increased  under  any  unusual 
excitement,  especially  of  the  Emotional  kind. 

419.  The  method  proposed  by  Dr.  Arnott  for  the  prevention  of  Stammering, 
consists  in  the  connection  of  all  the  words  by  a  vocal  intonation,  in  such  a 
manner,  that  there  shall  never  be  an  entire  stoppage  of  the  breath.  It  is  justly 
remarked  by  Mliller,  however,  that  this  plan  may  afford  some  benefit,  but 
cannot  do  every  thing ;  since  the  main  impediment  occurs  in  the  middle  of 
words  themselves.  One  important  remedial  means,  on  which  too  much  stress 
cannot  be  laid,  is  to  study  carefully  the  mechanism  of  the  articulation  of  the 
difficult  letters,  and  to  practise  their  pronunciation  repeatedly,  slowly,  and  ana- 

*  By  Dr.  Arnott  this  interruption  is  represented  as  taking  place  in  the  larynx;  that  such 
is  not  the  case,  the  Author  believes  that  a  little  attention  to  the  ordinary  phenomena  of 
voice  will  satisfactorily  prove. 


312  INFLUENCE  OF  THE  NERVOUS  SYSTEM 

lytically.  The  patient  would  at  first  do  well  to  practise  sentences,  from  which 
the  explosive  consonants  are  omitted ;  his  chief  difficulty  arising  from  the 
spasmodic  suspension  of  the  expiratory  movement,  being  thus  avoided.  Having 
mastered  these,  he  may  pass  on  to  others,  in  which  the  difficult  letters  are 
sparingly  introduced  ;  and  may  finally  accustom  himself  to  the  use  of  ordinary 
language.  One  of  the  chief  points  to  be  aimed  at,  is  to  make  the  patient  feel 
that  he  has  command  over  his  muscles  of  articulation  ;  and  this  is  the  best 
done,  by  gradually  leading  him  from  that  which  he  finds  he  can  do,  to  that 
which  he  fears  he  cannot.  The  fact  that  stammering  people  are  able  to  sing 
their  words  better  than  to  speak  them,  has  been  usually  explained  on  the  sup- 
position that,  in  singing,  the  glottis  is  kept  open,  so  that  there  is  less  liability 
to  spasmodic  action ;  if,  however,  as  here  maintained,  the  spasmodic  aption  is 
not  in  the  larynx,  but  in  the  velum  palati  and  the  muscles  of  articulation,  the 
difference  must  be  due  to  the  direction  of  the  attention  rather  to  the  muscles 
of  the  larynx  than  to  those  of  the  mouth.  Every  one  must  have  noticed  how 
much  the  impediment  of  Stammerers  is  increased,  when  they  are  particularly 
anxious  to  speak  fluently. 


CHAPTER    VII. 


INFLUENCE    OF    THE    NERVOUS   SYSTEM   ON   THE    ORGANIC    FUNCTIONS, 

420.  OF  the  modes  in  which  the  Nervous  System  influences  the  Organic 
Functions,  a  part  have  been  already  considered.  It  has  been  shown  (§  183)  that 
it  is  concerned  in  providing  the  conditions,  either  immediate  or  remote,  under 
which  alone  these  functions  can  be  performed ;  so  that,  when  its  activity  ceases, 
they  cannot  be  much  longer  maintained.  The  first  mode  in  which  it'operates 
upon  them  is,  therefore,  by  producing  sensible  movements  in  the  Muscles  or 
other  contractile  organs,  which  can  be  stimulated  to  action  through  it ;  and  the 
contractions  thus  induced  have  usually  an  important  effect  upon  them,  which 
varies,  however,  in  each  individual  case.  Thus,  the  process  of  Nutritive 
Absorption,  which  is  the  very  first  stage  in  the  operations  of  Vegetative  Life, 
and  which  is  accomplished  in  Plants  by  the  accidental  contact  of  the  aliment- 
ary materials  with  the  radical  fibres,  cannot  take  place  in  Animals  until  the 
muscular  apparatus  of  prehension  has  been  set  in  action  by  the  Will,  that  of 
deglutition  by  the  Reflex  Function,  and  that  of  the  intestinal  canal  by  direct 
stimulation,— the  two  former  kinds  of  contraction  being  accomplished  entirely 
through  the  Nervous  System,  and  the  latter  being  influenced  by  it.  The  Cir- 
culation of  Blood,  too,  is  chiefly  effected,  in  the  higher  Animals  at  least,  by  the 
contractions  of  a  muscular  organ  of  impulsion ;  which  contractions,  though 
not  essentially  dependent  upon  Nervous  action,  are  nevertheless  greatly  influ- 
enced by  it.  The  function  of  Respiration,  again,  cannot  be  maintained  even 
short  time,  without  muscular  movement,  excited  through  the  Nervous 
The  functions  of  Nutrition  and  Secretion  are  more  independent  of 
it;  taking  place,  as  in  Plants,  so  long  as  the  conditions  are  supplied  by  other 
Junctions,  without  any  sensible  movements  being  actually  concerned  in  them. 
We  shall  presently  see,  however,  that  they  are  subject  to  a  peculiar  kind  of 


ON  THE  ORGANIC  FUNCTIONS.  313 

Nervous  influence,  which  does  not  manifest  itself  in  obvious  movement,  but  in 
altered  performance  of  the  intimate  processes  themselves ;  showing  itself  in 
the  character  of  the  organized  tissue,  or  of  the  secreted  product.  The  act 
of  Excretion  is,  like  ingestion,  entirely  performed  by  muscular  movement, 
dependent  upon  Nervous  agency.  Now  wherever  such  movements  of  distant 
organs  are  usually  performed  in  connection  with  each  other,  there  is  an  obvious 
channel  for  one  kind  of  sympathy  between  them ;  an  interesting  example  of 
this,  is  the  contraction  of  the  uterus  which  may  be  frequently  made  to  occur, 
when  that  organ  is  in  a  relaxed  state  at  the  conclusion  of  labour,  by  applying 
suction  or  other  irritation  to  the  nipple. 

421.  Sympathetic  movements  of  this  kind  may  be  excited  either  through 
the  Cerebro-Spinal,  or  the  Ganglionic  systems  ;  and  we  shall  be  guided  in  our 
determination  of  their  channel  in  each  particular  case,  by  the  distribution  of 
these  systems  respectively  to  the  organ  affected.     The  sympathetic  movements 
of  the  Muscles  of  Animal  life  (§  366)  appear  to  be  chiefly,  if  not  entirely, 
excited  through  the  Cerebro-spinal  system;  whilst  those  of  the  contractile 
tissues  of  the  Viscera  (§  375)  are  probably  excited  through  nerves,  which, 
though  connected  with  the  Cerebro-spinal  system,  act  under  peculiar  condi- 
tions, and  are  commonly  spoken  of  as  forming  part  of  the  Sympathetic  system. 
It  has  been  shown  (§  200)  that  all  the  contractile  organs  which  may  be  excited 
through  the  Sympathetic  or  Visceral  system  of  nerves,  may  also  be  made  to 
act  by  stimuli  applied  to  the  roots  of  the  Spinal  nerves  ;  but  that  each  Cerebro- 
Spinal  fibre  appears  to  pass  through  several  Ganglia,  before  being  distributed 
to  the  organs  which  it  supplies.     Many  speculations  have  been  hazarded  as 
to  the  reasons  why  the  Visceral  nerves  are  destitute  of  sensibility ;  and,  at  the 
time  when  the  Sympathetic  was  supposed  to  be  merely  an  offset  from  the 
Cerebro-Spinal  system,  it  was  imagined  that  the  use  of  the  ganglia  upon  the 
roots  of  the  spinal  nerves  was  to  "cut  off  sensation"  from  those  concerned  in 
the  "  vital  and  involuntary  motions."     The  influence  of  Bichat's  ingenious 
hypothesis, — that  the  Sympathetic  system  is  complete  and  independent,  minis- 
tering to  the  functions  of  Organic  Life,  as  the  Cerebro-Spinal  does  to  those  of 
Animal  Life — for  a  time  caused  this  idea  to  be  abandoned.     Since,  however, 
it  has  been  anatomically  proved,  that  a  large  portion  of  the  filaments  of  the 
visceral  nerves  are  derived  from  the  Spinal  cord,  this  opinion  has  been  revived 
in  a  somewhat  modified  form.*     Nevertheless  the  evidence  in  its  support  is 
somewhat  vague  ;  especially  if  the  truth  of  the  doctrine  formerly  urged, — that 
the  Spinal  Cord  is  not  itself  a  centre  of  sensation, — be  admitted.     For  it  is 
only  necessary  to  suppose,  that  the  white  fibres  of  the  Sympathetic  nerve 
terminate  in  the  true  Spinal  Cord,  without  proceeding  to  the  Brain,  to  have 
an  explanation  of  the  absence  of  sensory  endowments  in  the  organs  to  which 
they  are  distributed,  and  of  the  complete  removal  of  the  muscles  supplied  by 
their  motor  nerves,  from  voluntary  control.     That  a  few  fibres,  of  which  the 
actions  cannot  be  excited  under  ordinary  circumstances,  pass  on  to  the  Brain, 
would  seem  probable  from  the  fact  of  the  sensibility  of  some  parts,  in  disease, 
which  are  totally  insensible  in  their  normal  condition ; — a  fact  in  the  explana- 
tion of  which,  the  hypothesis  just  alluded  to  affords  no  assistance. 

422.  It  appears,  then,  that  it  may  be  stated  as  a  general  proposition,  that 
all  the  evident  movements  which  can  be  excited,  by  irritation  applied  to  one  part 
of  the  body,  in  the  contractile  organs  or  tis'sues  of  another,  are  really  effected 
through  the  true  Spinal  Cord ;  whether  the  contractile  organ  be  a  powerful 
muscle,  or  a  thin  and  feeble  layer  of  fibres  around  a  blood-vessel  or  duct. 
Upon  the  reasons  why  the  fibres  of  the  Visceral  nerves  should  be  so  peculiarly 

*  See  Dr.  Alison  on  the  Nerves  of  the  Orbit;  Edinb.  Phil.  Trans.,  vol.  xv.;  and  Med 
Gaz.,  vol.  xxviii.  p.  378. 

27 


314  INFLUENCE  OF  THE  NERVOUS  SYSTEM 

separated  from  the  rest,  We  can  at  present  only  speculate  ;  but  it  may  not  be 
considered  improbable  that,  by  their  peculiar  plexiform  arrangement  in  the 
various  ganglia  through  which  they  pass,  connections  are  established  between 
remote  organs,  which  tend  to  bring  their  actions  into  closer  relation  with  each 
other  than  would  otherwise  be  the  case.  The  existence  of  such  connections, 
for  the  purpose  of  harmonizing  the  several  movements  of  the  Viscera  which 
are  concerned  in  the  various  and  complex  operations  of  Digestion  and  its 
attendant  processes,  may  be  inferred  from  the  perfect  conformity  which  exists 
between  them,  during  all  their  different  states  of  regular  action ;  and  still 
more,  perhaps,  from  the  phenomena  of  their  disordered  conditions.  The 
study  of  these  Sympathies  is  one  of  those  departments  of  Physiology,  in  which 
it  may  be  expected  that  much  will  be  gained,  by  patient  and  well-directed 
investigation. 

423.  The  movements  immediately  concerned  in  the  Organic  Functions, 
however,  are  not  influenced  by  Reflex  action  alone,  but  also  by  Emotional 
conditions  of  the  mind.     This  is  most  obvious  in  regard  to  the  Heart.     Every 
one  must  have  experienced  the  disturbance  of  its  pulsations,  consequent  upon 
excitement  of  the  feelings,  of  almost  any  description.     But  other  organs  pro- 
bably experience  similar  changes,  although  of  a  less  manifest  character.     It  is 
well  known  that  the  Sympathetic  system  is  largely  distributed  upon  the  trunks 
of  the  blood-vessels,  accompanying  them  to  their  minutest  ramifications  ;  and 
it  will  be  hereafter  shown  (§  504),  that  the  fibrous  tissue  of  the  walls  of  the 
arteries  is  probably  susceptible  01  influence  from  these  nerves.     There  can  be 
little  doubt,  therefore,  that  they  constitute  the  channel  through  which  Emotions 
operate,  in  producing,  sudden  distension  of  particular  parts  of  the  vascular 
system,  as  in  blushing,  erection,  &c.     And  to  the  same  kind  of  influence, 
more  gradually  exerted,  we  may  very  probably  attribute  the  regulation  of  the 
supply  of  blood  which  passes  to  different  secreting  organs,  in  varying  condi- 
tions of  the  system. 

424.  But  the  Sympathetic  System  does  not  consist  of  Cerebro-Spinal  fila- 
ments alone ;  nor  is  its  influence  exerted  only  upon  the  motor  or  contractile 
tissues  of  the  body.     There  is  good  evidence,  that  the  Nervous  System  has 
an  immediate  action  upon  the  molecular  changes  which  constitute  the  func- 
tions of  Nutrition,  Secretion,  &c. ;  and  the  channel  of  that 'influence  is  pro- 
bably to  be  found  in  that  system  of  organic  fibres  formerly  described  (§  1 10), 
which  constitutes  a  considerable  portion  of  the  Visceral  nerves,  existing  much 
more  sparingly  in  most  of  the  Cerebro-Spinal,  but  being  abundant  in  the  Fifth 
pair.     There  is  no  valid  reason,  however,  to  believe  that  any  of  the  processes 
of  Nutrition  and  Secretion  are  dependent  upon  this,  or  any  other  kind  of 
Nervous  agency.     These  processes  go  on  with  great  rapidity  and  energy  in 
the  Vegetable  kingdom,  in  which  nothing  approaching  to  a  Nervous  System 
exists ;  and  in  the  Animal  kingdom  they  take  place  with  equal  vigour,  long 
before  the  least  vestige  of  it  appears.     The  Embryological  researches  of  Dr. 
Barry  have  fully  proved  that  in  the  earliest  condition  of  foetal  life,  the  germ 
consists  but  of  a  congeries  of  cells,  which  have  all  originated  in  a  single  one ; 
and  from  this  mass  the  several  tissues  are  gradually  generated,  by  a  process 
which  is  technically  called  histological*  transformation, — one  set  of  cells  being 
converted   into   muscular   tissue,  another   into  nervous  tissue,  another  into 
mucous  membrane,  and  so  on.     Now  since  this  is  the  case,  it  is  evident  that 
all  these  processes  of  development  must  take  place,  in  virtue  of  the  inherent 
properties  of  the  primary  tissue  itself;    since  no  nervous  influence  can  be 
supposed  to  operate  before  nerves  are  called  into  existence.     Throughout  the 

*  This  term  is  used  in  contradistinction  to  morphological,  which  applies  to  the  altera- 
tions in  the/yr/7»  of  the  several  parts  of  the  embryo. 


ON  THE  ORGANIC  FUNCTIONS.  315 

j 

Animal  body,  it  may  be  observed  that,  the  more  Vegetative  the  nature  of  any 
function  the  less  is  it  connected  with  the  Nervous  System  ;  and  all  the  experi- 
ments, which  have  been  regarded  as  proving  that  the  Organic  functions  are 
dependent  upon  Nervous  influence,  are  really  explicable,  fully  as  well,  upon 
the  supposition  that  they  are  capable  of  being  affected  by  it,  either  in  the  way 
of  excitement  or  retardation  (see  §  237).  Moreover,  there  is  abundant  evi- 
dence, that  Secretion  may  take  place  after  the  death  of  the  general  system, 
through  the  persistence  of  certain  molecular  changes,  of  which  the  essential 
conditions  are  not  immediately  altered ;  and  the  growth  of  the  beard,  which 
has  also  been  occasionally  observed,  indicates  that  even  Nutrition  may  continue 
to  a  certain  degree.  In  such  a  case,  the  Animal  body  is  reduced  to  the  con- 
dition of  a  Plant;  since  the  influence  of  the  Nervous '  system  must  then  be 
entirely  extinct.  Upon  those  who  maintain  that  nervous  agency  is  a  con- 
dition essential  to  those  molecular  actions,  of  which  Nutrition  and  Secretion 
consist,  it  is  incumbent,  therefore,  to  offer  some  more  unexceptionable  proof  of 
their  position  than  has  yet  been  given ;  since  their  doctrine  is  opposed  by  so 
many  considerations  of  great  weight. 

425.  That  many  of  the  Organic  Functions,  however,  are  directly  influenced 
by  the  Nervous  System,  is  a  matter  which  does  not  admit  of  dispute ;  and  this 
influence,  exerted  sometimes  in  exciting,  sometimes  in  checking,  and  some- 
times in  otherwise  modifying  them,  may  well  be  compared  to  that. which  the 
hand  and  heel  of  the  rider  have  upon  his  horse,  or  which  the  engine-driver 
'exerts  over  a  locomotive.  It  is  most  remarkably  manifested  in  the  result  of 
severe  injury  of  the  nervous  centres, — such  as  concussion  of  the  Brain,  or  of 
the  Solar  plexus  ;*  for  this  does  not  merely  produce  a  suspension  of  the  respi- 
ratory and  other  movements,  which  minister  to  the  organic  functions,  and  hence 
a  gradual  stagnation  of  the  latter — but  a  sudden  and  complete  cessation  of  the 
whole  train  of  action ;  which  cannot  be  attributed  to  any  other  cause  than  a 
positive  depressing  influence  of  some  kind,  propagated  through  the  Nervous 
System.  It  will  hereafter  appear  (§  583),  that  in  such  cases  even  the  vitality 
of  the  Blood  is  often  affected ;  the  usual  coagulation  not-  taking  place  after 
death,  so  long,  at  least,  as  the  blood  remains  within  the  vessels.  A  similar 
general  depression  may  result  from  Mental  Emotion,  operating  through  the  same 
channel ;  but  this  more  commonly  has  rather  a  local  action,  or  operates  more 
gradually.  The  influence  of  the  Nervous  System  is  often  especially  exerted, 
in  giving  temporary  excitement  to  a  secreting  process  ;  which  need  not  be  kept 
in  constant  activity,  or  of  which  circumstances  may  occasionally  require  an 
increase.  This  is  the  case,  for  example,  in  regard  to  the  secretions  connected 
with  the  process  of  digestion, — the  Saliva,  Gastric  fluid,  Bile,  Pancreatic  fluid, 
&c. ;  all  of  these  being  excited  by  the  contact  of  the  substances  on  which  they 
act,  with  the  surfaces  on  which  their  respective  ducts  open.  The  secretion  of 
Milk,  again,  in  a  nursing  female,  may  be  excited  by  irritation  of  the  nipple  ; 
and  a  determination  of  blood  to  the  Mammae  during  pregnancy,  must  be  due 
to  increased  action  in  the  part,  excited  by  the  changes  occurring  in  the  Uterus, 
which  can  scarcely  operate  otherwise  than  through  the  Nervous  System.  No 
other  channel  of  influence  can  be  well  imagined  for  most  of  these  operations 
than  the  Sympathetic  system  of  Nerves ;  since  the  organs  in  question  are  for 
the  most  part  supplied  by  it.  There  is  an  apparent  exception,  however,  in  the 
case  of  the  Salivary  and  Lachrymal  glands,  which  are  supplied  by  the  Fifth 
pair :  but  this  nerve  contains  so  many  organic  filaments,  and  is  so  intimately 
connected  with  the  Sympathetic,  as  evidently  to  supply  (in  the  head)  the  place 

*  The  Author  has  no  doubt,  that  the  occasional  occurrence  of  death  from  blows  on  the 
epigastrium  is  to  be  attributed  to  this  cause:  in  all  the  instances  on  record,  the  stomach 
has  contained  food  at  the  time;  and  the  effect  of  the  blow  would,  therefore,  have  been 
propagated  to  the  rest  of  the  viscera,  and  to  the  nerves  distributed  upon  them. 


316  INFLUENCE  OF  THE  NERVOUS  SYSTEM 

of  a  separate  ganglionic  system.  It  is  by  nervous  influence,  that  the  mucous 
secretion  covering  the  membranes  is  caused  to  be  regularly  formed  for  their 
protection ;  for  it  is  shown  by  pathological  facts,  that,  when  this  influence  is 
interrupted,  and  the  secretion  is  no  longer  supplied,  the  membrane,  losing  its 
protection,  is  irritated  by  the  air  or  the  fluids  with  which  it  may  be  in  contact, 
and  passes  into  an  inflammatory  condition.  This  is  the  explanation  of  the 
fact,  which  has  been  well  ascertained,  that  the  Eye  is  liable  to  suppurate  when 
the  Fifth  pair  has  been  divided ;  and  that  the  mucous  membrane  of  the  Blad- 
der becomes  diseased  in  Paraplegia. 

426.  The  influence  of  particular  conditions  of  the  mind,  in  exciting  vari- 
ous Secretions,  is  a  matter  of  daily  experience.     The  flow  of  Saliva,  for  exam- 
ple, is  stimulated  by  the  idea  of  food,  especially  that  of  a  savoury  character. 
The  Lachrymal  secretion,  again,  which  is  continually  being  formed  to  a  small 
extent,  for  the  purpose  of  bathing  the  surface  of  the  eye,  is  poured  out  in  great 
abundance  under  the  moderate  excitement  of  the  emotions  either  of  joy,  ten- 
derness, or  grief.    It  is  checked,  however,  by  violent  emotions  ;  hence  in  intense 
grief  the  tears  do  not  flow.     It  is  a  well-known  proof  of  moderated  sorrow, 
when  this  takes  place ;  tears,  however,  do  not  bring  relief,  as  is  commonly 
believed,  but  they  indicate  that  it  has  been  brought.  Violent  emotion  may  also 
suspend  the  Salivary  secretion ;  as  is  shown  by  the  well-known  test,  often 
resorted  to  in  India,  for  the  discovery  of  a  thief  amongst  the  servants  of  a  family, 
— that  of  compelling  all  the  parties  to  hold  a  certain  quantity  of  rice  in  the 
mouth  during  a  few  minutes,— the  offender  being  generally  distinguished  by 
the  comparative  dryness  of  his  mouthful,  at  the  end  of  the  experiment.     The 
influence  of  the  emotion  of  love-of-offspring,  in  increasing  the  secretion  of 
Milk,  is  weil  known.     The  formation  of  this  fluid  is  continually  going  on 
during  the  period  of  lactation ;  but  it  is  greatly  increased  by  the  sight  of  the 
infant,  or  even  by  the  thought  of  him,  especially  when  associated  with  the  idea 
of  suckling;  this  gives  rise  to  the  sudden  rush  of  blood  to  the  gland,  which  is 
known  by  nurses  as  the  draught,  and  which  occasions  a  greatly  increased 
secretion.    The  strong  desire  to  furnish  milk,  together  with  the  irritation  of  the 
gland  through  the  nipple,  has  often  been  effectual  in  producing  the  secretion 
in  girls  and  old  women,  and  even  in  men  (§  683).     The  quantity  of  the  Gastric 
secretion  is  increased  by  exhilaration;  at  least  if  we  may  judge  from  the  in- 
crease of  the  digestive  powers  under  such  circumstances.     Freedom  from 
mental  anxiety  favours  the  secretion  of  fat ;  whilst  continual  solicitude  effectu- 
ally checks  the  disposition.     It  has  been  stated  that  total  despair  has  an  equal 
tendency,  with  absence  of  care,  to  produce  this  effect ;  persons  left  long  to  pine 
in  condemned  cells,  without  a  shadow  of  hope,  frequently  becoming  remarka- 
bly fat,  in  spite  of  their  slender  fare.*     The  odoriferous  secretion  of  the  Skin, 
which  is  much  more  powerful  in  some  individuals  than  in  others,  is  increased 
under  the  influence  of  certain  mental  emotions  (as  fear  or  bashfulness),  and 
commonly  also  by  sexual  desire.    The  Sexual  secretions  themselves  are  strongly 
influenced  by  the  condition  of  the  mind.     When  it  is  frequently  and  strongly 
directed  towards  objects  of  passion,  these  secretions  are  increased  in  amount,  to 
a  degree  which  may  cause  them  to  be  a  very  injurious  drain  on  the  powers  of 
the  system.     On  the  other  hand,  the  active  employment  of  the  mental  powers 
on  other  objects,  has  a  tendency  to  render  less  active,  or  even  to  check  alto- 
gether, the  processes  by  which  they  are  elaborated.! 

*  Fletcher's  Physiology, Part  II.,  b,  p.  11. 

f  This  is  a  simple  physiological  fact, but  of  high  moral  application.  The  Author 
would  say  to  those  of  his  younger  readers,  who  urge  the  wants  of  Nature  as  an  excuse 
for  the  illicit  gratification  of  the  sexual  passion,  "  Try  the  effects  of  close  mental 
cation  to  some  of  those  ennobling  pursuits,  to  which  your  profession  introduces  you,  i 
combination  with  vigorous  bodily  exercise  (for  the  effects  of  which  see  §  278) ;  befor 


; 


ON  THE  ORGANIC  FUNCTIONS.  317 

427.  No  secretion  so  evidently  exhibits  the  influence  of  the  depressing 
Emotions  as  that  of  the  Mammae  ;  but  this  may  be  partly  due  to  the  fact,  that 
the  digestive  system  of  the  Infant  is  a  more  delicate  apparatus  for  testing  the 
qualities  of  that  secretion  than  any  which  the  Chemist  can  devise ;  affording 
proof,  by  disorder  of  its  function,  of  changes  in  the  character  of  the  Milk,  which 
no  examination  of  its  physical  properties  could  detect.  The  following  remarks 
on  this  subject  are  abridged  from  Sir  A.  Cooper's  valuable  work  on  the  Breast. 
"  The  secretion  of  milk  proceeds  best  in  a  tranquil  state  of  mind,  and  with  a 
cheerful  temper ;  then  the  milk  is  regularly  abundant,  and  agrees  well  with 
the  child.  On  the  contrary,  a  fretful  temper  lessens  the  quantity  of  milk, 
makes  it  thin  and  serous,  and  causes  it  to  disturb  the  child's  bowels,  producing 
intestinal  fever  and  much  griping.  Fits  of  anger  produce  a  very  irritating 
milk,  followed  by  griping  in  the  infant,  with  green  stools.  Grief  has  a  great 
influence  on  lactation,  and  consequently  upon  the  child.  The  loss  of  a  near 
and  dear  relation,  or  change  of  fortune,  will  often  so  much  diminish  the  secre- 
tion of  milk,  as  to  render  adventitious  aid  necessary  for  the  support  of  the 
child.  Anxiety  of  mind  diminishes  the  quantity,  and  alters  the  quality,  of 
the  milk.  The  reception  of  a  letter  which  leaves  the  mind  in  anxious  sus- 
pense, lessens  the  draught,  and  the  breast  becomes  empty.  If  the  child  be  ill, 
and  the  mother  is  anxious  respecting  it,  she  complains  to  her  medical  attend- 
ant that  she  has  little  milk,  and  that  her  infant  Is  griped,  and  has  frequent 
green  and  frothy  motions.  Fear  has  a  powerful  influence  on  the  secretion  of 
milk.  I  am  informed  by  a  medical  man,  who  practices  much  among  the  poor, 

you  assert  that  the  appetite  is  unrestrainable,  and  act  upon  that  assertion."  Nothing 
tends  so  much  to  increase  the  desire,  as  the  continual  direction  of  the  mind  towards  the 
objects  of  its  gratification.  The  following  observations,  which  the  Author  believes  to  be 
strictly  correct,  are  extracted  from  a  valuable  little  work  (anonymous)  entitled,  "Be  not 
deceived,"  addressed  to  Young  Men  ;  they  are  directed  to  those  who  maintain  that,  the 
married  state  being  natural  to  man,  illicit  intercourse  is  necessary  for  those  who  are 
prevented  by  circumstances  from  otherwise  gratifying  the  sexual  passion.  "When  the 
appetite  is  naturally  indulged,  that  is,  in  marriage,  the  necessary  energy  is  supplied  by 
the  nervous  stimulus  of  its  natural  accompaniment  of  love  before  referred  to,  which  pre- 
vents the  injury  which  would  otherwise  arise  from  the  increased  expenditure  of  animal 
power:  and  in  like  manner  also,  the  function  being  in  itself  grateful,  this  personal  at- 
tachment performs  the  further  necessary  office  of  preventing  immoderate  indulgence,  by 
dividing  the  attention,  through  the  numerous  other  sources  of  sympathy  and  enjoyment 
which  it  simultaneously  opens  to  the  mind.  But  when  the  appetite  is  irregularly  indulged, 
that  is,  in  fornication,  for  want  of  the  healthful  vigour  of  true  love,  its  energies  become 
exhausted;  and  from  the  want  of  the  numerous  other  sympathetic  sources  of  enjoyment 
in  true  love,  in  similar  thoughts,  common  pursuits, and  above  all  in  common  holy  hopes, 
the  mere  gross  animal  gratification  of  lust  is  resorted  to  with  unnatural  frequency,  and 
thus  its  powers  become  still  further  exhausted,  and,  therefore,  still  more  unsatisfying, 
while,  at  the  same  time,  a  habit  is  thus  created,  and  these  jointly  cause  an  increased  crav- 
ing; and  the  still  greater  deficiency  in  the  satisfaction  experienced  in  its  indulgence  fur- 
ther, continually,  ever  in  a  circle,  increases — the  habit,  demand,  indulgence,  consequent 
exhaustion,  diminished  satisfaction,  and  again  demand,— till  the  mind  and  body  alike 
become  disorganized."  Such  considerations  as  these  may,  to  some  persons,  appear  mis- 
placed in  a  Physiological  Treatise — yet  the  Author  feels  sure  that,  by  his  well-judging 
readers  he  will  not  be  blamed  for  adverting  to  this  subject,  or  for  introducing  the  above 
quotation  from  a  writer,  of  whom  he  has  no  personal  knowledge,  but  whose  object  must 
be  confessed  by  all  to  be  laudable.  There  seems  to  be  something  in  the  process  of  train- 
ing young  men  for  the  Medical  Profession,  which  encourages  in  them  a  laxity  of  thought 
and  expression  on  these  matters,  that  generally  ends  in  a  laxity  of  action  and  of  princi- 
ple. It  might  have  been  expected  that  those,  who  are  so  continually  witnessing  the  melan- 
choly consequences  of  the  violation  of  the  Divine  law  in  this  particular,  would  be  the 
last  to  break  it  themselves;  but  this  is  unfortunately  very  far  from  being  the  caxe.  The 
Author  regrets  to  be  obliged  further  to  remark,  that  some  recent  works  which  have  issued 
from  the  Medical  press,  contain  much  that  is  calculated  to  excite,  rather  than  to  repress, 
the  propensity;  and  that  the  advice  sometimes  given  by  practitioners  to  their  patients,  is 
immoral  as  well  as  unscientific. 

27* 


318  INFLUENCE  OF  THE  NERVOUS  SYSTEM 

that  the  apprehension  of  the  brutal  conduct  of  a  drunken  husband,  will  put  a 
stop  for  a  time  to  the  secretion  of  milk.  When  this  happens,  the  breast  feels 
knotted  and  hard,  flaccid  from  the  absence  of  milk,  and  that  which  is  secreted 
is  highly  irritating,  and  some  time  elapses  before  a  healthy  secretion  returns. 
Terror,  which  is  sudden  and  great  fear,  instantly  stops  this  secretion."  Of 
this,  two  striking  instances,  in  which  the  secretion,  although  previously  abun- 
dant, was  completely  arrested  by  this  emotion,  are  detailed  by  Sir  A.  C. 
"  Those  passions  which  are  generally  sources  of  pleasure,  and  which,  when 
moderately  indulged,  are  conducive  to  health,  will,  when  carried  to  excess, 
alter,  and  even  entirely  check  the  secretion  of  milk." 

428.  The  following  is  perhaps  the  most  remarkable  instance  on  record  of 
the  effect  of  strong  mental  excitement  on  the  Mammary  secretion  ;  the  event 
could  hardly  be  regarded  as  more  than  a  simple  coincidence,  if  it  were  not 
borne  out  by  the  less  striking  but  equally  decisive  facts  already  mentioned. 
"A  Carpenter  fell  into  a  quarrel  with  a  Soldier  billeted  in  his  house,  and  was 
set  upon  by  the  latter  with  his  drawn  sword.  The  Wife  of  the  Carpenter  at 
first  trembled  from  fear  and  terror,  and  then  suddenly  threw  herself  furiously 
between  the  combatants,  wrested  the  sword  from  the  Soldier's  hand,  broke  it 
in  pieces,  and  threw  it  away.  During  the  tumult,  some  neighbours  came  in 
and  separated  the  men.  While  in  this  state  of  strong  excitement  the  mother 
took  up  her  child  from  the  cradle  where  it  lay  playing,  and  in  the  most  per- 
fect health,  never  having  had  a  moment's  illness ;  she  gave  it  the  breast,  and 
in  so  doing  sealed  its  fate.  In  a  few  minutes  the  infant  left  off  sucking,  be- 
came restless,  panted,  and  sank  dead  upon  its  mother's  bosom.  The  physician 
who  was  instantly  called  in,  found  the  child  lying  in  the  cradle,  as  if  asleep, 
and  with  its  features  undisturbed;  but  all  his  resources  were  fruitless.  It 
was  irrecoverably  gone."*  In  this  interesting  case,  the  milk  must  have 
undergone  a  change,  which  gave  it  a  powerful  sedative  action  upon  the 
susceptible  nervous  system  of  the  infant:  the  following,  which  recently  oc- 
curred within  the  Author's  own  knowledge,  is  perhaps  equally  valuable  to  the 
Physiologist,  as  an  example  of  the  similarly  fatal  influence  of  undue  emotion 
of  a  different  character;  and  both  should  serve  as  a  salutary  warning  to 
mothers,  not  to  indulge  either  in  the  exciting  or  depressing  passions.  A  lady 
having  several  children,  of  which  none  had  manifested  any  particular  tendency 
to  cerebral  disease,  and  of  which  the  youngest  was  a  healthy  infant  a  few 
months  old,  heard  of  the  death  (from  acute  hydrocephalus)  of  the  infant  child 
of  a  friend  residing  at  a  distance,  with  whom  she  had  been  on  terms  of  close 
intimacy,  and  whose  family  had  increased  almost  cotemporaneously  with  her 
own.  The  circumstance  naturally  made  a  strong  impression  on  her  mind; 
and  she  dwelt  upon  it  the  more,  perhaps,  as  she  happened  at  that  period  to 
be  separated  from  the  rest  of  her  family,  and  to  be  much  alone  with  her  babe. 
One  morning,  shortly  after  having  nursed  it,  she  laid  the  infant  in  its  cradle, 
asleep  and  apparently  in  perfect  health ;  her  attention  was  shortly  attracted  to 
it  by  a  noise ;  and,  on  going  to  the  cradle,  she  found  her  infant  in  a  convulsion, 

*Dr.  Von  Ammon,  in  his  treatise  "Die  ersten  Mutterpflichten  und  die  erste  Kindesp- 
flege,"  quoted  in  Dr.  A.  Combe's  excellent  little  work  on  the  Management  of  Infancy. 
Similar  facts  are  recorded  by  other  writers.  Mr.  Wardrop  mentions  (Lancet,  No.  516), 
that  having  removed  a  small  tumour  from  behind  the  ear  of  a  mother,  all  went  well,  until 
she  fell  into  a  violent  passion ;  and  the  child,  being  suckled  soon  afterwards,  died  in 
convulsions.  He  was  sent  for  hastily  to  see  another  child  in  convulsions,  after  taking 
the  breast  of  a  nurse  who  had  just  been  severely  reprimanded;  and  he  was  informed  by 
Sir  Richard  Croft,  that  he  had  seen  many  similar  instances.  Three  others  are  recorded 
by  Burdach  (Physiologic,  §  522);  in  one  of  them,  the  infant  was  seized  with  convulsions 
on  the  right  side,  and  hemiplegia  on  the  left,  on  sucking  immediately  after  its  mother  had 
met  with  some  distressing  occurrence.  Another  case  was  that  of  a  puppy,  which  was 
seized  with  epilepsy,  on  sucking  its  mother  after  a  fit  of  rage. 


ON  THE  ORGANIC  FUNCTIONS.  319 

which  lasted  for  a  few  moments  and  then  left  it  dead.  Now,  although  the 
influence  of  the  mental  emotion  is  less  unequivocally  displayed  in  this  case 
than  in  the  last,  it  can  scarcely  be  a  matter  of  doubt ;  since  it  is  natural  that 
no  feeling  should  be  stronger  in  the  mother's  mind,  under  such  circumstances, 
than  the  fear  that  her  own  beloved  child  should  be  taken  from  her  as  that  of 
her  friend  had  been ;  and  it  is  probable  that  she  had  been  particularly  dwell- 
ing on  it  at  the  time  of  nursing  the  infant  on  that  morning.* 

429.  Other  Secretions  are  in  like  manner  vitiated  by  mental  emotions, 
although  the  influence  is  not  always  so  manifest.  Thus,  the  halitus  from  the 
lungs  is  sometimes  almost  instantaneously  affected  by  bad  news,  so  as  to  pro- 
duce fcetid  breath.  A  copious  secretion  of  foetid  gas  not  unfrequently  takes 
place  in  the  intestinal  canal  under  the  influence  of  any  disturbing  emotion ; 
or  the  usual  fluid  secretions  from  its  walls  are  similarly  disordered.  The  ten- 
dency to  defecation  which  is  commonly  excited  under  such  circumstances,  is 
not,  therefore,  due  simply  to  the  relaxation  of  the  sphincter  ani  (as  commonly 
supposed),  but  is  partly  dependent  on  the  unusually  stimulating  character  of 
the  faeces  themselves.  The  same  may  be  said  of  the  tendency  to  micturition, 
which  is  experienced  under  similar  conditions ;  the  change  in  its  character 
becomes  perceptible  enough  among  many  animals,  in  which  it  acquires  a  pow- 
erfully disagreeable  odour  under  the  influence  of  fear;  and  thus  answers  the 
purpose  which  is  effected  in  others  by  a  peculiar  secretion.  It  is  a  prevalent, 
and  perhaps  not  an  ill-founded  opinion,  that  melancholy  and  jealousy  have  a 
tendency  to  increase  the  quantity  and  to  vitiate  the  quality  of  the  biliary  fluid; 
perhaps  the  disorder  of  the  organic  function  is  more  commonly  the  source  of 
the  former  emotion  than  its  consequence ;  but  it  is  certain  that  the  indulgence 
of  these  feelings  has  a  decidedly  morbific  effect  by  disordering  the  digestive 
processes,  and  thus  reacts  upon  the  nervous  system  by  impairing  its  healthy 
nutrition.  On  the  influence  of  mental  emotion  in  the  Mother,  on  the  Foetus 
in  utero,  some  remarks  will  be  offered  hereafter  (§  768). 

*  Another  instance,  in  which  the  maternal  influence  was  less  certain,  but  in  which  it 
was  not  improbably  the  immediate  cause  of  the  fatal  termination,  occurred  in  a  family 
nearly  related  to  the  Author's.  The  mother  had  lost  several  children  in  early  infancy, 
from  a  convulsive  disorder;  one  infant,  however,  survived  the  usually  fatal  period;  but 
whilst  nursing  him  one  morning,  she  had  been  strongly  dwelling  on  the  fear  of  losing 
him  also,  although  he  appeared  a  very  healthy  child.  In  a  few  minutes  after  the  infant 
had  been  transferred  in^p  the  arms  of  the  nurse,  and  whilst  she  was  urging  her  mistress 
to  take  a  more  cheerful  view,  directing  her  attention  to  his  thriving  appearance,  he  was 
seized  with  a  convulsion  fit,  and  died  almost  instantly.  Now  although  there  was  here 
unquestionably  a  predisposing  cause,  of  which  there  is  no  evidence  in  the  other  cases,  it 
can  scarcely  be  doubted  that  the  exciting  cause  of  the  fatal  disorder  is  to  be  referred  to 
the  mother's  anxiety.  This  case  offers  a  valuable  suggestion, — which,  indeed,  would 
be  afforded  by  other  considerations, — that  an  infant,  under  such  circumstances,  should 
not  be  nursed  by  its  mother,  but  by  another  woman  of  placid  temperament,  who  had 
reared  healthy  children  of  her  own. 


320  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 


CHAPTER    VIII. 

OF    DIGESTION   AND    NUTRITIVE   ABSORPTION. 

I.  Nature  and  Destination  of  the  Food  of  Animals. 

430.  Before  we  examine  the  nature  of  the  process  by  which  the  food  of 
Animals  is  prepared  for  absorption  into  -their  bodies,  it  will  be  desirable  to  con- 
sider the  characters  of  the  aliment  itself,  and  the  purposes  to  which  it  is  to  be 
applied.  Strictly  speaking,  the  term  aliment  may  be  applied  to  all  those  sub- 
stances, which,  when  introduced  into  the  living  body,  contribute  to  its  growth, 
or  to  the  repair  of  the  losses  which  it  is  continually  sustaining.*  But  in  gene- 
ral the  term  is  used  in  a  less  extensive  sense  ;  being  confined  to  those  mate- 
rials which  are  absorbed  and  applied  to  the  purpose  of  the  economy,  only  after 
undergoing  the  process  of  Digestion;  and  in  this  sense  it  will  be  here  employed. 
It  has  been  mentioned  (§  14)  as  a  general  principle,  that, — whilst  Plants  have 
the  power  of  combining  the  elements  supplied  by  the  inorganic  world,  into 
the  materials  of  their  nutrition, — Animals  can  only  subsist  upon  substances 
that  have  been  already  so  combined,  and  that  have  previously  formed  a  part  of 
some  organized  body,  either  Vegetable  or  Animal.  All  the  materials  used  as 
food,  therefore,  by  Animals,  are  derived  from  one  or  other  of  these  two  king- 
doms. They  may  be  conveniently  arranged  under  the  four  following  heads.t 
1.  The  Saccharine  group,  including  all  those  substances  derived  from  the 
Vegetable  kingdom,  which  are  analogous  in  their  composition  to  Sugar ; — con- 
sisting of  oxygen,  hydrogen,  and  carbon,  alone ;  and  having  the  two  first 
present  in  the  proportions  to  form  water.  To  this  group  belong  starch,  gum, 
woody  fibre,  and  the  various  tissues  of  Plants ;  which  closely  resemble  each 
other  in  the  proportion  of  their  elements,  and  which  may  be  converted  into 
Sugar  by  chemical  processes  of  a  simple  kind. — 2.  The  Oleaginous  group, 
including  oily  matters,  whether  derived  from  the  Vegetable  kingdom,  or  from 
the  fatty  portions  of  Animal  bodies.  The  characteristic  of  this  class,  is  the 
great  predominance  of  hydrogen  and  carbon,  the  small  proportion  of  oxygen, 
and  the  entire  absence  of  nitrogen. — 3.  The  Albuminous  group,  comprising 
all  those  substances,  whether  derived  from  the  Animal  or  Vegetable  kingdom, 
which  are  closely  allied  to  Albumen,  and  therefore  to  the  majority  of  the  Ani- 
mal tissues,  in  their  chemical  composition.  In  this  group,  a  large  proportion 
of  azote  is  united  with  the  oxygen,  hydrogen,  and  carbon  of  the  preceding. — 
4.  The  Gelatinous  group,  consisting  of  substances  derived  from  Animal  bodies 
only,  which  are  closely  allied  to  Gelatin  in  their  composition.  "  These  also 
contain  azote ;  but  the  proportion  of  their  components  differs  from  that  of  the 
preceding. — The  compounds  of  the  Saccharine  group  cannot,  without  under- 
going a  metamorphosis,  form  part  of  any  Animal  tissue ;  as  there  is  none 
which  they  resemble  in  composition.  It  will  be  shown,  however,  that  they 
are  convertible,  within  the  Animal  body,  into  those  of  the  Oleaginous  group ; 

*  Thus,  Water  and  Air  may  be  termed  aliments. 

f  Dr.  Prout's  classification  of  alimentary  substances  is  here  adopted,  with  a  slight 
modification;  not  as  being  altogether  unexceptionable,  but  as  being,  in  the  Author's 
opinion,  the  most  convenient  hitherto  proposed. 


NATURE  AND  DESTINATION  OF  THE  FOOD  OF  ANIMALS.  321 

and,  like  them,  may  be  deposited  in  the  form  of  Adipose  matter.  There  is  no 
other  tissue  in  the  body  into  which  they  can  enter  without  considerable 
change;  for  all  others  are  azotized;  and  it  is  a  most  important  question, 
whether  the  non-azotized  compounds  can,  under  any  circumstances,  be  con- 
verted within  the  body  into  compounds  of  the  albuminous  or  gelatinous  groups. 
This  question  can  scarcely  be  regarded  as  having  yet  received  a  definitive 
answer;  but  the  prevalent  opinion  amongst  Chemists  is  opposed  to  the  possi- 
bility of  such  transformation.  To  this  question  we  shall  hereafter  revert:  and 
at  present  we  may  be  satisfied  with  remarking,  that  many  alimentary  sub- 
stances constituting  the  staple  food  of  large  bodies  of  men, — such  as  Rice  and 
Potatoes, — which  were  formerly  supposed  to  be  entirely  made  up  of  starchy 
matters,  are  now  known  to  contain  azotized  compounds  of  the  Albuminous 
group,  to  an  amount  easily  recognizable.  Whether  their  quantity  be  suffi- 
cient for  the  requisite  nutrition  of  the  Albuminous  tissues  of  the  Human  body, 
is  a  question  to  be  determined  by  further  investigation.  At  present,  the  whole 
subject  of  inquiry  is  so  new,  that  it  would  be  premature  to  offer  a  decided 
opinion.  (See  §  567). 

431.  The  application  of  the  substances  forming  the  Albuminous  group,  to 
the  support  of  the  Animal  body,  by  affording  the  materials  for  the  nutrition 
and  re-formation  of  its  tissues,  needs  little  explanation.  The  proportions  of 
the  four  ingredients  of  which  they  are  all  composed,  are  so  nearly  the  same, 
that  no  essential  difference  appears  to  exist  among  them  (§  457);  and  it  is  a 
matter  of  little  consequence,  except  as  far  as  the  gratification  of  the  palate  is 
concerned,  whether  we  feed  upon  the  flesh  of  animals  (fibrin),  upon  the  white 
of  egg  (albumen),  the  curd  of  milk  (casein),  the  grain  of  wheat  (gluten),  or  the 
seed  of  the  pea  (legumin).  All  these  substances  are  reduced  in  the  stomach 
to  the  form  of  albumen;  which  resembles  the  gum  of  Plants  in  being  the  raw 
material,  as  it  were,  out  of  which  the  various  fabrics  of  the  body  are  constructed. 
But  the  rule  holds  good,  with  regard  to  these  also,  that  by  being  made  to  feed 
constantly  on  the  same  substance,— boiled  white  of  egg  for  instance,  or  meat 
deprived  of  the  principle  (osmazome)  that  gives  it  flavour, — an  animal  may 
be  effectually  starved ;  its  disgust  at  the  food  being  such,  that  even  if  it  be 
swallowed,  it  is  not  digested.  It  is  very  interesting  to  remark  that,  in  the 
only  instance  in  which  Nature  has  provided  a  single  article  of  food  for  the 
support  of  the  animal  body,  she  has  mingled  articles  from  all  the  three  pre- 
ceding groups.  This  is  the  case  in  Milk,  which  contains  a  considerable  quan- 
tity of  an  albuminous  substance,  casein,  \vhich  forms  its  curd;  a  good  deal  of 
oily  matter,  the  butter ;  and  no  inconsiderable  amount  of  sugar,  which  is  dis- 
solved in  the  whey.  The  proportions  of  these  vary  in  different  Mammalia ; 
and  they  depend  in  part  upon  the  nature  of  the  food  supplied  to  the  Animal 
that  forms  the  milk ;  but  the  substances  are  thus  combined  in  every  instance. 
Although  the  greater  part  of  the  organized  tissue  of  Animals  is  formed  at  the 
expense  of  the  Albumen  and  Fibrin  of  their  blood,  yet  many  of  them  also 
contain  a  large  quantity  of  Gelatin.  It  seems  certain  that  this  gelatin  may  be 
produced  out. of  fibrin  and  albumen;  since  in  animals  that  are  supported  on 
these  alone,  the  nutrition  of  the  gelatinous  tissues  does  not  seem  to  be  impaired. 
But  it  also  appears,  that  gelatin  taken  in  as  food  may  be  applied  to  this  pur- 
pose ;  for  ordinary  experience  shows  that  benefit  is  derived  from  jelly,  soup, 
broth,  &c. ;  peculiarly  by  persons  who  have  been  suffering  under  exhausting 
diseases,  such  as  fevers.  But  it  also  appears  certain,  that  it  cannot  be  applied 
to  the  nutrition  of  the  Albuminous  tissues.  Some  important  experiments  have 
been  recently  made  in  Paris  on  this  subject,  with  a  view  of  determining  how 
far  the  soup  made  from  crushed  bones,  which  constituted  a  principal  article 
of  diet  in  the  hospitals  of  Paris,  was  adequate  for  the  support  of  the  patients. 
The  result  of  these  has  been  quite  confirmatory  of  previous  conclusions, — 


322  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

namely,  that  Gelatin  may  be  advantageously,  mixed  with  albumen,  fibrin, 
gluten,  &c.,  and  those  other  ingredients  which  exist  in  meat-soup  and  bread; 
but  that,  when  taken  alone,  it  has  little  more  power  of  sustaining  life  than 
sugar  or  starch  possesses ;  and  that,  even  when  bread  is  united  with  the  gela- 
tin-soup, it  does  not  give  it  the  requisite  power  of  nutrition. 

432.  If  the  non-azotized  compounds,  which  exist  so  largely  in  the  food  of 
Herbivorous  animals,  are  not  destined  to  form  part  (in  any  considerable  degree 
at  least)  of  their  tissues,  the  question  arises, — what  becomes  of  them  ?     It  is 
not  enough  to  say  that  they  are  deposited  as  Fat ;  since  it  is  only  when  a 
large  quantity  of  them  is  taken  in,  that  there  is  any  increase  in  the  quantity 
of  fat  already  in  the  body.     We  shall  hereafter  see,  that  they  are  used  up  in 
the  process  of  Respiration,  one  great  object  of  which  is,  to  produce  a  certain 
amount  of  heat,  sufficient  to  keep  up  the  temperature  of  the  body,  in  warm- 
blooded animals,  to  a  high  standard.     We  might  almost  say  with  truth,  that  a 
great  part  of  the  Oleaginous  and  Saccharine  principles  is  burned  within  the 
body,  for  this  purpose.     The  process  will  be  hereafter  considered  more  in 
detail;  and  at  present  we  need  only  stop  to  remark  upon  the  adaptation 
between  the  food  provided  for  animals  in  different  climates,  and  the  amount 
of  heat  which  it  is  necessary  for  them  to  produce.     Thus  the  bears,  and  seals, 
and  whales,  from  which  the  Esquimaux  and  the  Greenlander  derive  their  sup- 
port, have  an  enormous  quantity  of  fat  in  their  massive  bodies :  this  fat  is  as 
much  esteemed  as  an  article  of  food  among  these  people,  as  it  would  be  thought 
repulsive  by  the  inhabitants  of  southern  climates;  and  by  the  large  quantity 
of  it  they  consume,  they  are  able  to  support  the  bitterness  of  an  Arctic  winter, 
without  appearing  to  suffer  more  from  the  extreme  cold  than  do  the  residents 
in  more  temperate  climes  during  their  winter.     On  the  other  hand,  the  ante- 
lopes, deer,  and  wild  cattle,  which  form  a  large  proportion  of  the  animal  food 
of  savage  or  half-cultivated  nations  inhabiting  temperate  or  tropical  regions, 
possess  very  little  fat;   and  the  comparatively  small  supply  of  carbon  and 
hydrogen,  whose  combustion  is  required  to  keep  up  the  bodily  temperature  of 
the  inhabitants  of  those  regions,  is  derived  from  the  flesh  of  those  animals  in 
the  manner  that  will  be  presently  explained.     Every  one  knows  how  much 
less  vigorous  the  appetite  becomes,  during  the  heat  of  summer,  than  it  is 
during  the  colder  portion  of  the  year ;  and  this  is  a  natural  result  of  the  dimin- 
ished demand  for  the  fuel  required  to  maintain  the  temperature.     And  one 
great  means  of  preserving  the  health,  during  a  prolonged  residence  in  a  hot 
climate,  is  to  attend  to  the  dictates  of  Nature,  in  regard  to  the  quantity  of  food 
ingested ;  instead  of  endeavouring  (as  is  the  prevalent  practice)  to  stimulate 
the  appetite  by  artificial  provocatives. 

433.  It  has  been  already  stated  (§  83),  that  all  the  living  tissues  of  the  body 
are  continually  undergoing  a  sort  of  death  and  decay ;  and  they  do  this  the 
more  rapidly,  in.  proportion  as  they  are  called  upon  for  the  discharge  of  their 
functions  (§  646).     This  is,  consequently,  the  chief  source   of  the   constant 
demand  for  aliment,  capable  of  replacing  that  which  has  been  lost.     Even  in 
young  actively  growing  animals,  the  quantity  of  .aliment  required  for  the 
increase  of  their  bodies,  constitutes  but  a  very  small  proportion  of  that  which 
is  taken  in :  of  the  remainder,  a. part  is  at  once  rejected  as  indigestible  ;  and 
the  rest  is  appropriated  to  the  repair  of  the  waste  which  is  continually  going 
on.     This  waste  is  much  greater  in  young  animals  than  in  adults ;  for  all 
their  vital  processes  are  more  actively  and  energetically  performed ;  their 
movements  are  quicker  in  proportion  to  their  size ;  and  injuries  are  more 
speedily  repaired.     Now  of  this  waste,  the  chief  part  is  carried  out  of  the  body 
by  the  various  processes  of  excretion;  and  among  these,  the  Respiration,  by 
which  a  large  quantity  of  carbon  and  hydrogen  is  carried  off  in  the  form  of 
carbonic  acid  and  water,  is  of  the  most  constant  importance,  on  account  of  the 


NATURE  AND  DESTINATION  OF  THE  FOOD  OF  ANIMALS.  323 

heat  which  it  thus  enables  the  animal  body  to  maintain.  This  temperature,  in 
Carnivorous  animals,  appears  to  be  sufficiently  kept  up  by  the  combustion  of 
the  carbon  and  hydrogen,  set  free  by  the  decay  (or  metamorphosis,  as  it  may  be 
termed,)  of  their  tissues  ;  but  this  combustion  goes  on  with  much  more  rapidity, 
in  consequence  of  their  almost  unceasing  activity,  than  it  does  in  the  Herbi- 
vorous animals,  which  lead  comparatively  inactive  lives.  Every  one  who  has 
visited  a  menagerie  must  have  noticed  the  continual  restlessness  of  the  Tigers, 
Leopards,  Hyaenas,  &c.,  which  keep  pacing  from  one  end  of  their  narrow 
cages  to  the  other  ;  and  it  would  seem  as  if  this  restlessness  were  a  natural 
instinct,  impelling  them  to  use  muscular  exertion  sufficient  for  the  metamor- 
phosis of  an  adequate  amount  of  -tissue,  that  enough  carbon  and  hydrogen  may 
be  set  free  for  the  support  of  the  respiratory  process.  And  we  see  a  corre- 
sponding activity  in  the  Human  hunters  of  the  swift-footed  Antelope  and  agile 
Deer,  which  answers  a  similar  purpose  ;  and  which  is  remarkably  contrasted 
with  the  stupid  inertness  of  the  inhabitants  of  the  frigid  zone,  which  is  only 
occasionally  interrupted  by  the  necessity  of  securing  the  supplies  of  food 
afforded  by  the  massive  tenants  of  their  seas.  The  nutrition  of  the  Carnivo- 
rous races  may,  then,  be  thus  described.  The  bodies  of  the  animals  upon 
which  they  feed  contain  flesh,  fat,  &c.,  in  nearly  the  same  proportion  as  their 
own  ;  and  all,  or  nearly  all,  the  aliment  they  consume,  goes  to  supply  the 
waste  in  the  fabric  of  their  own  bodies,  being  converted  into  its  various  forms 
of  tissue.  After  having  remained  in  this  condition  for  a  certain  time,  varying 
according  to  the  use  that  is  made  of  them,  these  tissues  undergo  another 
metamorphosis,  which  ends  in  restoring  them  to  inorganic  matter  ;  and  thus 
give  back  to  the  Mineral  world  the  materials  which  were  drawn  off  from  it  by 
Plants.  Of  these  materials,  part  are  burned  off,  as  it  were,  within  the  body, 
by  union  with  the  oxygen  of  the  air,  taken  in  through  the  lungs  ;  and  are 
discharged  from  these  organs,  in  the  form  of  carbonic  acid  and  water  ;  the 
remainder  are  carried  off  in  the  liquid  form  by  other  channels.  Hence  we 
may  briefly  express  the  destination  of  their  food  in  the  following  manner  :  — 


Food  consisting  of"}  c   T  .   .        ^     A    ,  .,.      fCarbonic     acid    and   water 

albumen,  fibrin,  and  1  Convert-  S  J^JgL  (   metamor-  J     thrown  off  b?  respiration. 
other  azotized  com-  \  ed  into   1    ^e.    CphoseT?ntb  1  Urea  and  biliarT  matter>  &c" 
pounds  J  ^thrown  off  by  other  excretions. 


But  in  regard  to  the  Herbivorous  animals,  the  case  is  different.  They  per- 
spire much  more  abundantly,  and  their  temperature  is  thus  continually  kept 
down.  They  consequently  require  '  a  more  active  combustion,  to  develop 
sufficient  bodily  heat  ;  and  the  materials  for  this  are  supplied,  as  we  have 
seen,  by  the  non-azotized  portions  of  their  food,  rather  than  by  the  metamor- 
phosis of  their  own  tissues,  which  takes  place  with  much  less  rapidity  than  in 
the  Carnivorous  tribes.  Hence  we  may  thus  express  the  destination  of  this 
part  of  their  food  ;  that  of  the  azotized  matter,  here  much  smaller  in  amount, 
will  be  the  same  as  in  the  preceding  case. 

Starch,  oil,  and  J  partly  I  Fatty  and"^  but  chiefly  CCarbonic  acid  and  Water,  dis- 
other  non-azotized  >  converted  <  other  an  i-  £>  th  ro  wn  off<  engaged  by  the  respiratory 
compounds  )  into  f  mal  tissues^  directly  as  (^process. 

The  proportion  ofvthe  food  deposited  as  fat,  will  depend  in  part  upon  the 
surplus  which  remains,  after  the  necessary  supply  of  materials  has  been 
afforded  to  the  respiratory  process.  Hence,  the  same  quantity  of  food  being 
taken,  the  quantity  of  fat  will  be  increased  by  causes  that  check  the  perspira- 
tion, and  otherwise  prevent  the  temperature  of  the  body  from  being  lowered, 
so  that  there  is  need  of  less  combustion  within  the  body  to  keep  up  its  heat. 


324  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

This  is  consistent  with  the  teachings  of  experience  respecting  the  fattening  of 
cattle ;  for  it  is  well  known  that  this  may  bfe  accomplished  much  sooner,  if  the 
animals  are  shut  up  in  a  warm  dwelling  and  covered  with  cloths,  than  if  they 
are  freely  exposed  in  the  open  air. — Now  the  condition  of  Man  may  be  regarded 
as  intermediate  between  these  two  extremes.  The  construction  of  his  digestive 
apparatus,  as  well  as  his  own  instinctive  propensities,  point  to  a  mixed  diet  as 
that  which  is  best  suited  to  his  wants.  It  does  not  appear  that  a  diet  composed 
of  ordinary  vegetables  only,  is  favourable  to  the  full  development  of  either 
his  bodily  or  mental  powers ;  but  this  cannot  be  said  in  regard  to  a  diet  of 
which  bread  is  the  chief  ingredient,  since  the  gluten  it  contains  appears  to  be 
as  well  adapted  for  the  nutrition  of  the  animal  tissues,  as  does  the  flesh  of 
animals.  On  the  other  hand,  a  diet  composed  of  animal  flesh  alone  is  the  least 
economical  that  can  be  conceived ;  for,  since  the  greatest  demand  for  food  is 
created  in  him  (taking  a  man  of  average  habits  in  regard  to  activity  and  the 
climate  he  inhabits),  by  the  necessity  for  a  supply  of  carbon  and  hydrogen  to 
support  his  respiration,  this  want  may  be  most  advantageously  fulfilled  by  the 
employment  of  a  certain  quantity  of  non-azotized  food,  in  which  these  ingre- 
dients predominate.  Thus  it  has  been  calculated,  that  some  fifteen  pounds  of 
flesh  contain  no  more  carbon  than  four  pounds  of  starch.  A  savage  with  one 
animal  and  an  equal  weight  of  starch,  could  support  life  for  the  same  length 
of  time,  during  which  another  restricted  to  animal  food,  would  require  five 
such  animals,  in  order  to  procure  the  carbon  necessary  for  respiration.  Hence 
we  see  the  immense  advantage  as  to  economy  of  food,  which  a  fixed  agricul- 
tural population  possesses  over  the  wandering  tribes  of  hunters,  which  still 
people  a  large  part  both  of  the  old  and  new  continents.  The  mixture  of  the 
azotized  and  non-azotized  compounds  (gluten  and  starch),  that  exists  in  wheat 
flour,  seems  to  be  just  that  which  is  most  useful  to  Man ;  and  hence  we  see 
the  explanation  of  the  fact,  that,  from  very  early  ages  bread  has  been  regarded 
as  the  "staff  of  life."  In  regard  to  the  nutritious  properties  of  different  arti- 
cles of  vegetable  food,  these  may  be  generally  estimated  by  the  proportion  of 
azote  they  contain ;  which  is  in  almost  every  instance  less  than  that  existing  in 
good  wheat  flour. 

434.  Besides  these  substances,  there  are  certain  Mineral  ingredients,  which 
may  be  said  to  constitute  part  of  the  food  of  Animals;  being  necessary  to'their 
support,  in  the  same  manner  as  other  mineral  substances  are  necessary  to 
the  support  of  Plants.  Of  this  kind  are  common  salt,  and  also  phosphorus, 
sulphur  and  lime,  either  in  combination  or  separate.  The  uses  of  Salt  are 
very  numerous  and  important.  It  consists  of  two  substances  of  opposite 
qualities,  muriatic  acid  and  soda;  and  the  former  is  the  essential  ingredient  in 
the  gastric  juice  ;  whilst  the  latter  performs  a  very  important  part  in  the  pro- 
duction of  bile.  Phosphorus  is  chiefly  required  to  be  united  with  fatty  matter, 
to  serve  as  the  material  of  the  nervous  tissue  ;  and  to  be  combined  with  oxygen 
and  lime,  to  form  the  bone-earth,  by  which  the  bone  is  consolidated.  Sulphur 
exists  in  small  quantities  in  several  animal  tissues ;  but  its  part  is  by  no  means 
so  important  as  that  performed  by  phosphorus.  Lime  is  required  for  the  con- 
solidation of  the  bones,  and  for  the  production  of  the  shells  and  other  hard 
parts  that  form  the  skeletons  of  the  Invertebrata.  To  these  ingredients  we 
may  also  add  Iron,  which  is  a  very  important  element  in  the  red  blood  of  Ver- 
tebrated  animals. — These  substances  are  contained,  more  or  less  abundantly, 
in  most  articles  generally  used  as  food;  and  where  they  are  deficient,  the  ani- 
mal suffers  in  consequence,  if  they  are  not  supplied  in  any  other  way.  Thus 
common  Salt  exists,  in  no  inconsiderable  quantity,  in  the  flesh  and  fluids  of 
animals,  in  milk,  and  in  the  egg :  it  is  not  so  abundant,  however,  in  plants ; 
and  the  deficiency  is  usually  supplied  to  herbivorous  animals  by  some  other 
means.  Thus  salt  is  purposely  mingled  with  the  food  of  domesticated  animals ; 


NATURE  OF  THE  DIGESTIVE  APPARATUS.  325 

and  in  most  parts  of  the  world  inhabited  by  wild  cattle,  there  are  spots  where 
it  exists  in  the  soil,  and  to  which  they  resort  to  obtain  it.  Such  are  the 
"  buffalo  licks"  of  North  America.  Phosphorus  exists  also  in  the  yolk  and 
white  of  the  Egg,  and  in  Milk,— the  substances  on  which  the  young  animal 
subsists  during  the  period  of  its  most  rapid  growth ;  and  it  abounds,  not  only 
in  many  animal  substances  used  as  food,  but  also  (in  the  state  of  phosphate  of 
lime  or  bone-earth)  in  the  seeds  of  many  plants,  especially  the  grasses.  In 
smaller  quantities  it  is  found  in  the  ashes  of  almost  every  plant.  When  flesh, 
bread,  fruit,  and  husks  of  grain,  are  used  as  the  chief  articles  of  food,  more 
phosphorus  is  taken  into  the  body  than  it  requires  ;  and  the  excess  has  to  be 
carried  out  in  the  excretions.  Sulphur  is  derived  alike  from  vegetable  and 
animal  substances.  It  exists  in  flesh,  eggs,  and  milk  ;  also  in  the  azotized  com- 
pounds of  plants ;  and  (in  the  form  of  sulphate  of  lime)  in  most  of  the  river 
and  spring-water  that  we  drink.  Iron  is  found  in  the  yolk  of  egg,  and  in 
milk,  as  well  as  in  animal  flesh ;  it  also  exists  in  small  quantities  in  most  vege- 
table substances  used  as  food  by  Man, — such  as  potatoes,  cabbage,  peas,  cucum- 
bers, mustard,  &c.;  and  probably  in  most  articles  from  which  other  animals 
derive  their  support.  Lime  is  one  of  the  most  universally  diffused  of  all  mineral 
bodies ;  for  there  are  very  few  animal  or  vegetable  substances,  in  which  it  does 
not  exist.  It  is  most  commonly  taken  in  among  the  higher  animals,  combined 
with  Phosphoric  acid,  so  as  to  form  bone  earth ;  and  in  this  state  it  exists  largely 
in  the  seeds  of  most  grasses,  especially  in  wheat-flour.  If  it  were  not  for  their 
deficiency  in  Phosphate  of  Lime,  beans  and  peas  would  be  more  nutritious 
than  wheaten-flour,  the  proportion  of  azotized  matter  they  contain  being  much 
larger.  A  considerable  Quantity  of  lime  exists,  in  the  state  of  carbonate  and 
sulphate,  in  all  hard  water. 

435.  The  introduction  of  alimentary  matter  into  the  system,  is  accomplished 
in  Animals  by  the  reception  of  food  into  an  internal  cavity,  where  it  is  sub- 
jected to  a  preparatory  process,  to  which  nothing  analogous  exists  in  Plants, 
and  which  is  termed  Digestion.  This  process  may  be  said  to  have"  three 
different  purposes  in  view ; — the  reduction  of  the  alimentary  matter  to  a  fluid 
form,  so  that  it  may  become  capable  of  absorption ; — the  separation  of  that 
portion  of  it  which  is  fit  to  be  assimilated  or  converted  into  organized  texture, 
from  that  which  cannot  serve  this  purpose,  and  which  is  at  once  rejected ; — 
and  the  alteration  (when  required)  of  the  chemical  constitution  of  the  former, 
which  prepares  it  for  the  important  changes  it  is  subsequently  to  undergo. 
The  simplest  conditions  requisite  for  the  accomplishment  of  these  purposes 
are  the  following : — a  fluid  capable  of  performing  the  solution  and  of  effecting 
the  required  chemical  changes ; — a  fluid  capable  of  separating  the  unorgan- 
izable  matter,  by  a  process  analogous  to  chemical  precipitation ;— and  a  cavity 
or  sac,  in  which  these  operations  may  be  performed.  In  the  lowest  Animals, 
we  find  this  cavity  formed  on  a  very  simple  plan ;  being  evidently  nothing 
else  than  an  inversion  of  the  external  integument,  communicating  with  the 
exterior  by  one  orifice  only,  through  which  the  food  is  drawn  in,  and  the 
excrementitious  matter  rejected.  The  fluid  necessary  to  dissolve  the  food, 
which  is  known  by  the  name  of  gastric  fluid  or  juice,  and  that  required  to 
separate  the  portion  which  is  to  be  thrown  off,  which  is  known  as  the  bile,  are 
secreted  in  the  walls  of  the  stomach.  In  the  Sea-Anemone,  which  affords  a 
very  characteristic  example  of  this  type  of  structure,  it  cannot  be  ascertained 
that  the  very  rapid  solution  of  food,  which  takes  place  in  the  digestive  cavity, 
is  assisted  by  any  movement  of  its  walls.  In  Polypes  of  a  higher  con- 
formation, however,  the  digestive  cavity  is  provided  with  a  second  orifice; 
the  stomach  opens  into  an  intestinal  tube,  through  which  the  excrement  is 
rejected  in  little  pellets;  and  the  food,  before  entering  the  true  digestive 
cavity,  is  submitted  to  a  powerful  gizzard  or  triturating  apparatus.  Still  the 
28 


326 


OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

[Fig.  80. 


A  view  of  the  Organs  of  Digestion,  opened  in  nearly  their  wholg  length ;  a  portion  of  the  O3sophagus  has 
been  removed  on  account  of  want  of  space  in  the  figure;  the  arrows  indicate  the  course  of  substances  along 
the  canal ;  1,  the  upper  lip,  turned  off  the  mouth ;  2,  its  frsenum;  3,  the  lower  lip,  turned  down ;  4,  its  frsenum ; 
5,  5,  inside  of  the  cheeks,  covered  by  the  lining  membrane  of  the  mouth;  6,  points  to  the  operting  of  the  duct 
of  Steno;  7,  roof  of  the  mouth;  8,  lateral  half  arches;  9,  points  to  the  tonsils;  10,  velum  pendulum  palati; 
11,  surface  of  the  tongue;  12,  papillae  near  its  point;  13,  a  portion  of  the  trachea;  14,  the  oesophagus;  15, 
its  internal  surface;  16,  inside  of  the  stomach;  17,  its  greater  extremity  or  great  cul-de-sac;  18,  its  lesser 
extremity  or  smaller  cul-de-sac ;  19,  its  lesser  curvature ;  20,  its  greater  curvature ;  21,  the  cardiac  orifice ; 
22,  the  pyloric  orifice;  23,  upper  portion  "of  duodenum;  24,  25,  the  remainder  of  the  duodenum;  26,  its 
valvulse  conniventus;  27,  the  gall  bladder;  28,  the  cystic  duct;  29, division  of  hepatic  ducts  in  the  liver; 
30,  hepatic  duct;  31,  ductus  communis  choledochus;  32,  its  opening  into  the  duodenum;  33,  ductus  Wir- 
sungii,  or  pancreatic  duct;  34,  its  opening  into  the  duodenum;  35,  upper  part  of  jejunum;  36,  the  ileum; 
37,  some  of  the  valvute  conniventus;  38,  lowej  extremity  of  the  ileum ;  39,  ileo-colic  valve ;  40, 41,  caecum, 
or  caput  coli ;  42,  appendicula  vermilbrmis ;  43,  44,  ascending  colon ;  45,  transverse  colon ;  46,  47,  descend- 
ing, colon;  48,  sigmoid  flexure  of  the  colon ;  49,  upper  portion  of  the  rectum;  50,  its  lower  extremity;  51, 
portion  of  the  levator-ani  muscle ;  52,  the  anus.] 

bile,  like  the  gastric  juice,  is  secreted  in  the  walls  of  the  stomach  ;  as  may  be 
distinctly  perceived  in  many  of  these  animals,  on  account  of  their  transparency, 
and  the  bright  yellow  colour  of  the  fluid.  As  we  ascend  the  animal  series, 


MASTICATION  AND  DEGLUTITION.  327 

we  find  no  essential  change  in  the  character  of  the  digestive  apparatus.  The 
biliary  follicles  are  gradually  collected  into  a  glandular  mass,  which  is  altoge- 
ther removed  from  the  walls  of  the  stomach,  and  which  pours  its  secretion  into 
the  intestinal  tube,  at  a  short  distance  from  its  commencement ;  the  gastric 
juice,  however,  is  still  secreted  in  minute  sacs  imbedded  in  the  substance  of 
the  membrane  ;  the  form  and  arrangement  of  these  will  be  hereafter  described 
(CHAP.  xii.).  Several  accessory  glands  are  added,  the  uses  of  which  are  not 
accurately  known ;  and  particular  modifications  of  the  apparatus  are  adapted 
to  peculiarities  in  the  nature  of  the  food,  or  in  the  mode  of  its  ingestion.  As 
a  general  rule  it  may  be  stated,  that  the  digestive  apparatus  is  most  simple  in 
Carnivorous  animals,  in  which  it  has  to  effect  little  change  upon  the  aliment, 
except  solution,  in  order  to  bring  it  to  the  state  fit  for  absorption ;  whilst  it  is 
most  complex  in  those  that  feed  upon  Vegetable  matter,  which  needs  to  un- 
dergo a  greater  change,  both  in  its  chemical  composition  and  in  the  mechanical 
arrangement  of  its  components,  before  it  can  be  rendered  subservient  to  animal 
nutrition. 

II.  Mastication  and  Deglutition. 

436.  The  first  step  in  the  process  of  reduction  is  the  Mastication  of  the 
food,  and  the  impregnation  of  its  comminuted  particles  with  the  salivary  secre- 
tion.    Mastication  is  evidently  of  great  importance,  in  preparing  the  sub- 
stances to  be  afterwards  operated  on,  for  the  action  of  their  solvent ;  and  it 
exactly  corresponds  with  the  trituration,  to  which  the  Chemist  would  submit 
any  solid  matter,  that  he  might  present  it  in  the  most  advantageous  form  to  a 
digestive  menstruum.     The  complete  disintegration  of  the  alimentary  matter, 
therefore,  is  of  great  consequence  ;  and,  if  imperfectly  effected,  the  subsequent 
processes  are  liable  to  derangement.     This  derangement  we  continually  meet 
with :  for  there  is  not,  perhaps,  a  more  frequent  source  of  Dyspepsia  (difficult 
digestion),  than  imperfect  mastication,  whether  resulting  from  the  haste  with 
which  the  food  is  swallowed,  or  from  the  want  of  the  proper  instruments. 
The  disintegration  of  the  food  by  mechanical  reduction  is  manifestly  aided 
by  Insalivation :   it  is  doubtful,  however,  to  what  degree  the  saliva  has  any 
chemical  effect  upon  it.     It  has  been  ascertained  that  this  fluid  has  the  power 
of  converting  starch  into  sugar, — a  conversion  which  does  take  place  in  the 
stomach ;  but  from  the  experiments  of  Berzelius  and  Miiller,  it  is  doubtful 
whether  the  solution  of  other  alimentary  substances  is  more  facilitated  by  the 
impregnation  of  them  with  saliva,  than  if  pure  water  only  had  been  employed.* 
The  chemical  nature  of  the  Salivary  secretion  will  be  described  at  the  same 
time  with  the  structure  of  the  gland  itself  (CHAP.  xn.). 

437.  When  the  reduction  of  the  food  in  the  mouth  has  been  sufficiently 
accomplished,  it  is  carried  into  the  oesophagus  by  the  action  of  Deglutition. 
The  share  which  the  nervous  system  has  in  this  action  has  been  already  stated 
(§  191) ;  and  it  here  only  remains  to  define  more  precisely  the  different  move- 
ments which  are  concerned  in  it.     These  were  first  described  in  detail  by  Ma- 
gendie  ;  but  his  account  requires  some  modification',  through  the  more  recent 
observations  of  Dzondi.t    The  first  stage  in  the  process  is  the  carrying  back 
of  the  food  until  it  has  passed  the  anterior  palatine  arch ;  this,  which  is  effected 
by  the  approximation  of  the  tongue  and  palate,  is  a  purely  voluntary  move- 

*  A  different  result  has  been  given,  however,  by  the  recent  experiments  of  Dr.  Wright ; 
and  perhaps  it  would  be  correct  .to  say,  that  the  peculiar  animal  matter  of  the  Saliva, 
being  itself  in  a  state  of  change,  is  capable  of  acting  on  substances  with  which  it  is 
brought  in  contact  somewhat  in  the  manner  of  a  ferment:  thus  commencing  the  pro- 
cess which  is  to  be  carried  on  in  the  stomach  (§  456). 

f  Miiller's  Physiology,  p.  501. 


338  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

[Fig.  81. 


A  view  of  the  Muscles  of  the  Tongue,  Palate.  Larynx  and  Pharynx— as  well  as  the  position  of  the  upper 
portion  of  the  (Esophagus,  as  shown  by  a  vertical  section  of  the  head;  1, 1,  the  vertical  section  of  the  head; 
2,  points  to  the  spinal  canal ;  3,  section  of  the  hard  palate ;  4,  inferior  spongy  bone ;  5.  middle  spongy  bone ; 
6,  orifice  of  the  right  nostril ;  7,  section  of  the  inferior  maxilla ;  8,  section  of  the  os  hyoides ;  9,  section  of 
the  epiglottis;  10,  section  of  the  ericoid  cartilage;  11,  the  trachea,  covered  by  its  lining  membrane;  12, 
section  of  sternum;  13,  inside  of  the  upper  portion  of  the  thorax;  14,  genio-hyo-glossus  muscle;  15,  its 
origin;  16, 17,  the  fan-like  expansion  of  the  fibres  of  this  muscle;  18,  superficialis  linguae  muscle;  19,  ver- 
ticales  linguse  muscle;  20,  genio-hyoideus  muscle;  21,  mylo-hyoideus  muscle;  22,  anterior  belly  of  digas- 
tricus ;  23,  section  of  platysma  myodes ;  24,  levator  menti ;  25.  orbicularis  oris ;  26,  orifice  of  Eustachian 
tube;  27,  levator  palati;  28,  internal  pterygoid;  29,  section  of  velum  pendulum  palati,  and  azygos  uvulse 
muscle;  30,  stylo-pharyngeus;  31,  constrictor  pharyngis  superior;  32,  constrictor  pharyngis  medius;  33, 
insertion  stylo-pharyngeus;  34,  constrictor  pharyngis  inferior;  35,  36,  37,  muscular  coat  of  oesophagus;  38> 
thyreo-arytenoid  muscle  and  ligaments,  and  above  is  the  ventricle  of  Galen;  39,  section  of  arytenoid  carti- 
lage ;  40,  border  of  sterno-hyoideus.] 

ment.  In  the  second  stage,  the  tongue  is  carried  still  further  backwards,  and 
the  larynx  is  drawn  forwards  under  its  root,  so  that  the  epiglottis  is  pressed 
down  over  the  rima  glottidis.  The  muscles  of  the  anterior  palatine  arch  con- 
tract after  the  morsel  has  passed  it,  and  assist  its  passage  backwards  ;  these, 
with  the  tongue,  cut  off  completely  the  communication  between  the  fauces  and 
the  mouth.  At  the  same  time,  the  muscles  of  the  posterior  palatine  arch  con- 
tract in  such  a  manner  as  to  cause  the  sides  of  the  arch  to  approach  each  other 
like  a  pair  of  curtains ;  so  that  the  passage  from  the  fauces  into  the  posterior 
nares  is  nearly  closed  by  them ;  to  the  cleft  between  the  approximated  sides, 
the  uvula  is  applied  like  a  valve.  A  sort  of  inclined  plane,  directed  obliquely 
downwards  and  backwards,  is  thus  formed;  and  the  morsel  slides  along  it  into 
the  pharynx,  which  is  brought  up  to  receive  it.  Some  of  these  acts  may  be 
performed  voluntarily  ;  but  the  combination  of  the  whole  is  instinctive.  The 
third  stage  of  the  process, — the  propulsion  of  the  food  down  the  oesophagus,— 
then  commences.  This  is  accomplished  in  the  upper  part  by  means  of  the 
constrictors  of  the  pharynx ;  and  in  the  lower  by  the  muscular  coat  of  the  oeso- 
phagus itself.  When  the  morsels  are  small,  and  are  mixed  with  much  fluid, 
the  undulating  movements  from  above  downwards  succeed  each  other  very 


ACTION  OF  THE  STOMACH.  329 

rapidly ;  this  may  be  well  observed  in  Horses  whilst  drinking ;  large  morsels, 
however,  are  frequently  some  time  in  making  their  way  down.  Each  portion 
of  food  and  drink  is  included  in  the  contractile  walls,  which  are  closely  applied 
to  it  during  the  whole  of  its  transit.  The  gurgling  sound  which  is  observed 
when  drink  is  poured  down  the  throat  of  a  person  in  articulo  mortis,  is  due  to 
the  want  of  this  contraction.  The  whole  of  the  third  stage  is  completely  in- 
voluntary.— The  usual  peristaltic  movements  of  the  oesophagus  are  reversed 
in  Vomiting ;  and  this  reversion  has  been  observed,  even  after  the  separation 
of  the  stomach  from  the  oesophagus,  as  a  consequence  of  the  injection  of  tartar- 
ized  antimony  into  the  veins.  At  the  point  where  the  oesophagus  enters  the 
stomach,— the  cardiac  orifice  of  the  latter,— there  is  a  sort  of  sphincter,  which 
is  usually  closed.  This  opens  when  there  is  a  sufficient  pressure  on  it,  made 
by  accumulated  food ;  and  afterwards  closes,  so  as  to  retain  the  food  in  the 
stomach.  The  opening  of  the  cardia  is  one  of  the  first  acts  which  take  place 
in  vomiting.  When  the  sphincter  is  paralyzed  by  division  of  the  pneumo- 
gastric  nerve,  the  food  regurgitates  into  the  oesophagus. 

III.  Action  of  the  Stomach. 

438.  A  remarkable  opportunity  of  ascertaining  the  condition  of  the  Stomach 
during  Digestion,  has  lately  presented  itself,  in  a  case  in  which  a  large  fistu- 
lous  aperture  remained  after  a  wound  that  laid  open  the  cavity,  but  in  which 
the  general  health  has  been  completely  recovered,  so  that  the  process  may  be 
considered  as  normally  performed.*  "  The  inner  coat  of  the  stomach,  in  its 
natural  and  healthy  state,  is  of  a  light  or  pale  pink  colour,  varying  in  its  hues, 
according  to  its  full  or  empty  state.  It  of  a  soft  or  velvet-like  appearance,  and 
is  constantly  covered  with  a  very  thin,  transparent,  viscid  mucus,  lining  the 
whole  interior  of  the  organ.  By  applying  aliment  or  other  irritants,  to  the  in- 
ternal coat  of  the  stomach,  and  observing  the  effect  through  a  magnifying  glass, 
innumerable  lucid  points,  and  very  fine  nervous  or  vascular  papillae,  can  be 
seen  arising  from  the  villous  membrane,  and  protruding  through  the  mucous 
coat,  from  which  distils  a  pure,  limpid,  colourless,  slightly  viscid  fluid.  The 
fluid  thus  excited  is  invariably  distinctly  a,cid.  The  mucus  of  the  stomach  is 
less  fluid,  more  viscid  or  albuminous,  semi-opaque,  sometimes  a  little  saltish, 
and  does  not  possess  the  slightest  character  of  acidity.  The  gastric  fluid  never 
appears  to  be  accumulated  in  the  cavity  of  the  stomach  while  fasting ;  and  is 
seldom,  if  ever,  discharged  from  its  proper  secerning  vessels,  except  when 
excited  by  the  natural  stimulus  of  aliment,  mechanical  irritation  of  tubes,  or 
other  excitants.  When  aliment  is  received,  the  juice  is  given  out  in  exact  pro- 
portion to  its  requirements  for  solution,  except  when  more  food  has  been  taken 
than  is  necessary  for  the  wants  of  the  system."  That  the  quantity  of  the 
Gastric  Juice  secreted  from  the  walls  of  the  stomach  depends  rather  upon  the 
general  requirements  of  the  system,  than  upon  the  quantity  of  food  introduced 
into  the  digestive  cavity,  is  a  principle  of  the  highest  practical  importance,  and 
cannot  be  too  steadily  kept  in  view  in  Dietetics.  A  definite  proportion  only 
of  aliment  can  be  perfectly  digested  in  a  given  quantity  of  the  fluid  ;  the  action 
of  which,  like  that  of  other  chemical  operations,  ceases  after  having  been  exer- 
cised on  a  fixed  and  definite  amount  of  matter.  "  When  the  juice  has  become 

*  See  the  case  of  Alexis  St.  Martin,  with  the  observations  and  experiments  of  Dr.  Beau- 
mont, republished  in  this  country  by  Dr.  A.  Combe.  [A  very  extended  examination  of 
the  phenomena  of  gastric  digestion  has  been  made  by  M.Blondlot.  The  chief  subject  of 
experiment  was  a  dog.  in  which  he  maintained,  without  affecting  the  health,  a  fismlous 
opening  into  the  stomach  for  more  than  two  years.  His  examinations  have  furnished 
many  new  and  important  facts,  and  have  confirmed  those  of  Dr.  Beaumont  made  on 
Alexis  St.  Martin  in  nearly  every  point.] 

28* 


330  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

saturated,  it  refuses  to  dissolve  more  ;  and,  if  an  excess  of  food  has  been  taken, 
the  residue  remains  in  the  stomach,  or  passes  into  the  bowels  in  a  crude  state, 
and  becomes  a  source  of  nervous  irritation,  pain  and  disease,  for  a  long  time." 
The  unfavourable  effect  of  an  undue  burthen  of  food  upon  the  stomach  itself 
interferes  with  its  healthy  action ;  and  thus  the  quantity  really  appropriate  is 
not  dissolved.  The  febrile  disturbance  is  thus  increased ;  and  the  mucous 
membrane  of  the  stomach  exhibits  evident  indications  of  its  morbid  condition. 
The  description  of  these  indications,  given  by  Dr.  Beaumont,  is  peculiarly 
graphic,  as  well  as  Hygienically  important. 

439.  "In  disease  or  partial  derangement  of  the  healthy  function,  the  mucous 
membrane  presents  various  and  essentially  different  appearances.  In  febrile 
conditions  of  the  system,  occasioned  by  whatever  cause, — obstructed  perspira- 
tion, undue  excitement  by  stimulating  liquors,  overloading  the  stomach  with 
food,  fear,  anger,  or  whatever  depresses  or  disturbs  the  nervous  system, — the 
villous  coat  becomes  sometimes  red  and  dry,  at  other  times  pale  and  moist, 
and  loses  its  smooth  and  healthy  appearance  ;  the  secretions  become  vitiated, 
greatly  diminished,  or  even  suppressed ;  the  coat  of  mucus  scarcely  perceptible, 
the  follicles  flat  and  flaccid,  with  secretions  insufficient  to  prevent  the  papillae 
from  irritation.  There  are  sometimes  found  on  the  internal  coat  of  the  stomach 
eruptions  of  deep-red  pimples,  not  numerous,  but  distributed  here  and  there 
upon  the  villous  membrane,  rising  above  the  surface  of  the  mucous  coat. 
These  are  at  first  sharp-pointed,  and  red,  but  frequently  become  filled  with 
white  purulent  matter.  At  other  times,  irregular,  circumscribed  red  patches, 
varying  in  size  and  extent  from  half  an  inch  to  an  inch  and  a  half  in  circum- 
ference, are  found  on  the  internal  coat.  These  appear  to  be  the  effects  of 
congestion  in  the  minute  blood-vessels  of  the  stomach.  There  are  also  seen 
at  times  small  aphthous  crusts,  in  connection  with  these  red  patches.  Abra- 
sion of  the  lining  membrane,  like  the  rolling  up  of  the  mucous  coat  into  small 
shreds  or  strings,  leaving  the  papillae  bare  for  an  indefinite  space,  is  not  an 
uncommon  appearance.  These  diseased  appearances,  when  very  slight,  do 
not  always  affect  essentially  the  gastric  apparatus.  When  considerable,  and 
particularly  when  there  are  corresponding  symptoms  of  disease, — as  dryness 
of  the  mouth,  thirst,  accelerated  pulse,  &c. — no  gastric  juice  can  be  extracted 
by  the  alimentary  stimulus.  Drinks  are  immediately  absorbed  or  otherwise 
disposed  of;  but  food  taken  in  this  condition  of  the  stomach  remains  undigested 
for  twenty-four  or  forty-eight  hours,  or  more,  increasing  the  derangement  of 
the  alimentary  canal,  and  aggravating  the  general  symptoms  of  disease.  After 
excessive  eating  or  drinking,  chymification  is  retarded  ;  and,  though  the  appe- 
tite be  not  always  impaired  at  first,  the  fluids  become  acrid  and  sharp,  excori- 
ating the  edges  of  the  aperture,  and  almost  invariably  producing  aphthous 
patches  and  the  other  indications  of  a  diseased  state  of  the  internal  membrane. 
Vitiated  bile  is  also  found  in  the  stomach  under  these  circumstances,  and  floc- 
culi  of  mucus  are  more  abundant  than  in  health.  Whenever  this  morbid 
condition  of  the  stomach  occurs,  with  the  usual  accompanying  symptoms  of 
disease,  there  is  generally  a  corresponding  appearance  of  the  tongue.  When 
a  healthy  state  of  the  stomach  is  restored,  the  tongue  invariably  becomes 
clean."* 

*  Dr.  A.  Combe's  commentary  on  the  above  passage  is  too  apposite  to  be  omitted. 
"Many  persons  who  obviously  live  too  freely,  protest  against  the  fact,  because  they  feel 
no  immediate  inconvenience,  either  from  the  quantity  of  food,  or  the  stimulants  in  which 
they  habitually  indulge;  or,  in  other  words,  because  they  experience  no  pain,  sickness, 
or  headache,— nothing,  perhaps,  except  slight  fulness  and  oppression,  which  soon  go  off. 
Observation  extended  over  a  sufficient  length  of  time,  however,  shows  that  the  conclu- 
sion drawn  is  entirely  fallacious,  and  that  the  real  amount  of  injury  is  not  felt  at  the 
moment,  merely  because,  for  a  wise  purpose,  nature  has  deprived  us  of  any  conscious- 


ACTION  OF  THE  STOMACH.  331 

440.  In  regard  to  the  cause  of  the  sense  of  Hunger,  many  different  theories 
have  been  propounded.     The  following  positions  may  be  considered  as  well 
ascertained.      The  sense  of  Hunger,  although  referred  to  the  stomach,  is 
governed  by  the  condition  of  the  system  at  large  ;  being  increased,  when  the 
demand  for  Nutrition  is  greater  than  that  which  the  Blood  can  supply  ;  and 
being  diminished,  when  such  an  addition  is  made  to  the  nutritive  ingredients 
contained  in  the  latter,  as  renders  it  adequate  for  this  purpose,  even  though 
this  addition  be  not  made  through  the  introduction  of  food  in  the  usual  man- 
ner.    It  is,  however,  immediately  dependent  on  some  condition  of  the  stomach 
itself;  for  it  is  abated,  if  not  arrested,  by  section  of  the  eighth  pair  of  nerves 
(§  199) ;  and  it  may  be  temporarily  alleviated  by  introducing  into  its  cavity 
matter  which  is  not  alimentary,  but  which  causes  pressure  on  its  walls,  and 
probably  a  flow  of  gastric  juice.     It  may  subside  instantaneously  under  the 
influence  of  mental  emotion,  or  of  other  strong  impressions  on  the  nervous 
system.     It  is  easy  to  prove  that  many  of  the  causes  which  have  been  assigned 
for  it,  are  but  little,  or  not  at  all,  concerned  in  the  production  of  the  sensation. 
Thus,  mere  emptiness  of  the  stomach  does  not  produce  it ;  since,  if  the  pre- 
vious meal  have  been  sufficient,  the  food  passes  from  its  cavity  some  time 
before  a  renewal  of  hunger  is  felt.     It  cannot  be  due  to  the  action  of  the  gastric 
fluid  upon  the  coats  of  the  stomach  themselves ;  since  this  fluid  is  not  poured 
into  the  stomach,  except  when  the  production  of  it  is  stimulated  by  the  irrita- 
tion of  its  secreting  follicles.     By  Dr.  Beaumont  it  is  thought,  that  the  distension 
of  these  follicles  by  the  secreted  fluid  is  the  proximate  cause  of  hunger ;  but 
there  is  no  more  reason  to  believe  that  the  secretion  of  Gastric  fluid  is  accumu- 
lating during  the  intervals  when  it  is  not  required,  than  there  is  in  regard  to 
Saliva,  the  Lachrymal  fluid,  or  any  other  secretions  which  are  occasionally 
poured  out  in  large  quantities  under  the  influence  of  a  particular  stimulus; 
and,  moreover,  it  is  difficult  to  imagine  how  mental  emotion,  or  any  impression 
on  the  nervous  system  alone  (which  is  able,  as  is  well  known,  to  dissipate  the 
keenest  appetite  in  a  moment),  can  relieve  such  distension. 

441.  It  may,  perhaps,  be  a  more  probable  supposition,  that  there  is  a  cer- 
tain condition  of  the  Capillary  circulation  in  the  Stomach,  which  is  prepara- 
tory to  the  secretion,  and  which  is  excited  by  the  influence  of  the  Sympathetic 
nerves,  that  communicate  (as  it  were)  the  wants  of  the  general  system.     This 
condition  may  be  easily  imagined  to  be  the  proximate  cause  of  the  sensation 
of  hunger,  by  acting  on  the  Par  Vagum.     When  food  is  introduced  into  the 
stomach,  the  act  of  secretion  is  directly  excited;  the  capillary  vessels  are 
gradually  unloaded;  and  the  immediate  cause  of  the  impression  on  the  par 
vagum  is  withdrawn.     By  the  conversion  of  the  alimentary  matter  into  mate- 
rials fit  for  the  nutrition  of  the  system,  the  remote  demand  also  is  satisfied ; 
and  thus  it  is,  that  the  condition  of  the  stomach  just  referred  to,  is  permanently 
relieved  by  the  ingestion  of  substances  that  can  serve  as  food.     But  if  the 
ingested  matter  be  not  of  a  kind  capable  of  solution  and  assimilation,  the  feel- 
ing of  hunger  is  only  temporarily  relieved,  and  soon  returns  in  greater  force 
than  before. — The  theory  here  given  seems  reconcilable  with  all  that  has  been 
said  of  the  conditions  of  the  sense  of  hunger ;  and  particularly  with  what  is 

ness  of  either  the  existence  or  the  state  of  the  stomach  during  health.  In  accordance 
with  this,  Dr.  Beaumont's  experiments  prove,  that  extensive  erythematic  inflammation  of 
the  mucous  coat  of  the  stomach  was  of  frequent  occurrence  in  St.  Martin,  after  excesses 
in  eating,  and  especially  in  drinking,  even  when  no  marked  general  symptom  was 
present  to  indicate  its  existence.  Occasionally,  febrile  heat,  nausea,  headache,  and 
thirst  were  complained  ot*  but  not  always.  Had  St.  Martin's  stomach,  and  its  inflamed 
patches,  not  been  visible  to  the  eye,  he  too  might  have  been  pleased  that  his  temporary 
excesses  did  him  no  harm;  but,  when  they  presented  themselves  in  such  legible  cha- 
racters, that  Dr.  Beaumont  could  not  miss  seeing  them,  argument  and  supposition  were 
at  an  end,  and  the  broad  fact  could  not  be  denied." 


332  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

known  of  the  effect  produced  upon  it  by  nervous  impressions,  which  have  a 
peculiar  influence  upon  the  capillary  circulation.  It  also  corresponds  exactly 
with  what  we  know  of  the  influence  of  the  nervous  system,  and  of  mental 
impressions,  upon  other  secretions  ($  426). 

442.  The  sense  of  Hunger,  like  other  sensations,  may  not  be  taken  cogni- 
zance of  by  the  mind,  if  its  attention  be  strongly  directed  towards  other  objects ; 
of  this  fact,  almost  every  one  engaged  in  active  occupations,  whether  mental 
or  bodily,  is  occasionally  conscious.  The  nocturnal  student,  who  takes  a  light 
and  early  evening  meal,  and,  after  devoting  himself  to  his  pursuits  for  several 
hours  uninterruptedly,  retires  to  rest  with  a  wearied  head  and  an  empty 
stomach,  but  without  the  least  sensation  of  hunger,  is  frequently  prevented 
from  sleeping  by  an  indescribable  feeling  of  restlessness  and  deficiency;  and 
the  introduction  of  a  small  quantity  of  food  into  the  stomach  will  almost  instan- 
taneously allay  this,  and  procure  comfortable  rest.  Many  persons,  again,  who 
desire  to  take  active  exercise  before  breakfast,  are  prevented  from  doing  so 
by  the  lassitude  and  even  faintness  which  it  induces, — the  bodily  exercise 
increasing  the  demand  for  food,  whilst  it  draws  off  the  attention  from  the  sen- 
sation of  hunger.  The  Author  may  be  excused  for  mentioning  the  following 
circumstance,  which  some  years  ago  occurred  to  himself;  and  which  seems  to 
him  a  good  illustration  of  the  principle,  that  the  sense  of  hunger  originates 
in  the  condition  of  the  general  system,  and  that  its  manifestation  through  a 
peculiar  action  in  the  stomach,  is  to  be  regarded  as  a  secondary  phenomenon, 
. — adapted,  under  ordinary  circumstances,  to  arouse  the  mind  to  the  actions 
necessary  for  the  supply  of  the  physical  wants, — but  capable  of  being  over- 
looked, if  the  attention  of  the  mind  be  otherwise  directed.  He  was  walking 
alone  through  a  beautiful  country,  and  with  much  to  occupy  his  mind;  and, 
having  expected  to  meet  with  some  opportunity  of  obtaining  refreshment  on 
his  road,  he  had  taken  no  food  since  his  breakfast.  This  expectation,  how- 
ever, was  not  fulfilled ;  but,  as  he  felt  no  hunger,  he  thought  little  of  the  dis- 
appointment. It  was  evening  before  he  approached  the  place  of  his  destina- 
tion, after  having  walked  about  twenty  miles,  resting  frequently  by  the  way ; 
and  he  then  began  to  feel  a  peculiar  lassitude,  different  from  ordinary  fatigue, 
which  rapidly  increased,  so  that  during  the  last  mile  he  could  scarcely  support 
himself.  The  "  stimulus  of  necessity,"  however,  kept  him  up ;  but  on  arriving 
at  his  temporary  home,  he  immediately  fainted.  It  is  obvious  that,  in  this 
case,  the  occupation  of  the  mind  on  the  objects  around,  and  on  its  own  thoughts, 
had  prevented  the  usual  warning  of  hunger  from  being  perceived;  and  the 
effect  which  succeeded  was  exactly  what  was  to  be  anticipated,  from  the 
exhaustion  of  the  supply  of  food  occasioned  by  the  active  and  prolonged  exer- 
tion. 

443.  The  conditions  of  the  sense  of  Thirst  appear  to  be  very  analogous  to 
those  of  hunger.  This  sense  is  not  referred,  however,  to  the  stomach,  but  to 
the  fauces.  It  is  generally  considered  that  it  immediately  results  from  an 
impression  on  the  nerves  of  the  stomach ;  since,  if  liquids  are  introduced  into 
the  stomach  through  an  oesophagus  tube,  they  are  just  as  effectual  in  allaying 
thirst,  as  if  they  are  swallowed  in  the  ordinary  manner.  It  may,  however,  be 
doubted  whether  the  sense  of  thirst  is  not  even  more  immediately  connected 
with  the  state  of  the  general  system  than  that  of  hunger;  for  the  immediate 
relief  afforded  by  the  introduction  of  liquid  into  the  stomach  is  fully  accounted 
for,  by  the  instantaneous  absorption  of  the  fluid  into  the  veins,  which  is  known 
to  take  place,  when  there  is  a  demand  for  it,  not  only  from  Dr.  Beaumont's 
observations,  but  from  many  experiments  made  with  reference  to  this  particu- 
lar question.  This  demand  is  increased  with  almost  equal  rapidity,  by  any 
excess  in  the  amount  of  the  fluid  excretions ;  and  it  may  be  satisfied  without 


ACTION  OF  THE  STOMACH. 


333 


the  introduction  of  water  into  the  stomach*  (§  464).  Thirst  may  also  be  pro- 
duced, however,  by  the  impression  made  by  peculiar  kinds  of  food  or  drink 
upon  the  walls  of  the  alimentary  canal;  thus  salted  or  highly-spiced  meat, 
fermented  liquors  when  too  little  diluted,  and  other  similarly  irritating  agents, 
excite  thirst ;  the  purpose  of  which  is  obviously  to  cause  ingestion  of  fluid,  by 
which  they  may  be  diluted. 

444.  The  food  which  is  propelled  along  the  03sophagus,  enters  the  Stomach 
through  its  cardiac  orifice,  in  successive  waves ;  and  it  is  immediately  sub- 
jected to  a  peculiar  peristaltic  movement,  which  has  for  its  object  to  produce 
the  thorough  intermixture  of  the  gastric  fluid  with  the  alimentary  mass,  and 
also  to  aid  the  solution  of  the  latter  by  the  gentle  trituration  to  which  it  is  thus 

[Fig.  82. 


A  front  view  of  the  Stomach,  distended  by  flatus,  with  the  Peritoneal  Coat  turned  off;  1,  anterior  face  of 
the  oesophagus ;  2,  the  cul-de-sac,  or  greater  extremity ;  3,  the  lesser  or  pyloric  extremity;  4,  the  duodenum ; 
5,  5,  a  portion  of  the  peritoneal  coat  turned  back ;  6,  a  portion  of  the  longitudinal  fibres  of  the  muscular 
coat;  7,  the  circular  fibres  of  the  muscular  coat;  8,  the  oblique  muscular  fibres,  or  muscle  of  Gavard;  9, 
a  portion  of  the  muscular  coat  of  the  duodenum,  where  its  peritoneal  coat  has  been  removed.] 


A  view  of  the  interior  of  the  Stomach,  as  given  by  the  removal  of  its  anterior  parietes ;  1,  oesophagus ;  2, 
cardiac  orifice  of  the  stomach ;  3,  its  greater  extremity,  or  cul-de-sac;  4,  the  greater  curvature ;  5,  line  of 
the  attachment  of  the  omentum  majus;  6,  the  muscular  coat;  7,  the  anterior  cut  edge  of  the  mucous  coat; 
8,  the  rugae  of  the  mucous  coat;  9.  the  lesser  curvature;  10,  the  beginning  of  the  duodenum;  11,  pyloric 
orifice,  or  valve ;  12,  the  first  turn  of  the  duodenum  downwards.] 

*  This  was  among  the  remarkable  results  of  the  injection  of  fluid  into  the  veins,  in  the 
Asiatic  Cholera. 


334  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION, 

[Fig.  84. 


A  view  of -the  interior  of  the  Stomach  and  Duodenum  in  situ,  the  inferior  portion  of  each  having  been 
removed;  1, 1,  the  under  side  of  the  liver;  2,  the  gall  bladder;  3,  3,  the  lesser  curvature  and  anterior  faces, 
as  seen  from  below ;  4,  the  rugae,  about  the  cardiac  orifice ;  5,  the  pyloric  orifice ;  6,  the  rugse,  and  thickness 
of  this  orifice  ;  7,  7,  the  duodenum ;  8,  lower  end  of  the  right  kidney.] 

subjected.  The  muscular  fasciculi  composing  the  human  stomach,  are  so 
disposed  as  to  shorten  its  diameter  in  every  direction ;  and  by  the  alternate 
contraction  and  relaxation  of  these  bands,  a  great  variety  of  motion  is  induced 
in  this  organ,  sometimes  transversely,  and  at  other '  times  longitudinally. 
**  These  motions,"  Dr.  Beaumont  remarks,  "  not  only  produce  a  constant  dis- 
turbance or  churning  of  the  contents  of  the  stomach,  but  they  compel  them,  at 
the  same  time,  to  revolve  about  the  interior  from  point  to  point,  and  from  one 
extremity  to  the  other."  In  addition  to  these  movements,  there  is  a  constant 
agitation  of  the  stomach,  produced  by  the  respiratory  muscles.  The  motions 
of  the  stomach  itself  are  not  performed  on  any  very  exact  plan,  and  are  much 
influenced  by  the  character  of  the  ingesta,  the  state  of  the  general  system,  and 
by  other  circumstances.  The  following  is  the  ordinary  course,  however,  of 
the  revolutions  of  the  food.  "  After  passing  the  oesophageal  ring,  it  moves 
from  right  to  left,  along  the  small  arch  ;  thence,  through  the  large  curvature, 
from  left  to  right.  The  bolus,  as  it  enters  the  cardia,  turns  to  the  left,  passes 
the  aperture,*  descends  into  the  splenic  extremity,  and  follows  the  great 
curvature  towards  the  pyloric  end.  It  then  returns,  in  the  course  of  the 
smaller  curvature,  makes  its  appearance  again  at  the  aperture  in  its  descent 
into  the  great  curvature,  to  perform  similar  revolutions.  These  revolutions 
are  completed  in  from  one  to  three  minutes.  They  are  probably  induced  in  a 
great  measure,  by  the  circular  or  transverse  muscles  of  the  stomach.  They 
are  slower  at  first,  than  after  chymification  has  considerably  advanced  ;"  at 
which  time  also  there  is  an  increased  impulse  towards  the  pylorus.  It  is 
probable  that,  from  the  very  commencement  of  chymification,  until  the  organ 
becomes  empty,  portions  of  chyme  are  continually  passing  into  the  duodenum  ; 
for  the  bulk  of  the  alimentary  mass  progressively  diminishes,  and  this  the 
more  rapidly  as  the  process  is  nearer  its  completion. 

445.  The  accelerated  expulsion  appears  to  be  effected  by  a  peculiar  action 
of  the  transverse  muscles ;  and  especially  of  that  portion  o£  them,  which  sur- 
rounds the  stomach  at  about  four  inches  from  its  pyloric  extremity.  This 
band  is  so  forcibly  contracted  in  the  latter  part  of  the  digestive  process,  that  it 
almost  separates  the  two  portions  of  the  stomach  into  a  sort  of  hour-glass  form ; 
and  Dr.  B.  states  that  when  he  attempted  to  introduce  a  long  thermometer 
tube  into  the  pyloric  portion  of  the  stomach,  the  bulb  was  at  first  gently 

*  The  fistulous  orifice  in  St.  Martin's  stomach,  through  which  these  observations  were 
made. 


ACTION  OF  THE  INTESTINAL  TUBE.  335 

resisted,  then  allowed  to  pass,  and  then  grasped  by  the  muscular  parietes 
beyond,  so  as  to  be  drawn  in :  whence  it  is  evident  that  the  contraction  has 
for  its  object,  to  resist  the  passage  of  solid  bodies  into  the  pyloric  extremity  of 
the  stomach,  at  this  stage  of  digestion,  whilst  the  matter  which  has  been 
reduced  to  the  fluid  form  is  pumped  away  (as  it  were)  by  the  action  of  that 
portion  of  the  viscus.  These  peculiar  motions  continue,  until  the  stomach  is 
perfectly  empty,  and  not  a  particle  of  food  or  chyme  remains.  Of  the  degree 
in  which  they  are  dependent  upon  the  influence  of  the  Nervous  System,  some 
idea  has  been  already  given  (§  235) ;  there  is  yet  much  to  be  learned,  how- 
ever, especially  in  regard  to  the  degree  in  which  the  movements  may  be 
checked  or  altered,  by  impressions  transmitted  through  the  nervous  system. 
It  is  stated  by  Brachet  that,  in  some  of  his  experiments  upon  the  Par  Vagum, 
some  hours  after  the  section  of  the  nerve  on  both  sides,  the  surface  only  of  the 
alimentary  mass  was  found  to  have  undergone  solution,  the  remainder  of  the 
mass  remaining  in  the  condition  in  which  it  was  first  ingested  ;  and  if  this 
statement  can  be  relied  on,  it  would  appear  that  the  movements  of  the  stomach, 
like  those  of  the  heart,  can  be  readily  affected  by  a  strong  nervous  impression. 
It  may  be  partly  in  this  manner,  therefore,  and  not  by  acting  upon  the  secre- 
tions alone,  that  strong  Emotions  influence  the  process,  as  they  are  well 
known  to  do.  On  the  other  hand,  the  moderate  excitement  of  pleasurable 
emotions  may  be  favourable  to  the  operation,  not  only  by  giving  firmness  and 
regularity  to  the  action  of  the  heart,  and  thence  promoting  the  circulation  of 
the  blood,  and  the  increase  of  the  gastric  secretion,  but  also  in  imparting  firm- 
ness and  regularity  to  the  muscular  contractions  of  the  stomach. 

IV.  Action  of  the  Intestinal  Tube. 

446.  The  pulpy  substance  to  which  the  aliment  is  reduced,  by  the  me- 
chanical reduction  and  chemical  solution  it  has  undergone  in  the  mouth  and 
stomach,  is  termed  chyme.  The  consistency  of  this  will  of  course  vary  in 
some  degree  with  the  quantity  of  fluid  ingested;  in  general  it  is  grayish, 
semifluid,  and  homogeneous ;  and  possesses  a  slightly  acid  taste,  but  is  other- 
wise insipid.  Dr.  Beaumont  describes  it  as  varying  in  its  aspect, — from  that 
of  cream,  which  it  presents  when  the  food  has  been  of  a  rich  character, — to 
that  of  gruel,  which  it  possesses  when  the  diet  has  been  farinaceous.  The 
passage  of  the  chyme  through  the  pyloric  orifice  is  at  first  slow ;  but  when 
the  digestive  process  is  nearly  completed,  it  is  transmitted  in  much  larger 
quantities.  From  the  time  that  the  ingested  matter  enters  the  intestinal 
canal,  it  is  propelled  by  the  simple  peristaltic  action  of  its  muscular  coat,  which 
is  directly  excited  by  the  contact  either  of  this  matter,  or  of  the  secretions 
which  are  mingled  with  it  ;*  and  all  that  is  not  absorbed  is  thus  conducted  to 
the  rectum,  its  expulsion  from  which  is  due  to  an  action  of  a  distinctly  reflex 
kind,  excited  through  the  nervous  centres  (§  202).  During  its  progress 
through  the  intestinal  tube,  the  product  of  the  gastric  operation  undergoes 
very  important  changes.  The  chyme  is  mingled  in  the  duodenum  with  the 
biliary  and  pancreatic  secretions,  which  effect  an  immediate  alteration  both  in 
its  sensible  and  chemical  properties.  The  nature  of  this  alteration  can  be  best 
estimated,  by  mingling  bile  with  chyme  removed  from  the  body.  This  has 
been  done  by  several  experimenters  on  the  lower  animals  ;  and  by  Dr.  Beau- 
mont in  the  case  already  referred  to,  which  afforded  him  the  means  of  obtaining 
not  only  chyme,  but  bile  and  pancreatic  fluid.  The  effect  of  this  admixture 

*  The  bile  seems  to  have  an  important  share  in  producing  this  effect;  since,  when  the 
ductus  choledochus  is  tied,  constipation  always  occurs.  The  action  of  mercury  as  a 
purgative  appears  to  take  place  through  the  increase  of  the  hepatic  and  other  secretions 
which  it  induces. 


336  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

was  to  separate  the  chyme  into  three  distinct  parts, — a  reddish-brown  sedi- 
ment at  the  bottom, — a  whey-coloured  fluid  in  the  centre, — and  a  creamy 
pellicle  at  the  top.  The  central  portion  is  probably  that  which  is  absorbed  as 
chyle  ;  the  sediment,  partly  consisting  of  the  insoluble  portion  of  the  food,  and 
partly  of  tne  biliary  matter  itself,  is  evidently  excrementitious  ;  the  creamy  or 
oily  portion  is  probably  taken  up  by  the  lacteals,  and  appears  as  fatty  matter 
in  the  fluid  drawn  from  them.  It  is  not  until  the  food  has  passed  the  orifice 
of  the  Ductus  Choledochus,  that  the  absorption  of  chyle  begins, — the  lacteals 
not  being  distributed  upon  the  Stomach,  or  the  higher  part  of  the  Duodenum. 

447.  By  the  gradual  withdrawal  of  their  fluid  portion,  the  contents  of  the 
alimentary  canal  are  converted  into  a  mass  of  greater  consistence ;  and  this, 
as  it  advances  through  the  small  intestines,  assumes  more  and  more  of  a  fsecal 
character.     A  part  of  the  faeces,  however,  may  be  derived  from  the  secretions 
of  the  enteritic  mucous  membrane,  and  of  its  glandulse ;  the  surface  of  the 
former  with  its  simple  follicles,  probably  secretes  nothing  else  than  mucus ; 
but  the  glandulae,  with  which  it  is  so  thickly  studded,  appear  to  serve  as  the 
channel  for  the  elimination  of  putrescent  matter  from  the  blood.     There  can 
be  no  doubt,  that  a  large  quantity  of  fluid  is  poured  out  by  these  glandulse, 
when  they  are  in  a  state  of  irritation  from  disease,  or  from  the  stimulus  of  a 
purgative  medicine  ;  since  the  amount  of  water  discharged  from  the  bowels  is 
often  much  greater  than  that  which  has  been  ingested,  and  must  be  derived 
from  the  blood. — The  secretion  of  the  caecum  has  bejsn  ascertained  to  be  in 
herbivorous  animals,  distinctly  acid  during  digestion  ;"  and  there  is  reason  to 
believe  that  the  food  there  undergoes  a  second  process  analogous  to  that  to 
which  it  has  been  submitted  in  the  stomach,  and  fitted  to  extract  from  it  what- 
ever undissolved  alimentary  matter  it  may  still  contain.  There  is  no  evidence, 
however,  that  this  is  the  case  in  Man,  whose  ccecum  (commonly  termed  the 
appendix  cosci  vermiformis)  is  very  small,  compared  to  that  of  most  herbivorous 
animals. 

V.  Nature  of  Chy unification. 

448.  The  causes  of  the  reduction  of  the  food  in  the  Stomach  have  long  been 
a  fruitful  source  of  discussion  amongst  physiologists  ;  and  various  hypotheses 
have  been  devised  to  account  for  it.     Some  have  compared  the  Stomach  of 
Man  to  the  Gizzard  of  a  fowl,  and  have  supposed  that  the  trituration  of  the 
food  between  its  walls  was  the  essential  element  in  the  process  ;  but  this 
doctrine  is  completely  incompatible  with  the  fact,  that  digestible  substances, 
inclosed  in  metallic  balls  with  perforations  in  their  sides,  are  still  dissolved  by 
the  power  of  the  gastric  fluid,  though  the  walls  of  the  stomach  do  not  come  in 
contact  with  them.  Others,  again,  have  imagined  that  the  process  of  digestion 
is  one  of  putrefaction  ;  but  this  idea,  putting  aside  its  inherent  absurdity,  is 
proved  to  be  incorrect  by  the  fact,  that  the  gastric  juice  has  a  decidedly  anti- 
septic quality.     Others,  in  despair  of  obtaining  any  other  solution,  have  attri- 
buted the  operation  to  the  direct  agency  of  the  vital  principle ;  forgetting  that, 
as  long  as  the  aliment  remains  within  the  stomach  and  intestinal  canal,  it  can 
no  more  be  the  subject  of  any  peculiarly  vital  process,  than  if  it  were  in  contact 
with  the  skin,  of  which  the  mucous  membrane  is  out  an  internal  reflexion. 
The  theory  of  chemical  solution,  which  was  at  first  regarded  by  many  as  quite 
untenable,  has  been  of  late  years  so  much  strengthened  by  new  facts  and 
arguments,  that  there  now  appears  no  valid  reason  for  withholding  our  assent 
from  it ;  even  though  it  cannot  yet  give  a  complete  explanation  of  the  complex 
phenomena  in  question.     The  chief  opposition  to  this  theory  has  arisen  from 
the  difficulty  of  imagining  that  any  simply  chemical  solvent  should  have  the 
power  of  acting  on  so  great  a  variety  of  substances,  and  of  reducing  them  to 


NATURE  OF  CHYMIFICATION.  337 

a  state  so  homogeneous.  This  difficulty,  however,  seems  now  in  a  great 
degree  removed,  by  the  discovery  of  the  close  Chemical  relation  that  subsists 
between  the  various  substances  of  each  of  the  groups  already  enumerated 
(§  430) ;  which  renders  it  easy  to  conceive  that  the  changes  involved  in  their 
reduction  may  be  of  a  very  simple  character. 

449.  The  first  series  of  facts  which  will  be  here  adduced,  as  throwing  light 
on  the  process  of  chymification,  is  that  which  has  been  obtained  by  the  expe- 
riments of  Dr.  Beaumont  upon  the  individual  already  alluded  to  (434).     By 
introducing  a  tube  of  India-rubber  into  the  empty  stomach,  he  was  able  to 
obtain  a  supply  of  Gastric  Juice  whenever  he  desired  it ;  for  the  tube  served 
the  purpose  of  stimulating  the  follicles  to  pour  forth  their  secretion,  and  at  the 
same  time  conveyed  it  away.     This  fluid,  of  which  the  existence  has  been 
denied  by  some  physiologists,  is  not  very  unlike  saliva  in  its  appearance ;  it 
is,  however,  distinctly  acid  to  the  taste  ;  and  chemical  analysis  shows  that  it 
contains  a  considerable  proportion  of  free  muriatic  acid,  and  also  some  acetic 
acid.     The  former  must  evidently  be  derived  from  the  decomposition  of  the 
muriate  of  soda  contained  in  the  blood,  the  remote  source  of  which  is  the  salt 
ingested  with  the  food.     The  latter  is  an  organic  compound,  probably  formed 
at  the  expense  of  some  of  the  saccharine  matter  of  the  previous  aliment.     Of 
equal  importance  with  the  free  acids,  is  an  animal  matter,  soluble  in  cx>ld 
water,  but  insoluble  in  hot,  bearing  considerable  resemblance  to  albumen.    Of 
this  more  will  be  said  hereafter.     Besides  these  principal  ingredients,  the 
gastric  fluid  contains 'muriates  and  phosphates  of  potass,  soda,  magnesia,  and 
lime.     It  possesses  the  power  of  coagulating  albumen  in  an  eminent  degree  ; 
it  is  powerfully  antiseptic,  checking  the  putrefaction  of  meat ;  and  it  is  effec- 
tually restorative  of  healthy  action,  when  applied  to  old  foetid  sores  and  foul 
ulcerating  surfaces.     It  may  be  kept  for  many  months,  if  excluded  from  the 
air,  without  becoming  foetid. 

[The  most  remarkable  results  of  M.  Blondlot's  investigations*  relate  to  the  compo- 
sition of  the  gastric  fluid,  and  different  as  his  conclusions  may  be  from  those  usually 
received,  yet  the  large  quantity  of  fluid  he  was  enabled  to  collect  in  a  purer  state  than 
any  one  hitherto  has  collected  it,  entitles  his  account  to  every  consideration.  He  very 
carefully  distilled  on  a  sand-bath  3875  grains  of  pure  gastric  fluid  obtained  after  feeding 
his  dog  with  raw  meat;  he  repeated  the  distillation,  and  repeated  the  whole  experiment, 
several  times,  with  the  gastric  fluid  of  other  animals  as  well  as  of  the  same  dog,  and  the 
constant  result  was,  that  the  product  of  the  distillation  did  not  once  exhibit  the  slightest 
acid  reaction ;  but  the  residue  in  the  retort  was  always  strongly  acid.  It  was  thus  proved 
that  the  acid  of  the  gastric  fluid  cannot  be  either  the  hydrochloric  or  the  acetic,  for  both 
these  are  volatile  at  the  boiling  point  of  water,  and  would  have  distilled  over. 

A  further  proof  that  it  is  neither  of  these  nor  lactic  acid,  was  furnished  by  the  fact 
that  no  effervescence  is  produced  when  chalk,  marble,  or  any  other  carbonate  of  lime  is 
added  to  the  gastric  fluid:  and  it  was  this  fact  which  chiefly  led  M.  Blondlot  to  his  con- 
clusion, that  the  true  and  almost  only  source  of  the  acidity  of  healthy  gastric  fluid  is  the 
presence  of  superphosphate  and  biphosphate  of  lime.  The  evidence  which  he  gives  in 
addition  to  the  above  is:  1st.  There  is  no  acid  salt,  except  this  superphosphate  of  lime 
which  could  retain  its  acidity  and  remain  in  contact  with  carbonate  of  lime  without 
exciting  decomposition;  2d.  Sulphuric  acid,  added  to  gastric  fluid,  produces  an  abundant 
precipitate  of  sulphate  of  lime,  and  oxalic  acid  a  similar  one  of  oxalate  of  lime.  3d. 
Potash,  soda,  ammonia,  and  lime-water,  produce  abundant  precipitates  of  neutral  phos- 
phate of  lime.  4th.  The  calcined  ash  of  gastric  fluid  was  not  deliquescent,  was  dissolved 
without  effervescence  by  a  few  drops  of  hydrochloric  acid,  with  which  it  formed  chloride 
of  calcium;  it  had,  therefore,  contained  neutral  phosphate  of  lime,  the  excess  of  the  acid 
having  been  decomposed  in  the  calcination. 

The  general  conclusion  of  his  analysis  is,  that  the  gastric  fluid  is  composed  of  ninety- 
nine  parts  of  water,  with  one  part  of  superphosphate  of  lime,  superphosphate  of  am- 
monia, chloride  of  sodium,  mucus,  an  aromatic,  and  a  peculiar  principle.  Similar 
results  were  obtained  from  the  analysis  of  the  gastric  fluid  of  several  animals. — M.  C.] 

450.  The  Gastric  Juice  obtained  from  the  stomach,  was  found  by  Dr.  Beau- 
mont to  possess  the  power  of  dissolving  various  kinds  of  alimentary  substances, 

*  Traite  Analytique  de  la  Digestion,  Paris,  1844. 
29 


338  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

when  these  were  submitted  to  its  action  at  a  constant  temperature  of  100° 
(which  is  about  that  of  the  stomach),  and  were  frequently  agitated.  The 
solution  appeared  to  be  in  all  respects  as  perfect  as  that  which  naturally  takes 
place  in  the  stomach  ;  but  required  a  longer  time.  This  is  readily  accounted 
for,  when  we  remember  that  no  ordinary  agitation  can  produce  the  same  effect 
with  the  curious  movements  of  the  stomach ;  and  that  the  continual  removal 
from  its  cavity  of  the  matter  which  has  been  already  dissolved,  must  aid  the 
operation  of  the  solvent  on  the  remainder.  The  following  is  one  out  of  many 
experiments  detailed  by  Dr.  Beaumont.  "At  llj  o'clock,  A,  M.,  after  having 
kept  the  lad  fasting  for  17  hours,  I  introduced  a  gum-elastic  tube,  and  drew  off 
one  ounce  of  pure  gastric  liquor,  unmixed  with  any  other  matter,  except  a 
small  proportion  of  mucus,  into  a  three-ounce  vial.  I  then  took  a  solid  piece 
of  boiled  recently-salted  beef,  weighing  three  drachms,  and  put  it  into  the 
liquor  in  the  vial ;  corked  the  vial  tight,  and  placed  it  in  a  saucepan  filled 
with  water,  raised  to  the  temperature  of  100°,  and  kept  at  that  point  on  a 
nicely-regulated  sand-bath.  In  forty  minutes,  digestion  had  distinctly  com- 
menced over  the  surface  of  the  meat.  In  fifty  minutes,  the  fluid  had  become 
quite  opaque  and  cloudy ;  the  external  texture  began  to  separate  and  become 
loose.  In  sixty  minutes,  chyme  began  to  form.  At  1  o'clock,  p.  M.,  (digestion 
having  progressed  with  the  same  regularity  as  in  the  last  half-hour),  the  cel- 
lular texture  seemed  to  be  entirely  destroyed,  leaving  the  muscular  fibres  loose 
and  unconnected,  floating  about  in  fine  small  shreds,  very  tender  and  soft.  At 
3  o'clock,  the  muscular  fibres  had  diminished  one-half  since  the  last  exami- 
nation. At  five  o'clock  they  were  nearly  all  digested ;  a  few  fibres  only 
remaining.  At  7  o'clock  the  muscular  texture  was  completely  broken  down, 
and  only  a  few  of  the  small  fibres  could  be  seen  floating  in  the  fluid.  At  9 
o'clock  every  part  of  the  meat  was  completely  digested.  The  gastric  juice, 
when  taken  from  the  stomach,  was  as  clear  and  transparent  as  water.  The 
mixture  in  the  vial  was  now  about  the  colour  of  whey.  After  standing  at  rest 
a  few  minutes,  a  fine  sediment  of  the  colour  of  the  meat  subsided  to  the  bottom 
of  the  vial.  A  piece  of  beef,  exactly  similar  to  that  placed  in  the  vial,  was 
introduced  into  the  stomach,  through  the  aperture,  at  the  same  time.  At  12 
o'clock  it  was  withdrawn,  and  found  to  be  as  little  affected  by  digestion  as  that 
in  the  vial ;  there  was  little  or  no  difference  in  their  appearance.  It  was 
returned  to  the  stomach ;  and,  on  the  string  being  drawn  out  at  1  o'clock,  p. 
M.,  the  meat  was  found  to  be  all  completely  digested  and  gone.  The  effect  of 
the  gastric  juice  on  the  piece  of  meat  suspended  in  the  stomach  was  exactly 
similar  to  that  in  the  vial,  only  more  rapid  after  the  first  half-hour,  and  sooner 
completed.  Digestion  commenced  on,  and  was  confined  to,  the  surface  entirely 
in  both  situations.  Agitation  accelerated  the  solution  in  the  vial,  by  removing 
the  coat  that  was  digested  on  the  surface,  enveloping  the  remainder  of  the  meat 
in  the  gastric  fluid,  and  giving  this  fluid  access  to  the  undigested  portions."* 
451.  Many  variations  were  made  in  other  experiments,  some  of  which 
strikingly  displayed  the  effects  of  thorough  mastication  in  aiding  both  natural 
and  artificial  digestion.  The  following  table  exhibits  some  of  the  most  inte- 
resting results  of  these  experiments.  It  may  also  be  regarded  as  affording 
some  approximation  to  the  relative  solubility  of  different  kinds  of  aliment ;  but 
a  more  accurate  series  of  experiments,  conducted  with  an  express  view  to  the 
determination  of  the  quantity  of  albumen  formed  in  each  case,  is  still  required 
for  this  purpose.  The  proportion  of  gastric  juice  to  aliment,  in  artificial  diges- 
tion, was  generally  calculated  at  one  ounce  of  the  former  to  one  drachm  of  the 
latter.  In  several  of  the  experiments,  the  limited  extent  of  the  powers  of  the 
solvent  was  very  evident ;  its  character  thus  corresponding  exactly  with  that 
of  ordinary  chemical  agents. 

*  Experiments  2  and  3,  of  First  Series. 


•4 

NATURE  OF  CHYMIFICATIONT. 

Mean  Time  of  Chymification. 


339 


ARTICLES  OF  DIET. 

In  Stomach. 

In  Vials. 

Preparation. 

H.    M. 

Preparation. 

H.    M. 

Beef,  with  salt  only 

Boiled 

2-45 

Boiled 

9-  30 

Beef-steak 

Broiled 

3-    0 

Masticated 

8-  15 

Beef,  fresh,  lean,  dry 
Beef,  old,  hard,  salted 

Roasted 
Boiled 

3-30 
4-  15 

Roasted 

7-45 

Mutton,  fresh 

Broiled 

3-    0 

Masticated 

6-45 

Do.        do. 

Boiled 

3-    0 

Do.        do. 

Roasted 

3-  15 

Lamb,  fresh 

Broiled 

2-30 

Venison  steak 

Broiled 

1-35 

Pork,  recently  salted 

Raw 

3-    0 

Raw 

8-30 

Do/              do. 

Fried 

4-  15 

Do.               do. 

Boiled 

4-  30 

Masticated 

6-30 

Pork,  fat  and  lean 

Roasted 

5-  15 

Pig,  sucking 

Roasted 

2-  30 

Veal;  fresh 

Broiled 

4-    0 

Do.      do. 

Fried 

4-  30 

%• 

Liver,  beef's,  fresh 

Broiled 

2-    0 

Cut  fine 

6-  30» 

Heart,  animal 

Fried 

4-    0 

Entire  piece 

13-30 

Brains,  animal 

Boiled 

1-45 

Boiled 

4-  30 

Pig's  feet,  soused 

Boiled 

1-    0 

Tripe,  soused 

Boiled 

1-    0 

Eggs,  whipped 

Raw 

1-30 

Whipped 

4-    0 

Do.   fresh 

Raw 

2-    0 

Raw 

4-  15 

Do.      do. 

Soft  boiled 

3-    0 

Soft  boiled 

6-  13 

Do.      do. 

Hard  boiled 

3-30 

Hard  boiled 

8-    0 

Do.      do. 

Roasted 

2-  15 

Do.      do. 

Fried 

3-30 

Turkey,  wild 

Roasted 

2-  18 

Do.       domestic 

Roasted 

2-30 

Goose,  wild 

Roasted 

2-30 

Ducks,  domestic 

Roasted 

4-    0 

Fowls,        do. 

Boiled 

4-    0 

Do.            do. 

Roasted 

4-    0 

Ducks,  wild 

Roasted 

4-30 

4 

Trout,  salmon,  fresh 

Boiled 

1-30 

Boiled 

3-30 

Cod-fish,  cured,  dry 

Boiled 

2-    0 

Boiled 

5-    0 

Salmon,  salted 

Boiled 

4-    0 

Boiled 

7-45 

Oysters,  fresh 
Do.        do. 

Raw 
Stewed 

2-55 
3-30 

Raw,  entire 
Stewed 

7-30 

8-25 

Sago 

Boiled 

1-45 

Boiled 

3-  15 

Tapioca 

Boiled 

2-    0 

Boiled 

3-20 

Cabbage,  with  vinegar 

Raw 

2-    0 

Shaved 

10-  15 

Do.   "           do. 

Boiled 

4-30 

Boiled 

20-    0 

Beans 

Boiled 

2-30 

Parsnips 

Boiled 

2-30 

Mashed 

6-45 

Potatoes 

Roasted 

2-30 

Bread,  wheat,  fresh 

Baked 

3-  30 

Masticated 

4-  30 

Potatoes 

Boiled 

3-  30 

Mashed 

8-30 

Chicken-soup 

Boiled 

3-    0 

Soup,  beef,  vegetables  and  bread 

Boiled 

4-    0 

Gelatin 

Boiled 

2-30 

Boiled 

4-  45 

Milk 

Boiled 

2-    0 

Boiled 

4-  15 

Cheese,  old,  strong 

Raw 

3-30 

Masticated 

7-  15 

Suet,  mutton,  boiled 

Boiled 

4-  30 

Divided 

10-    0 

340  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

452.  That  the  foregoing  table  can  only  be  regarded  as  approximative,  is 
shown  by  the  fact  substantiated  by  Dr.  Beaumont,  that  the  rapidity  of  diges- 
tion varies  greatly  according  to  the  quantity  eaten,  the  nature  and  amount  of 
the  previous  exercise,  the  interval  since  the  preceding  meal,  the  state  of  health 
and  of  the  weather,  and  the  condition  of  the  mind.     In  scarcely  any  of  the 
experiments  have  these  circumstances  been  carefully  noted ;    and,  as  Dr.  B. 
himself  remarks,  "the  only  way  of  insuring4  minuteness  and  accuracy,  as  to 
the  relative  digestibility  of  "different  kinds  of  diet,  would  be  to  try  the  effect  of 
the  gastric  juice,  in  a  series  of  experiments,  first  on  one  article  of  diet,  and 
then  on  another,  repeating  and  adapting  them  to  meet  all  the  various  condi- 
tions of  the  stomach,  and  the  vicissitudes  and  irregularities  of  the  system,  until 
the  whole  range  should  be  completed, — a  Herculean  task,  which  it  would  take 
years  to  accomplish."     Some  important  inferences,  however,  may  be  drawn 
from  the  foregoing  results.     It  seems  to  be  a  general  rule,  that  the  flesh  of  wild 
animals  is  more  easy  of  digestion  than  that  of  the  domesticated  races  which 
approach  them  most  nearly.     This  may,  perhaps,  be  partly  attributed  to  the 
small  quantity  of  fatty  matter  that  is  mixed  up  with  the  flesh  of  the  former, 
whilst  that  of  the  latter  is  largely  pervaded  by  it.     For  it  appears  from  Dr. 
B.'s  experiments,  that  the  presence  in  the  stomach  of  any  substance  which  is 
difijcult  of  digestion,  interferes  with  the  solution  of  food  that  would  otherwise 
be  soon  reduced.     It  seems  that,  on  the  whole,  beef  is  more  speedily  reduced 
than  mutton,  and  mutton  sooner  than  either  veal  or  pork.     Fowls  are  far  from 
possessing  the  digestibility  that  is  ordinarily  imputed  to  them;  but  turkey  is,  of 
all  kinds  of  flesh  except  venison,  the  most  soluble.     Dr.  B.  has  also  ascertained 
that  moderate  exercise  facilitates  digestion,  though  severe  and  fatiguing  exercise 
retards  it.     If  even  moderate  exercise  be  taken  immediately  after  a  full  meal, 
however,  it  is  probably  rather  injurious  than  beneficial ;  but  if  an  hour  be  per- 
mitted to  elapse,  or  if  the  quantity  of  food  taken  has  been  small,  it  is  of  decided 
benefit. 

453.  The  presence  of  Bile  in  the  stomach  has  been  regarded  by  some  phy- 
siologists as  an  ordinary  occurrence  during  digestion  ;  but  according  to  Dr.  B. 
this  is  not  the  case,  except  in  morbid  conditions  of  the  organ,  or  after  a  long 
perseverance  in  the  use  of  fat  or  oily  food.     It  is  not  impossible  that  the  con- 
version of  such  food  may  be  aided  by  the  bile,  the  free  alkali  of  which  will 
have  a  chemical  operation  upon  it.     Dr.  A.  Combe  suggests  whether  the 
circumstance  of  the  peculiar  digestibility  of  a  piece  of  fat  bacon  in  certain 
forms  of  dyspepsia,  may  not  be  accounted  for  by  the  presence  of  bile  in  the 
stomach  in  this  condition. — Dr.  B.'s  experiments  further  show  that  bulk  is  as 
necessary  for  healthy  digestion,  as  the  presence  of  the  nutrient  principle  itself. 
This  fact  has  been  long  known  by  experience  to  uncivilized  nations.     The 
Kamschatdales,  for  example,  are  in  the  habit  of  mixing  earth  or  saw-dust  with 
the  train-oil,  on  which  alone  they  are  frequently  reduced  to  live.     The  Ved- 
dahs,  or  wild  hunters  of  Ceylon,  on  the  same  principle,  mingle  the  pounded 
fibres  of  soft  and  decayed  wood  with  the  honey,  on  which  they  feed  when 
meat  is  not  to  be  had ;  and  on  one  of  them  being  asked  the  reason  of  the  prac- 
tice, he  replied,  "I  cannot  tell  you,  but  I  know  that  the  belly  must  be  filled." 
It  is  further  shown  by  Dr.  B.,  that  soups  and  fluid  diet  are  not  more  readily 
chymified  than  solid  aliment,  and  are  not  alone  fit  for  the  support  of  the  system  ; 
and  this,  also,  is  conformable  to  the  well-known  results  of  experience  ;  for  a 
dyspeptic  patient  will  frequently  reject  chicken-broth,  when  he  can  retain  solid 
food  or  a  richer  soup.     Perhaps,  as  Dr.  A.  Combe  remarks,  the  little  support 
gained  from  fluid  diet,  is  due  to  the  rapid  absorption  of  the  watery  part  of  it ; 
so  that  the  really  nutritious  portion  is  left  in  too  soft  and  concentrated  a  state  to 
excite  the  healthy  action  of  the  stomach. 

454.  From  the  foregoing  statements  we  may  conclude,  that  the  process  by 


NATURE  OF  CHYMIFICATION.  341 

which  the  food  is  dissolved  in  the  Gastric  fluid  is  of  a  purely  Chemical  nature, 
since  it  takes  place  out  of  the  living  body  as  well  as  in  it, — allowance  being 
made  for  the  difference  in  its  physical  condition.  That  the  natural  process  of 
digestion  is  imitated,  when  the  food  is  submitted  to  the  action  of  the  gastric 
juice  in  a  vial,  not  only  in  regard  to  the  disintegration  of  its  particles,  but  as 
to  the  change  of  character  which  they  are  made  to  undergo,  is  proved  by  the 
fact,  that  the  artificial  chyme  thus  formed  exhibits  the  same  changes  as  the 
real  chyme,  when  submitted  to  the  action  of  the  bile  (§  446).  The  process 
of  digestion,  however,  may  be  freely  conceded  to  be  vital,  in  so  far  as  it  is 
dependent  upon  the  agency  of  a  secreted  product,  which  vitally  alone  (so  far 
at  least  as  we  at  present  know)  can  elaborate ;  and  all  for  which  it  is  here 
contended  is,  that,  when  this  product  is  once  formed,  it  has  an  agency  upon 
the  alimentary  matter,  which,  though  not  yet  fully  understood,  is  conformable, 
in  all  that  is  known  of  its  operation,  to  the  ordinary  laws  of  chemistry.  Thus, 
Digestion  is  conformable  to  Chemical  solution, — -first,  in  the  assistance  which 
both  derive  from  the  minute  division  of  the  solids  submitted  to  it ; — secondly, 
in  the  assistance  which  both  derive  from  the  successive  addition  of  small  por- 
tions of  the  comminuted  solid  to  the  solvent  fluid,  and  from  the  thorough  inter- 
mixture of  the  two  by  continual  agitation; — thirdly,  in  the  limitation  of  the 
quantity  of  food  on  which  a  given  amount  of  gastric  juice  can  operate,  which 
is  precisely  the  case  with  chemical  solvents;— fourthly,  in  the  assistance 
which  both  derive  from  an  elevation  of  temperature,* — the  beneficial  influence 
of  heat  being  only  limited,  in  the  case  of  digestion,  by  its  tendency  to  produce 
decomposition  of  the  gastric  fluid ;— -fifthly,  in  the  different  action  of  the  same 
solvent  upon  the  various  solids  submitted  to  it. 

455.  We  have  now  to  inquire  what  information  has  been  obtained,  with 
regard  to  the  chemical  nature  of  the  organic  principle,  which  performs  so 
important  a  part  in  the  digestive  process.  It  may  be  considered  a  well-esta- 
blished fact,  that  diluted  acids  alone  have  no  power  of  chymifying  alimentary 
substances,  although  capable  of  partially  dissolving  some  of  them ;  but  that 
their  presence  in  the  gastric  fluid  is  essential  to  its  effectual  action.  Thus 
Muller  states  that,  when  small  pieces  of  meat,  or  small  cubes  of  coagulated 
white  of  egg,  have  been  macerated  for  some  time  in  equal  quantities  of  much- 
diluted  muriatic,  acetic,  tartaric,  and  oxalic  acids,  a  precipitate  or  turbidity 
may  be  produced  by  the  ordinary  re-agents ;  but  that  the  masses  are  not  per- 
ceptibly changed,  the  cubes  of  coagulated  white  of  egg  preserving  their  angles 
and  edges  for  weeks.  Small  pieces  of  meat  were  also  placed  in  a  solution  of 
common  salt,  and  submitted  to  the  action  of  a  powerful  galvanic  battery,  which 
would  set  free  muriatic  acid ;  without  the  change  being  perceptibly  accele- 
rated. From  the  subsequent  experiments  of  Eberle  and  Schwann,  however, 
it  appears  that,  although  acids  alone  have  so  little  power  of  digesting  food, 
they  act  energetically  when  combined  with  mucus  of  the  stomach.t  The 
following  is  an  outline  of  these  experiments.  The  mucous  membrane  of  the 
fourth  stomach  of  the  calf,  being  dissected  from  the  other  coats,  and  washed 
with  cold  water  until  it  no  longer  gives  evidence  of  containing  a  free  acid,  is 
macerated  in  water  acidulated  with  muriatic  acid;  and  after  some  time,  the 

*  The  influence  of  temperature  is  remarkably  shown  in  some  of  Dr.  B.'s  experiments. 
He  found  that  the  gastric  juice  had  scarcely  any  influence  on  the  food  submitted  to  it, 
when  the  bottle  was  exposed  to  the  cold  air,  instead  of  being  kept  at  a  temperature  of 
100°.  He  observed  on  one  occasion,  that  the  injection  of  a  single  gill  of  water  at  50° 
into  the  stomach,  sufficed  to  lower  its  temperature  upwards  of  30°;  and  that  its  natural 
heat  was  not  restored  for  more  than  half  an  hour.  Hence  the  practice  of  eating  ice  after 
dinner,  or  even  of  drinking  largely  of  cold  fluids,  is  very  prejudicial  to  digestion. 

f  By  Eberle  it  was  stated  that  the  acidulated  mucus  of  any  membrane  is  an  efficient 
solvent;  but  this  has  been  found  by  Muller  and  Schwann  to  be  an  error,  only  the  mucus 
of  the  stomach  possessing  this  property. 

29* 


342  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

liquor  being  filtered  is  found  to  have  the  property  of  reducing  most  alimentary 
substances,  submitted  to  its  action  at  a  slightly  elevated  temperature ;  even 
though  the  membrane  have  been  previously  dried.  Pieces  of  meat  and  of 
hard-boiled  egg  are  softened  within  twelve  hours;  and  they  disappear  almost 
entirely  after  twelve  hours  more  :  the  fluid  acquires  a  peculiar  sourish  odour, 
which  is  not,  however,  of  a  putrescent  character.  When  the  fluid  is  not 
acidulated,  it  is  found  to  have  no  more  solvent  power  than  simple  water  would 
have.  It  was  stated  by  Schwann,  as  the  result  of  his  experiments,  that  the 
quantity  of  free  acid  remains  the  same  at  the  end  of  the  digestive  process  as  it 
was  at  its  commencement ;  whence  he  inferred,  that  the  acid  does  not  enter 
into  combination  with  the  substances  dissolved:  but  this  was  probably  an 
error,  resulting  from  the  weakness  of  the  organic  base  with  which  the  acid 
combines. 

456.  The  active  agent  in  the  process  appears  to  be  an  organic  compound, 
to  which  the  name  of  pepsin  has  been  given.  The  properties  of  this  have 
been  investigated  by  Wasmann,  who  first  succeeded  in  obtaining  it  in  an 
isolated  state  ;*  his  observations  were  made  upon  the  mucous  membrane  of  the 
stomach  of  the  Pig,  which  greatly  resembles  that  of  Man.  When  this  mem- 
brane is  digested  in  a  large  quantity  of  water  at  from  85°  to  95°,  many  other 
matters  are  removed  from  it  besides  pepsin ;  but  if  this  water  be  removed,  and 
the  digestion  be  continued  with  fresh  water  in  the  cold,  very  little  but  pepsin 
is  then  taken  up.  Pepsin  appears  to  be  but  sparingly  soluble  in  wrater;  when 
its  solution  is  evaporated  to  dryness,  there  remains  a  brown,  grayish,  viscid 
mass,  with  the  odour  of  glue,  and  having  the  appearance  of  an  extract.  The 
solution  of  this  in  water  is  turbid,  and  still  possesses  a  portion  of  the  charac- 
teristic power  of  pepsin,  but  greatly  reduced.  When  strong  alcohol  is  added 
to  a  fresh  solution  of  pepsin,  the  latter  is  precipitated  in  white  flocks,  \vhich 
may  be  collected  on  a  filter,  and  produce  a  gray  compact  mass  when  dried. 
Pepsin  enters  into  chemical  combination  with  many  acids,  forming  compounds 
which  still  redden  litmus  paper;  and  it  is  when  thus  united  with  acetic  and 
muriatic  acids,  that  its  solvent  powers  are  the  greatest.  "  In  regard  to  the 
solvent  power  of  pepsin  for  coagulated  albumen,  it  was  observed  by  M.  Was- 
mann that  a  liquid  which  contains  17-10,000ths  of  acetate  of  pepsin,  and  6 
drops  of  hydrochloric  acid  per  ounce,  possesses  a  very  sensible  solvent  power, 
so  that  it  will  dissolve  a  thin  slice  of  coagulated  albumen  in  the  course  of  6  or 
8  hours'  digestion.  With  12  drops  of  hydrochloric  acid  per  ounce,  the  white 
of  egg  is  dissolved  in  2  hours.  A  liquid  which  contains  3  gr.  of  acetate  of 
pepsin,  and  to  which  hydrochloric  acid  and  white  of  egg  are  alternately  added, 
so  long  as  the  latter  dissolves,  is  capable  of  dissolving  210  grains  of  coagulated 
white  of  egg  at  a  temperature  between  95°  and  104°.  It  would  appear,  from 
such  experiments,  that  the  hydrochloric  acid  is  the  true  solvent,  and  that  the 
action  of  the  pepsin  is  limited  to  that  of  disposing  the  white  of  egg  to  dissolve 
in  hydrochloric  acid.  The  acid  when  alone  dissolves  white  of  egg  by  ebulli- 
tion, just  as  it  does  under  the  influence  of  pepsin;  from  which  it  follows  that 
pepsin  replaces  the  effect  of  a  high  temperature,  which  is  not  possible  in  the 
stomach.  The  same  acid  with  pepsin  dissolved  blood,  fibrin,  meat,  and 
cheese;  while  the  isolated  acid  dissolved  only  an  insignificant  quantity  at  the 
same  temperature ;  but  when  raised  to  the  boiling  point,  it  dissolved  nearly  as 
much,  and  the  part  dissolved  appeared  to  be  of  the  same  nature.  The  epider- 
mis, horn,  the  elastic  tissue  (such  as  the  fibrous  membrane  of  arteries)  do  not 

*  Graham's  Elements  of  Chemistry,  [Am.  Ed.  p.  695.]— It  is  considered  by  Liebig,  how- 
ever, that  Pepsin  has  no  proper  existence  as  such;  and  that  the  dissolving  power  of  the 
animal  membrane  is  due  to  the  state  of  decomposition,  which  has  been  induced  in  it  by 
exposure  to  air.  It  does  not  appear,  however,  that  any  other  membrane  than  that  of  the 
Stomach  can  undergo  this  change. 


NATURE  OF  CHYMIFICATION.  343 

) 

dissolve  in  a  dilute  acid  containing  pepsin.  M.  Wasmann  has  remarked  that 
the  pepsin  of  the  stomach  of  the  pig  is  entirely  destitute  of  the  power  to  coagu- 
late milk,  although  the  pepsin  of  the  stomach  of  the  calf  possesses  it  in  a 
very  high  degree ;  from  which  he  is  led  to  suppose,  that  the  power  of  the 
latter  depends  upon  a  particular  modification  of  pepsin,  or  perhaps  upon 
another  substance  accompanying  it,  which  ceases  to  be  formed  when  the 
young  animal  is  no  longer  nourished  by  the  milk  of  its  mother."* — It  appears 
from  the  recent  inquiries  of  Liebig  and  others,  that  the  solvent  principle  is  a 
protein-compound  in  a  state  of  change;  and  that,  like  ferments  in  general,  it 
possesses  the  property  of  exciting  change  in  other  substances,  with  which  it  is 
brought  in  contact. — Hence  we  should  regard  the  Digestive  process,  as  result- 
ing from  the  combined  actions  of  Fermentation  and  Chemical  solution; — the 
alimentary  substances  being  first  made  to  undergo  an  incipient  fermentation, 
by  the  agency  of  the  pepsin,  which  so  alters  their  condition,  as  to  dispose  them 
to  solution  in  hydrochloric  and  acetic  acids,  with  which  they  form  definite 
chemical  compounds.  This  view  harmonizes  completely  with  the  fact  just 
stated, — that  a  small  quantity  of  pepsin  will  perform  its  part  in  the  digestion 
of  an  unlimited  quantity  of  aliment,  which  is  analogous  to  what  we  know  of 
the  action  of  true  ferments ; — whilst  only  a  definite  quantity  can  be  dissolved 
in  a  limited  amount  of  acid,  which  is  the  case  with  all  acts  of  proper  chemical 
solution. 

457.  Our  knowledge  of  the  nature  of  the  Digestive  process  has  lately- 
received  another  important  addition  from  the  discovery,  that  the  chief  proxi- 
mate principles  of  the  animal  tissues,  and  those  which  have  been  regarded  as 
most  nutritious  among  vegetables,  have  almost  identically  the  same  chemical 
composition.  This  conformity  will  appear  from  the  following  comparative 
analysis,  lately  executed  in  the  laboratory  of  Liebig. 

ALBUMEN. 

FIBRIN.        { A ^        CASEIN. 

Of  E<™:s.  Of  Serum. 

Carbon 54-56  54-48  54-84  54-96 

Nitrogen 15-72  15-70  15-83  15-80 

Hydrogen 6-90  7-01  7-09  7-15 

Oxygen ""] 

Phosphorus j>     22-82  22-81  22-24  22-09 

Sulphur J 

100-00       100-00  100-00       100-00 

The  proportion  of  carbon  to  nitrogen  in  all  these  substances,  is  that  of  8  equi- 
valents of  the  latter  to  one  of  the  former.  They  differ  slightly  in  the  quantity 
of  phosphorus  and  sulphur  which  they  contain ;  but  agree  in  many  other  im- 
portant chemical  properties.  Thus,  they  all  dissolve,  with  the  aid  of  heat,  in 
concentrated  muriatic  acid  ;  and  the  solutions,  kept  for  a  time  at  a  pretty  high 
temperature,  first  assume  a  beautiful  lilac,  and  then  a  rich  violet-blue  colour. 
At  this  stage  of  the  decomposition,  each  of  the  three  substances  reacts  in  the 
same  way  with  carbonate  of  ammonia  and  other  reagents.  The  parallel  vege- 
table principles  are  vegetable  fibrin  (a  constituent  of  gluten  first  properly  dis- 
tinguished by  Liebig),  gluten  itself,  vegetable  albumen,  and  legumin  ;  this  last 
is  termed  by  Liebig  vegetable  casein,  from  its  holding  the  same  relation  to 
vegetable  albumen  that  animal  casein  does  to  animal  albumen.  The  following 
is  the  elementary  composition  of  these  substances : — 

*  Graham,  op.  cit.  [Am.  Ed.  p.  696  ] 


344  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 


VEGETABLE  FIBRIN. 

GLUTEN.       VEG.  ALBUMEN. 

LEGUMEN. 

Carbon     .     . 

.     .     .         54-60 

55-22 

55-01 

54-14 

Nitrogen 

.     .     .          15-81 

15-98 

15-92 

15-67 

Hydrogen     . 

.     .     .           7.30 

7-42 

7-23 

7.15 

Oxygen   .     . 
Phosphorus 

!'.!}>  22-28 

21-38 

21-84 

23-03 

Sulphur J 

Thus  it  appears  that  the  azotized  vegetable  principles  may  be  converted  into 
those  organic  compounds  which  have  been  ordinarily  considered  as  peculiar 
to  animals,  without  any  essential  change  in  their  chemical  composition. 

458.  When  Albumen  or  Fibrin  is  dissolved  in  a  moderately  strong  solution 
of  caustic  potass,  and  is  heated  to  about  120°,  the  small  portions  of  phosphorus 
and  sulphur  it  contains  are  separated  in  the  form  of  phosphate  of  potass  and 
sulphuret  of  potassium ;  and  when  this  solution  is  saturated  with  acetic  acid, 
a  gelatinous  substance  is  precipitated,  which  is  the  same  in  aspect  and  consti- 
tution, whether  obtained  from  fibrin  or  albumen.     To  this  the  term  Protein 
has  been  given.     After  being  washed,  it  is  still  gelatinous,  of  a  grayish  colour, 
and  semi-transparent ;    when  dried,  it  is  yellowish,  hard,  easily  pulverized, 
tasteless,  insoluble  in  water  and  alcohol ;    and,  like  fibrin  and  albumen,  it  is 
not  fusible  by  heat  without  decomposition.     The  formula  for  Protein,  accord- 
ing to  Mulder,  is, — 40  Carbon,  31  Hydrogen,  5  Nitrogen,  12  Oxygen.*     It 
may  be  obtained  equally  well  from  the  globulin  of  blood,  from  the  casein  of 
milk,  and  from  vegetable  albumen ;  whence  it  is  evident  that  these  substances 
are  all  to  be  regarded  as  modifications  of  a  common  principle.     The  nature  of 
these  modifications  may  be  partly  understood  from  the  fact  that  Protein  unites, 
according  to  strictly  chemical  principles,  with  many  inorganic  substances; 
forming  new  compound  acids  when  combining  with  acids ;  and  acting  in  some 
degree  as  an  acid,  when  brought  into  relation  with  bases,  such  as  the  oxides 
of  lead  and  silver,  of  which  one  atom  combines  with  10  of  protein.     Viewed 
as  chemical  compounds,  fibrin  and  albumen  may  be  regarded  as  the  products 
of  the  union  of  protein  with  definite  proportions  of  sulphur  and  phosphorus. 
The  following  are  their  formulae,  according  to  Mulder. 

Fibrin,  and  the  albumen  of  eggs     .     10  Pro.  +  1  Sulph.  -f  |  Phos. 
Albumen  of  Serum      .....     10  Pro.  +  2  Sulph.  +  £  Phos. 

459.  From  these  facts,  taken  in  combination  with  those  already  mentioned, 
it  seems  scarcely  possible  to  resist  the  conclusion  that  the  process  of  Digestion 
(strictly  so  called)  is  one  of  a  purely  Chemical  nature.     The  conversion  of  the 
azotized  animal  and  vegetable  substances  into  Albumen,  can  scarcely  be  viewed 
in  any  other  light ;  for  the  change  of  form  and  of  external  characters  is  in  no 
instance  so  great  as  that  which  starch  and  gum  undergo  during  their  con- 
version into  sugar,  which  is  well  known  to  be  of  a  strictly  chemical  nature. 
The  albumen  thus  formed  is  dissolved  in  the  water  that  has  been  ingested, 
and  in  the  gastric  secretion;    and  becomes  one  of  the  most  important  and 
characteristic  ingredients   of  chyle.     According  to  Dr.  Prout,  the  albumen 
which  is  first  formed  in  the  stomach,  differs  from  the  principle  elsewhere 
known  under  that  name,  in  its  imperfect  coagulation,  when  acted  on  either  by 
acids  or  heat.     This  is  noticed,  even  when  pure  albumen  has  been  introduced 
into  the  stomach ;  for  it  is  first  coagulated,  and  then  dissolved,  so  as  to  present 
the  same  characters  with  the  albumen  formed  from  other  substances.     In  this 
process  it  appears  to  enter  into  chemical  combination  with  a  large  quantity  of 

*  Liebig  takes  rather  a.  different  view  of  its  composition,  which  is,  however,  equally 
conformable  with  analytic  results.  His  formula  is,— 48  Carbon,  36  Hydrogen,  6  Nitro- 
gen, 14  Oxygen. 


NATURE  OF  CHYMIFICATION.  345 

water.  "The  solid  and  tenacious  albumen  is  thus  reduced  to  the  weakest 
possible  state, — to  the  state  as  it  were  of  infancy ;  in  short,  to  a  state  precisely 
analogous  to  that  of  the  weak  sugars  and  other  organic  compounds,  as  compared 
with  the  strong  and  perfect  varieties  of  the  same  substances."  * 

460.  In  regard  to  the  operation  of  the  Digestive  process  upon  the  non-azotized 
vegetable  matters,  which  belong  to  the  class  of  saccharine  compounds,  less  cer- 
tain information  has  been  obtained.     As  already  stated  (§  430)  it  seems  to  be 
the  prevalent  belief  of  Chemists  of  the  present  day,  that  they  are  incapable  of 
undergoing  conversion  into  protein-compounds.     By  Dr.  Prout,  however,  it  is 
distinctly  asserted  that,  where  no  azotized  matter*  existed  in  the  food,  (the  ani- 
mal being  fed,  for  example,  upon  pure  starch,)  and  where  no  albumen  was 
found  in  the  stomach,  that  principle  was  distinctly  traceable  in  the  contents  of 
the  duodenum,  after  the  admixture  of  the  biliary  and  pancreatic  fluids.     Still 
there  is  not  sufficient  evidence  that  such  a  conversion  takes  place;  for  the 
albumen  might  have  been  derived  from  the  blood  circulating  in  the  walls  of 
the  cavity,  the  fluid  portion  of  which  would  naturally  undergo  an  interchange 
with  the  thick  gummy  solution  in  the  intestine,  by  a  process  of  Endosmose. 
By  Dr.  Proutt  it  is  supposed  that,  "under  ordinary  circumstances,  the  azote 
is   principally  furnished  by  a  highly  azotized  substance  (organized  urea?) 
secreted  from  the  blood,  either  into  the  stomach  or  duodenum,;]:  or  into  both  these 
localities ;  and  that  the  portion  of  the  blood  thus  deprived  of  its  azote  is  sepa- 
rated from  the  general  mass  of  blood  by  the  liver,  as  one  of  the  constituents 
of  the  bile  ;  which  secretion,  as  a  whole,  is  remarkably  deficient  in  azote." 
As  the  Saccharine  principles  cannot  be  distinctly  recognized  either  in  the 
blood  or  chyle  (in  a  state  of  health),  it  is  doubtful  whether  they  can  be  absorbed 
without  undergoing  conversion.     Their  simplest  transformation  is  into  lactic 
acid;    which  may  probably  be  absorbed  directly  from  the  stomach,  by  the 
blood-vessels  of  its  villi.     But  there  is  evidence  that  they  may  be  also  con- 
verted into  oleaginous  compounds;    and  they  probably  form  a  considerable 
part  of  the  fatty  matter  contained  in  the  chyle,  the  quantity  of  which  seems 
often  greater  than  that  pre-existing  in  the  food.     The  possibility  of  such  a 
conversion  (which  has  been  denied  by  some  eminent  chemists),  has  recently 
been  demonstrated  by  the  careful  repetition  of  the  old  experiment  of  Huber ; 
who  showed  that  Bees,  when  fed  upon  honey  alone,  have  the  power  of  form- 
ing wax  to  an  amount  much  greater  than  that  which  the  honey  contained. 
The  oleaginous  compounds  forming  part  of  the  food  are  probably  absorbed  as 
such ;    and,  in  common  with  those  produced  by  the  transformation  just  de- 
scribed, are  either  used  for  the  maintenance  of  the  respiratory  process,  or  are 
deposited  as  fat.     The  question  whether  they  can  ever,  by  any  addition  of 
highly-azotized  matter,  be  converted   into   protein-compounds,  and  thus  be 
applied  to  the  nutrition  of  the  azotized  tissues,  still,  in  the  Author's  opinion, 
remains  undecided;  although  there  are  not  wanting  those  who  speak  quite 
decidedly  upon  the  impossibility  of  such  transformation. 

VI.  Lacteal  and  Lymphatic  Absorption. 

461.  Although  there  can  be  no  doubt  that  the  Mucous  membrane  is  capable 
of  absorbing  by  its  whole  surface,  it  can  scarcely  be  questioned  that  this  func- 
tion is  most  energetically  performed  by  the  villi  which  cover  it.     These  are 
short  processes,  from  a  quarter  of  a  line  to  a  line  and  a  half  in  length  ;  giving 
to  the  membrane,  where  they  are  most  numerous,  a  fleecy  appearance.     In 

*  Bridgewaler  Treatise,  p.  503* 

f  On  Stomach  and  Urinary  Diseases,  [Am.  ed.,  p.  370,  note.] 

*  May  this  be  the  function  of  the  glands  of  Brunner,  which  are  situated  in  the  duode- 
dum  and  commencement  of  the  jejunum  only?  w.  u.  c. 


346 


OF  DIGESTION  ANI>  NUTRITIVE  ABSORPTION. 

Fig.  85.  Fig.  86. 


Vessels  of  an  Intestinal  Villus  of  a  Hare,  from  a 
dry  preparation  by  Dollinger;  1,  1,  veins  filled 
with  white  injection;  2,  2,  arteries  injected  red. 
Magnified  about  45  diameters. 


A.  apex  of  intestinal  villus  from  the  duodenum 
of  human  female ;  B,  a  mesh  of  the  vascular  net- 
work, 1. 1.  filled  up  with  delicate  cellular  tissue.  2. 
Magnified  about  45  diameters.  (After  Wagner.) 


Fig.  87. 


Man  thoy  are  commonly  cylindrical  or  nearly  so ;  but  in  many  of  the  lower 
animals  they  are  spread  out  into  broader  laminae  at  their  base,  and  are  con- 
nected together  so  as  to  form  ridges  or  folds.  It  was  formerly  believed  that 
the  villi  were  not  supplied  with  blood-vessels.  So  far  is  this  from  being  the 
case,  however,  that  in  each  villus  there  is  a  minute  plexus  of  blood-vessels,  of 
which  the  larger  branches  may  even  be  seen  with  the  naked  eye,  when  they 
are  distended  with  blood.  It  can  scarcely  be  doubted  that  through  these 
capillaries  takes  place  the  absorption  of  fluid  from  the  digestive  cavity,  which 
will  be  immediately  stated  to  convey  a  portion  of  their  contents  directly  into 
the  veins  (§  463).  The  Lacteal  vessels,  which  are  distributed  upon  the  walls 
of  the  intestine,  but  not  upon  those  of  the  stomach, 
occupy  the  interior  of  the  villi  of  the  former ;  each 
lacteal  tube  commencing,  as  it  were,  in  the  midst  of 
the  tissue  of  a  villus.  The  accompanying  figure 
represents  the  appearance  offered  by  the  incipient 
lacteals  in  the  villi  of  the  jejunum  of  a  young  man, 
who  had  been  hung  soon  after  taking  a  full  meal  of 
farinaceous  food.  The  lacteal  that  issued  from  each 
villosity  arose  by  several  smaller  branches,  in  some  of 
which  free  extremities  could  be  traced,  whilst  others 
anastomozed  with  each  other.  It  is  certain  that  the 
lacteals  never  open  by  free  orifices  on  the  surface  of 
the  intestine,  as  was  formerly  imagined;  and  the  same 
is  true  of  the  lymphatics,  which  originate  in  the  sub- 
stance of  the  various  tissues.  From  the  recent  ob- 
servations of  Mr.  Goodsir,*  it  appears  that  the  villi  are 


One  of  the  intestinal  villi, 
with  the  commencement  of  a 
lacteal.  After  Krause. 


*  Edinb.  New  Phil.  Journal,  July,  1842. 


LACTEAL  AND  LYMPHATIC  ABSORPTION.  347 

enclosed  in  a  very  delicate  membrane  (analogous  to  that  which  lies  under  the 
epidermis  and  epithelium  in  the  skin  and  mucous  membrane,  (§  640) ;  and 
that  when  digestion  is  not  going  on,  they  are  covered  by  an  epithelium.  The 
space  between  the  reticulations  of  the  blood-vessels  and  lymphatics,  towards 
the  extremity  of  each  villus,  is  occupied,  whilst  the  absorption  of  chyle  is 
taking  place,  by  a  number  of  spherical  vesicles  or  cells,  varying  in  diameter 
from  the  l-1000th  to  1 -2000th  of  an  inch,  and  containing  an  opalescent  fluid. 
At  the  part  where  the  vesicles  approach  the  granular  texture  of  the  substance 
of  the  villus,  minute  granular  or  oily  particles  are  seen.  When  the  intestine 
contains  no  more  chyme,  the  vesicles  disappear  almost  entirely,  the  lacteals 
empty  themselves,  and  the  villi  become  flaccid ;  the  epithelium,  which  had 
fallen  off'  during  the  process  of  Absorption,  is  then  renewed.  The  vesicles  at 
the  extremities  of  the  villi  can  scarcely  be  regarded  in  any  other  light  than  as 
cells,  whose  lives  have  but  a  very  brief  duration,  selecting  from  the  materials 
in  contact  with  the  surface  of  the  villi,  and  appropriating  these  to  their  own 
growth,  then  liberating  them,  by  solution  or  disruption  of  the  cell-wall,  in  a 
situation  where  they  can  be  absorbed  by  the  lacteals. 

462.  In  regard  to  the  degree  in  which  the  function  of  Nutritive  Absorption 
is  performed  by  the  Lacteals  and  by  the  Venous  System  respectively,  con- 
siderable difference  of  opinion  has  prevailed.  When  the  Absorbent  vessels 
were  first  discovered,  and  their  functional  importance  perceived,  it  was  ima- 
gined that  the  introduction  of  alimentary  fluid  into  the  vascular  system  took 
place  by  them  alone.  A  slight  knowledge  of  Comparative  Anatomy,  however, 
might  have  sufficed  to  correct  this  error ;  since  no  lacteals  exist  in  the  Inver- 
tebrated  animals,  the  function  of  Absorption  being  performed  by  the  Mesenteric 
veins  alone ;  from  which  it  is  evident  that  the  veins  do  possess  the  power  of 
absorption :  and  it  is  scarcely  to  be  supposed  that  they  should  not  exercise 
this  power  in  Vertebrated  animals  also,  since  their  disposition  on  the  walls  of 
the  intestinal  cavity  is  evidently  favourable  to  it.  On  the  other  hand,  the 
introduction  of  a  new  and  distinct  system  of  vessels  would  seem  to  indicate 
that  they  must  have  some  special  purpose  ;  and  there  can  be  no  doubt  that  the 
absorption  of  nutritive  matter  is  that  for  which  they  are  peculiarly  designed. 
The  fluid  found  in  the  lacteals  is  almost  invariably  the  same ;  being  that  to 
which  the  name  chyle  has  been  applied,  and  which  may  be  regarded  as  im- 
perfectly elaborated  blood.  It  appears  from  the  uniformity  of  its  composition, 
which  forms  a  striking  contrast  with  the  diversity  of  the  food  from  which  it  is 
obtained,  that  the  lacteals  have  in  some  degree  the  power  of  selecting  the  par- 
ticles of  which  it  is  composed ;  and  that,  whilst  they  take  up  such  a  proportion 
of  each  class  of  alimentary  materials,  as  will  rightly  blend  with  the  rest  in 
the  nutritious  fluid,  they  reject  not  only  the  remainder,  but  also  (for  the  most 
part  at  least)  any  other  ingredients  which  may  be  contained  in  "the  fluid  of  the 
intestines.  Such  may  be  stated  as  the  general  result  of  the  experiments  that 
have  been  made  to  determine  their  function ;  though  it  is  unquestionable  that 
extraneous  substances,  especially  of  a  saline  nature,  occasionally  find  their 
way  into  this  system  of  vessels.  This  may  not  improbably  be  due  to  a  cor- 
respondence in  the  size  and  form  of  the  ultimate  particles  of  such  substances, 
with  those  of  the  materials  normally  absorbed  by  the  lacteals.* — From  Mr. 
Goodsir's  observations,  it  would  appear  that  the  power  of  selection  is  a  pecu- 
liar vital  endowment  of  the  cells  at  the  extremities  of  the  villi,  rather  than  of 

*  Experiments  upon  the  function  of  Absorption  in  Plants,  whose  radical  vessels  have 
a  corresponding  power  of  selection,  appear  likely  to  assist  in  elucidating  this  interesting 
subject.  By  the  experiments  of  Dr.  Daubeny  it  has  been  ascertained,  that  if  a  plant 
absorb  any  particular  saline  compound,  it  can  also  be  made  to  absorb  those  which  are 
isomorphous  with  it,  though  it  will  reject  most  others. — See  Princ.  of  Gen.  and  Comp. 
Phys.  §  294. 


348  OF  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

the  lacteals ;  and  it  appears  strictly  analogous  to  the  property  which  is  pos- 
sessed by  the  different  cells  of  Plants,  of  selecting,  from  the  pabulum  common 
to  all  of  them,  the  materials  requisite  for  the  elaboration  of  their  own  peculiar 
products, — such  as  colouring  matter,  starch,  oil,  &c. 

463.  On  the  other  hand,  the  Veins  seem  to  be  less  concerned  in  nutritive 
absorption,  but  take  up  from  the  alimentary  canal  a  portion  of  almost  any  fluid 
matters  which  it  may  contain.  This  seems  to  have  been  established  by  the 
carefully  conducted  experiments  of  MM.  Tiedemann  and  Gmelin,  who  mingled 
with  the  food  of  animals  various  substances,  which,  by  their  colour,  odour,  or 
chemical  properties,  might  be  easily  detected  in  the  fluids  of  the  body.  After 
some  time  the  animal  was  examined ;  and  the  result  was,  that  unequivocal 
traces  of  the  substances  were  not  unfrequently  detected  in  the  venous  blood 
and  in  the  urine ;  whilst  it  was  only  in  a  very  few  instances,  that  any  indi- 
cation of  them  could  be  discovered  in  the  chyle.  The  colouring  matters  em- 
ployed were  various  vegetable  substances ;  such  as  gamboge,  madder,  and 
rhubarb :  the  odorous  substances  were  camphor,  musk,  assafoetida,  &c. ;  while, 
in  other  cases,  various  saline  bodies,  such  as  muriate  of  barytes,  acetate  of  lead 
and  of  mercury,  and  some  of  the  prussiates,  which  might  easily  be  detected 
by  chemical  tests,  were  mixed  with  the  food.  The  colouring  matters,  for  the 
most  part,  were  carried  out  of  the  system,  without  being  received  either  into 
the  veins  or  lacteals ;  the  odorous  substances  were  generally  detected  in  the 
venous  blood  and  in  the  uterine,  but  not  in  the  chyle ;  whilst  of  the  saline 
substances  many  were  found  in  the  blood  and  in  the  urine,  and  a  very  few 
only  in  the  chyle.  A  similar  conclusion  might  be  drawn  from  the  numerous 
instances  in  which  various  substances  introduced  into  the  intestines  have  been 
detected  in  the  blood,  although  the  thoracic  duct  had  been  tied ;  but  these 
results  are  less  satisfactory,  because  even  if  there  is  no  direct  communication 
(as  maintained  by  many)  between  the  lacteals  and  the  veins  in  the  mesenteric 
glands,  the  partitions  which  separate  their  respective  contents  are  evidently  so 
thin,  that  transudation  may  readily  take  place  through  them.  It  would  seem 
probable,  that  substances  perfectly  dissolved  in  the  fluids  of  the  stomach,  are 
taken  into  the  blood-vessels  so  copiously  distributed  on  its  walls,  by  the  simple 
and  necessary  process  of  Endosmose  ;  in  this  manner  we  may  account  for  the 
fact,  that  saline  substances  are  for  the  most  part  readily  absorbed  into  the 
blood ;  and  there  seems  reason  to  believe  that  the  albuminous  portion  of  the 
chyme,  together  with  the  saccharine  principles  or  the  products  of  their  trans- 
formation, may  thus  be  introduced  directly  into  the  circulating  current,  without 
passing  through  the  lacteals. — On  this  subject  there  is  much  need  of  further 
information. 

VII.  Absorption  by  the  General  Surface. 

464.  The  Mucous  Membrane  of  the  alimentary  canal  is  by  no  means  the 
only  channel  through  which  nutritive  or  other  substances  may  be  introduced 
into  the  system.  In  the  lowest  tribes  of  animals,  and  in  the  earliest  condition 
of  the  higher,  it  would  seem  as  if  Absorption  by  the  external  surface  is  almost 
equally  important  to  the  maintenance  of  life,  with  that  which  takes  place 
through  the  internal  reflexion  of  it  forming  the  walls  of  the  digestive  cavity. 
In  the  adult  condition  of  the  higher  animals,  however,  the  special  function  of 
the  latter  is  so  much  exalted,  that  it  usually  supersedes  the  necessity  of  any 
other  supply;  and  the  function  of  the  cutaneous  and  pulmonary  surfaces  may 
be  considered  as  rather  that  of  exhalation  than  of  absorption.  But  there  are 
peculiar  conditions  of  the  system,  in  which  the  imbibition  of  fluid  through  these 
surfaces  is  performed  with  great  activity,  supplying  what  would  otherwise  be 
a  most  important  deficiency.  It  may  take  place  either  through  the  direct 


ABSORPTION  BY  THE  GENERAL  SURFACE.  349 

application  of  fluid  to  the  surface,  or  even  through  the  medium  of  the  atmo- 
sphere, in  which  a  greater  or  less  proportion  of  watery  vapour  is  usually  dis- 
solved. This  absorption  occurs  most  vigorously  when  the  system  has  been 
drained  of  its  fluid,  either  by  an  excess  of  the  excretions,  or  by  a  diminution 
of  the  regular  supply.  It  may  be  desirable  to  adduce  some  individual  cases, 
which  will  set  this  function  in  a  striking  point  of  view.  It  is  well  known  that 
shipwrecked  sailors,  and  others,  who  are  suffering  from  thirst,  owing  to  the 
want  of  fresh  water,  find  it  greatly  alleviated  or  altogether  relieved,  by  dipping 
their  clothes  into  the  sea,  and  putting  them  on  whilst  still  wet,  or  by  frequently 
immersing  their  own  bodies. — Dr.  Currie  relates  the  case  of  a  patient  labour- 
ing under  dysphagia  in  its  most  advanced  stage ;  the  introduction  of  any 
nutriment,  whether  solid  or  fluid,  into  the  stomacn,  having  become  perfectly 
impracticable.  Under  these  melancholy  circumstances,  an  attempt  was  made 
to  prolong  his  existence  by  the  exhibition  of  nutritive  enemata,  and  by  im- 
mersion of  the  body,  night  and  morning,  in  a  oath  of  milk  and  water.  During 
the  continuance  of  this  plan,  his  weight,  which  had  previously  been  rapidly 
diminishing,  remained  stationary,  although  the  quantity  of  the  excretions  was 
increased.  How  much  of  the  absorption  which  must  have  taken  place,  to 
replace  the  amount  of  excreted  fluid,  is  to  be  attributed  to  the  baths,  and  how 
much  to  the  enemata,  it  is  not  easy  to  say ;  but  it  is  important  to  remark  that 
"  the  thirst,  which  was  troublesome  during  the  first  days  of  the  patient's  ab- 
stinence, was  abated,  and,  as  he  declared,  removed  by  the  tepid  bath,  in  which 
he  had  the  most  grateful  sensations."  "  It  cannot  be  doubted,"  Dr.  Currie 
observes,  "  that  the  discharge  by  stool  and  perspiration  exceeded  the  weight 
of  the  clysters  ;"  and  the  loss  by  the  urinary  excretion,  which  increased  from 
24oz.  to  36oz.  under  this  system,  is  only  to  be  accounted  for  by  the  cutaneous 
absorption. — Dr.  S.  Smith  mentions  that  a  man  who  had  lost  nearly  31bs.  by 
perspiration,  during  an  hour  and  a  quarter's  labour  in  a  very  hot  atmosphere, 
regained  8oz.  by  immersion  in  a  warm  bath  at  95°,  for  half  an  hour. — The 
experiments  of  Dr.  Madden*  show  that  a  positive  increase  usually  takes  place 
in  the  weight  of  the  body  during  immersion  in  the  warm  bath,  even  though 
there  is  at  the  same  time  a  continual  loss  of  weight  by  pulmonary  exhalation, 
and  by  transudationt  from  the  skin.  This  increase  was,  in  some  instances, 
as  much  as  5  drachms  in  half  an  hour ;  whilst  the  loss  of  weight  during  the 
previous  half  hour  had  been  6£  drachms :  so  that  if  the  same  rate  of  loss  were 
continued  in  the  bath,  the  real  gain  by  absorption  must  have  been  nearly  an 
ounce  and  a  half.  Why  this  gain  was  much  less  than  in  the  cases  just  alluded 
to,  is  at  once  accounted  for  by  the  fact,  that  there  was  no  deficiency  in  the 
latter  case  in  the  fluids  naturally  present  in  the  body. 

465.  The  quantity  of  water  which  may  be  imbibed  from  the  vapour  of  the 
atmosphere,  would  exceed  belief,  were  not  the  facts  on  which  the  assertion 
rests,  beyond  all  question.  Dr.  Dill  relates  the  case  of  a  diabetic  patient,  who 
for  five  weeks  passed  24  Ibs.  of  urine  every  twenty-four  hours ;  his  ingesta 
during  the  same  period  amounted  to  22  Ibs.  At  the  commencement  of  the 
disease  he  weighed  145  Ibs. ;  and  when  he  died,  27  Ibs.  of  loss  had  been  sus- 
tained. The  daily  excess  of  the  excretions  over  the  ingesta  could  not  have 
been  less  than  4  Ibs. ;  making  140  Ibs.  for  the  thirty-five  days  during  which 
the  complaint  lasted.  If  from  this  we  deduct  the  amount  of  diminution  which 
the  weight  of  the  body  sustained  during  the  time,  we  shall  still  have  113  Ibs. 
to  be  accounted  for,  which  can  only  have  entered  the  body  from  the  atmo- 

*  Prize  Essay  on  Cutaneous  Absorption,  pp.  59—63. 

f  That  part  of  the  function  of  cutaneous  transpiration,  which  consists  in  simple  exha- 
lation, is  of  course  completely  checked  by  such  immersion;  but  that  which  is  the  result 
of  an  actual  secreting  process  in  the  cutaneous  glands  (CHAP,  xn.)  is  increased  by  heat, 
even  though  this  be  accompanied  with  moisture. 
30 


350  ON  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

sphere. — A  case  of  ovarian  dropsy  has  been  recorded,  in  which  it  was  observed 
that  the  patient,  during  eighteen  days,  drank  692  oz.  or  43  pints  of  fluid,  and 
that  she  discharged  by  urine  and  by  paracentesis  1298  oz.  or  91  pints,  which 
leaves  a  balance  of  606  oz.  or  38  pints  to  be  similarly  accounted  for.* — The 
following  remarkable  fact  is  mentioned  by  Dr.  Watson  in  his  Chemical  Essays. 
"  A  lad  at  Newmarket  having  been  almost  starved,  in  order  that  he  might  be 
reduced  to  a  proper  weight  "for  riding  a  match,  was  weighed  at  9  A.  M.,  and 
again  at  10  A.  M.;  and  he  was  found  to  have  gained  nearly  30  oz.  in  weight 
in  the  course  of  this  hour,  though  he  had  only  drunk  half  a  glass  of  wine  in 
the  interim. — A  parallel  instance  was  related  to  the  Author  by  the  late  Sir  G. 
Hill,  then  Governor  of  St.  Vincent.  A  jockey  had  been  for  some  time  in 
training  for  a  race  in  which  that  gentleman  was  much  interested,  and  had  been 
reduced  to  the  proper  weight.  On  the  morning  of  the  trial,  being  much 
oppressed  with  thirst,  he  took  one  cup  of  tea ;  and  shortly  afterwards  his 
weight  was  found  to  have  increased  ft  Ibs.;  so  that  he  was  incapacitated  for 
riding.  Nearly  the  whole  of  the  increase  in  the  former  case,  and  at  least 
three-fourths  of  it  in  the  latter,  must  be  attributed  to  cutaneous  absorption ; 
which  function  was  probably  stimulated  by  the  wine  that  was  taken  in  the  one 
case,  and  by  the  tea  in  the  other. 

466.  Not  only  water,  but  substances  dissolved  in  it,  may  be  thus  introduced. 
It  has  been  found  that  after  bathing  in  infusions  of  madder,  rhubarb,  and  tur- 
meric, the  urine  was  tinged  with  these  substances ;  and  that  a  garlic  plaster 
affected  the  breath,  when  every  care  was  taken,  by  breathing  through  a  tube 
connected  with  the  exterior  of  the  apartment,  that  the  odour  should  not  be 
received  into  the  lungs.t  Gallic  acid  has  been  found  in  the  urine,  after  the 
external  application  of  a  decoction  of  a  bark  containing  it ;  and  the  soothing 
influence,  in  cases  of  neuralgic  pain,  of  the  external  application  of  cherry- 
laurel  water,  is  well  known.  Many  saline  substances  are  absorbed  by  the 
skin,  when  applied  to  it  in  solution ;  and  it  is  interesting  to  remark  that,  con- 
trary to  what  happens  in  regard  to  the  absorption  of  these  from  the  alimentary 
canal,  they  are  for  the  most  part  more  readily  discoverable  in  the  absorbents 
than  in  the  veins.  This  is  probably  due  to  the  fact,  that  the  imbibition  of 
them  is  governed  entirely  by  physical  laws  ;  in  obedience  to  which,  they  pass 
most  readily  into  the  vessels  which  present  the  thinnest  walls  and  the  largest 
surface.  In  the  intestines,  the  vascular  plexus  on  each  villus  is  far  more 
extensive  than  the  ramifying  lacteal  which  originates  in  it ;  and  as  the  walls 
of  the  veins  are  thin,  there  is  considerable  facility  for  the  entrance  of  saline 
.  and  other  substances  into  the  general  current  of  the  circulation ;  but  in  the 
skin,  the  lymphatics  are  distributed  much  more  minutely  and  extensively  than 
the  veins;  and  soluble  matters,  therefore,  enter  them  in  preference  to  the 
veins.  The  absorbent  power  of  the  Lymphatics  of  the  Skin  is  well  shown  by 
the  following  experiment.  A  bandage  having  been  tied  by  Schreger  round 
the  hind-leg  of  a  Puppy,  the  limb  was  kept  for  twenty-four  hours  in  tepid 
milk ;  at  the  expiration  of  this  period,  the  lymphatics  were  found  full  of  milk, 
whilst  the  veins  contained  none.  In  repeating  this  experiment  upon  a  young 
man,  no  milk  could  be  detected  in  blood  drawn  from  a  vein.  It  has  been 
shown  by  Miiller  that  when  the  posterior  extremities  of  a  Frog  were  kept  for 
two  hours  in  a  solution  of  prussiate  of  potass,  the  salt  had  freely  penetrated 
the  lymphatics,  but  had  not  entered  the  veins.  It  does  not  follow,  however, 
from  these  and  similar  experiments,  that  in  all  tissues  the  lymphatics  absorb 
more  readily  than  the  veins;  for  as  the  capillary  blood-vessels  in  the  lungs 
are  much  more  freely  exposed  to  the  surface  of  the  air-cells  than  are  the 
lymphatics,  we  should,  on  the  principles  just  now  stated,  expect  the  former  to 

*  Madden,  loc.  cit.  f  Dunglison's  Physiology,  vol.  L  p.  644. 


ABSORPTION  BY  THE  GENERAL  SURFACE.  351 

absorb  more  readily.  This  appears  from  experiment  to  be  the  fact ;  for,  when 
a  solution  of  prussiate  of  potass  was  injected  by  Mayer  into  the  lungs,  the  salt 
could  be  detected  in  the  serum  of  the  blood  much  sooner  than  in  the  lymph, 
and  in  the  blood  of  the  left  cavities  of  the  heart,  before  it  had  reached  that  of 
the  right. 

467.  It  is  not,  however,  from  the  external  world  alone,  that  Animals  derive 
the  materials  of  their  Nutrition.     It  has  been  stated  (§  84)  that  the  necessity 
for  a  constant  supply  of  food,  arises  from  the  continual  decomposition  which  is 
taking  place  within  the  living  body ;  and  it  will  be  hereafter  shown  that  this 
decomposition  is  connected  with  the  death  of  the  cells,  of  which  the  several 
parts  are  constructed,  these  having  an  independent  life  of  their  own,  and  con- 
sequently a  limited  duration,  which  has  no  immediate  connection  with  that  of 
the  organism  at  large  (§  646).     In  every  portion  of  the  body,  therefore,  mate- 
rials for  nutrition  are  continually  being  set  free  ;  and  we  find  a  peculiar  pro- 
vision for  the  re-introduction  of  these  into  the  circulating  fluid.     All  animals 
which  have  a  lacteal  system  have  also  a  lymphatic  system,  closely  correspond- 
ing to  it  in  aspect,  but  consisting  of  vessels  that  are  distributed  through  the 
whole  body,  instead  of  on  the  intestinal  surface  only,  permeating  almost  every 
tissue,  and  in  many  forming  a  most  minute  plexus.     These  vessels  pass,  like 
the  lacteals,  through  conglobate  glands,  in  which  they  are  brought  into  inti- 
mate relation  with  blood-vessels ;  and  they  empty  their  contents  into  the  same 
receptacle,  so  as  to  pour  them  into  the  blood  in  precisely  the  same  manner. 
The  evident  conformity  in  the  nature  of  the  fluid  which  these  two  sets  trans- 
mit,— joined  to  the  fact  of  the  fluid  Lymph,  like  the  Chyle,  being  conveyed 
into  the  general  current  of  the  circulation  just  before  the  blood  is  again  trans- 
mitted to  the  system  at  large, — almost  inevitably  leads  to  the  inference,  that 
the  lymph  is,  like  the  chyle,  a  nutritious  fluid,  and  is  not  of  an  excrementitious 
character,  as  formerly  supposed.     The  following  is  the  most  recent  compara- 
tive analysis  of  the  two,  as  performed  by  Dr.  G.  O.  Rees ;  the  fluids  were 
procured  from  the  lacteal  and  lymphatic  vessels  of  a  donkey,  previously  to 
their  entrance  into  the  thoracic  duct ;  the  animal  was  killed  seven  hours  after 
a  full  meal. 

Chyle.  Lymph. 

Water  90-237  98-536 

Albuminous  matter        -  3-516  1-200 

Fibrinous  matter  0-370  0-120 

Animal  extractive  matter,  soluble  in  water  and  alcohol  0-332  0-240 

Animal  extractive  matter,  soluble  in  water  only  1-233  1-319 

Fatty  matter     -  3-601  a  trace 

Salts  ; — Alkaline  chloride,  sulphate  and  carbonate,  with  >  n-711  0-585 
traces  of  alkaline  phosphate,  oxide  of  iron                     5 

100-00       100-00 

From  this  analysis  it  appears  that  the  chief  chemical  difference  between  the 
chyle  and  lymph  consists  in  a  much  larger  proportion  of  assimilable  sub- 
stances,— albumen,  fibrin,  and  fatty  matter, — contained  in  the  former:  the 
nature  and  amount  of  the  less  clearly-defined  animal  principles,  and  of  the 
saline  ingredients,  appear  to  be  nearly  identical  in  both. 

468.  Hence  it  can  scarcely  be  doubted  that,  to  use  Dr.  Prout's  expression, 
"  a  sort  of  digestion  is  carried  on  in  all  parts  of  the  body ;"  and  that  such  of 
the  products  of  that  digestion  as  are  fit  to  be  again  converted  into  organized 
tiss.ue,  are  re-introduced  into  the  current  of  the  circulation  by  the  Lymphatics ; 
whilst  those  which  have  undergone  too  great  a  degree  of  decomposition,  are 
carried  off  by  the  Excreting  processes.    In  this  way,  Animals,  when  deprived 


352  ON  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

of  a  sufficient  supply  of  food,  may  live  upon  their  own  flesh  ;  and  there  seems 
no  reason  why  it  should  not  be  as  capable  of  re-conversion  into  living  tissues, 
as  is  that  of  the  animals  on  which  they  feed.  A  very  similar  phenomenon  is 
observed  in  Vegetables.*  It  may  be  stated,  then,  as  a  general  fact,  that  the 
function  of  the  Absorbent  System  is  to  take  up,  and  to  convey  into  the  Circu- 
lating apparatus,  such  substances  as  are  capable  of  appropriation  to  the  nutri- 
tive process ;  whether  these  substances  be  directly  furnished  by  the  external 
world,  or  be  derived  from  the  disintegration  of  the  organism  itself.  We  have 
seen  that,  in  the  Lacteals,  the  selecting  power  is  such,  that  these  vessels  are 
not  disposed  to  convey  into  the  system  any  substances  but  such  as  are  de- 
stined for  this  purpose ;  and  that  extraneous  matters  are  absorbed  in  preference 
by  the  Mesenteric  Veins.  The  case  is  different,  however,  with  regard  to  the 
Lymphatics ;  for  there  is  reason  to  believe  that  they  are  more  disposed  than 
the  veins  to  the  absorption  of  other  soluble  matters  ;  especially  when  these  are 
brought  into  relation  with  the  skin,  through  which  the  lymphatic  vessels  are 
very  profusely  distributed. 

469.  Since  the  time  of  Hunter,  who  first  brought  prominently  forwards  the 
doctrine  alluded  to,  it  has  been  commonly  supposed  that  the  function  of  the 
Lymphatics  is  to  remove,  by  interstitial  absorption,  the  effete  matter,  which  is 
destined  to  be  carried  out  of  the  system;  and  any  undue  activity  in  this  pro- 
cess (such  as  exists  in  ulceration),  or  any  deficiency  in  its  energy  (such  as 
gives  rise  to  dropsical  effusions,  and  other  collections  of  the  same  kind),  have 
been  attributed  to  excess  or  diminution  in  the  normal  operation  of  the  Absorb- 
ent System.  From  what  has  been  stated,  however,  it  appears  that  the  special 
function  of  the  Lymphatics,  like  that  of  the  Lacteals,  is  nutritive  absorption  ;t 

*  See  Principles  of  General  and  Comparative  Physiology,  §  403. 

f  The  Author,  at  the  time  of  the  publication  of  the  First  Edition  of  this  work,  believed 
this  view  to  be  altogether  novel;  he  has  since  learned,  however,  that  a  similar  doctrine 
had  been  put  forward  by  Dr.  Moultrie,  of  South  Carolina,  in  the  American  Journal  of  the 
Medical  Sciences,  for  the  year  1827. 

[In  the  American  Journal  of  the  Medical  Sciences,  for  1827,  Dr.  James  Moultrie  pub- 
lished an  essay  on  the  "  Uses  of  the  Lymph,"  in  which,  amongst  other  things,  attempted 
to  be  sustained,  will  be  found  the  following  views. 

1.  The  lacteals  and  lymphatics  do  not  constitute,  as  they  are  supposed  to  do,  the 
absorbent  system  of  the  animal  economy  ;  they  do  not,  as  the  absorbent  theory  supposes, 
remove  from  the  organs  the  "  cast  off  molecules"  of  which  they  are  composed,  or  carry 
out  of  the  body  the  "effete"  particles  disintegrated  by  the  act  of  the  assimilative  function. 
The  one  is  engaged  in  the  preparation  and  introduction  of  chyle,  and  chyle  only,  into 
the  blood;  the  other  in  elaborating  an  organizable  product — a  recrementitious  secretion 
destined  to  unite  with  it  for  objects  of  a  common  and  nutritious  nature.  2.  The  primary 
object  of  the  lymph,  and  that  for  which  it  is  made  to  commingle  with  the  chyle  in  the 
thoracic  duct,  is  the  vitalization  of  the  latter  fluid.  3.  The  truly  "effete"  matter  of  the 
body  is  the  carbonaceous  element  of  the  venous  blood,  to  which  may  be  added  the  urea 
or  azotic  element  of  the  urine.  Than  these,  we  know  of  nothing  to  which  that  term  can 
be  applied.  4.  The  venous  and  not  the  lacteal  or  lymphatic  system,  therefore,  is  the 
"  absorbent  system,"  in  any  disintegratory  or  effete  sense  of  the  phrase.  5.  Nature,  in 
effecting  the  elimination  of  excrementitious  matter  from  the  constituency  of  the  solid  or 
fluid  parts,  appears  to  aim  at  restoring  to  the  physical  universe,  the  matter  temporarily 
borrowed  for  subsistence,  in  a  state  of  elementary  simplicity,  or  an  approximation  there- 
to ;  that  is,  the  carbon  as  carbon,  the  azote  as  azote,  and  hydrogen  and  oxygen  as  hydro- 
gen and  oxygen.  The  lungs  she  uses  as  one  medium  of  escape  ;  the  kidneys  as  a  second  ; 
and  the  skin  as  a  third,  &c.  Hence,  the  carbonic  acid  gas  of  respiration;  the  urea  of 
the  kidneys,  and  the  aqueous  exhalations  of  the  skin,  pulmonary  transpiration  and 
urine. 

These  doctrines  have  been  regularly  taught  by  Dr.  M.,  in  his  course  of  lectures  on 
physiology,  delivered  in  the  Medical  College  of  the  State  of  South  Carolina,  since  the 
establishment  of  the  College  in  1833.  They  have  also  been  recently  enforced  in  a  bro- 
chure published  by  Dr.  M.,  in  which  he  asserts  and  vindicates  his  claim  to  their  paternity. 
On  the  Organic  Functions  of  Animals.  By  JAMES  MOULTBIE,  M.  D.,  etc.,  Charleston,  S.  C. 
1844.— M.  C.] 


SUPPLY  OF  FOOD  REQUIRED  BY  MAN.  353 

and  that  the  reception  of  any  other  substances  into  their  interior,  must  he 
looked  upon  as  resulting  simply  from  the  permeability  of  their  walls.  This 
statement  applies  to  the  not  unfrequent  occurrence  of  the  absorption  of  bile 
and  other  fluids,  from  the  walls  of  the  cavities  in  which  they  were  collected ; 
with  regard  to  the  absorption  of  pus,  however,  which  has  been  occasionally 
noticed  to  take  place,  both  from  internal  collections,  and  from  open  ulcers,  it 
may  be  remarked,  that  the  lymphatic  vessels  were  not  improbably  laid  open 
by  ulceration ;  since  in  no  other  way  can  be  understood  the  entrance  of  glo- 
bules so  large  as  those  of  pus  into  their  interior.  If  this  view  of  the  function 
of  the  Lymphatics  be  correct,  it  follows  that  we  must  attribute  to  the  Blood- 
vessels the  absorption  of  the  truly  effete  particles  ;  and  in  this  there  would 
seem  no  improbability.  We  know  that  venous  blood  contains  the  elements  of 
two  important  excretions,  that  of  the  lungs  and  that  of  the  bile,  in  a  far  higher 
amount  than  does  arterial  blood ;  and  we  shall  hereafter  see,  that  there  is  a 
certain  portion  of  the  fluid  which  consists  of  "ill-defined  animal  principles" 
that  seem  ready  to  be  thus  thrown  off.  Moreover,  the  materials  of  a  large 
part  of  the  excretory  products  are  probably  derived  from  the  processes  of 
assimilation  themselves ;  each  tissue  appropriating'  the  principles  which  it 
needs,  and  leaving  the  remainder  in  the  fluid  as  superfluous  matter.  It  may 
be  further  remarked,  that  the  reciprocal  part  which  Hunter  imagined  the 
Arteries  and  Lymphatics  to  perform  in  the  function  of  Nutrition,  is  quite 
inconsistent  with  what  is  now  known  of  the  nature  of  that  process  ;  for,  as  will 
subsequently  appear,  it  entirely  consists  in  a  reaction  between  the  tissues  and 
the  nutritious  fluid,  in  which  the  vessels  have  no  share  save  as  the  channels 
of  supply.  When  these  channels  are  obstructed,  or  the  supply  of  new  matter 
is  cut  off  in  any  other  way,  the  removal  of  the  old  by  interstitial  absorption 
becomes  evident ;  and  that  this  is  accomplished  at  least  as  much  by  the  veins 
as  by  the  lymphatics,  appears  from  the  fact,  that  in  some  tissues,  in  which  it 
may  take  place  with  rapidity,  lymphatics  do  not  exist. 

VIII.  Supply  of  Food  required  by  Man. 

470.  The  quantity  of  food  required  for  the  maintenance  of  the  Human 
body  in  health,  varies  so  much  with  the  age,  sex  and  constitution  of  the  indi- 
vidual, and  with  the  circumstances  in  which  he  may  be  placed,  that  it  would 
be  absurd  to  attempt  to  fix  any  standard,  which  should  apply  to  every  particu- 
lar case.  The  appetite  is  the  only  sure  guide  for  the  supply  of  the  wants  of 
each ;  but  its  indications  must  not  be  misinterpreted.  To  eat  when  we  are 
hungry,  is  an  evidently  natural  disposition  ;  but  to  eat  as  long  as  we  are 
hungry  may  not  always  be  prudent.  Since  the  feeling  of  hunger  does  not 
depend  so  much  upon  the  state  of  fulness  or  emptiness  of  the  stomach,  as  upon 
the  condition  of  the  general  system,  it  appears  evident  that  the  ingestion  of 
food  cannot  at  once  produce  the  effect  of  dissipating  it,  though  it  will  do  so 
after  a  short  time  ;  so  that,  if  we  eat  with  undue  rapidity,  we  may  continue 
swallowing  food  long  after  we  have  taken  as  much  as  will  really  be  required 
for  the  wants  of  the  system  ;  and  every  superfluous  particle  is  not  merely  use- 
less but  injurious.  Hence,  besides  its  other  important  ends,  the  process  of 
thorough  mastication  is  important,  as  prolonging  the  meal,  and  giving  time  to 
the  system  to  become  acquainted  (as  it  were)  that  the  supply  of  its  wants  is  in 
progress  ;  so  that  its  demand  may  be  abated  in  due  time  to  prevent  the  inges- 
tion of  more  than  is  required.  It  is  very  justly  remarked  by  Dr.  Beaumont, 
that  the  cessation  of  this  demand,  rather  than  the  positive  sense  of  satiety,  is 
the  proper  guide.  "  There  appears  to  be  a  sense  of  perfect  intelligence  con- 
veyed to  the  encephalic  centre,  which,  in  health,  invariably  dictates  what 
quantity  of  aliment  (responding  to  the  sense  of  hunger  and  its  due  satisfaction) 

30* 


354  ON  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

is  naturally  required  for  the  purposes  of  life  ;  and  which,  if  noticed  and  pro- 
perly attended  to,  would  prove  the  most  salutary  monitor  of  health,  and 
effectual  preventive  of  disease.  It  is  not  the  sense  of  satiety,  for  this  is  be- 
yond the  point  of  healthful  indulgence,  and  is  Nature's  earliest  indication  of 
an  abuse  and  overburden  of  her  powers  to  replenish  the  system.  It  occurs 
immediately  previous  to  this ;  and  may  be  known  by  the  pleasurable  sensa- 
tions of  perfect  satisfaction,  ease  and  quiescence  of  body  and  mind.  It  is  when 
the  stomach  says,  enough  ;  and  it  is  distinguished  from  satiety  by  the  differ- 
ence of  sensations, — the  latter  saying  too  much."  Every  medical  man  is 
well  aware  how  generally  this  rule  is  transgressed ;  some  persons  making  a 
regular  practice  of  eating  to  repletion ;  and  others  paying  far  too  little  atten- 
tion to  the  preliminary  operations,  and  thus  ingesting  more  than  is  good  for 
them,  even  though  they  may  actually  leave  off  with  an  appetite. 

471.  Although  no  universal  law  can  be  laid  down  for  individuals,  however, 
it  is  a  matter  of  much  practical  importance  to  be  able  to  form  a  correct  average 
estimate  ;  and  there  is  no  more  difficulty  in  accomplishing  this  than  there  is 
in  forming  tables  of  mortality.     It  is  by  estimating  the  average  duration  of  life 
that  Insurance  Companies  make  their  calculations  of  the  probable  duration  of 
any  one — and  though  the  actual  result  may,  in  every  individual  case,  be  dif- 
ferent from  that  estimate,  yet  it  holds  good  perfectly  well  for  a  large  number. 
It  is  from  the  experience  afforded  by  the  usual  consumption  of  food  by  large 
bodies  of  men,  therefore,  that  our  data  are  obtained ;  and  these  data  are  suf- 
ficient to  enable  us  to  predict  with  tolerable  accuracy  what  will  be  required  by 
similar  aggregations,  though  they  can  afford  no  guide  to  the  consumption  of 
individuals.     We  shall  first  consider  the  quantity  sufficient  for  men  in  regular 
active  exercise ;  and  then  inquire  how  far  that  may  be  safely  reduced  for 
those  who  lead  a  more  sedentary  life.     The  Diet-scale  of  the  British  Navy  may 
be  advantageously  taken  as  a  specimen  of  what  is  required  for  the  first  class. 
It  is  well  known  that  an  extraordinary  improvement  has  taken  place  in  the 
health  of  seamen  during  the  last  80  years ;  so  that  three  ships  can  now  be 
kept  afloat  with  only  the  same  number  of  men,  which  were  formerly  required 
for  two.     This  is  due  to  the  improvement  in  the  quality  of  the  food,  in  combi- 
nation with  other  prophylactic  means.     At  present  it  may  safely  be  affirmed, 
that  it  would  not  be  easy  to  conceive  of  any  diet-scale  more  adapted  to  answer 
the  required  purpose.     The  health  of  crews  that  have  been  long  afloat,  and 
have  been  exposed  to  every  variety  of  external  conditions,  appears  to  be  pre- 
served (at  least  when  they  are  under  the  direction  of  judicious  officers),  to  the 
full  as  well  as  that  of  persons  subject  to  similar  vicissitudes  on  shore ;  and 
there  can  be  no  complaint  of  insufficiency  of  food,  although  the  allowance 
cannot  be  regarded  as  superfluous.     It  consists  of  from  31  to  35^  ounces  of 
dry  nutritious  matter  daily  ;  of  this  26  oz.  are  vegetable  ;  and  the  rest  animal ; 
9  oz.  of  salt  meat,  or  4£  oz.  fresh,  being  the  allowance  of  the  latter.     This  is 
found  to  be  amply  sufficient  for  the  support  of  strength ;  and  considerable 
variety  is  produced  by  exchanging  various  parts  of  the  diet  for  other  articles. 
This,  however,  is  sometimes  done  erroneously ;  thus  8  oz.  of  fresh  vegetables, 
which  contain  only  1£   oz.  of  solid  nutriment,  are  exchanged  for  12  oz.  of 
flour,  which  is  almost  all  nutritious.      Sugar  and  Cocoa  are  also  allowed; 
partly  in  exchange  for  a  portion  of  the  Spirits  formerly  served  out,  the  dimi- 
nution of  which,  especially  in  the  case  of  boys,  has  been  attended  with  great 
benefit. 

472.  A  considerable  reduction  in  this  amount  is  of  course  admissible,  where 
little  bodily  exertion  is  required,  and  where  there  is  less  exposure  to  low  tem- 
peratures.    In  the  case  of  Prisoners,  the  diet  should  of  course  be  as  spare  as 
possible,  consistently  with  health ;  but  it  should  be  carefully  modified,  in  indi- 
vidual cases,  according  to  several  collateral  circumstances,  such  as  depression 


SUPPLY  OF  FOOD  REQUIRED  BY  MAN.  355 

of  mind,  compulsory  labour,  previous  intemperate  habits,  and  especially  the 
length  of  confinement.  It  has  been  supposed  by  some,  that  prisoners  require 
a  fuller  diet  than  persons  at  large ;  this  is  probably  erroneous  :  but  more  variety 
is  certainly  desirable,  to  counteract,  as  far  as  possible,  the  depressing  influence 
of  their  condition  upon  the  digestive  powers.  The  circumstances  which  oc- 
curred at  the  Mil Ibank  Penitentiary  in  1823,  form  a  lamentable  warning  against 
the  reduction  of  the  diet-scale  to  an  insufficient  amount.  The  allowance  to 
the  prisoners  had  formerly  been  from  31  to  33  oz.  of  dry  nutriment  daily,  and 
the  prison  was  considered  healthy  ;  but  in  1822,  it  was  reduced  to  21  oz. "  The 
health  of  the  prisoners  continued  unbroken  for  nearly  six  months ;  but  scurvy 
then  showed  itself  unequivocally ;  and  out  of  860  prisoners,  437,  or  52  -per 
cent,  were  affected  with  it.  The  effect  of  previous  confinement  here  became 
remarkable ;  for  those  were  chiefly  attacked  who  had  been  in  the  prison  for 
two  years,  a  year,  or  six  months.  Again,  the  prisoners  employed  in  the 
kitchen,  who  had  8  oz.  of  bread  additional  per  day,  were  not  attacked,  except 
three  who  had  only  been  there  a  few  days.  After  the  epidemic  had  spread 
to  a  great  extent,  it  was  found  that  the  addition  of  8  oz.  to  the  daily  allowance 
of  vegetable  food,  and  £  oz.  to  the  animal,  facilitated  the  operation  of  the  reme- 
dies which  were  used  for  the  restoration  of  the  health  of  the  prisoners. — The 
effects  of  confinement  have  been  further  shown  in  the  experience  of  the  Edin- 
burgh House  of  Refuge,  which  was  first  established  in  1832,  for  the  reception 
of  beggars  during  the  cholera,  and  which  has  been  continued  to  the  present 
time.  The  diet  was  at  first  a  quart  of  oatmeal  porridge  for  each  person, 
morning  and  evening;  and  at  dinner  1  oz.  of  meat,  in  broth,  with  7  oz.  of 
bread ;  making  altogether  about  23  oz.  of  solid  food  a  day.  During  some 
months,  this  diet  seemed  to  answer  very  well ;  the  people  went  out  fatter  than 
they  came  in,  owing  to  the  diet  being  better  than  that  to  which  they  had  been 
accustomed ;  but  afterwards,  a  proneness  to  disease  manifested  itself  in  those 
who  had  been  residents  there  for  a  considerable  time,  and  the  diet  was,  there- 
fore, somewhat  increased,  with  good  effect.  The  quantity  of  animal  food  was 
probably  here  too  small ;  and  the  total  weight  might  still  have  been  sufficient, 
if  it  had  been  differently  apportioned.  In  a  Convict-ship,  which  took  out  433 
prisoners  to  New  Holland  in  1802,  the  mortality  was  very  trifling,  and  the 
general  health  good ;  although  these  prisoners  were  supported  on  16  oz.  of 
vegetable  food,  and  7  5  oz.  of  animal  food  per  day, — a  quantity  which  was 
found  to  be  perfectly  sufficient  for  them.  The  aged  inmates  of  work-houses, 
especially  those  who  have  been  accustomed  to  poor  food  during  their  whole 
lives,  require  much  less  than  this  ;  their  vital  functions  being  comparatively 
inactive,  and  their  amount  of  labour  or  exercise  small.  In  the  Edinburgh 
work-house,  of  which  the  inmates  have  usually  good  health,  they  are  fed  upon 
oatmeal-porridge  morning  and  evening,  with  barley-broth  at  dinner;  the  total 
allowance  of  dry  nutriment  is  about  17  oz., — namely,  13  oz.  vegetable,  and  4 
oz.  animal. — It  is  a  curious  effect  of  insufficient  nutriment,  as  shown  by  the 
recent  inquiries  of  Chossat,*  that  it  produces  an  incapability  of  digesting  even 
the  limited  amount  supplied.  He  found  that,  when  turtle-doves  were  supplied' 
with  limited  quantities  of  corn,  but  with  water  at  discretion,  the  whole  amount 
of  food  taken  was  scarcely  ever  actually  digested ;  a  part  of  it  being  rejected 
by  vomiting,  or  passing  off  by  diarrhoea,  or  accumulating  in  the  crops.  It 
seems  as  if  the  vital  powers  were  not  sufficient  to  furnish  the  requisite  supply 
of  gastric  fluid,  when  the  body  began  to  be  enfeebled  by  insufficient  nutrition ; 
or  perhaps  we  might  well  say,  the  materials  of  the  gastric  fluid  were  wanting. 
Hence  the  loathing  of  food,  often  manifested  by  those  who  have  been  subjected 
to  the  influence  of  an  insufficient  diet-scale  in  our  prisons  and  poor-houses, — 

*  Recherches  Experimentales  sur  1'Inanition,  1843. 


356  ON  DIGESTION  AND  NUTRITIVE  ABSORPTION. 

which  has  been  set  down  to  caprice  or  obstinacy,  and  punished  accordingly, — 
may  be  actually  a  proof  of  the  deficiency  of  the  supply,  which  we  might 
expect  to  have  been  voraciously  devoured,  if  really  less  than  the  wants  of  the 
system  require. 

473.  The  smallest  quantity  of  food  upon  which  life  is  known  to  have  been 
supported  with  vigour,  during  a  prolonged  period,  is  that  on  which  Cornaro 
states  himself  to  have  subsisted.  This  was  no  more  than  12  oz.  a  day,  chiefly 
of  vegetable  matter,  for  a  period  of  58  years.  There  is  only  one  instance  on 
record  in  which  his  plan  was  followed ;  and  there  are  probably  few  who  could 
long  persevere  in  it,  at  least  among  those  whose  avocations  require  much 
mental  or  bodily  exertion.  It  is  certain,  however,  that  life,  with  a  moderate 
amount  of  vigour,  may  be  preserved  for  some  time  with  a  very  limited  amount 
of  food  ;  this  appears  from  the  records  of  shipwreck  and  similar  disasters.  In 
regard,  however,  to  those  who  have  been  stated  to  fast  for  a  period  of  months 
or  even  years,  taking  no  nutriment,  but  maintaining  an  active  condition,  it  may 
be  safely  asserted  that  they  were  impostors, — probably  possessing  unusual 
powers  of  abstinence,  which  they  took  care  to  magnify.  The  instances  in 
which  the  life  of  man,  or  of  other  mammalia,  has  been  prolonged  to  the  greatest 
extent  without  water,  are  those  in  which,  from  the  peculiarity  of  the  circum- 
stances, the  cutaneous  exhalation  must  have  been  reduced  to  a  very  small 
amount,  or  in  which  there  may  have  been  an  actual  absorption  of  water  by  the 
skin  and  lungs.  Thus,  Fodere  mentions  that  some  workmen  were  extricated 
alive,  after  fourteen  days'  confinement  in  a  cold  damp  cavern,  in  which  they 
had  been  buried  under  a  ruin.  And  there  is  a  well-known  case  of  a  hog, 
which  was  buried  in  its  stye  for  160  days,  under  thirty  feet  of  the  chalk  of 
Dover  clifT,  and  was  dug  out  alive  at  the  end  of  that  time,  reduced  in  weight 
from  160  Ibs.  to  40  Ibs.:  here  the  temperature  would  be  kept  up  by  the  non- 
conducting power  of  the  chalk  around ;  and  the  air  surrounding  the  animal 
would  soon  become  sufficiently  charged  with  fluid  to  resist  further  evaporation. 
The  time  during  which  life  can  be  supported  under  total  abstinence,  is  usually 
stated  to  vary  from  8  to  10  days ;  the  period  may  be  greatly  prolonged,  how- 
ever, by  the  occasional  use  of  water,  and  still  more  by  a  very  small  supply  of 
food.  In  a  case  recorded  by  Dr.  Willan,  of  a  young  gentleman  who  starved 
himself  under  the  influence  of  religious  delusion,  life  was  prolonged  for  60  days ; 
during  the  whole  of  which  time  nothing  else  was  taken  than  a  little  orange 
juice.  In  a  somewhat  similar  case  which  occurred  under  the  Author's  notice, 
in  the  person  of  a  young  French  lady,  more  than  15  days  elapsed  between  the 
time  that  she  ceased  to  eat  regularly  and  the  time  of  her  being  compelled  to 
take  nourishment ;  during  this  period  she  took  a  good  deal  of  exercise,  and 
her  strength  seemed  to  suffer  but  little,  although  she  swallowed  solid  food  only 
once,  and  then  in  small  quantity.  If  the  cessation  of  muscular  exertion  be 
complete,  it  seems  that  life  is  usually  more  prolonged  than  where  exercise  of 
any  kind  is  performed  ;  and  this  is  what  might  naturally  be  expected.  In  certain 
states  of  the  system,  commonly  known  as  Hysterical,  there  is  frequently  a  very 
remarkable  disposition  for  abstinence,  and  power  of  sustaining  it.  In  a  case 
of  this  kind,  which  occurred  under  the  Author's  own  notice,  a  young  lady 
who  had  suffered  severely  from  the  tetanic  form  of  hysteria  was  unable  to  take 
food  for  three  weeks.  The  slightest  attempt  to  introduce  a  morsel  of  solid 
matter  into  the  stomach,  occasioned  very  severe  vomiting  and  retching ;  and 
the  only  nourishment  taken  during  the  period  mentioned,  was  a  cup  of  tea 
once  or  twice  a  day, — on  many  days  not  even  this  being  swallowed.  Yet  the 
strength  of  the  patient  rather  increased  than  diminished  during  this  period ; 
her  muscles  became  firmer  and  her  voice  more  powerful.  It  may  be  well  to 
remark  that,  under  such  circumstances,  the  continual  persuasions  of  anxious 


SUPPLY  OF  FOOD  REQUIRED  BY  MAN.  357 

friends  are  very  injurious  to  the  patient ;  who  is  much  more  likely  to  come 
round,  if  left  entirely  to  herself. 

474.  Of  the  quantity  which  can  be  devoured  at  a  time,  it  is  scarcely  the 
place  to  speak  ;  since  such  feats  of  gluttony  only  demonstrate  thdtextraordinary 
capacity  which  the  stomach  may  be  made  to  attain  by  continual  practice. — 
Many  amusing  instances  are  related  by  Captain  Parry  in  his  Arctic  Voyages  ; 
in  one  case,  a  young  Esquimaux,  to  whom  he  had  given  (for  the  sake  of 
curiosity)  his  full  tether,  devoured  in  four-and-twenty  hours,  no  less  than  35 
Ibs.  of  various  kinds  of  aliment,  including  tallow  candles.  A  case  has  recently 
been  published  of  a  Hindoo,  who  can  eat  a  whole  sheep  at  a  time ;  this  pro- 
bably surpasses  any  other  instance  on  record.  The  half-breed  voyageurs  of . 
Canada,  according  to  Capt.  Franklin,  and  the  wandering  Cossacks  of  Siberia, 
as  testified  by  Capt.  Cochrane,  habitually  devour  a  quantity  of  animal  food 
which  would  be  soon  fatal  to  any  one  unused  to  it.  The  former  are  spoken  of 
as  very  discontented  when  put  on  a  short  allowance  of  8  Ibs.  of  meat  a  day ; 
their  usual  consumption  being  from  12  to  20  Ibs.  That  a  much  larger  quantity 
of  food  than  that  already  specified,  may  be  taken  with  perfect  freedom  from 
injurious  consequences,  under  a  particular  system  of  exercise,  &c.,  appears 
from  the  experience  of  those  who  are  trained  for  feats  of  strength,  pugilistic 
encounters,  &c.  The  ordinary  belief,  that  the  athletic  constitution  cannot  be 
long  maintained,  appears  to  have  no  real  foundation  ;  nor  does  it  appear  that 
any  ultimate  injury  results  from  the  system  being  persevered  in  for  some  time. 
That  trained  men  often  fall  into  bad  health  on  the  cessation  of  the  plan,  is 
probably  owing  in  part  to  the  intemperance  and  other  bad  habits  of  persons 
of  the  class  usually  subjected  to  this  discipline.  The  effects  of  trainers'  regi- 
men are,  hardness  and  firmness  of  the  muscles,  clearness  of  the  skin,  capability 
of  bearing  continued  severe  exercise,  and  a  feeling  of  freedom  and  lightness 
(or  'corkiness')  in  the  limbs.  During  the  continuance  of  the  system,  it  is 
found  that  the  body  recovers  with  wonderful  facility  from  the  effects  of  injuries  ; 
wounds  heal  very  rapidly  ;  and  cutaneous  eruptions  usually  disappear.  Clear- 
ness and  vigour  of  mind,  also,  are  stated  to  be  results  of  this  plan ;  and  it  is 
probable  that,  where  persevering  attention  and  intense  application  are  neces- 
sary, a  modification  of  this  system,  in  which  due  allowance  should  be  made  for 
the  diminished  quantity  of  exercise,  would  be  found  advantageous.* 

*  The  method  of  training  employed  by  Jackson  (a  celebrated  trainer  of,  prize-fighters 
in  modern  times),  as  deduced  from  his  answers  to  questions  put  to  him  by  John  Bell,  was 
to  begin  on  a  clear  foundation,  by  an  emetic  and  two  or  three  purges.  Beef  and  mutton, 
the  lean  of  fat  meat  being  preferred,  constituted. the  principal  food;  veal,  lamb  and  pork, 
were  said  to  be  less  digestible  ("the  last  purges  some  men").  Fish  was  said  to  be  "  a 
watery  kind  of  diet ;"  and  is  employed  by  jockeys  who  wish  to  reduce  weight  \ty  sweating. 
Stale  bread  was  the  only  vegetable  food  allowed.  The  quantity  of  fluid  permitted  was  3£ 
pints  per  diem ,-  but  fermented  liquors  were  strictly  forbidden.  Two  full  meals,  with  a 
light  supper,  were  usually  taken.  The  quantity  of  exercise  employed  was  very  consider- 
able, and  such  as  few  men  of  ordinary  strength  could  endure.  This  account  corresponds 
very  much  with  that  which  Hunter  gave  of  the  North  American  Indians,  when  about  to 
set  out  on  a  long  march. 


358  OF  THE  CIRCULATION  OF  BLOOD. 


CHAPTER    IX. 

OF  THE  CIRCULATION  OF  BLOOD. 

I.  Of  the  Circulation  in  General. 

475.  THE  Circulation  of  nutritive  fluid  through  the  body  has  for  its  object, 
to  convey  to  every  part  of  the  organism  the  materials  for  its  growth  and  reno- 
vation, as  well  as  the  supply  of  oxygen  which  is  required  for  the  performance 
of  its  vital  actions  :  and  also  to  carry  off  the  particles  which  are  set  free  by  the 
disintegration  or  waste  of  the  system,  and  which  are  to  be  removed  from  it  by 
excreting  processes.  Of  these  processes,  the  one  most  constantly  in  operation 
as  well  as  most  necessary  for  the  maintenance  of  the  purity  of  the  blood,  is  the 
extrication  of  carbonic  acid  from  the  respiratory  organs ;  and  this  is  made  sub- 
servient to  the  introduction  of  oxygen  into  the  system.  The  extent,  therefore, 
to  which  a  circulating  apparatus  is  developed  in  the  animal  kingdom,  is  partly 
dependent  upon  the  degree  in  which  the  function  of  nutritive  absorption  is 
limited  to  one  part  of  the  body,  and  partly  upon  the  arrangement  of  the  excret- 
ing surfaces,  and  especially  of  the  respiratory  apparatus.  Where  the  digestive 
cavity  itself  extends  through  the  whole  system,  so  that  every  part  can  absorb 
at  once  from  its  parietes, — and  where  the  whole  external  surface  is  adapted,  by 
its  softness  and  permeability,  to  expose  the  fluids  of  the  body  to  the  aerating 
medium  around, — there  is  no  necessity  for  any  transmission  of  fluid  from  one 
part  to  another ;  and  accordingly,  in  the  lowest  animals,  which  are  thus  formed, 
no  true  circulation  exists.  Again,  in  the  insect  tribes,  in  whose  bodies  the 
absorption  of  fluid  can  only  take  place  at  fixed  points,  there  is  a  circulation,  for 
the  purpose  of  transmitting  the  absorbed  matter  to  the  remote  parts  of  the  body  ; 
but,  as  every  part  of  the  interior  is  permeated  by  air,  the  second  of  the  above- 
named  purpose  is  already  answered  ;  and  the  circuit  of  the  blood  through  the 
vessels,  therefore,  is  not  accomplished  with  the  energy  and  activity  which, 
from  the  vigorous  movements  performed  by  these  little  beings,  might  have  been 
supposed  necessary.  On  the  other  hand,  in  the  Mollusca,  the  absorption  of 
fluid  is  liraited,  and  the  respiratory  action  equally  so  ;  and  among  these  we  find 
the  circulation  performed  with  nearly  as  much  vigour  as  it  is  in  the  Vertebrata. 
*  476.  In  Man,  as  in  other  Vertebrated  animals,  there  is  a  regular  and  con- 
tinuous movement  of  the  nutritive  fluid  through  the  vascular  system;  and 
upon  the  maintenance  of  this,  the  activity  of  all  parts  of  the  organism  is  de- 
pendent. The  course  of  the  Blood  may  be  likened  to  the  figure  8 ;  for  there 
are  two  distinct  circles  of  vessels  through  which  it  is  transmitted;  and  the 
Heart  is  placed  at  the  junction  of  these.  The  Systemic  and  Pulmonary  circu- 
lations are  entirely  separate,  and  might  be  said  to  have  distinct  hearts ;  for  the 
left  and  right  sides  of  the  heart,  which  are  respectively  appropriated  to  these, 
have  no  direct  communication  with  each  other,  (in  the  perfect  adult  condition, 
at  least,)  and  are  merely  brought  together  for  economy  of  material.  At  an 
early  period  of  fetal  life,  as  in  the  permanent  state  of  the  Dugong,  the  heart 
is  so  deeply  cleft,  from  the  apex  towards  the  base,  as  almost  to  give  the  idea 
of  two  separate  organs.  Each  system  has  its  own  set.of  arteries,  or  efferent 
vessels,  and  veins  or  afferent  trunks;  th£se  communicate  at  their  central 


OF  THE  CIRCULATION  IN  GENERAL. 


359 


extremity  by  the  Heart ;  and  at  their  peripheral  extremity  by  the  Capillary 
vessels,  which  are  nothing  else  than  the  minutest  ramifications  of  the  two  sys- 
tems, inosculating  into  a  plexus.  The  systemic  arteries  all  proceed  from  one 
trunk,  the  Aorta;  which  first  ascends,  and  gives  off -branches  to  the  head  and 
superior  extremities ;  then  descends  through  the  thorax  and  abdomen,  giving 
off  branches  to  the  parts  near  which  it  passes ;  and  terminates  in  the  two  large 
trunks  that  proceed  to  the  inferior  extremities.  Although  the  diameters  of 
the  branches,  at  each  subdivision,  together  exceed  that  of  the  trunk,  yet  there 
is  but  little  real  difference  in  their  size.  For,  according  to  a  well-known  geo- 
metrical law,  the  areas  of  circles  are  as  the  squares  of  their  diameters;  and, 
as  the  calibre  of  a  tube  is  estimated  by  its  area,  not  by  its  diameter,  it  follows 
that,  in  comparing  the  size  of  a  trunk  with  that  of  its  branches,  we  are  to  square 
the  diameter  of  the  former,  and  compare  the  result  with  the  sum  of  the  squares 
of  the  diameters  of  the  branches.  When  this  is  done,  there  is  found  to  be  a 
very  close  correspondence.  The  following  table  gives  the  result  of  eight 
measurements,  taken  with  a  view  to  determine  the  question.  The  first  three 
were  taken  from  the  mesenteric  artery  of  a  Sheep ;  the  next  three  from  the 
aorta  and  iliac  arteries ;  the  last  two  from  the  Horse.* 


TRUNK. 


Diameter. 
I.         9 
II.       7.2 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 


3.5 
7.0 
17 
10 
4.5 
8 


Square. 

81 

51.64 

12.25 

49 

289 

100 

20.25 

64 


BRANCHES. 


Diameters. 

7.5+5 

6+4 

3+2 

5  +  5 

10+10+9.5 

7+7+2 

3.5  +  3 

4+7 


Sum  of  Squares. 

81.25 

52 

13 

50 

290.25 

102 

21.25 

65 


The  discrepancy  between  the  two  results  must  be  considered  extremely  small, 

Fig.  88. 


Web  of  Frog's  foot,  stretching  between  two  toes,  magnified  3  diameters— showing  the  blood-vessels  and 
their  anastomoses;  1, 1,  veins ;  2,  2,  2,  arteries.    (After  Wagner.) 

*  Ferneley,  in  Medical  Gazette,  Dec.  7,  1839. 


360 


OF  THE  CIRCULATION  OF  BLOOD. 


when  it  is  stated  that  the  unit,  in  the  above  measurements,  is  no  more  than 
one-fortieth  of  an  inch;  and  when  it  is  remembered  that  any  error  in  the 
measurement  is  greatly  increased  in  the  calculation.* 

477.  The  ultimate  ramifications  of  the  Arteries  usually  pass  so  insensibly 
into  those  of  the  Veins,  that  the  line  of  demarkation  between  them  cannot  be 
distinctly  drawn.  Hence  there  is  no  ground  for  the  assumption  that  the 
Capillaries  form  a  distinct  system  of  vessels,  in  which  the  Arteries  terminate 
and  the  Veins  arise.  They  are  in  no  respect  different,  except  in  size,  from 
the  other  vessels.  Their  anastomosis  is  very  frequent,  so  that  a  minute  net- 
work is  formed  by  them ;  but  this  is  also  seen  in  the  distribution  of  the  larger 
vessels.  It  has  been  maintained  by  some,  that  they  are  mere  passages,  chan- 
neled out  of  the  tissues  through  which  they  convey  the  blood ;  but  this,  again, 
is  incorrect,  for  recent  microscopical  observations  have  shown,  that  they  have 


Fig.  89. 


a  A 


Capillary  circulation  in  a  portion  of  the  web  of  a  .Frog's  foot,  magnified  110  diameters;  1,  trunk  of  vein  ; 
2,  2,  2,  its  branches ;  3,  3,  pigment-cells.  (After  Wagner.) 

*  From  Mr.  Paget's  observations,  it  appears  that  there  is  seldom  an  exact  equality  be- 
tween the  area  of  the  trunk  and  that  of  its  branches;  but  the  area  sometimes  increases, 
and  sometimes  diminishes ;— the  former  being  the  general  rule  for  the  subdivision  of  the 
aorta  and  its  principal  branches  in  the  upper  extremities ; — the  latter  in  the  lower.  The 
following  Table  shows  the  relative  areas  of  several  arterial  trunks,  and  of  the  branches 
proceeding  from  them. 

Trunk. 

Arch  of  Aorta        • 

Innominata  -  ... 

Common  carotid  ... 

External  carotid 


Subclavian  - 

Abdominal  Aorta,  to  last  lumbar  art. 

,  just  before  dividing 

Common  Iliac 
External  Iliac 


Branches. 

1-055 

1-147 

1-013 

1-19 

1-055 

1-183 

•893 

•982 

1-15 


OF  THE  CIRCULATION  IN  GENERAL.  301 

distinct  parietes,  and  that  these  are  composed  of  a  fibrous  structure  analogous 
to  the  muscular.  Their  mode  of  origin,  again,  refutes  such  a  supposition; 
for  there  can  be  no  doubt  that  they  are  produced,  in  any  newly  forming 
tissue, — not  by  the  retirement  of  its  cells,  one  from  the  other,  so  as  to  leave 
passages  between  them, — but  by  the  formation  of  communications  among  cer- 
tain cells,  whose  cavities  become  connected  with  each 
other,  so  as  to  constitute  a  plexus  of  tubes,  of  which  Fig.  90. 

the  original  cell-walls  become  the  parietes.  The  pro- 
cess may  be  most  clearly  traced  in  Plants,  in  which 
(among  the  Phanerogarnia  at  least)  a  distinct  system 
of  capillary  vessels  exists ;  but  it  may  also  be  seen  in 
the  germinal  membrane  of  the  Ovum,  in  which  the 
capillaries  distinctly  originate  before  the  trunks ;  and 
this  view  of  it  is  confirmed  by  the  fact,  that  the  nuclei 
or  cytoblasts  of  the  original  cells,  may  often  be  seen 
imbedded  in  the  walls  of  the  fully-formed  capillary 
vessels.  In  regard  to  the  size  of  the  capillary  vessels, 
there  is  considerable  variation ;  some  being  so  small, 

as  only  to  admit  globules  of  blood  in  single  file ;  whilst  First  appearance  of  blood- 
others,  passing  directly  between  arteries  and  veins,  vessels  in  the  vascular  layer 
admit  several  rows  at  once.  From  the  measurements  of 'he  7gem?na' ''™™bnn?  °( 

e  TTT   i  it/f    n  11-  i  a  Fowl  at  the  36th  hour  of  m- 

of  Weber,  Muller,  and   others,  it  appears  that   the     cubauon.   (After  Wagner.) 
capillaries  in  Man  vary  from  about  ^Tn^  to  T3Votn 

of  an  inch ;  whilst  the  blood-corpuscles  vary  from  about  T^j-7th  to  o-j V^tn  °f 
an  inch  in  diameter.  As  the  capillaries  cannot  be  examined  in  the  human 
body  until  after  death,  and  then  only  by  means  of  forcible  injections,  these 
measurements  may  be  somewhat  inaccurate.  To  the  larger  tubes,  (which 
may  perhaps  be  more  numerous  in  cold-blooded  than  in  warm-blooded  Verte- 
brata),  some  would  deny  the  term  capillary;  but  in  the  sense  in  which  that 
word  is  here  employed,  it  is  strictly  applicable  to  all  those  minute  vessels 
which  connect  the  arterial  and  venous  systems. 

478.  The  Size  of  the  Capillary  vessels  in  any  part  is  continually  under- 
going variation ;  sometimes  all  of  them  enlarging  or  contracting  simultaneously ; 
and  one  sometimes  contracting,  whilst  others  enlarge.  In  regard  to  the  first 
of  these  phenomena,  more  will  be  said  hereafter ;  the  second  is  here  noticed, 
because  it  explains  an  occasional  appearance,  on  which  some  have  founded 
their  belief  in  the  non-existence  of  distinct  parietes  to  these  vessels.  In 
watching  the  capillary  circulation  in  any  transparent  part,  we  not  unfrequently 
see  the  globules  of  blood  running  into  passages  of  the  tissue,  which  we  did  not 
perceive  before  ;  but  on  a  more  careful  examination,  the  observer  may  satisfy 
himself  that  these  passages  existed  previously,  and  that  the  fluid  part  of  the 
blood  was  transmitted  through  them ;  the  stoppage  of  the  red  particles  being 
in  a  great  measure  dependent  on  some  partial  or  local  impediments.  The 
compression  of  one  of  the  small  arteries,  for  instance,  will  generally  occasion 
an  oscillation  of  the  globules  of  blood  in  the  smallest  capillaries,  which  will  be 
followed  by  the  disappearance  of  some  of  them ;  but  when  the  obstruction  is 
removed,  the  blood  soon  regains  its  former  velocity  and  force,  and  flows  exactly 
into  the  same  passages  as  before.*  It  may  also  be  frequently  observed,  that 
the  rate  of  motion  is  very  different  in  the  different  parts  of  the  network ;  and 
that  an  entire  stagnation  of  the  current  sometimes  takes  place  in  some  particular 
tube,  the  motion  of  the  globules  recommencing,  but  in  an  opposite  direction. 
Irregularities  of  this  kind,  however,  are  more  frequent  when  the  Heart's 
action  is  partially  interrupted ;  as  it  usually  is  by  the  pressure  to  which  the 

*  Dr.  Allen  Thomson,  in  Cyclop,  of  Anat.  and  Phys.,  Art.  Circulation. 
31 


362  OF  THE  CIRCULATION  OF  BLOOD. 

Tadpole  or  other  animal  must  be  subjected,  in  order  to  allow  microscopic 
observations  to  be  made  upon  its  circulation.  Under  such  circumstances,  the 
varieties  in  the  capillary  circulation,  induced  by  causes  purely  local,  become 
very  conspicuous ;  for  when  the  whole  current  has  nearly  stagnated,  and  a 
fresh  impulse  from  the  heart  renews  it,  the  movement  is  not  by  any  means 
uniform  (as  it  might  have  been  expected  to  be)  through  the  whole  plexus 
supplied  by  one  arterial  trunk,  but  is  much  greater  in  some  of  the  tubes  than 
it  is  in  others  ;  the  variation  being  in  no  degree  connected  with  their  size,  and 
being  very  different  at  short  intervals. 

479.  The  opinion  was  long  entertained,  that  there  are  vessels  adapted  to 
the  supply  of  the  white  or  colourless  tissues ;  which  carry  from  the  arteries 
the  liquor  sanguinis,  or  fluid  portion  of  the  blood,  leaving  the  globules  behind. 
Many  objections  might  be  raised  against  such  a  supposition ;  one  of  the  most 
obvious  of  which  is  the  mechanical  obstacle  that  would  be  created  at  the 
entrances  to  such  a  system  of  tubes,  by  the  retention  of  the  globules  in  the 
larger  vessels  from  which  they  diverged.  No  such  vessels  have  ever  been 
observed ;  and  it  may  be  safely  affirmed,  that  the  supposition  of  their  existence 
is  not  required.  For  any  one  who  observes  the  smaller  capillary  vessels  may 
perceive,  that  the  current  of  blood  which  passes  through  them  is  entirely  free 
from  colour,  as  the  corpuscles  themselves  appear  to  be  when  spread  out  in  a 
single  layer.  Tissues  which  are  rather  scantily  permeated  by  such  vessels, 
therefore,  may  still  be  white ;  and  it  is  only  where  the  network  is  very  close, 
and  the  quantity  of  blood  which  passes  through  it  is  consequently  great,  that 
a  perceptible  colour  will  be  communicated  by  the  red  corpuscles.  On  the 
other  hand,  the  supposition  that  Nutrition  can  only  be  carried  on  by  means  of 
Capillary  vessels,  is  entirely  gratuitous,  as  will  be  hereafter  shown  (CHAP. 
xi.) ;  and  it  would  appear  from  the  late  researches  of  Mr.  Toynbee,*  that  car- 
tilages in  general,  the  true  cornea,  crystalline  lens,  and  vitreous  humour, 
together  with  the  epidermic  appendages,  are  entirely  destitute  of  them.  He 
has  demonstrated,  by  means  of  injections,  that  the  arteries,  which  previous 
anatomists  had  supposed  to  penetrate  into  their  substance,  either  as  serous 
vessels,  or  as  red  vessels  too  minute  for  injection,  actually  terminate  in  veins 
before  reaching  them  ;  he  also  shows  that,  around  these  non-vascular  tissues, 
there  are  numerous  vascular  convolutions,  large  dilatations,  and  intricate 
plexuses  of  blood-vessels  (Fig.  112) :  the  object  of  which  he  believes  to  be  to 
arrest  the  progress  of  the  blood,  so  that  its  nutrient  portion  may  penetrate  into 
and  be  diffused  through  them.  There  is,  as  will  hereafter  appear,  no  essential 
difference  between  the  nutrition  of  the  non-vascular  tissues,  and  that  of  the 
islets  in  the  midst  of  the  network  of  capillary  vessels  which  traverses  the  most 
vascular  (Fig.  89).  In  both  cases  the  nutrient  materials  conveyed  by  the 
blood  are  absorbed  by  the  cells  of  the  tissue  immediately  adjoining  'the  vessels, 
and  are  imparted  by  them  to  others  which  are  further  removed ;  and  the  only 
variation  that  exists,  is  in  the  amount  of  the  portion  of  tissue,'  which  has  to  be 
thus  traversed.  There  is  great  variety  in  this  respect,  among  the  tissues  that 
are  traversed  by  vessels ;  and  we  are  only  required  to  extend  our  ideas  from 
the  largest  of  the  islets  which  we  find  in  these,  to  the  still  more  isolated  struc- 
tures, of  which  the  non-vascular  tissues  are  composed.  In  the  Vegetable 
Kingdom,  as  among  the  lowest  Animals,  there  are  entire  organisms  of  con- 
siderable size,  throughout  which  nutriment  is  conveyed  by  mere  transudation 
from  cell  to  cell ;  and  this  seems  to  be  the  case,  in  "those  parts  of  the  highest 
Animals  in  which  the  vital  changes  are  least  active. 

*  Philosophical  Transactions,  1841.    * 


ACTION  OF  THE  HEART.  363 


II.  Action  of  the  Heart. 

480.  The  Heart  is  endowed  in  an  eminent  degree  with  the  property  of 
irritability,  by  which  is  meant  the  capability  of  being  easily  excited  to  move- 
ments of  contraction  alternating  with  relaxation  (§  366).  Thus,  after  the 
Heart  has  been  removed  from  the  body,  and  has  ceased  to  contract,  a  slight 
irritation  will  cause  it  to  execute,  not  one  movement  only,  but  a  series  of 
alternate  contractions  and  dilatations,  gradually  diminishing  in  vigour  until 
they  cease.  To  this  property,  the  contact  of  blood  with  the  membrane  lining 
its  cavity,  appears  to  be  the  usual  stimulus ;  and,  when  this  is  withdrawn,  its 
action  will  cease  after  a  certain  time  ;  whilst  its  movements  may  be  prolonged, 
by  means  of  artificial  respiration  (which  assists  in  maintaining  the  circulation 
through  the  lungs),  for  a  much  greater  duration, — even  after  the  Brain  and 
Spinal  Cord  have  been  removed,  and  when  animal  life  is,  therefore,  completely 
extinct.  Hence  we  see  that  the  Irritability  of  this  organ  must  be  an  endow- 
ment properly  belonging  to  it,'  and  not  derived  from  the  Nervous  System. 
Like  the  contractility  of  other  muscles,  it  can  only  be  sustained  for  any  great 
length  of  time  by  a  supply  of  Arterial  blood  to  its  own  tissue  (§  392).  It  is 
much  less  speedily  lost  in  cold-blooded  animals,  however,  than  in  warm- 
blooded ;  the  heart  of  the  Frog,  for  example,  will  go  on  pulsating  for  many 
hours  after  its  removal  from  the  body ;  and  it  is  stated  by  Dr.  Mitchell*  that 
the  heart  of  a  Sturgeon,  which  he  had  inflated  with  air,  continued  to  beat  until 
the  auricle  had  absolutely  become  so  dry  as  to  rustle  during  its  movements. 
It  is  commonly  supposed  that  when  it  is  empty  of  blood,  the  contact  of  air 
with  its  internal  cavities  is  the  stimulus  by  which  the  irritability  is  excited ; 
but  Dr.  J.  Reid  has  proved  that  this  is  not  a  sufficient  explanation,  by  placing 
under  an  air-pump  a  Frog's  heart  in  a  state  of  activity,  which  still  continued 
after  the  receiver  had  been  exhausted.!  It  is  thought  by  Dr.  Alison,  that  the 
succession  of  movements  may  be  in  some  degree  accounted  for,  by  the  pecu- 
liar arrangement  of  the  fibres  of  the  heart,  which  may  cause  one  set,  in  con- 
tracting, to  press  on  and  irritate  another ;  and  this  idea  may  be  considered  as 
by  no  means  unworthy  of  adoption,  although  it  can  scarcely  account  for  the 
whole  of  the  phenomena.  In  all  experiments  made  upon  the  cause  of  the 
Heart's  contraction,  "it  must  be  carefully  borne  in  mind,  that  the  slightest  dis- 
turbance of  the  organ  will  frequently  renew  its  motions,  after  they  have  ceased 
for  some  time  ;  the  neglect  of  which  fact  has  led  to  several  erroneous  conclu- 
sions. It  has  been  thought  by  some  that  the  contraction  of  the  ventricle  is 
the  necessary  sequence  of  the  contraction  of  the  auricle, — a  doctrine  which 
might  seem  to  follow  inevitably  from  the  circumstance  (ascertained  by  Dr. 
Knox)  that  when  the  irritability  is  nearly  exhausted,  contractions  excited 
in  the  auricle  are  sometimes  followed  by  contractions  of  the  ventricle,  when 
irritation  of  the  outer  surface  of  the  ventricle  itself  produced  no  effect.  But  it 
is  to  be  remembered  that  the  irritability  of  the  internal  surface  is  much  greater 
than  that  of  the  external ;  and  that  the  movement  of  the  auricle  will  excite 
that  of  the  ventricle,  by  forcing  blood  into  its  cavity,  and  thus  renewing  the 
usual  stimulus.  That  this  is  the  true  explanation,  is  shown  by  the  facts  observed 
by  Dr.  Reid  and  others, — that  the  usual  relation  between  the  movements  of 
the  auricles  and  ventricles  is  often  so  much  disturbed,  when  the  irritability 
is  becoming  exhausted,  that  these  do  not  regularly  alternate  with  each  other, 
— that  the-  contraction  of  the  auricle  frequently  ceases  before  that  of  the  ven- 
tricle, on  the  left  side  particularly, — and  that  both  sets  of  movements  will  con- 
tinue, when  the  auricle  and  ventricle  have  been  separated  from  each  other. 

*  American  Journal  of  the  Medical  Sciences,  vol.  vii.  p.  58. 
f  Cyclopaedia  of  Anatomy  and  Physiology,  vol.  ii.  p.  611. 


364  OF  THE  CIRCULATION  OF  BLOOD. 

481.  It  was  formerly  supposed,  that  the  movements  of  the  Heart  were  de- 
pendent upon  its  connection  with  the  centres  of  the  Cerebro-Spinal  nervous 
system ;  and  the  experiments  of  Legallois  and  others,  who  found  that  they 
were  arrested  by  crushing,  or  otherwise  suddenly  destroying,  large  portions 
of  these  centres,  appeared  to  favour  the  supposition.     But  it  has  been  shown 
by  Dr.  Wilson  Philip  and  his  successors  in  the  same  inquiry,  that  the  whole 
Cerebro-Spinal  axis  might  be  gradually  removed,  without  any  such  conse- 
quence ;  which  fact  harmonizes  perfectly  with  the  "  experiments  prepared  for 
us  by  Nature,"  in  the  production  of  monsters  destitute  of  these  centres,  which 
nevertheless  possessed  a  regularly  pulsating  heart.     It  has  latterly  been  the 
fashion  with  many,  however,  to  attribute  the  action  of  the  Heart  to  the  Gan- 
glionic  system ;  but  of  this  there  is  no  sufficient  evidence.     As  has  already 
been  generally  remarked  on  this  subject,  the  possibility  of  exciting  the  action 
of  the  heart  through  the  Sympathetic  nerve,  shows  that  this  may  have  an 
influence  on  its  movements ;  whilst  the  great  difficulty  with  which  any  evi- 
dence to  this  effect  can  be  procured,  is  in  itself  a  sufficient  proof,  that  this 
influence  cannot  be  nearly  adequate  to  the  constant  maintenance  of  this  ener- 
getic function  (§  209).     It  would  appear,  however,  that  changes  in  the  Gan- 
glionic  nerves,  like  strong  impressions  upon  the  cerebro-spinal  system,  may 
have  the  effect  of  impeding  or  even  checking  the  Heart's  action  ;  for  a  case 
has  lately  been  recorded,  in  which  the  movements  were  occasionally  checked 
for  an  interval  of  from  4  to  6  beats,  its  cessation  of  action  giving  rise  to  the 
most  fearful  sensations  of  anxiety,  and  to  acute  pain  passing  up  to  the  head 
from  both  sides  of  the  chest, — these  symptoms  being  connected,  as  it  proved 
on  a  post-mortem  examination,  with  the  pressure  of  an  enlarged  bronchial 
gland  upon  the  great  cardiac  nerve.*     It  may  be  surmised,  that  in  many  cases 
of  angina  pectoris,  in  which  no  lesion  sufficient  to  account  for  death  could  be 
discovered,  some  affection  of  the  cardiac  plexus  might  have  been  traced  on  a 
more  careful  examination.    Brachet  has  asserted  that,  by  section  of  the  cardiac 
ganglion,  he  has  caused  the  movements  of  the  heart  to  be  suddenly  arrested ; 
but  this  result  has  not  been  confirmed  by  other  experimenters. 

482.  When  the  Heart  is  exposed  in  a  living  animal,  and  its  movements  are 
attentively  watched,  they  are  seen  to  be  of  a  peculiarly  rhythmical  character  ; 
one  series  following  another  with  great  regularity.     In  an  active  and  vigorous 
state  of  the  circulation,  however,  they  are  so  linked  together,  that  it  is  not  easy 
to  distinguish  them  into  periods.     A  case  has  recently  fallen  under  the  notice 
of  Prof.  Cruveilhier,  in  which  the  heart  was  exterior  to  the  chest,  having 
escaped  from  it  by  a  perforation  in  the  superior  part  of  the  sternum  ;  and  his 
observations  upon  it  may  be  perhaps  regarded  as  more  satisfactory  than  such 
as  are  made  after  the  very  severe  operation  required  for  the  artificial  exposure 
of  the  organ  ;  although  they  are  liable  to  some  exception,  from  the  very  early 
age  of  the  subject  of  them,  which  had  only  been  born  nine  hours.     His  con- 
clusions will  be  here  adopted,  with  such  additional  remarks  as  are  suggested 
by  the  experimental  researches  of  others,  who  have  made  this  question  a 
subject  of  special  attention.!     It  is  universally  admitted,  that  both  Auricles 
contract,  and  also  dilate   simultaneously;  and  that  both  Ventricles   do  the 
same :— also  that  the  systole  or  contraction  of  the  ventricles  corresponds  with 
the  projection  of  blood  into  the  arteries,  causing  the  pulse  ;  whilst  the  diastole 
or  dilatation  of  the  ventricles  coincides  with  the  collapse  of  the  arteries.     It 
is  further  admitted,  that  the  contraction  of  the  Ventricles,  and  that  of  the  Auri- 
cles, alternate  with  one  another ;  each  taking  place  (for  the  most  part,  at  least), 
during  the  dilatation  of  the  other.     But  it  is  a  question,  whether  there  is  any 

*  Mailer's  Archiv.  1841,  heft  iii.;  and  Brit,  and  For.  Med.  Rev.,  Oct.  1841. 
t  spe  also  another  case,  recently  observed  by  M.  Monod,  in  Bullet,  de  1'Acad.  de  Med. 
Fevr.,  1843;  and  Edinb.  Med.  and  Surg.  Journ.,  July  1843. 


ACTION  OF  THE  HEART.  365 

interval  between  them.  In  the  case  just  alluded  to,  the  contraction  of  the 
Ventricles  is  stated  to  have  been  precisely  synchronous  with  the  dilatation  of 
the  Auricles ;  and  the  dilatation  of  the  Ventricles  to  have  been  performed  at 
the  same  time  with  the  contraction  of  the  Auricles,  no  period  of  repose  inter- 
vening between  the  two  sets  of  actions.  It  appears,  however,  from  the  con- 
current testimony  of  numerous  experimenters,  that  whilst  the  contraction  of 
the  Ventricle  immediately  succeeds  that  of  the  Auricle,  an  interval,  which  is 
usually,  however,  extremely  brief,  may  elapse  between  the  partial  dilatation  of 
the  Ventricles  and  the  succeeding-  systole  of  the  Auricles.  The  Ventricular 
diastole  max  be  distinguished  into  two  stages,  of  which  the  first  immediately 
succeeds  its  systole,  and  manifests  itself  in  the  recession  of  the  Heart's  apex 
from  the  front  of  the  chest ;  whilst  the  second  is  attended  with  an  enlargement 
of  the  heart  in  all  its  dimensions,  and  is  synchronous  with  the  Auricular  con- 
traction. It  is  between  these  two  that  the  interval  of  *repose  occurs  where  it 
can  be  observed.  The  following  tabular  view  will,  perhaps,  make  this  account 
more  intelligible ;  it  is  framed  in  such  a  manner  as  to  commence  with  the 
Auricular  contraction ;  but  when  considering  the  Sounds  of  the  heart,  it  will 
be  necessary  to  commence  with  the  Ventricular  systole. 

Auricles.  Ventricles. 

Contraction.  2d  stage  of  dilatation. 

Dilatation.  Contraction. — Pulse. 

1st  stage  of  dilatation. 
Brief  interval  of  Repose. 

Contraction.  2d  stage  of  dilatation. 

Dilatation.  Contraction. — Pulse. 

483.  The  duration  of  the  contraction  of  the  Ventricles  is,  according  to 
Cruveilhier,  double  that  of  their  Dilatation,  and  the  same  holds  good  of  the 
Auricles.  In  the  Systole  of  the  Ventricles,  their  surface  becomes  rugous;  the 
superficial  veins  swell ;  the  carnese  columnae  of  the  left  ventricle  are  deline- 
ated ;  and  the  curved  fibres  of  the  conical  termination  of  the  left  ventricle, 
which  alone  constitutes  the  apex  of  the  heart,  become  more  manifest.  During 
their  contraction,  every  diameter  of  the  Ventricles  is  lessened ;  their  shorten- 
ing is  the  most  sensible  change ;  but  this  is  owing  to  the  vertical  diameter 
being  the  greatest.  The  lower  extremity  of  the  left  ventricle,  or,  in  other 
words,  the  apex  of  the  heart,  describes  a  spiral  movement  from  right  to  left, 
and  from  behind  forwards.  It  is  to  this  slow,  gradual,  and  as  it  were  succes- 
sive spiral  contraction,  that  the  forward  movement  of  the  apex  of  the  heart  is 
owing,  and  its  consequent  percussion  against  the  thoracic  parietes.  The 
ventricular  systole  is  not  accompanied  by  a  projection  of  the  entire  heart  for- 
wards (as  some  have  maintained) ;  for  it  is  exclusively  the  spiral  contraction, 
which  determines  the  approach  of  the  apex  of  the  heart  and  the  thoracic 
parietes.  The  Diastole  of  the  heart,  according  to  Cruveilhier,  has  the  rapidity 
and  energy  of  an  active  movement,  triumphing  over  pressure  exercised  upon 
the  organ,  so  that  the  hand  closed  upon  it  is  opened  with  violence.  This  is 
an  observation  of  great  importance ;  but  of  the  cause  to  which  this  active  dila- 
tation is  due,  no  definite  account  can  be  given.  It  may  partly  be  explained, 
perhaps,  by  the  elasticity  of  the  tissue,  interwoven  with  muscular  fibre  in  the 
substance  of  the  heart;  and  this  may  be  the  cause  of  the  first  Ventricular  dila- 
tation, the  second  being  produced  by  the  ingress  of  blood  occasioned  by  the 
auricular  systole.  But  the  dilatation  of  the  Auricles  appears  to  be  much 
greater  than  can  be  accounted  for  by  any  vis  a  tergo  (which,  as  will  hereafter 
appear,  is  extremely  small  in  the  venous  system),  or  by  the  elasticity  of  it! 
substance  ;  for  it  was  observed  in  this  case  to  be  so  great,  that  the  right  auricle 

31* 


366  *    OF  THE  CIRCULATION  OF  BLOOD. 

seemed  ready  to  burst,  so  great  was  its  distension,  and  so  thin  were  its  walls. 
Moreover,  the  large  Veins  near  the  heart  contract  simultaneously  with  the 
auricular  Systole,  and  not  with  its  Diastole ;  so  that  they  can  have  no  influence 
in  causing  its  dilatation.  The  Ventricular  diastole  is  accompanied  with  a 
projection  of  the  heart  downwards ;  this  motion  was  at  its  maximum  when 
the  child  was  placed  vertically,  and  was  very  strongly  marked. 

484.  When  the  ear  is  applied  over  the  cardiac  region,  during  the  natural 
movements  of  the  Heart,  two  successive  sounds  are  heard  ;  each  pair  of  which 
corresponds  with  one  pulsation.     The  whole  interval  between  one  beat  of  the 
Heart,  and  the  next,  may  be  divided  into  four  parts ;   of  which  ^ie  two  first 
are  occupied  by  what  is  commonly  known  as  the  first  sound  ;  the  third,  by 
the  second  sound ;  whilst  the  fourth  is  a  period  of  repose. — The  first  sound 
is  dull  and  prolonged ;  it  is  evidently  synchronous  with  the  impulse  of  the 
Heart  against  the  parietes  of  the  chest,  and  also  with  the  pulse,  as  felt  rtfear 
the  heart ;  it  must,  therefore,  be  produced  during  the  Ventricular  Systole. — 
The  second  sound  follows  so  immediately  upon  the  conclusion  of  the  first, 
that  it  can  scarcely  be  imagined  to  take  place  during  the  auricular  systole,  as 
some  have  supposed,  but  must  be  assigned  to  the  period  of  the  first  stage  of 
the  Ventricular  Diastole.      This,  indeed,  may  now  be  regarded  as  clearly 
established ;  for  it  has  been  fully  demonstrated,  that  the  second  sound  is  due 
to  the  sudden  filling-out  of  the  Semilunar  valves  of  the  aorta  and  pulmonary 
artery,  with  blood  ;  when  the  outward  current  through  them  has  ceased,  and 
the  incipient  dilatation  of  the  ventricles  occasions  a  vacuum  behind  them.     If 
one  of  these  valves  be  hooked  back  by  a  curved  needle  against  the  side  ofthe 
artery,  so  that  a  reflux  of  blood  is  permitted,  the  sound  is  entirely  suppressed. 

485.  The  first  sound  cannot  be  so  readily  or  satisfactorily  accounted  for. 
That  it  is  partly  due  to  the  Impulse  of  the  apex  of  the  Heart,  seems  proved  by 
the  fact  that,  when  this  impulse,  is  prevented,  the  sound  is  much  diminished 
in  intensity ;  and  also  by  the  circumstance,  that,  when  the  Ventricles  contract 
with  vigour,  the  greatest  intensity  of  the  sound  is  over  the  point  of  percussion. 
But  that  it  is  not  entirely  due  to  this  cause  is  also  evident,  from  the  fact,  that 
a  sound  may  still  be  heard,  when  the  Heart  is  contracting  out  of  the  body :  as 
in  the  case  observed  by  Prof.  Cruveilhier.     This  sound  has  been  attributed  by 
some  experimenters  to  the  flapping-back  of  the  auriculo-ventricular  valves  ; 
by  others,  to   the   muscular  contraction    of  the  walls  of  the  ventricles;   by 
others  again  to  the  rush  of  blood  along  the  irregular  walls  of  the  ventricles, 
and  through  the  comparatively  narrow  orifices  of  the  aorta  and  pulmonary 
artery.     This  last  is  probably  the  most  consistent  with  truth  ;  as  would  appear 
from  the  following  interesting  observations  made  by  Cruveilhier.     By  apply- 
ing the  finger  to  the  origin  of  the  pulmonary  artery  (which  is  situated  in  front 
ofthe  aorta,  and  completely  conceals  it), a  perfectly  distinct  vibratory  fremisse- 
?nent,  corresponding  with  the  ventricular  diastole,  was  perceived :  but  no  such 
vibratory  thrill  could  be  felt  by  the  finger,  when  applied  to  any  part  of  the 
base  of  the  ventricles :  whence  it  was  evident,  that  no  action  takes  place  in 
the  mitral  and  tricuspid  valves,  which  can  give  rise  to  the  same  palpable  effects 
as  those  produced  by  the  semilunar  valves.     The  same  was  ascertained  regard- 
ing the  valvular  sound,  which  could  be  distinctly  heard  by  laying  the  finger 
against  the  origin  of  the  pulmonary  artery,  and  applying  the  ear  to  it  as  to 
a  stethoscope :  whilst  nothing  of  the  kind  could  be  perceived  in  the  region 
of  the  auriculo-ventricular  valves.     Hence  it  seems  quite  certain,  that  the 
natural  first  sound  cannot  be  dependent  in  any  way  upon  the  action  of  the 
mitral  and  tricuspid  valves.     It  appeared,  on  the  contrary,  that  the  maximum 
intensity  of  the  first  sound  was  in  precisely  the  same  situation  as  the  maximum 
intensity  |f  the  second—namely,  at  the  origin  of  the  large  arteries;  and  that 
it  diminished,  as  the  ear  was  carried  from  the  base  towards  the  apex  of  the 


ACTION  OF  THE  HEART.  367 

heart.  Moreover,  the  first  sound  was  observed  to  be  of  exactly  the  same 
character  with  the  second  (the  complicating  effect  of  the  impulse  being  here 
withdrawn),  except  as  to  its  intensity,  which  was  less, — and  its  duration, 
which  was  greater. 

486.  Hence,  although  these  observations  do  not  entitle  us  to  dehy  the  par- 
ticipation of  the  muscular  contraction,  and  of  the  movement  of  the  blood  over 
the  ventricular  walls,  in  the  production  of  the  first  sound,  they  establish  (if 
correct),  that  the  principal  cause  of  it  exists  at  the  entrances  to  the  arterial 
trunks ;  and  it  does  not  seem  that  any  other  reason  can  be  assigned  for  it  than 
the  prolon^d  rush  of  blood  through  their  orifices,  and  the  throwing  back  of 
the  SemiluMir  valves ;  which,  in  suddenly  flapping  down  again,  produce  the 
second  sound. — That  an  exaggeration  of  the  first  sound,  not  essentially  differ- 
ing from  it  in  character,  is  often  produced  by  disease  of  the  sigmoid  valves, 
wMch  causes  an  obstruction  of  their  orifice,  has  long  been  known  ;  and  in  such 
cases,  the  character  of  the  second  sound  is  also  changed.     Indeed,  M.  Cruveil- 
hier  states  it  as,  in  his  opinion,  an  uniform  occurrence,  that  disease  of  the 
Semilunar  valves  alters  both  sounds.     When  this  disease  is  such  as  to  prevent 
the  valves  from  effectually  closing,  a  reflux  of  blood  takes  place  into  the  ven- 
tricle at  the  time  of  its  diastole ;  causing  a  rushing  sound,  more  or  less  pro- 
longed, to  be  heard  in  the  intervals  of  the  pulse,  instead  of  with  it.     These 
considerations  appear  to  prove  almost  incontestably,  that  the  cause  of  the  first 
sound,  and  Hiat  of  the  second,  are  very  closely  allied ;  and  this  view,  which  if 
correct,  is  of  great  importance  in  the  explanation  of  numerous  morbid  phe- 
nomena, harmonizes  well  with  the  known  effect  of  a  slight  obstruction  in  a 
tube,  through  which  fluid  is  being  rapidly  forced,  in  producing  a  prolonged 
sound,  very  analogous  to  the  first  sound  of  the  heart.     The  following  table  may 
assist  the  student  in  connecting  the  sounds  of  the  Heart  with  its  movements. 

FIRST  SOUND.  Ventricular  Systole,  and  Auricular  Diastole.  Impulse 
of  apex  against  parietes  of  chest.  Pulsation  in  arteries. 

SECOND  SOUND.     First  stage  of  Ventricular  Diastole. 

INTERVAL.  Short  repose ;  then  Auricular  Systole,  and  second  stage 

of  Ventricular  Diastole. 

487.  The  course  of  the  circulating  fluid  through  the  Heart,  and  the  action 
of^ts  different  valves,  will  now  be  briefly  described.     The  Venous  blood, 
which  is  returned  by  the  ascending  and  descending  Vena  Cava,  enters  the 
right  Auricle  during  its  diastole  ;  and,  when  it  contracts,  is  forced  between  the 
Tricuspid  valves,  into  the  Ventricle.     The  reflux  of  blood  into  the  veins,  during 
the  auricular  systole,  is  prevented  by  the  valves  with  which  they  are  furnished  ; 
but  these  valves  are  so  formed,  as  not  to  close  accurately,  especially  when  the 
tubes  are  distended  ;  so  that  a  small  amount  of  reflux  usually  takes  place,  and 
this  is  much  increased  when  there  is  any  obstruction  to  the  pulmonary  circu- 
lation.    Whilst  the  right  Ventricle  is  contracting  upon  the  blood  that  has 
entered  it,  the  carnese  columns,  which  contract  simultaneously  with  its  proper 
walls,  put  the  chordae,  tendinese  upon  the  stretch ;  and  these  draw  the  flaps  of 
the  Tricuspid  valve  into  the  auriculo-ventricular  axis.     The  blood  then  getting 
behind  them,  and  being  compressed  by  the  contraction  of  the  ventricle,  forces 
the  flaps  together  in  such  a  manner  as  to  close  the  orifice ;  but  they  do  not 
fall  suddenly  against  each  other,  as  is  the  case  with  the  semilunar  valves,  since 
they  are  restrained  by  the  chordse  tendinese ;  whence  it  is  that  no  sound  is 
produced  by  their  closure.     The  blood  is  expelled  by  the  ventricular  systole 
into  the  Pulmonary  Artery,  which  it  distends,  passing  freely  through  the  Semi- 
lunar  valves  ;  but  as  soon  as  the  vis  a  tergo  ceases,  and  reflux  might  take  place 
by  the  contraction  of  the  arterial  walls,  the  valves  are  filled  out  h|  the  back- 
ward tendency  of  the  blood,  and  completely  check  the  return  ofjlny  portion 


368 


OF  THE  CIRCULATION  OF  BLOOD. 

Fig.  91. 


The  Anatomy  of  the  Heart;  1,  the  right  auricle;  2,  the  entrance  of  the  superior  vena  cava;  3,  the 
entrance  of  the  inferior  cava;  4,  the  opening  of  the  coronary  vein,  half  closed  by  the  coronary  valve;  5, 
the  Eustachian  valve;  6,  the  fossa  ovalis,  surrounded  by  the  annulis  ovalis;  7,  the  tuberculum  Loweri;  8, 
the  musculi  pectinati  in  the  appendix  auriculae;  9,  the  auriculo-venlricular  opening;  10,. the  cavity  of  the 
right  ventricle;  11,  the  tricuspid  valve,  attached  by  the  chorda?  tendineEe  to  the  carneae  columnae  (12);  13, 
the  pulmonary  artery,  guarded  at  its  commencement  by  three  semilunar  valves;  14.  the  right  pulmonary 
artery,  passing  beneath  the  arch  and  behind  the  ascending  aorta;  15,  the  left  pulmonary  artery,  crossing 
in  front  of  the  descending  aorta;  *,  the  remains  of  the  ductus  arteriosus,  acting  as  a  ligament  between  the 
pulmonary  artery  and  arch  of  the  aorta;  the  arrows  mark  the  course  of  the  venous  blood  through  the  right 
side  of  the  heart;  entering  the  auricle  by  the  superior  and  inferior  cava,  it  passes  through  the  auriculo- 
ventricular  opening  into  the  ventricle,  and  thence  through  the  pulmonary  artery  to  the  lungs ;  16,  the  left 
auricle;  17,  the  openings  of  the  four  pulmonary  veins;  18,  the  auriculo- ventricular  opening;  19,  the  left 
ventricle;  20,  the  mitral  valve,  attached  by  its  chordae  tendineae  to  two  large  columnar  carnerc.  which 
project  from  the  walls  of  the  ventricle;  21,  the  commencement  and  course  of  the  ascending  aorta  behind 
the  pulmonary  artery,  marked  by  an  arrow ;  the  entrance  of  the  vessel  is  guarded  by  three  semilunar 
valves;  22,  the  arch  of  the  aorta.  The  comparative  thickness  of  the  two  ventricles  is  shown  in  the  dia- 
gram. The  course  of  the  arterial  blood  through  the  left  side  of  the  heart  is  marked  by  arrows.  The  blood 
is  brought  from  the  lungs  by  the  four  pulmonary  veins  into  the  left  auricle,  and  passes  through  the  auriculo- 
ventricular  opening  into  the  left  ventricle,  whence  it  is  conveyed  by  the  aorta  to  every  part  of  the  body. 

of  it  into  the  ventricle.  The  blood,  after  having  circulated  through  the  lungs, 
returns  as  Arterial  blood,  by  the  Pulmonary  Veins,  to  the  left  Auricle ;  whence 
it  passes  through  the  mitral  valves  into  the  left  Ventricle,  and  thence  into  the 
Aorta, — in  the  same  manner  with  that  on  the  other  side,  as  just  described. 

488.  There  are,  however,  some  important  differences  in  the  structure  and 
functional  actions  of  the  two  divisions  of  the  Heart,  which  should  be  here 
adverted  to.  The  walls  of  the  left  Ventricle  are  considerably  thicker  than 
those  of  the  right;  and  its  force  of  contraction  is  much  greater.  The  follow- 
ing are  the  comparative  results  of  M.  Bizot's  recent  measurements,  taking  the 
average  of  males  from  16  to  89  years. 

Base.  Middle.  Apex. 

Left  Ventricle  4£  lines  5*-  lines  3|  lines 

Right  Ventricle  1  La  lines  If  lines  1^- lines 

In  the  female,  the  average  thickness  is  somewhat  less.  It  will  be  seen  that 
the  point  of  greatest  thickness  in  the  left  Ventricle  is  near  its  middle ;  while 
in  the  right,  it  is  nearer  the  base.  The  thickness  of  the  former  goes  on 
increasing  during  all  periods  of  life,  from  youth  to  advanced  age ;  whilst  that 
of  the  righ|  is  nearly  stationary.  The  left  Auricle  is  somewhat  thicker  than 
the  right;  the  average  thickness  of  the  former  being,  according  to  Bouillaud, 


ACTION  OF  THE  HEART.  369 

a  line  and  a  half;  whilst  that  of  the  latter  is  only  a  line.  In  regard  to  the 
relative  capacities  of  the  right  and  left  cavities,  much  difference  of  opinion  has 
prevailed.  The  right  Auricle  is  generally  allowed  to  be  more  capacious  than 
the  left;  and  the  same  is  commonly  taught  of  the  right  Ventricle.  So  much 
fallacy  may  arise,  however,  from  the  peculiar  condition  of  the  animal  at  the 
moment  of  death,  that  this  is  not  easily  proved,  and  is  indeed  by  no  means 
certain.  Many  eminent  Anatomists  maintain,  that  the  two  cavities  are  equal. 
The  capacity  of  each  of  the  cavities  may  be  estimated,  in  the  full-sized  Heart, 
at  about  two  ounces ;  that  of  the  Auricles  being  probably  a  little  less ;  and 
that  of  the  Ventricles  a  little  greater.  That  the  Ventricles  receive  more  blood 
from  the  Auricles  than  the  latter  could  transmit  to  them  by  simply  emptying 
themselves  once,  seems  therefore  probable  ;.  and  may  be  accounted  for  by  the 
fact  already  stated,  regarding  the  slight  intermission  in  the  Ventricular  Diastole, 
during  which  more  blood  may  enter  the  Auricle  from  the  veins. 

489.  There  is  a  well-known  anatomical  difference  between  the  Auriculo- 
Ventricular  valves  on  the  two  sides,  which  has  given  rise  to  the  diversity  of 
name.     This  seems,  from  the  researches  of  Mr.  King,*  to  be  connected  with 
an  important  functional  difference.     The  Mitral  valve  closes  much  more  per- 
fectly than  the  Tricuspid  ;  and  the  latter  is  so  constructed",  as  to  allow  of  con- 
siderable reflux,  when  the  cavities  are  greatly  distended.     Many  occasional 
causes  tend  to  produce  an  accumulation  of  blood  in  the  venous  system,  and  in 
the  right  side  of  the  Heart :  thus,  any  obstruction  to  the  pulmonary  circulation, 
cold,  compression  of  the  venous  system  by  muscular  action,  &c.,  are  known 
to  favour  such  a  condition.     This  is  a  state  of  peculiar  danger,  from  the  lia- 
bility which  over-distension  of  the  Ventricular  cavity  has  to  produce  a  state 
of  muscular  paralysis ;  and  in  the  structure  of  the  Heart  itself,  there  seems  to 
be  a  provision  against  it.     For,  when  the  Ventricle  is  thus  distended,  the 
Tricuspid  valves  do  not  close  properly ;  and  a  reflux  of  blood  is  permitted,  not 
only  into  the  Auricle,  but  also  (through  the  imperfect  closure  of  their  valves 
under  the  same  circumstances)  into  the  large  veins.     This  is  proved  by  the 
fact,  several  times  observed  by  Dr.  J.  Reid  in  his  experiments  upon  Asphyxia, 
&c.,  that,  when  the  action  of  the  Right  Ventricle  had  ceased  from  over-disten- 
sion, he  could  frequently  re-excite  it,  not  merely  by  puncturing  its  walls,  but 
by  making  an  opening  in  the  Jugular  vein.     This  fact  evidently  affords  an 
indication  of  great  importance  in  the  treatment  of  Asphyxia ;  and  it  explains 
the  reflux  of  blood,  or  venous  pulse,  which  is  frequently  observed  in  cases  of 
pulmonary  disease,  and  which,  according  to  Mr.  King,  always  exists,  though 
in  a  less  striking  degree. 

490.  It  is  not  quite  certain  whether  the  Ventricles  empty  themselves  com- 
pletely at  each  contraction ;  but  it  seems  probable  that  the  blood  which  they 
contain  is  not  entirely  forced  into  the  arteries.     The  quantity  which  is  pro- 
pelled by  each  Ventricle,  at  every  stroke,  may  be  estimated,  therefore,  at  from 
1£  oz.  to  2  oz.     If  we  adopt  the  lower  of  these  numbers,  we  shall  find  that, 
reckoning  75  pulsations  of  the  Heart  to  a  minute,  112  oz.,  or. 7  Ibs.,  of  blood 
pass  through  each  Ventricle  in  that  time  ;  and,  on  the  higher  estimate,  150 
oz.,  or  9  Ibs.  6  oz.,  would  pass  through  in  the  same  period.     Now  the  whole 
quantity  of  blood  contained  in  the  human  body,  according  to  the  estimate  of 
Haller  (which  is  considered  by  Dr.  Allen  Thomson  to  be  near  the  truth),  is 
about  one-fifth  of  the  weight  of  the  body  or  28  pounds  in  a  person  weighing 
140  Ibs.t     This  quantity  would  pass  through  the  Heart,  therefore,  in  four 
minutes,  on  the  lower  of  the  two  preceding  estimates,  or  in  three  minutes  on 
the  higher ;  and  would  circulate  afresh,  fifteen  or  twenty  times  in  an  hour. 

*  Guy's  Hospital  Reports,  vol.  ii. 

•j-  Cyclopaedia  of  Anatomy,  Art.  Circulation.    See  also  §  581. 

- 


370  OF  THE  CIRCULATION  OF  BLOOD. 

It  would  appear,  however,  that  this  estimate  of  the  rapidity  of  the  circulation 
is  very  far  from  the  truth ;  for  recent  experiments  have  shown  that  substances 
introduced  into  the  Venous  circulation,  may  be  detected  in  the  remotest  parts 
of  the  Arterial  circulation,  even  in  animals  larger  than  Man,  in  less  than  half 
a  minute.— The  earliest  of  such  experiments  were  those  of  Hering,*  who 
endeavoured  to  ascertain  the  rapidity  of  the  circulation,  by  introducing  Prus- 
siate  of  Potash  into  one  part  of  the  system,  and  drawing  blood  from  another. 
He  states  that  he  detected  this  salt  in  blood  drawn  from  one  of  the  Jugular 
veins  of  the  Horse,  within  20  or  30  seconds  after  it  had  been  introduced  into 
the  other ;  in  which  brief  space  the  blood  must  have  been  received  by  the 
Heart,  must  have  been  transmitted  through  the  Lungs,  have  returned  to  the 
Heart  again,  have  been  sent  through  the  Carotid  artery,  and  have  traversed 
its  capillaries.  From  experiments  of  a  similar  nature  upon  other  veins,  he 
states  that  the  salt  passed  from  the  Jugular  vein  into  the  Saphena  in  20  se- 
conds; into  the  Masseteric  artery  in  from  15  to  20  seconds  ;  into  the  External 
Maxillary  artery  in  from  10  to  25  seconds  :  and  into  the  Metatarsal  artery  in 
from  20  to  40  seconds.  An  attempt  has  been  made  to  invalidate  the  inference 
which  seems  inevitably  to  flow  from  these  experiments,  in  regard  to  the  rate 
of  the  circulation,  by  attributing  the  transmission  of  the  salt  to  the  permea- 
bility of  the  animal  tissues  ;t  but  it  has  never  been  shown  that  even  Prussiate 
of  Potash  (which  is  probably  more  transmissible  through  this  channel  than 
any  other  salt)  can  be  carried  from  one  part  to  another  with  a  rapidity  at  all 
proportional  to  this.  The  only  mode  in  which  this  property  can  be  conceived 
materially  to  facilitate  the  transmission  of  the  salt  through  the  vascular  system, 
would  be  by  allowing  it  to  pass  through  the  septum  of  the  auricles,  and  thus 
to  make  its  way  from  the  right  to  the  left  side  of  the  heart,  without  passing 
through  the  pulmonary  circulation ;  and  this  it  could  scarcely  do,  to  the  large 
amount  which  is  evidently  transmitted,  in  so  short  a  time. 

491.  The  experiments  of  Hering  have  been  recently  fully  confirmed  by 
those  of  Mr.  Blake,J  who  varied  them  by  employing  different  substances,  and 
took  other  precautions  against  sources  of  fallacy.  Ten  seconds  after  having 
injected  a  solution  of  Nitrate  of  Baryta  into  the  Jugular  vein  of  a  horse,  he 
drew  blood  from  the  Carotid  artery  of  the  opposite  side  ;  after  allowing  this  to 
flow  for  five  seconds,  he  substituted  another  vessel,  which  received  the  blood 
that  flowed  during  the  five  ensuing  seconds ;  and  the  blood  that  flowed  after 
the  twentieth  second,  by  which  time  the  action  of  the  Heart  had  stopped,  was 
received  into  a  third  vessel.  These  different  specimens  were  carefully  ana- 
lyzed. No  trace  of  Baryta  could  be  detected  in  the  blood  which  had  escaped 
from  the  artery  between  the  tenth  and  fifteenth  second  after  the  injection  of 
the  poison;  but  in  that  which  was  drawn  between  the  fifteenth  and  the 
twentieth  second,  the  salt  was  found  to  be  present  and  in  greater  abundance 
than  in  the  blood  which  had  subsequently  flowed.  Moreover,  the  coincidence 
between  the  cessation  of  the  Heart's  action,  and  the  diffusion  of  the  salt  through 
the  arterial  blood,  bears  a  striking  correspondence  ;  and  it  may  be  hence  in- 
ferred that  the  arrestment  of  its  muscular  movement  is  due  to  the  effect  of  this 
agent  upon  its  tissue,  when  immediately  operating  upon  it  through  the  capil- 
laries of  the  coronary  artery.  This  conclusion  is  borne  out  by  a  variety  of 
other  experiments ;  which  show  that  the  time  of  the  agency  of  other  poisons, 
that  suddenly  check  the  Heart's  action  (which  is  the  especial  property  of 
mineral  poisons),  nearly  coincides,  in  different  animals,  with  that  which  is 
required  to  convey  them  into  the  Arterial  capillaries.  And  it  seems  to  derive 
full  confirmation  from  the  fact  that  poisons  which  act  locally  on  other  parts, 

*  Tiedemann's  Zeitschrift,  vol.  iii.  p.  85. 
f  See  Dr.  Allen  Thomson,  Joe.  tit. 

*  Edinb.  Med.  and  Surg.  Journal,  Oct.,  1841. 


ACTION  OF  THE  HEART. 


371 


[Fig.  92. 


give  the  first  indications  of  their  operation  in  the  same  period,  after  they  have 
been  introduced  into  the  Venous  circulation.  Thus,  in  the  Horse,  the  time 
that  is  required  for  the  blood  to  pass  from  the  Jugular  vein  into  the  capillary 
terminations  of  the  Coronary  arteries,  is  16  seconds ;  as  is  shown  by  the 
power  of  Nitrate  of  Potass  to  arrest  the  Heart's  action  within  that  time ;  and 
Nitrate  of  Strychnia,  injected  into  a  vein,  gave  the  first  manifestation  of  its 
action  on  the  Spinal  Cord  in  precisely  the  same  number  of  seconds.  In  the 
Dog,  the  Heart's  action  was  arrested  by  the  Nitrate  of  Potass  in  11  or  12 
seconds  ;  and  the  tetanic  convulsions  occasioned  by  Strychnia  also  commenced 
in  12  seconds.  In  the  Fowl,  the  former  period  was  6  seconds,  and  the  latter 
6£  ;  in  the  Rabbit,  the  first  was  4,  and  the  other  4|  seconds.  From  these 
experiments,  it  seems  difficult  to  resist  the  conclusion,  that  the  rapidity  of  the 
Circulation  is  very  much  underrated  in  any 
estimate  that  we  found  upon  the  capacity  of 
the  Heart,  and  its  number  of  pulsations  in  a 
given  time ;  and  that  some  other  force  than  its 
contractions,  must  have  a  share  in  producing 
the  movement  of  the  blood  through  the  vessels. 
492.  The  force  with  which  the  heart  propels 
the  blood,  may  be  estimated  in  two  ways  ; — 
either  by  ascertaining  the  height  of  the  column 
of  that  fluid,  which  its  contractile  action  will 
support ;  or  by  causing  the  blood  to  act  upon  a 
shorter  column  of  mercury.  The  former  me- 
thod was  the  one  adopted  by  Hales,  who  intro- 
duced a  long  pipe  into  the  carotid  artery  of  a 
horse,  and  found  that  the  blood  would  some- 
times rise  in  it  to  the  height  of  ten  feet.  From 
parallel  experiments  upon  sheep,  oxen,  dogs, 
and  other  animals,  and  by  comparing  the  cali- 
bre of  their  respective  vessels  with  that  of  the 
human  aorta,  Hales  concluded  that  the  usual 
force  of  the  heart  in  man  would  sustain  a  column 
of  blood  7|  feet  high,  the  weight  of  which 
would  be  about  4  Ibs.  6  oz.  The  second  me- 
thod is  that  more  recently  adopted  by  Pois- 
seuille ;  and  the  instrument  which  he  contrived 
for  carrying  it  into  practice  (termed  by  him  the 
Hsemadynamometer)  has  been  the  means  of 
aiding  many  valuable  inquiries  on  the  physio- 
logy of  the  circulation.  The  result  of  his  ex- 
periments is  Very  nearly  the  Same  as  that  Of  bent  glass  tube,  filled  with  mercury  in 
Hales;  his  estimate  of  the  force  With  which  the  lower  part,  a  d  e.  The  horizontal  part 

the  blood  is  propelled  into  the  aorta  being  4 

Ibs.  3  oz.     The  backward  pressure  upon  the 

walls  of  the  heart,  or  in  other  words  the  force 

which  they  have  to  overcome  in  propelling  the     blood  to  prevent  its  coagulation,  when 

blood,  is  properly  estimated  by  multiplying  the     the  blood  presses  on  the  fluid  in  the 

pressure  of  blood  in  the  aorta  into  the  surface     >™tal  limb' the  rise  of  the  mercury 

of  a  plane  passing  through  the  base  and  apex 

of  the  left  ventricle  ;  by  which  calculation  it  is 

found  to  be  about  13  Ibs.*     The  pressure  ap- 

*  The  extreme  latitude  of  the  estimates  which  have  been  made  of  this  force,  has  been 
a  subject  of  not  undeserved  ridicule.  Borelli  imagined  it  to  be  180,000  Ibs.;  whilst  by 
Keill  it  was  supposed  to  be  no  more  than  from  5  to  8  ounces. 


HoemadynamometerofPoisseuille.  A 


&,  is  provided  with  a  brass  head,  which 
fits  into  the  artery.  A  small  quantity  of 
a  solution  of  the  carbonate  of  soda  is  in- 
terposed between  the  mercury  and  the 


towards  e.  measured  from  the  level  to 

which  h  has  fa]|en  towards  fl>  gives  the 

pressure  under  which  the  blood  moves.] 


372  OF  THE  CIRCULATION  OF  BLOOD. 

pears,  from  the  experiments  of  Poisseuille,  to  be  very  nearly  equal  for  equal 
surfaces,  throughout  the  larger  arterial  branches,  since  it  diminishes  regularly 
in  proportion  to  their  calibre  ;  in  the  radial  artery  at  the  wrist,  it  was  estimated 
by  him  at  4  drachms. 

493.  The  number  of  contractions  of  the  heart  in  a  given  time,  is  liable  to 
great  variation,  within  the  limits  of  ordinary  health,  from  several  causes ;  the 
chief  of  these  are,  diversities  of  age,  of  sex,  of  muscular  exertion,  of  the  con- 
dition of  the  mind,  of  the  state  of  the  digestive  system,  and  of  the  period  of 
the  day.  Putting  aside  the  other  causes  of  uncertainty,  the  following  table 
may  be  regarded  as  an  approximation  to  the  average  frequency  of  the  pulse, 
at  the  several  ages  specified  in  it. 

Beats  per  minute. 

In  the  foetus  in  utero          .  .  140  —  150 

Newly-born  infant  .  .  130  —  140 

During  the  first  year          .  .  115  —  130 

During  the  second  year     .  .  100  —  115 

During  the  third  year        .  .  90  —  100 

About  the  seventh  year      .  .  85  —    90 . 

Age  of  puberty  .  .  80—85 

Manhood  .  .  70—    80 

Old  age  .  .  50—65 

The  difference  caused  by  sex  is  very  considerable,  especially  in  adult  age ;  it 
appears  from  the  inquiries  of  Dr.  Guy,*  that  the  pulse  of  the  adult  female  ex- 
ceeds in  frequency  the  pulse  of  the  adult  male,  at  the  same  mean  age,  by  from 
10  to  14  beats  in  a  minute.  The  effect  of  muscular  exertion  in  raising  the 
pulse  is  well  known;  as  is  also  the  fact,  which  is  one  exemplification  of  it,  that 
the  pulse  varies  considerably  with  the  posture  of  the  body.  The  amount  of 
this  variation  has  been  made  the  subject  of  extensive  inquiry  by  Dr.  Guy,  and 
the  following  are  his  results.  In  100  healthy  males,  of  the  mean  age  of  27 
years,  in  a  state  of  rest,  the  average  frequency  of  the  pulse  was,  when  stand- 
ing, 79  ;  when  sitting,  70 ;  and  when  lying,  07  per  minute.  Several  excep- 
tions occurred,  however,  to  the  general  law ;  and  when  these  were  excluded, 
the  average  numbers  were,  standing,  81 ;  sitting,  71 ;  and  lying,  66  ;  so  that 
the  difference  between  standing  and  sitting  was  10  beats,  or  jth  of  the  whole  ; 
the  difference  between  sitting  and  lying  was  5  beats,  or  T^th  of  the  whole  ;  and 
the  difference  between  standing  and  lying  was  15  beats,  or  -}th  of  the  whole.  In 
50  healthy  females,  of  the  same  mean  age,  the  average  pulse  when  standing 
was  89 ;  when  sitting,  81 ;  and  when  lying,  80.  When  the  exceptions  (which 
were  more  numerous  in  proportion  than  in  males)  were  excluded,  the  averages 
were,  standing,  91 ;  sitting,  84 ;  lying,  79 ;  the  difference  between  standing 
and  sitting  was  thus  7  beats,  or  TL th  of  the  whole  ;  that  between  sitting  and  lying 
was  4,  or  ^rst  °f  tne  whole  ;  and  that  between  standing  and  lying  was  11,  or 
|th  of  the  whole.  In  both  sexes,  the  effect  produced  by  change  of  posture  in- 
creases with  the  usual  frequency  of  the  pulse ;  whilst  the  exceptions  to  the 
general  rule  are  more  numerous  as  the  pulse  is  less  frequent.  The  variation 
is  temporarily  increased  by  the  muscular  effort  involved  in  the  absolute  change 
of  the  posture ;  and  it  is  only  by  the  use  of  a  revolving  board,  by  which  the 
position  of  the  body  can  be  altered  without  any  exertion  on  the  part  of  the 
subject  of  the  observation,  that  correct  results  can  be  obtained.  That  the  differ- 
ence between  standing  and  sitting  should  be  greater  than  that  between  sitting 
and  lying,  is  just  what  we  should  expect,  when  we  compare  the  amount  of 
muscular  effort  required  in  the  maintenance  of  the  two  former  positions 
respectively. 

*  Guy's  Hospital  Reports,  vol.  iii.,  p.  312. 


MOTION  OF  THE  BLOOD  IN  THE  VESSELS.  373 

494.  The  Pulse  is  well  known  to  be  much  accelerated  by  Mental  excite- 
ment, especially  by  that  of  the  Emotions ;  it  is  also  quicker  during  Digestion ; 
but  on  neither  of  these  points  can  any  exact  numerical  statement*be  given. 
The  diurnal  variation  of  the  pulse,  however,  has  been  made  the  subject  of 
observation  by  Dr.  Guy  ;*  and,  as  the  result  of  his  inquiries  have  much  in- 
terest, although  (from  having  been  made  only  on  his  own  person)  they  may 
ultimately  require  some  modification,  they  will  be  here  stated.  "  1.  The  pulse 
of  a  healthy  male  in  a  state  of  rest,  unexcited  either  by  food  or  exercise,  is 
most  frequent  in  the  morning,  and  gradually  diminishes  as  the  day  advances. 
2.  The  pulse  diminishes  in  frequency  more  rapidly  in  the  evening  than  in 
the  morning.     3.  The  diminution  in  the  frequency  of  the  pulse  (after  excite- 
ment) is  more  regular  and  progressive  in  the  evening  than  in  the  morning. 
4.  The  effect  of  food  is  greater  and  more  lasting  in  the  morning  than  in  the 
evening ;  and  in  some  instances,  the  same  food,  which  in  the  morning  pro- 
duces an  effect  considerable  both  in  amount  and  duration,  has  no  effect  what- 
ever in  the  evening."     It  may  be  hoped  that,  ere  long,  this  interesting  and 
important  subject  will  receive  further  elucidation. 

[Dr.  Valleix  has  recently  publishedf  a  series  of  interesting  observations  on  the  fre- 
quency of  the  pulse  in  newly-born  infants,  and  in  children  aged  from  seven  months  to 
six  years.  He  obtained  the  following  results:  1.  At  birth  the  pulse  is  less  frequent  than 
at  six  months;  the  number  of  beats  in  a  minute  may  be  stated  with  considerable  exact- 
ness to  be  between  90  and  100.  2.  Increase  of  temperature,  even  in  the  slightest  degree, 
invariably  produces  a  notable  acceleration  of  the  pulse.  The  exact  ratio  between  the 
degree  of  elevation  of  temperature  and  the  increase  in  the  frequency  of  the  pulse,  is  not 
yet  accurately  ascertained.  3.  Although  the  observations  of  Dr.  Valleix  show  a  progres- 
sive diurnal  diminution  in  the  frequency  of  the  pulse,  still,  he  thinks,  that  it  would  be 
premature  to  conclude  that  these  facts  support  those  of  Dr.  Guy.  Dr.  Valleix  examined 
his  patients  in  the  morning  after  they  had  been  eating,  and  to  this  fact,  he  thinks,  should 
be  attributed  the  acceleration  of  the  pulse  in  the  early  part  of  the  day,  and  its  subsequent 
diminution,  towards  evening.  4.  The  slightest  muscular  effort  in  children  is  sufficient  to 
augment  considerably  the  number  of  pulsations.  The  same  is  true  of  any  moral  emo- 
tion. 5.  The  influence  of  sex  on  the  pulse  is  very  marked  in  young  children.  The  pulse 
is  much  more  frequent  in  young  girls  than  in  boys  of  the  same  age.  6.  During  sleep 
there  is  a  decided  diminution  in  the  number  of  beats.  7.  Between  7  and  27  months 
there  is  no  sensible  change  in  the  frequency  of  the  pulse.  Its  mean  may  be  stated  at 
126  beats  in  the  minute,  without  distinction  of  sex.  If  sex  be  considered,  it  would  be  121 
for  males  and  128  for  females.  These  numbers  express  the  frequency  of  the  pulse  at 
this  age  under  ordinary  circumstances,  but  if  a  state  of  perfect  calm  is  supposed,  the 
numbers  would  be  119  for  the  males,  and  124  for  females.  8.  After  some  observations, 
not  very  numerous,  however,  the  pulse  would  appear  to  range  a  little  above  100  till  six 
years  of  age.  9.  The  mean  number  of  inspirations  in  a  minute  in  children  aged  from  7 
months  to  two  years  and  a  half,  is  between  30  and  32,  and  is  to  number  of  pulsations  : : 
1  :  4.— M.  C.] 

III.  Causes  influencing  the  Circulation  in  the  Arteries  and  Capillaries. 

495.  That  the  movement  of  the  Blood  through  the  Arterial  trunks  and  the 
Capillary  tubes  is,  in  Man,  and  in  other  warm-blooded  animals,  chiefly  de- 
pendent upon  the  action  of  the  Heart,  there  can  be  no  doubt  whatever.    It  can 
be  easily  shown  by  experiment,  that,  if  the  Arterial  current  be  checked,  the 
Capillaries  will  immediately  cease  almost  entirely  to  deliver  the  blood  into  the 
veins,  and  the  Venous  circulation  will  be  instantaneously  arrested.     And  it 
has  also  been  proved,  that  the  usual  force  of  the  Heart  is  sufficient  to  propel 
the  blood,  not  only  through  the  Arterial  tubes,  but  through  the  Capillaries, 
into  the  Veins ;  since  even  a  less  force  wityserve  to  propel  warm  water  through 

*  Op.  cit.,  vol.  iv.  p.  69. 

f  [Memoires  de  la  Societe  Medicale  d'Observation  de  Paris.   Tome  Deuxieme,  IS 
p.  300,  et  seq.] 
32 


374  OF  THE  CIRCULATION  OF  BLOOD. 

the  vessels  of  an  animal  recently  dead.*  But  there  are  certain  "  residual 
phenomena"  even  in  Man,  which  clearly  indicate  that  this  is  not  the  whole 
truth ;  and  that  forces  existing  in  the  Blood-vessels  have  a  considerable  influ- 
ence in  producing  both  local  and  general  modifications  of  the  effects  of  the 
Heart's  action.  There  are  also  indications  of  the  nature  of  an  influence,  in 
which  the  blood-vessels  do  not  partake,  arising  from  those  changes  occurring 
between  the  Blood  and  the  Tissues,  that  constitute  the  processes  of  Nutrition, 
Secretion,  &c.  Such,  for  instance,  would  appear  to  be  the  interpretation  of 
the  fact,  that  whilst  any  variations  in  the  action  of  the  Heart  affect  the  whole 
system  alike,  there  are  many  variations  in  the  Circulation,  which,  being  very 
limited  in  their  extent,  cannot  be  attributed  to  such  central  disturbances,  and 
must  therefore  be  dependent  on  causes  purely  local. — Of  the  nature  of  these 
influences,  and  of  the  mode  of  their  operation,  we  shall  probably  arrive  at  a 
more  correct  knowledge,  if  we  examine  the  phenomena  of  the  Circulation  in 
those  beings  in  which  the  moving  power  is  less  concentrated  than  it  is  in  the 
higher  Animals  ;  for  just  as  we  find  in  the  latter,  that  the  development  of 
special  absorbent  vessels  does  not  exclude  the  function  of  absorption  from  being 
still  performed  by  the  general  vascular  system  (§  463),  so  may  we  here  be  led  to 
perceive  that  there  is  a  generally  diffused  force,  to  which  alone  the  Circulation 
of  the  nutritious  fluid  in  the  lowest  organisms  is  due,  and  wrhich  is  not  alto- 
gether replaced  by  the  special  organ  of  impulsion,  that  is  developed  in  the 
centre  of  the  system  in  the  higher. 

496.  The  ascent  of  the  sap  in  Vegetables  is  probably  to  be  regarded  as  due, 
in  part,  to  the  vis  a  tergo  occasioned  by  the  action  of  Endosmose  at  the  roots ; 
and  in  part,  to  the  demand  for  fluid,  occasioned  by  the  vital  processes  taking 
place  in  the  leaves.  For  if  the  stem  of  a  Vine,  in  which  the  sap  is  rising,  be 
cut  across,  the  sap  will  continue  to  flow  for  some  time  from  the  top  of  the  lower 
portion ;  and  its  force  of  ascent  may  be  shown  to  be  very  considerable,  by 
tying  over  the  cut  surface  a  piece  of  'bladder,  which  will  be  speedily  burst, — 
or  by  affixing  to  it  a  bent  tube,  containing  a  column  of  mercury,  which  will 
be  raised  to  the  height  of  forty  inches  or  more.  On  the  other  hand,  the  attrac- 
tive force  of  the  leaves  is  shown  by  the  fact,  that  if  the  lower  end  of  the  upper 
division  be  put  into  water,  it  will  continue  to  absorb,  as  long  as  the  vital  actions 
of  the  leaves  are  being  performed  with  vigour  ;  but,  if  the  branch  be  carried 
into  a  dark  room,  the  exhalation  from  the  leaves  is  immediately  checked,  and 
absorption  is  checked  also.  The  influence  of  the  actions  at  the  periphery  of 
the  circulating  system  in  maintaining  the  flow  of  fluid  towards  the  part,  is 
further  shown  by  the  fact,  that  if  a  shoot  of  an  evergreen  species  be  grafted 
on  a  stock  of  one  with  deciduous  leaves,  a  continual  and  unwonted  ascent  of 
sap  will  be  kept  up  in  the  latter  through  the  winter ;  this  being  evidently  due 
to  the  demand  occasioned  at  its  summit.  Again,  the  recommencement  of  the 
annual  flow  of  sap  in  an  ordinary  tree  has  been  found  to  take  place,  in  the 
first  instance,  not  at  its  roots,  but  in  the  neighbourhood  of  the  buds ;  for  their 
expansion,  under  the  influence  of  the  returning  warmth,  exhausts  the  fluid 
from  the  vessels  of  their  neighbourhood ;  this,  again,  occasions  a  demand  from 
below;  and  thus  the  motion  is  gradually  propagated  to  the  roots.  Now  it  has 
been  experimentally  ascertained,  that,  if  a  branch  of  a  vine  growing  in  the 
open  air  be  trained  into  a  hot-house,  it  may  be  made  to  vegetate  during  the 
winter,  and  to  draw  up  fluid  through  the  stems  and  roots,  whose  condition  has 
not  been  changed.  It  is  evident,  then,  that  in  Plants,  the  demand  for  fluid  in 
the  organs  to  which  it  is  distributed  by  the  vascular  system,  is  one  of  the 
chief  forces  by  which  the  supply  is  obtained. 

*  See  Dr.  Williams's  Principles  of  Medicine,  [Am.  ed.,  by  Dr.  Clymer,  p.  155,  note.] 


MOTION  OF  THE  BLOOD  IN  THE  VESSELS.  375 

497.  This  is  still  more  evidently  the  case  in  regard  to  the  Circulation  of 
nutritious  or  elaborated  sap,  which  takes  place  in  the  under  surface  of  the 
leaves  and  in  the  bark.     The  object  of  this  movement  is  not  to  convey  the 
fluid  in  a  direct  line  from  one  point  to  another  (as  in  the  case  with  the  ascend- 
ing current),  but  to  supply  every  part  with  materials  for  its  growth,  or  for  the 
production  of  its  peculiar  secretions.     Hence  the  vessels  in  which  it  takes 
place,  form  a  minutely  anastomozing  network,  instead  of  consisting  of  a  system 
of  straight  and  distinct  tubes.     Through  this  network,  the  latex  or  elaborated 
sap  is  seen  to  move,  exactly  as  does  the  blood  through  the  capillary  vessels  of 
animals.     The  movement  takes  place,  under  favourable  circumstances,  with 
considerable  rapidity ;  it  is  accelerated  by  heat,  and  retarded  by  cold ;  and  it  is 
subject  to  all  those  minor  irregularities  (such  as  the  cessation  of  movement,  or 
change  in  the  direction  of  the  current,  in  a  particular  channel),  which  are  so 
constantly  to  be  noticed  by  any  one  who  attentively  watches  the  capillary 
circulation  of  Animals,  and  which  clearly  prove  the  operation  of  some  causes 
independent  of  the  heart's  action  (§  478).     The  general  direction  of  the  ela- 
borated sap,  through  this  capillary  system,  is  downwards;  but  that  the  force 
of  gravity  cannot  have  much  to  do  with  the  movement,  is  shown  by  the  fact 
that,  in  a  dependent  branch,  it  has  to  ascend  towards  the  stem,  which  it  will 
do  without  interruption  from  this  cause. 

498.  In  the  lowest  Animals,  the  movement  of  the  circulating  fluid  seems  as 
independent  of  any  central  organ  of  impulsion  as  it  has  been  shown  to  be  in 
Plants.     Thus,  in  the  living  Sponge,  a  current  of  water  is  continually  flowing 
through  the  tubes  and  channels,  by  which  its  substance  is  traversed,  the  fluid 
being  taken  in  by  the  small  orifices,  and  ejected  in  powerful  streams  from  the 
large  ones  ;  and  yet  the  most  attentive  examination  has  not  revealed  any 
mechanical  cause  for  this  movement.     In  some  of  the  compound  Polypifera,  a 
similar  current  may  be  seen  ;  and  it  is  curious  that,  in  many  species,  its  direc- 
tion undergoes  a  periodical  change  ;  being  reversed  at  intervals  of  a  certain 
number  of  seconds.     In  the  Star-fish  and  Sea-Urchin  tribe,  a  complex  circula- 
tion of  blood  takes  place,  through  regular  vessels ;  and  here  we  find  some 
indication  of  a  contractile  cavity,  by  the  power  of  which  it  may  be,  in  some 
degree,  kept  up  ;  but  its  feeble  pulsations  can  scarcely  be  regarded  as  having 
any  great  share  in  the  movement  of  the  fluid  which  passes  through  it.     In 
the  Articulated*  series,  there  is,  with  a  few  exceptions,  an  absence  of  any  cen- 
tral organ  of  impulsion,  possessed  of  power  sufficient  to  carry  the  blood  through 
the  vascular  system,  by  its  contractions  alone.    In  many  of  the  aquatic  worms 
and  larvae,  the  movement  of  the  blood,  and  the  pulsations  of  the  dorsal  vessel, 
may  be   distinctly  seen :  and  the  thinness  of  the  walls  of  the  latter,  and  the 
character  of  its  movements  seem  clearly  to  show,  that  these  can  scarcely  be 
regarded  as  propulsive,  but  that  they  merely  result  from  the  variations  in  the 
current  which  passes  through  it, — the  sides  flapping  together  when  there  is 
an  outward  flow,  and  bulging  out  when  there  is  an  influx.     It  is  in  these 
Articulata,  in  which  there  is  a  provision  for  respiration  throughout  the  whole 
structure,  as  is  especially  the  case  in  Insects,  that  the  absence  of  any  central 
impulsive  power  is  most  remarkable.     In  the  Crustacea,  and  in  the  Mollusca 
in  general,  the  respiration  is  aquatic,  and  is  restricted  to  a  particular  organ ; 
and  in  these,  the  heart  is  found  to  be  more  muscular,  and  the  circulation  to  be 
more  under  its  control.     It  is  curious  to  remark,  however,  that,  in  some  of  the 
lower  Mollusca,  which  exhibit  a  tendency  to  aggregation  into  compound  struc- 
tures, like  those  of  the  Polypifera,  there  is  the  same  want  of  definiteness  in 
the  course  of  the  circulation,  as  has  been  just  stated  to  exist  in  the  latter 
group  ; — the  flow  of  blood  through  their  complex  apparatus  of  nutritive  organs, 
being  arrested  at  regular  intervals,  and  then  recommencing  in  the  reverse 
direction. 


376  OF  THE  CIRCULATION  OF  BLOOD. 

499.  Even  in  Vertebrated  animals,  we  find  indications  of  the  same  defi- 
ciency of  central  power,  over  the  peripheral  circulation.     When  we  look  at 
the  simple,  thin-walled  heart  of  Fishes,  for  example,  it  seems  impossible  that 
it  should  have  rnuch  power  over  the  current  of  blood  flowing  back  to  it  by  the 
veins ;  for  of  this  blood,  a  considerable  portion  has  to  pass  through  three  sets 
of  capillaries,  between  its  ejection  from  the  heart  and  its  return  to  it.     It  is 
first  transmitted  through  the  respiratory  capillaries,  for  the  purpose  of  aera- 
tion ;  the  confluent  vessels,  which  collect  the  arterial  blood  from  these,  termi- 
nate in  the  general  systemic  trunk  or  Aorta,  in  which,  as  in  the  veins  of  Man, 
there  is  an  absence  of  pulsation,  and  by  these  it  is  distributed  to  the  systemic 
capillaries ;  and  the  blood  which,  after  passing  through  these,  returns  from 
the  posterior  part  of  the  body,  and  from  the  viscera,  passes  through  ariother 
set  of  capillaries,  those  of  the  liver  and  kidneys,  before  it  returns  to  the  heart. 
Even  in  the  warm-blooded  Vertebrata,  in  which  the  respiratory  circulation  is 
separately  performed,  the  blood,  which  is  returned  from  the  intestines,  passes 
into  a  trunk,  the  Vena  Portse,  which  again  subdivides  into  capillary  ramifi- 
cations, being  transmitted  over  the  plexus  of  biliary  ducts,  of  which  the  liver 
is  chiefly  composed ;  and  thus  the  Vena  Portse,  as  Hunter  justly  observed, 
should  be  considered  rather  in  the  light  of  an  artery,*  resembling  as  it  does 
the  aorta  of  Fishes.     Considering  the  small  amount  of  pressure  which  is 
exerted  by  the  blood,  upon  the  sides  of  the  vessels  that  are  formed  by  the 
reunion  of  capillaries,  it  seems  impossible  to  imagine  that  the  vis  a  tergo, 
derived  from  the  impulsive  action  of  the  Heart,  can  be  alone  sufficient  to 
maintain  the  portal  circulation. 

500.  We  have  next  to  consider  the  influence  of  the  Arterial  tubes,  on  the 
flow  of  blood  through  them.    This  influence  is  exerted  by  the  middle  or  fibrous 
coat,  which  alone  is  possessed  of  contractile  properties.     We  find  in  this  coat, 
a  layer  of  annular  fibres,  possessing  no  small  resemblance  to  that  of  which  the 
muscular  coat  of  the  alimentary  canal  is  composed.     On  the  outside  of  this, 
is  a  layer  of  yellow  elastic  tissue,  which  is  much  thicker  in  the  larger  arteries, 
in  proportion  to  their  size,  than  in  the  smaller.     To  this  last  tissue  is  due  the 
simple  elasticity  of  the  arterial  walls,  which  is  a  physical  property  that  per- 
sists after  death,  until  a  serious  change  takes  place  in  their  composition : 
whilst  to  the  one  first  mentioned,  we  are  to  attribute  the  property  which  they 
unquestionably  possess — in  common  with  proper  muscular  tissue, — of  con- 
tracting on  the  application  of  a  stimulus,  so  long  as  their  vitality  remains. 
These  two  endowments  exist,  in  various  proportional  degrees,  in  the  different 
parts  of  the  Arterial  system.     Thus  it  was  justly  remarked  by  Hunter,  that 
elasticity,  being  the  property  by  which  the  interrupted  force  of  the  Heart  is 
made  equable  and  continuous,  is  most  seen  in  the  large  vessels  more  imme- 
diately connected  with  that  organ.     On  the  other  hand,  the  contractility  is 
most  observable  in  the  smaller  vessels,  where  it  is  more  required  for  regulating 
the  flow  of  blood  towards  particular  organs. 

501.  It  is  easily  shown  that  the  action  of  the  Elasticity  of  the  Arterial  tubes 
is  one  of  a  purely  physical  character ;  and  that  its  purpose  is  to  convert  the 
intermitting  impulses,  which  the  fluid  receives  from  the  heart,  into  a  continu- 
ous current.     The  former  are  very  evident  in  the  larger  trunks;  but  they 
diminish  with  the  subdivision  of  these,  until  they  entirely  disappear  in  the 
capillaries,  in  which  the  stream  is  usually  equable  or  nearly  so.     We  may 
imagine  a  powerful  forcing-pump  injecting  water,  by  successive  strokes,  into 
a  system  of  tubes  with  unyielding  walls ; — the  flow  of  fluid  at  the  farther 

*  That  it  conveys  venous  blood,  is  no  reason  to  the  contrary;  since  this  is  the  case 
with  the  pulmonary  artery.  The  character  of  an  artery  is  derived  from  the  division  of 
its  current  into  several  diverging  streams. 


MOTION  OF  THE  BLOOD  IN  THE  ARTERIES.  377 

extremities  of  these  tubes,  would  be  as  much  interrupted  as  its  entrance  into 
them.  But  if  an  air-vessel  (like  that  of  a  fire-engine)  were  placed  at  their 
commencement,  the  flow  would  be  in  great  degree  equalized ;  since  a  part  of 
the  force  of  each  stroke  would  be  spent  upon  the  compression  of  the  air 
included  in  it ;  and  this  force  would  be  restored  by  the  elasticity  of  the  air 
during  the  interval,  which  would  propel  the  stream,  until  directly  renewed  by 
the  next  impulse.  A  much  closer  imitation  of  the  natural  apparatus  would 
be  afforded,  by  a  pipe  which  had  elastic  walls  of  its  own ;  if  water  were 
forced  by  a  syringe  into  a  long  tube  of  caoutchouc,  for  example,  the  stream 
would  be  equalized  before  it  had  proceeded  far.  This  effect  is  found  to  be 
accomplished,  at  any  point  of  the  Arterial  circulation,  in  a  degree  proportionate 
to  its  distance  from  the  Heart ;  and  it  is  another  effect  of  the  same  cause,  that 
the  pressure  of  the  blood  upon  the  walls  of  the  arteries  (as  shown  by  the 
experiments  of  Poisseuille)  is  nearly  the  same  ail  over  the  system.  It  is  to 
the  distension  of  the  arterial  tubes,  both  in  their  length  and  calibre,  that  their 
pulsation  is  due.  Their  elongation  is  the  more  considerable  of  the  two  effects ; 
and  it  causes  the  artery  to  be  lifted  from  its  seat  and  to  become  curved.  The 
transverse  dilatation  has  been  denied  by  some  physiologists ;  but  it  has  been 
recently  proved  to  take  place,  by  an  ingenious  experiment  of  Poisseuille's. 
The  increase  of  capacity,  however,  is  not  more  than  one-tenth;  so  that  the 
increase  of  diameter  will  not  be  so  much  as  one-twentieth, — a  quantity  scarcely 
perceptible  to  ordinary  measurement.  The  transmission  of  the  pulse-wave 
through  the  whole  system  is  not  instantaneous,  but  takes  place  in  an  appre- 
ciable time.  The  pulsation  of  the  large  arteries  near  the  Heart  is  synchronous 
with  the  Ventricular  systole ;  but  that  of  other  arteries  is  somewhat  later, — the 
difference  varying  with  their  distance,  and  amounting  in  some  instances  to 
between  one-sixth  and  one-seventh  of  a  second. 

502.  It  has  been  denied  by  many  Physiologists,  that  the  middle  coat  of  the 
arteries  possesses  any  property,  which  can  be  likened  to  Muscular  Contrac- 
tility; and  it  will  therefore  be  desirable  to  enter  somewhat  in  detail  into  the 
question.     That  it  cannot  be  readily  stimulated  to  contraction,  through  the 
medium  of  its  nerves,  is  universally  admitted;  but  the  same  is  the  case  in 
regard  to  the  Muscular  coat  of  the  alimentary  canal,  which  contracts  most 
vigorously  on  the  direct  application  of  stimuli  to  itself;  and  Valentin  and 
others  have  recently  succeeded  in  producing  evident  contractions  in  both,  by 
irritation  of  the  Sympathetic  nerve,  and  of  certain  roots  of  the  Spinal  nerves 
(§  209).     Further,  although  many  experimenters  have  failed  in  producing 
contractions  of  this  tissue,  by  stimuli  directly  applied  to  itself,  yet  others  have 
distinctly  witnessed  them ;  and,  in  any  question  of  this  kind,  the  positive  evi- 
dence must  be  held  to  outweigh  the  negative.    Thus  Verschuir  states,  that  he 
has  seen  arteries  contract,  when  stimulated  by  the  mineral  acids,  by  electricity, 
and  by  the  application  of  the  point  of  a  scalpel.     Dr.  Thomson  also  saw  them 
contract,  on  the  application  of  ammonia,  and  when  punctured  with  the  point 
of  a  fine  needle,  in  the  living  body.     It  has  been  ascertained  by  the  direct 
and  careful  experiments  of  Poisseuille,  that,  when  the  artery  is  dilated  by  the 
blood  injected  into  it  from  the  heart,  it  reacts  with  a  force  superior  to  the 
impressing  impulse ;  and  he  has  also*  shown  that,  if  a  portion  of  an  artery 
from  an  animal  recently  dead  (in  which  the  vital  contractility  seems  to  be  pre- 
served), and  one  from  an  animal  that  has  been  dead  some  days  (in  which 
nothing  but  the  elasticity  remains),  be  distended  with  an  equal  force,  the 
former  becomes  much  more  contracted  than  the  latter,  after  the  distending  force 
is  removed. 

503.  Several  experiments  also  indicate  the  existence  of  a  power  of  slow 
contraction  in  the  arteries,  which  has  been  distinguished  by  the  appellation 

32* 


378  OF  THE  CIRCULATION  OF  BLOOD. 

Tonicity;  but  which  does  not  seem  any  thing  else  than  a  particular  mani- 
festation of  the  general  property  of  vital  contractility,  and  is  certainly  of  a 
nature  quite  distinct  from  ordinary  elasticity.  Thus,  when  a  ligature  is  placed 
upon  an  artery  in  a  living  animal,  the  part  of  the  artery  beyond  the  ligature 
becomes  gradually  smaller,  and  is  emptied  to  a  certain  degree,  if  not  completely, 
of  the  blood  it  contained.  Again,  when  part  of  an  artery  in  a  living  animal  is 
isolated  by  means  of  two  ligatures,  and  is  punctured,  the  blood  issues  from  the 
orifice,  and  the  enclosed  portion  of  the  artery  is  almost  completely  emptied  of 
its  contents.  The  exposure  of  arteries  to  the  air  was  found  by  Hunter  to  occa- 
sion their  contraction  to  such  an  extent,  that  obliteration  of  their  tube  was  the 
result;  and  this  statement  has  been  subsequently  confirmed.  Further,  every 
surgeon  knows,  that  the  contraction  of  divided  arteries  is  an  efficient  means 
of  the  arrest  of  hemorrhage  from  them,  especially  when  they  are  of  small 
calibre ;  so  that,  in  the  case  of  the  temporal  artery,  for  example,  the  complete 
division  of  the  tube  is  often  the  readiest  means  of  checking  the  flow  of  blood 
from  it,  when  it  has  been  once  wounded.  This  contraction  is  much  greater 
than  could  be  accounted  for  by  the  simple  elasticity  of  the  tissue ;  anti  is  more 
decided  in  small  than  in  large  vessels.  The  empty  condition  of  the  arteries, 
generally  found  within  a  short  time  after  death,  seems  to  be  in  part  due  to  the 
same  cause ;  since  their  calibre  is  usually  much  diminished  and  is  sometimes 
completely  obliterated.  A  remarkable  example  of  the  same  slow  contraction, 
is  that  which  takes  place  in  the  end  of  the  upper  portion  of  an  arterial  trunk, 
when  the  passage  of  blood  through  it  is  interrupted  by  a  ligature  ;  for  the  cur- 
rent of  blood  then  passes  off  by  the  nearest  large  lateral  branch ;  and  the  tube 
of  the  artery  shrivels,  and  soon  becomes  impervious,  from  the  point  at  which 
the  ligature  is  applied,  back  to  the  origin  of  that  branch.  This  last  fact  is 
important,  as  proving  how  little  influence  the  vis  a  tergo  possesses  over  the 
calibre  of  arterial  tubes ;  since,  without  any  interruption  to  the  pressure  of 
blood  occasioned  by  it,  the  tube  becomes  impervious. — It  is  to  the  moderate 
action  of  the  Tonicity  of  arteries,  that  their  contraction  upon  the  stream  of 
blood  passing  through  them  (which  serves  to  keep  the  tubes  always  full)  is 
due.  If  the  tonicity  be  excessive,  the  pulse  is  hard  and  wiry ;  but  if  it  be 
deficient,  the  pulse  is  very  compressible,  though  bounding,  and  the  flow  of 
blood  through  the  arteries  is  retarded.  Dr.  Williams  has  performed  some 
ingenious  experiments,  which  prove  that  the  force  required  to  propel  fluid 
through  a  tube,  whose  sides  are  yielding,  is  very  much  greater  than  that 
which  will  carry  it  through  an  even  smaller  tube,  with  rigid  parietes  ;  conse- 
quently, a  loss  of  tonicity  in  the  blood-vessels  retards  the  flow  of  blood  through 
them;  whilst  an  increase  hastens  it.  The  Tonicity  of  the  arteries  differs 
from  their  ordinary  Contractility,  in  being  augmented  by  cold,  and  diminished 
by  warmth.  Hence  cold  and  heat  are  two  most  valuable  remedial  agents, 
when  this  property  is  deficient  or  in  excess. 

504.  It  is  still  to  be  inquired,  in  what  manner  the  Contractility  of  the  Arte- 
ries is  to  be  regarded  as  influencing  the  flow  of  Blood  through  them.  It  is  at 
once  evident,  that  any  general  contraction  of  the  arterial  tubes  would  have 
rather  the  effect  of  opposing  than  of  assisting  the  flow ;  but  if  the  fibrous  coat 
of  the  Arteries  is  in  some  degree  disposed  to  the  alternate  contraction  and 
relaxation,  which  are  so  remarkable  in  the  Heart,  they  may  exert  a  force  which 
shall  be  supplementary  to  that  of  the  Heart's  impulse, — relaxing  to  receive 
the  blood  from  it,  and  contracting  upon  their  contents,  with  a  power  superior 
to  that  by  which  they  were  distended.  It  is  difficult  to  say  whether  or  not 
this  be  the  case  ;  though  there  would  certainly  appear  some  evidence  in  favour 
of  the  supposition.  The  loss  of  the  Heart's  power  over  the  currents  of  blood, 
in  proportion  to  their  degree  of  subdivision,  occasioned  by  the  increased  fric- 


MOTION  OF  THE  BLOOD  IN  THE  CAPILLARIES.  379 

tion  to  which  they  will  be  subjected,  would  seem  to  require  some  compensat- 
ing power,  in  order  that  the  perfect  equality  of  pressure  may  be  obtained, 
which  has  been  spoken  of  as  existing  in  all  parts  of  the  arterial  system.  In 
no  other  way  than  this,  can  the  fibrous  coat  of  the  Arteries  be  regarded  as 
having  any  propulsive  power  over  their  contents ;  except  by  a  peristaltic  or 
vermicular  movement,  resembling  that  which  takes  place  in  the  alimentary 
canal ;  and  of  such  there  is  no  evidence  whatever. — A  very  important  use 
may  be  assigned  to  this  muscular  coat,  which  has  been  generally  overlooked 
by  physiologists, — that  of  regulating  the  diameter  of  the  tubes,  in  accordance 
with  the  quantity  of  blood  to  be  conducted  through  them  to  any  part,  which 
will  depend  upon  its  peculiar  circumstances  at  the  time.  Such  local  changes 
are  continually  to  be  observed,  in  the  various  phases  of  normal  life,  as  well  as 
in  diseased  states  ;  and  they  will  be  found  to  be  constantly  in  harmony  with 
the  particular  condition  of  the  processes  of  Nutrition,  Secretion,  &c.,  to  which 
the  Capillary  circulation  ministers.  Of  this  kind  are  the  enlargement  of  the 
trunks  of  the  Uterine  and  Mammary  arteries,  at  the  epochs  of  pregnancy  and 
lactation ; — the  enlargement  and  strongly  increased  pulsation  of  the  Radial 
artery,  when  there  is  any  active  inflammation  in  the  thumb ; — the  enormous 
diameter  which  the  Spermatic  artery  will  attain,  when  the  testicle  is  greatly 
increased  in  size  by  diseased  action  ;  and  many  other  similar  phenomena.  In 
such  cases,  it  cannot  be  the  action  of  the  Heart  that  increases  the  calibre  of 
the  vessels;  since  this  is  commonly  unaltered,  and  is  itself  unable,  as  we  have 
just  seen,  even  to  maintain  their  permeability.  It  must,  therefore,  be  by  a 
power  inherent  in  themselves,  that  their  dilatation  is  effected.  The  minute  dis- 
tribution of  the  Sympathetic  nerve  upon  the  walls  of  the  arteries,— -the  known 
power  which  this  has  of  producing  contractions,  alike  in  their  fibrous  coat,  and 
in  the  muscular  tunic  of  the  intestinal  canal, — and  various  phenomena,  which 
indicate  the  power  of  certain  states  of  mind  over  the  dimensions  of  the  arte- 
ries, in  particular  parts  of  the  body  at  least, — render  it  highly  probable,  that 
the  calibre  of  the  arteries  is  regulated  in  no  inconsiderable  degree  through  its 
intervention.*  The  permanent  dilatation,  however,  which  is  seen  in  the  arte- 
ries supplying  parts  that  are  undergoing  enlargement,  must  be  due,  not  to 
simple  dilatation  merely,  but  to  increased  nutrition ;  since  we  find  that  their 
walls  are  thickened  as  well  as  extended.  And,  on  the  other  side,  when  slow 
contraction  occurs  in  these  tubes,  as  a  consequence  of  disease,  it  must  be  in 
part  occasioned  by  atrophy ;  since  their  nutrition  is  so  much  diminished,  that 
in  time  they  almost  entirely  disappear, — a  portion  of  a  large  artery  occasionally 
shriveling  into  a  ligamentous  band. 

505.  We  now  come  to  the  last  head  of  the  inquiry  into  the  powers  which 
convey  the  blood  through  the  Capillary  system ; — that,  namely,  which  con- 
cerns the  agencies  existing  in  the  capillaries  themselves.  Many  discussions 
on  this  subject  may  be  found  in  physiological  writings;  and  it  has  so  imme- 
diate a  bearing  on  one  of  the  most  important  questions  in  Pathology, — the 
nature  of  inflammation, — that  it  deserves  the  fullest  attention.  The  chief 
question  in  debate,  is  the  degree  in  which  the  Capillary  circulation  is  influ- 
enced by  any  other  agency  than  the  contractile  power  of  the  Heart  and  Arte- 
rial system ; — some  physiologists  maintaining,  that  this  alone  is  sufficient  to 
account  for  all  the  phenomena  of  the  Capillary  circulation  ; — and  others  assert- 
ing, that  it  is  necessary  to  admit  some  supplementary  force,  which  may  be 
exerted  either  to  assist,  retard,  or  regulate  the  flow  of  blood  from  the  Arteries 
into  the  Veins.  We  shall  first  inquire  what  evidence  there  is  of  the  existence 

*  For  Anatomical  evidence  to  this  effect,  see  Henle  on  the  Contractility  of  the  Blood- 
vessels, in  Casper's  Wochenschrift,  May,  1840,  and  Brit,  and  For.  Med.  Rev.,  vol.x.  p.  551. 


380  OF  THE  CIRCULATION  OF  BLOOD. 


of  any  such  force ;  and,  when  led  to  an  affirmative  conclusion,  we  shall 
examine  into  its  nature. — No  physiological  fact  is  more  clearly  proved  than  the 
existence,  in  the  lower  classes  of  Animals,  as  well  as  in  Plants,  of  some  power 
independent  of  a  vis  a  tergo,  by  which  the  circulating  fluid  is  caused  to  move 
through  their  vessels  (§§  496 — 498).  This  power  seems  to  originate  in  them- 
selves, and  to  be  closely  connected  with  the  state  of  the  Nutritive  and  Secreting 
processes :  since  any  thing  which  stimulates  these  to  increased  energy,  accele- 
rates the  circulation ;  whilst  any  check  to  them,  occasions  a  corresponding 
stagnation.  It  may  be  convenient  to  designate  this  motor  force,  by  the  name 
of  capillary  power  ;  it  being  clearly  understood,  however,  that  no  mechanical 
propulsion  is  thence  implied.  On  ascending  the  Animal  scale,  we  find  the 
power  which,  in  the  lower  organisms,  is  diffused  through  the  whole  system, 
gradually  concentrated  in  a  single  part ;  a  new  force,  that  of  the  Heart,  being 
brought  into  operation,  and  the  Circulation  placed,  in  a  greater  or  less  degree, 
under  its  control.  Still  there  is  evidence,  that  the  movement  of  blood  through 
the  capillaries  is  not  entirely  due  to  this ;  since  it  may  continue  after  the  ces- 
sation of  the  Heart's  action, — may  itself  cease  in  particular  organs  when  the 
Heart  is  still  acting  vigorously, — and  is  constantly  being  affected  in  amount 
and  rapidity,  by  causes  originating  in  the  part  itself,  and  in  no  way  affecting 
the  Heart.  The  chief  proofs  of  these  statements  will  now  be  adverted  to. 

506.  The  movement  of  the  blood  in  the  Capillaries  of  cold-blooded  animals, 
after  complete  excision  of  the  Heart,  has  been  repeatedly  witnessed.     In  warm- 
blooded animals,  this  cannot  be  satisfactorily  established  by  experiment,  since 
the  shock  occasioned  by  so  severe  an  operation  much  sooner  destroys  the  gene- 
ral vitality  of  the  system ;  but  it  may  be  proved  in  other  ways  to  take  place. 
After  most  kinds  of  natural  death,  the  arterial  system  is  found,  subsequently 
to  the  lapse  of  a  few  hours,  almost  or  completely  emptied  of  blood ;  this  is 
partly,  no  doubt,  the  effect  of  the  tonic  contraction  of  the  tubes  themselves ; 
but  the  emptying  is  commonly  more  complete  than  could  be  thus  accounted 
for,  and  must,  therefore,  be  due  to  the  continuance  of  the  capillary  circulation. 
Moreover,  when  death  has  taken  place  suddenly  from  some  cause,  (as,  for 
instance,  a  sudden  electric  shock,)  that  destroys  the  vitality  of  the  whole  system 
at  once,  the  arterial  tubes  are  found  to  contain  their  due  proportion  of  blood. 
Further,  it  has  been  well  ascertained,  that  a  real  process  of  secretion  not  unfre- 
quently  continues,  after  general  or  somatic  death;  urine  has  been  poured  out 
by  the  ureters,  sweat  exuded  from  the  skin,  and  other   peculiar  secretions 
formed  by  their  glands ;  and  these  changes  could  not  have  taken  place,  unless 
the  capillary  circulation  were  still  continuing.     In  the  early  embryonic  condi- 
tion of  the  highest  animals,  the  movement  of  blood  seems  to  be  unquestionably 
due  to  some  diffused  power,  independent  of  any  central  impulsion  ;  for  it  may 
be  seen  to  commence  in  the  Vascular  Area,  before  the  development  of  the 
Heart.     The  first  movement  is  towards,  instead  of  from  the  centre  ;  and  even 
for  some  time  after  the  circulation  is  fairly  established,  the  walls  of  the  Heart 
consist  merely  of  vesicles  loosely  attached  together,  and  can  hardly  be  sup- 
posed to  have  any  great  contractile  power. 

507.  The  last  of  these  facts  may  be  said  not  to  have  any  direct  bearing  on 
the  question,  whether  the  Capillary  power  has  any  existence  in  the  adult  condi- 
tion ;  but  the  phenomena  occasionally  presented  by  the  Foetus,  at  a  later  stage, 
appear  decisive.     Cases  are  of  no  very  unfrequent  occurrence,  in  which  the 
heart  is  absent  during  the  whole  of  embryonic  life,  and  yet  the  greater  part  of 
the  organs  are  well  developed.     In  most  or  all  of  these  cases,  however,  a  perfect 
twin  fcstus  exists ;  of  which  the  placenta  is  in  some  degree  united  with  that  of 
the  imperfect  one ;  and  it  has  been  customary  to  attribute  the  circulation  in  the 
latter  to  the  influence  of  the  heart  of  the  former,  propagated  through  the  pla- 


MOTION  OF  THE  BLOOD  IN  THE  CAPILLARIES.  381 

cental  vessels.  The  supposition  has  not  been  disproved  (however  improbable 
it  might  seem)  until  recently ;  when  a  case  of  this  kind  occurred,  which  was 
submitted  to  the  most  careful  examination  by  an  accomplished  anatomist  ;*  and 
this  decisive  result  was  obtained, — that  it  seemed  impossible  for  the  heart  of 
the  twin  foetus  to  have  occasioned  the  movement  of  blood  in  the  imperfect  one ; 
and  that  -some  cause,  present  in  the  latter,  must  have  been  sufficient  for  the 
propulsion  of  blood  through  its  vessels.  It  was  a  very  curious  anomaly  in  this 
case,  that  the  usual  functions  of  the  Arteries  and  Vpins  must  have  been  reversed ; 
for  the  Vena  Cava,  receiving  its  blood  from  the  Umbilical  Vein  nearly  as  usual, 
had  no  communication  with  the  Arterial  system  (the  Heart  being  absent), 
except  through  the  Systemic  Capillaries  ;  to  which,  therefore,  the  blood  must 
have  next  proceeded,  returning  to  the  placenta  by  the  Umbilical  Artery.  This 
view  of  the  course  of  the  blood  was  confirmed  by  the  fact,  that  the  veins  were 
everywhere  destitute  of  valves. — It  is  evident  that  a  single  case  of  this  kind, 
if  unequivocally  demonstrated,  furnished  all  the  proof  that  can  be  needed  of 
the  existence,  even  in  the  highest  animals,  of  a  capillary  power,  which, 
though  usually  subordinate  to  the  Heart's  action,  is  sufficiently  strong  to  main- 
tain the  circulation  by  itself,  when  the  power  of  the  central  organ  is  diminished. 
In  this,  as  in  many  other  cases,  we  may  observe  a  remarkable  power  in  the 
living  system,  to  adapt  itself  to  exigences.  In  the  acardiac  Foetus,  the  capil- 
lary power  supplies  the  place  of  the  Heart,  up  to  the  period  of  birth ;  after 
which,  of  course,  the  circulation  ceases,  for  want  of  due  aeration  of  the  blood. 
It  has  occasionally  been  noticed,  that  a  gradual  degeneration  in  the  structure  of 
the  Heart  has  taken  place  during  life,  to  such  an  extent  that  scarcely  any  mus- 
cular tissue  could  at  last  be  detected  in  it,  without  any  such  interruption  to 
the  circulation,  as  must  have  been  anticipated,  if  it  were  the  sole  impelling 
force. 

508.  It  is  equally  capable  of  proof,  on  the  other  hand,  that  the  Capillaries 
may,  by  an  influence  peculiar  to  them,  afford  a  complete  check  to  the  circu- 
lation in  the  part ;  even  when  the  Heart's  action  is  unimpaired,  and  no 
mechanical  impediment  exists  to  the  transmission  of  blood.  Thus,  cases  of 
spontaneous  gangrene  of  the  lower  extremities  are  of  no  unfrequent  occurrence, 
in  which  the  death  of  the  solid  tissues  is  clearly  connected  with  a  local  decline 
of  the  circulation ;  and  in  which  it  has  been  shown  by  examination  of  the 
limb  after  its  removal,  that  both  the  larger  tubes  and  the  capillaries  were 
completely  pervious ;  so  that  the  cessation  of  the  flow  of  blood  could  not  be 
attributed  to  any  impediment,  except  that  arising  from  the  cessation  of  some 
power  which  exists  in  the  capillaries,  and  which  is  necessary  for  the  main- 
tenance of  the  current  through  them.  The  most  remarkable  evidence  on  this 
point,  however,  is  derived  from  the  phenomena  of  Asphyxia,  which  will  be 
more  fully  explained  in  the  succeeding  Chapter.  At  present  it  may  be  stated 
as  a  fact,  which  has  now  been  very  satisfactorily  ascertained,  that  if  admission 
of  air  into  the  lungs  be  prevented,  the  circulation  through  them  will  be  brought 
to  a  stand,  as  soon  as  the  air  which  they  contain  has  been  to  a  great  degree 
deprived  of  its  oxygen,  or  rather  has  become  loaded  with  carbonic  acid ;  and 
this  stagnation  .will,  of  course,  be  communicated  to  all  the  rest  of  the  system. 
Yet,  if  it  have  not  continued  sufficiently  long  to  cause  the  loss  of  vitality  in 
the  nervous  centres,  the  movement  may  be  renewed  by  the  admission  of  air 
into  the  lungs.  Now,  although  it  has  been  asserted,  that  the  stagnation  is  due 

*  See  Dr.  Houston  in  the  Dublin  Medical  Journal,  1837.  An  attempt  has  been  recently 
made  by  Dr.  M.  Hall  (Edinb.  Monthly  Journal,  1843)  to  disprove  Dr.  Houston's  infer- 
ences; but  a  most  satisfactory  reply  has  been  made  by  Dr.  Houston,  at  the  Meeting  of 
(he  British  Association,  August,  1843,  and  published  in  the  Dublin  Journal,  Jan.,  1844. 
See  also  Edinb.  Med.  and  Surg.  Journ.,  July,  1844. 


382  OF  THE  CIRCULATION  OF  THE  BLOOD. 

to  a  mechanical  impediment,  resulting  from  the  contracted  state  of  the  lungs 
in  such  cases,  this  has  heen  clearly  proved  not  to  be  the  fact,  by  causing 
animals  to  breathe  a  gas  destitute  of  oxygen,  so  as  to  cause  Asphyxia  in  a 
different  manner ;  the  same  stagnation  results  as  in  the  other  case.  The 
influence  of  the  prolonged  application  of  cold  to  a  part,  may  be  quoted  in 
support  of  the  same  general  proposition;  for,  although  the  calibre  of  the 
vessels  may  be  diminished  by  this  agent,  yet  their  contraction  is  not  sufficient 
to  account  for  that  complete  cessation  of  the  flow  of  blood  through  them  which 
is  well  known  to  occur,  and  to  terminate  in  the  loss  of  their  vitality. 

509.  Many  of  the  facts  which  indicate  the  influence  of  the  Capillaries  on 
the  amount  and  rapidity  of  the  circulation  through  them,  have  been  already 
adverted  to.     It  is  a  general  principle,  unquestioned  by  any  physiologists, 
and  embodied  in  the  ancient  aphorism   Ubi  stimulus  ibi  fluxus,  that  when 
there  is  any  local  excitement  to  the  processes  of  Nutrition,  Secretion,  &c.,  a 
determination  of  blood  towards  the  part  speedily  takes  place,  and  the  motion 
of  blood  through  it  is  increased  in  rapidity  ;  and  although  it  might  be  urged 
that  this  increased  determination  may  not  be  the  effect,  but  the  cause,  of  the 
increased  local  action,  such  an  opinion  could  not  be  sustained  without  many 
inconsistencies  with  known  facts.     For  it  is  known  that  such  local  determina- 
tions may  take  place,  not  only  as  a  part  of  the  regular  phenomena  of  growth 
and  development  (as  in  the  case  of  the  entire  genital  system  at  the  time  of 
puberty  and  of  periodical  heat,  the  uterus  after  conception,  and  the  mammae 
after  parturition),  but  also  as  a  consequence  of  a  strictly  local  cause.     Thus, 
the  student  is  well  aware  that  after  several  hours'  close  application,  there  is 
commonly  an  increased  determination  of  blood  to  the  brain,  causing  a  sense  of 
oppression,  a  feeling  of  heat,  and  frequently  a  diminished  action  in  other  parts  ; 
and,  again,  when  the  capillary  circulation  is  being  examined  under  the  micro- 
scope, it  is  seen  to  be  quickened  by  moderate  stimuli,  and  equally  retarded  by 
depressing  agents.     All  these  facts  harmonize  completely  with  the  phenomena, 
which  are  yet  more  striking  in  the  lower  classes  of  organized  beings,  and 
which  are  evidently  the  results  of  the  same  laws. 

510.  If  the  phenomena  which  have  been  here  brought  together  be  con- 
sidered  as  establishing  the  existence,  in  all  classes  of  beings  possessing  a 
circulating  apparatus,  of  a  Capillary  power,  which  affords  a  necessary  con-v 
dition  for  the  movement  of  the  nutritious  fluid  through  those  parts  in  which  it  ^ 
comes  into  more  immediate  relation  with  the  solids, — the  question  still  remains ' j 
open,  as  to  its  nature.     That  the  Capillaries  possess  a  contractile  power,  far  - 
higher  in  degree  than  that  of  the  large  Arteries,  and  more  easily  excited  than  * 
that  of  the  smaller,  appears  scarcely  to  admit  of  doubt ;  though  to  what  it  is  " 
due  may  be  reasonably  questioned.     It  has  been  recently  asserted  by  Schwann, 
that  they  possess  the  same  kind  of  fibrous  tissue  in  their  walls  as  do  the  large 
vessels  :  and  this  cannot  be  regarded  as  improbable.     It  is  not  possible,  how- 
ever, that  their  contractility  could  have  any  influence  in  aiding  the  continuous 
motion  of  blood  through  them ;  unless  it  were  exercised  in  a  very  different 
manner  from  that  of  which  observation  affords  us  evidence.     For,  when  we 
are  microscopically  examining  the  Capillary  circulation  of  any  part,  it  is  at 
once  seen  that  the  vessels  present  no  obvious  movement ;  and  that  the  stream, 
now  rendered  continuous  by  the  elasticity  of  the  arteries,  passes  through  them 
as  through  unelastic  tubes.     The  only  method  in  which  the  contractility  of 
the  Capillaries  could  produce  a  regular  influence  on  the  current  of  blood, 
would  be  an  alternate  contraction  and  dilatation,  or  a  peristaltic  movement ; 
and  of  neither  of  these  can  the  least  traces  be  discerned.     Hence  we  should 
altogether  dismiss  from  our  minds  the  idea  of  any  mechanical  assistance, 
afforded  by  the  action  of  the  Capillaries,  to  the  movement  of  the  blood. 
That  the  contractile  coat  of  the  Capillaries  has  for  its  office,  to  regulate  the 


MOTION  OF  THE  BLOOD  IN  THE  CAPILLARIES.  383 

calibre  of  the  vessels,  can  scarcely  be  doubted ;  but  any  general  permanent 
contraction  would  only  occasion  an  obstacle  to  the  circulation, — as  is  shown  by 
the  effects  of  stimulating  injections,  which,  if  thrown  into  the  vessels  before 
their  vitality  has  been  lost,  will  not  pass  through  the  capillaries.  It  would 
appear,  therefore,  to  be  through  their  action  on  this  coat  that  local  stimuli 
occasion  a  contraction  of  the  capillaries  ;  their  effect,  however,  is  different  from 
what  might  have  been  anticipated  ;  for,  instead  of  the  capillary  circulation 
being  retarded,  it  is  accelerated,  at  least  until  an  abnormal  condition  results 
from  their  continued  operation.  Here,  again,  is  another  evidence,  that  some- 
thing different  from  mechanical  power  must  be  the  agent  that  operates  in  all 
the  foregoing  cases. 

511.  The  nature  of  this  agent  is  at  present  very  obscure ;  and  it  may- not 
be  in  our  power  for  some  time  to  unveil  it.     The  conditions  of  its  action,  how- 
ever, lie  open  for  investigation  ;  and  it  appears  from  the  foregoing  facts  that  a 
very  simple  and  constant  expression  of  these  may  be  given.     Whilst  the 
injection  of  blood  into  the  capillary  vessels  of  every  part  of  the  system  is  due 
to  the  action  of  the  heart,  its,  rate  of  passage  through  those  vessels  is  greatly 
modified  by  the  degree  of  activity  in  the  processes,  to  which  it  should  normally 
be  subservient  in  them ;  the  current  being  rendered  more  rapid  by  an  increase 
in  their  activity,  and  being  stagnated  by  their  depression  or  total  cessation. — 
Thus  it  seems  that  "the  capillaries  possess  a  distributive  power  over  the  blood, 
regulating  the  local  circulation  independently  of  the  central  organ,  in  obedience 
to  the  necessities  of  each  part."*     If  this  be  true,  it  is  evident  that  the  dilata- 
tion or  contraction  of  the  capillaries  will  only  have  a  secondary  influence  on 
the  movement  of  the  blood  through  them.     The  former  condition  is  usually 
an  indication  of  diminished  vital  energy  ;  and  when  it  is  observed,  it  is  almost 
invariably  accompanied  by  a  retardation  or  partial  stagnation  of  the  current ; 
on  the  other  hand,  the  application  of  a  moderate  stimulus,  which  excites  the 
contractility,  accelerates  for  a  time  the  motion  of  the  blood,  by  rendering  more 
energetic  that  reaction  between  the  fluids  and  the  surrounding  tissues,  which 

^)is  the  condition  that  really  has  the  most  influence  over  the  current.  It  is  not 
^enough  to  object  to  such  a  doctrine,  that  we  know  nothing  of  the  mode  in  which 
i  this  reaction  affects  the  movement  of  the  blood ;  since  we  are  equally  ignorant 
f\)f  the  modus  operandi  of  many  other  causes  whose  real  existence  is  fully 
Acknowledged, — as,  for  instance,  the  effect  of  a  stimulus  applied  to  a  motor 
j*Yierve,  in  causing  contraction  of  the  muscle  supplied  by  it. 

512.  An  attempt  has  been  made  by  Dr.  Alison,  to  give  more  precision  to 
foregoing  statement,  by  attributing  the  effect  to  a  series  of  "  vital  attrac- 
s  and  repulsions,"  created  by  the   operations  to  which  the  blood  in  the 

pillaries  is  subservient.  He  considers  that  the  particles  of  blood  are  drawn 
irds  the  solids  surrounding  the  capillaries,  so  long  as  they  have  not  come 
close  relation  with  them ;  but  that,  after  accomplishing  the  purposes  of 
•  circulation,  they  are  again  repelled  by  the  same  property.  It  is  very 
possible  that  these  attractions  and  repulsions  may  have  a  real  existence,  and 
may  be  the  operative  causes  in  producing  the  phenomena  in  question,  without 
being  essentially  different  in  character  from  those  which  are  witnessed  in  physics 
and  chemistry  :  it  seems  desirable,  therefore,  not  to  apply  to  them  the  term  vital, 
which  denotes,  if  it  mean  any  thing,  that  they  are  to  be  referred  to  a  set  of  laws 
entirely  distinct.  That  alterations  in  the  chemical  state  of  the  blood  (involving, 
of  course,  important  changes  in  its  vital  properties),  are  capable  of  exercising 
a  most  important  effect  on  the  capillary  circulation,  is  shown  not  merely  by  the 
phenomena  of  Asphyxia,  already  referred  to,  but  by  the  curious  fact  recently 
ascertained  by  Dr.  J.  Reid, — that  the  blood,  when  imperfectly  arterialized,  is 

*  See  Palmer's  edition  of  Hunter,  vol.  iii.,  p.  232.    Note  by  Mr.  P. 


384  OF  THE  CIRCULATION  OF  BLOOD. 

retarded  in  the  systemic  capillaries,  causing  an  increased  pressure  on  the  walls 
of  the  arteries.  He  found  that,  when  the  Ingress  of  air  through  the  trachea 
of  a  dog  was  prevented,  and  the  Asphyxia  was  proceeding  to  the  stage  of  in- 
sensibility,— the  attempts  at  inspiration  being  few  and  laboured,  and  the  blood 
in  an  exposed  artery  being  quite  venous  in  its  character, — the  pressure  upon 
the  arterial  walls,  as  indicated  by  the  haemadynamometer  applied  to  the  femoral 
artery,  was  much  greater  than  usual.  Upon  applying  a  similar  test  to  a  vein, 
however,  it  was  found  that  the  pressure  was  proportionably  diminished  ;  whence 
it  became  apparent,  that  there  was  an  unusual  obstruction  to  the  passage  of 
venous  blood  through  the  systemic  capillaries.  After  this  period,  however, 
the  mercury  in  the  hsemadynamometer  applied  to  the  artery  began  to  fall  stea- 
dily, and  at  last  rapidly,  in  consequence  of  the  diminished  force  of  the  heart, 
and  the  retardation  of  the  blood  in  the  pulmonic  capillaries ;  but,  if  atmo- 
spheric air  was  admitted,  the  mercury  rose  very  speedily, — showing  that  the 
renewal  of  the  proper  chemical  state  of  the  blood  restored  the  condition  neces- 
sary for  its  circulation  through  the  capillaries. 

513.  It  can  be  scarcely  doubted,  that  it  is  by  some  influence  exercised  over, 
the  molecular  actions,  to  which  the  Blood  is  subject  in  the  Capillaries,  that  the 
Nervous  system  can  operate  on  the  functions  of  Nutrition,  Secretion,  &c.,  in 
the  manner  already  alluded  to  (Chap,  vn.) ;  and  this  influence  may  be  not 
improperly  termed  vital,  if  by  so  designating  it  we  merely  imply  that  its 
nature  and  mode  of  operation  are  unknown,  but  that  it  is  closely  connected 
with  those  actions  which  are  altogether  peculiar  to  living  beings.     The  fol- 
lowing experiment,  made  by  Dr.  Wilson  Philip,  exhibits,  in  a  convincing 
manner,  the  possibility  of  such  an  influence.     "  The  web  of  one  of  the  hind 
legs  of  a  frog  was  brought  before  the  microscope  ;  and  while  Dr.  Hastings 
observed  the  circulation,  which  was  vigorous,  the  brain  was  crushed  by  the 
blow  of  a  hammer.     The  vessels  of  the  web  instantly  lost  their  power,  the 
circulation  ceasing;  an  effect  which  cannot  arise,  as  we  have  seen,  from  the 
ceasing  of  the  action  of  the  heart.     [Dr.  P.  here  refers  to  experiments,  by 
which  it  was  ascertained  that  the  circulation  in  the  capillary  vessels  of  the 
frog  will  continue  for  several  minutes  after  the   interruption  of  the  heart's 
action.]     In  a  short  time  the  blood  again  began  to  move,  but  with  less  force. 
This  experiment  was  repeated  with  the  same  result.     If  the  brain  is  not  com- 
pletely crushed,  although  the  animal  is  killed,  the  blow,  instead  of  destroying 
the  circulation,  increases  its  rapidity."*     We  are  not  hence  to  conclude,  how- 
ever, that  the  Nervous  system  supplies  any  influence  which  is  essential  to  the 
continuance  of  the  Circulation ;  since  it  is  only  by  such  sudden  and  severe 
injuries  to  the  nervous  centres,  as  instantaneously  destroy  the  vitality  of  the 
whole  system  ( 386),  that  the  movement  of  the  blood  is  arrested.     The  experi- 
ments of  Miiller  and  others  satisfactorily  prove,  that  mere  action  of  the  Nerves 
does  not  produce  any  direct  effect  upon  the  Capillary  circulation ;  and  this 
corresponds  with  the  well-known  fact,  that  the  Nutritive  processes  may  con- 
tinue as  usual,  after  this  action  has  been  suspended.     All  the  facts  which  bear 
upon  the  question  of  the  connection  between  nervous  agency  and  the  Capil- 
lary Circulation,  have  an  equal  relation  to  the  functions  of  Nutrition  and 
Secretion  in  general. 

IV.  Of  the  Venous  Circulation. 

514.  The  Venous  system  takes  its  origin  in  the  small  trunks  that  are 
formed  by  the  re-union  of  the  Capillaries ;  and  it  returns  the  blood  from  these 
to  the  Heart.     The  'structure  of  the  Veins  is  essentially  the  same  with  that  of 

•^Experimental  Inquiry  into  the  Laws  of  the  Vital  Functions,  4th  edition,  p.  52. 


VENOUS  CIRCULATION.  385 

the  Arteries ;  but  the  fibrous  tissue,  of  which  their  middle  coat  is  /made  up, 
bears  more  resemblance  to  the  areolar  tissue  of  the  skin  than  it  does  either  to 
muscular  fibre,  or  to  ,the  true  elastic  tissue.  The  Elasticity  of  the  Veins, 
however,  is  shown  by  the  jet  of  blood  which  at  first  spouts  out  in  ordinary 
venesection;  when,  by  means  of  the  ligature,  a  distension  has  been  occasioned 
in  the  tubes  below  it.  A  slight  Contractility  on  the  application  of  stimuli  has 
been  observed;  but  this  is  not  so  decided  as  in  the  Arteries.  The  whole 
capacity  of  the  Venous  system  is  considerably  greater  than  that  of  the  Arte- 
rial ;  the  former  is  usually  estimated  to  contain  from  2  to  3  times  as  much 
blood  as  the  latter,  in  the  ordinary  condition  of  the  circulation ;  and  when  we 
consider  the  great  proportion  which  the  Veins,  in  almost  every  part  of  the  body, 
bear  to  the  arteries,  we  shall  scarcely  regard  even  the  larger  of  these  ratios  as 
exaggerated.  Of  course  the  rapidity  of  the  movement  of  the  blood  in  the  two 
systems,  will  bear  an  inverse  ratio  to  their  respective  capacities  ;  thus  if,  in  a 
given  length ;  the  Veins  contain  three  times  as  much  blood  as  the  Arteries,  the 
fluid  will  move  with  only  one-third  of  the  velocity.  Even  at  their  origins  in 
the  Capillary  plexus,  the  Veins  are  larger  than  are  the  Arteries  which  termi- 
nate in  the  same  plexus  ;  so  that,  wherever  the  arterial  and  venous  networks 
form  distinct  strata,  they  are  readily  distinguished  from  each  other.  The 
Veins  are  remarkable  for  the  number  of  valves  which  they  contain,  formed  of 
duplicatures  or  loose  folds  of  the  internal  tunic,  between  the  component  laminae 
of  which  contractile  fibres  are  interposed ;  arid  for  the  dilatations  behind 
these,  which,  when  distended,  give  them  a  varicose  appearance.  The  valves 
are  single  in  the  small  veins,  the  free  edge  of  the  flap  closing  against  the 
opposite  wall  of  the  vein ;  in  the  larger  trunks  they  are  double  ;  and  in  a  few 
instances  they  are  composed  of  three  flaps.  The  object  of  these  valves  is  evi- 
dently to  prevent  the  reflux  of  blood ;  and  we  shall  presently  see  that  they 
are  of  important  use  in  assisting  in  the  maintenance  of  the  venous  circulation. 
They  are  most  numerous  in  those  Veins  which  run  among  parts  affected  by 
muscular  movement ;  and  they  are  not  found  in  the  veins  of  the  lungs,  of  the 
abdominal  viscera,  or  of  the  brain.  « 

515.  The  movement  of  the  blood  through  the  Veins  is,  without  doubt,  chiefly 
effected  by  the  vis  a  tergo  or  propulsive  force ;  which  results  from  the  action 
of  the  Heart  and  Arteries,  and  from  the  additional  power  generated  in  the 
Capillary  vessels.  This  is  shown  by  the  immediate  arrestment  of  it,  which 
takes  place  when  these  forces  are  suspended.  There  are  some  concurrent 
causes,  however,  which  are  supposed  by  some  to  have  much  influence  upon 
it,  and  of  which  the  consideration  must  not  be  neglected. — One  of  these,  is 
the  suction  power  attributed  to  the  Heart ;  acting  as  a  vis  a  fronte,  in  draw- 
ing the  blood  towards  it.  It  is  very  doubtful  how  far  the  Auricles  have  such 
a  power  of  active  dilatation  as  that  which  would  be  required  for  this  purpose ; 
and  no  sufficient  evidence  has  been  given  that  the  current  of  blood  at  any  dis- 
tance from  the  Heart  is  affected  by  it.  Indeed,  for  a  reason  to  be  presently 
given,  this  may  be  regarded  as  impossible. — Another  important  agency  has 
been  found  by  some  physiologists,  in  the  Inspiratory  movement ;  this  is  sup- 
posed to  draw  the  blood  of  the  Veins  into  the  chest,  in  order  to  supply  the 
vacuum  which  is  created  there,  at  the  moment  of  the  descent  of  the  Dia- 
phragm. That  the  movement  in  question  has  some  influence  on  the  flow  of 
Venous  blood  into  the  chest,  is  evident  from  the  occurrence  of  the  respiratory 
pulse,  long  ago  described  by  Haller ;  which  may  be  seen  in  the  veins  of  the 
neck  and  shoulder  in  thin  persons,  and  in  those  especially  who  are  suffering 
from  pulmonary  diseases.  During  Inspiration,  the  Veins  are  seen  to  be 
partially  emptied :  whilst  during  Expiration  they  become  turgid,  partly  i 
consequence  of  the  accumulation  from  behind,  and  of  the  check  in  front ;  and 
partly  (it  may  be)  in  some  cases,  through  an  absolute  reflux  from  the  veins 
33 


386  OF  THE  CIRCULATION  OF  BLOOD. 

within  the  chest  (§  489).— It  was  maintained  by  Sir  D.  Barry,  that,  the  suction 
of  the  blood  towards  the  chest  in  Inspiration,  is  one  of  the  most  important 
causes  of  the  maintenance  of  the  Venous  circulation  ;  but  several  considera- 
tions agree  in  pointing  to  the  conclusion,  that  no  great  influence  can  be  rightly 
attributed  to  it.  The  Pulmonary  circulation,  being  entirely  within  the  chest, 
cannot  be  affected  by  variations  in  atmospheric  pressure ;  and  it  may  be  further 
remarked,  that  the  whole  mechanism  of  respiration  is  so  different  in  Birds 
from  that  which  exists  in  Mammalia,  that  no  vacuum  can  ever  be  said  to  exist 
in  their  chests,  although  the  venous  circulation  is  performed  as  actively  as 
usual.  The  Venous  circulation  of  the  fetus,  also,  is  independent  of  any  such 
agency.  Again,  it  has  been  shown  experimentally  by  Dr.  Arnott  and  others, 
that  no  suction-power  exerted  at  the  farther  end  of  a  long  tube,  whose  wralls 
are  so  deficient  in  firmness  as  are  those  of  the  Veins,  can  occasion  any  accele- 
ration in  a  current  of  fluid  transmitted  through  it ;  for  the  effect  of  the  suction 
is  destroyed,  at  no  great  distance  from  the  point  at  which  it  is  applied,  by  the 
flapping  together  of  the  sides  of  the  vessel.  There  can  be  no  question  about 
the  fact,  however,  that  in  the  immediate  neighbourhood  of  the  chest,  the  flow 
of  blood  towards  the  heart  is  aided  by  Inspiration  and  impeded  by  Expiration ; 
for  Sir  D.  Barry's  experiment, — which  consisted  in  introducing  one  extremity 
of  a  tube  into  the  Jugular  vein  of  a  Horse,  and  the  other  into  water,  which 
exhibited  an  alternate  elevation  and  depression  with  inspiration  and  expira- 
tion,— has  been  repeated  and  confirmed  by  several  physiologists.  It  is 
evident,  that  the  suction  of  blood  into  the  chest  will  aid  the  flow  through  the 
Veins,  by  removing  the  obstacle  to  it  in  front ;  although  it  does  not  exercise 
any  more  direct  influence  over  the  current  at  a  distance.  On  the  other  hand, 
the  expiratory  movement,  while  it  directly  causes  accumulation  in  the  Veins, 
will  assist  the  Heart  in  propelling  the  blood  into  the  Arteries ;  and  by  the 
combined  action  of  these  two  causes  is  produced,  among  other  effects,  the 
rising  and  sinking  of  the  Brain,  synchronously  with  expiration  and  inspiration, 
which  are  observed  when  a  portion  of  the  cranium  is  removed. 

516.  One  of  the  most  powerful  of  the  general  causes  which  influence  the 
Venous  circulation,  is  doubtless  the  frequently  recurring  action  of  the  Muscles 
upon  their  trunks.  In  every  instance  that  Muscular  movement  takes  place,  a 
portion  of  the  Veins  of  the  part  will  undergo  compression ;  and  as  the  blood 
is  prevented  by  the  valves  in  the  veins  from  being  driven  back  into  the  small 
vessels,  it  is  necessarily  forced  on  towards  the  Heart.  As  each  set  of  muscles 
is  relaxed,  the  Veins  compressed  by  it  fill  out  again, — to  be  again  compressed 
by  the  renewal  of  the  force.  That  the  general  Muscular  movement  is  an 
important  agent  in  maintaining  the  Circulation  at  a  point  above  that  at  which 
it  would  be  kept  by  the  action  of  the  Heart  and  Capillaries  alone,  appears  from 
several  considerations.  The  pulsations  are  diminished  in  frequency  by  rest, 
accelerated  by  exertion,  and  very  much  quickened  by  violent  effort.  In  all 
kinds  of  exercise,  and  in  almost  every  sort  of  effort,  there  is  that  alternate 
contraction  and  relaxation  of  particular  groups  of  Muscles,  which  has  been 
just  mentioned,  as  affecting  the  flow  of  blood  through  the  Veins ;  and  there 
can  be  little  doubt,  that  the  increased  rapidity  of  the  return  of  blood  through 
them,  is  of  itself  a  sufficient  cause  for  the  accelerated  movements  of  the  Heart. 
When  a  large  number  of  Muscles  are  put  in  action  after  repose,  as  is  the  case 
when  we  rise  up  from  a  recumbent  or  a  sitting  posture,  the  blood  is  driven  to 
the  Heart  with  a  very  strong  impetus  ;  and  if  that  organ  should  be  diseased, 
it  may  arrive  there  in  a  quantity  larger  than  can  be  disposed  of;  so  that  sudden 
death  may  be  the  result.  Hence  the  necessity  for  the  avoidance  of  all  sudden 
and  violent  movements  on  the  part  of  those  who  labour  under  either  a  func- 
tional or  structural  disease  of  the  centre  of  the  circulation.  That  Gravity  has 
an  influence  in  modifying  the  Circulation  in  particular  parts,  is  a  fact  well 


PECULIARITIES  OF  CIRCULATION.  387 

known,  especially  in  certain  diseased  states  ;  and  the  keeping  an  inflamed  part 
at  as  high  a  level  as  possible,  is  often  one  of  the  most  important  therapeutic 
means  that  can  be  adopted. 

V.  Peculiarities  of  the  Circulation  in  different  parts. 

517.  In  several  portions  of  the  Human  body,  there  are  certain  varieties  in 
the  distribution,  and  in  the  functional  actions  of  the  Blood-vessels,  which  should 
not  be  omitted  in  a  general  account  of  the  Circulation.     Of  these,  we  have  in 
the  first  place  to  notice  the  apparatus  for  the  Pulmonary  circulation ;  the  chief 
peculiarity  of  which  is,  that  venous  blood  is  sent  from  the  heart,  through  a 
tube  which  is  Arterial  in  its  structure,  whilst  arterial  blood  is  returned  to  the 
heart,  through  a  vessel  whose  entire  character  is  that  of  a  Vein.     The  move- 
ment of  the  blood  through  these  is  considerably  affected  by  the  physical  state 
of  the  Lungs  themselves  ;  being  retarded  by  any  causes  which  can  occasion 
pressure  on  the  vessels  (such  as  over-distension  of  the  cells  with  air,  ob- 
struction of  their  cavity  by  solid  or  fluid  depositions,  or  by  foreign  substances 
injected  into  them,  &c.) ;  and  proceeding  with  the  greatest  energy  and  regu- 
larity, when  the  respiratory  movements  are  freely  performed. — The  Portal 
circulation,  again,  is  peculiar,  in  being  a  kind  of  offset  from  the  general  or 
systemic  circulation  ;  and  also  in  being  destitute  of  valves;  and  it  may  be  sur- 
mised with  much  probability,  that  the  purpose  of  their  absence  is,  to  allow  of 
an  unusually  free  passage  of  blood  from  one  part  of  that  system  to  another, 
during  the  very  varying  conditions  to  which  it  is  subjected  (§  709). 

518.  Another  very  important  modification  of  the  circulating  system,  is  that 
which  presents  itself  within  the  Cranium.     From  the  circumstance  of  the 
cranium  being  a  closed  cavity,  which  must  be  always  filled  with  the  same  total 
amount  of  contents,  the  flow  of  blood  through  its  vessels  is  attended  with  some 
peculiarities.     The  pressure  of  the  atmosphere  is  here  exerted,  rather  to  keep 
the  blood  in  the  head  than  to  force  it  out ;  and  it  might  accordingly  be  inferred 
that,  whilst  the  quantity  of  cerebral  matter  remains  the  same,  the  amount  of 
blood  in  the  cranial  vessels  must  also  be  invariable.     This  inference  appears 
to  derive  support  from  the  experiments  of  Dr.  Kellie.*     On  bleeding  animals 
to  death,  he  found  that,  whilst  the  remainder  of  the  body  was  completely  ex- 
sanguine, the  usual  quantity  of  blood  remained  in  the  arteries  and  veins  of  the 
cranium ;  but  that,  if  an  opening  was  made  in  the  skull,  these  vessels  were 
then  as  completely  emptied  as  the  rest.     It  is  not  to  be  hence  inferred,  how- 
ever, that  the  absolute  quantity  of  blood  within  the  cranium  is  not  subject  to 
variation ;  and  that  in  the  states  of  inflammation,  congestion,  or  other  morbid 
affections,  there  is  only  a  disturbance  of  the  usual  balance  of  the  arterial  and 
venous  circulation.     The  fact  in  all  probability  is  rather  that  the  softness  of 
the  cerebral  tissue,  and  its  varying  functional  activity,  render  it  peculiarly  liable 
to  undergo  alterations  in  bulk  ;  and  that  the  amount  of  the  cerebro-spinal  fluid 
varies  considerably  at  different  times ;  so  that  the  quantity  of  blood  may  thus, 
even  in  a  healtfiy  condition,  be  continually  changing.    Moreover,  in  disordered 
states  of  the  circulation,  the  quantity  of  blood  in  the  vessels  of  the  cranium  may 
be  for  a  time  diminished  by  sudden  extravasation,  either  of  blood  or  serum, 
into  the  cerebral  substance  ;  and  the  amount  of  interior  pressure  upon  the  walls 
of  the  vesssels  may  also  be  considerably  altered,  even  when  there  is  no  differ- 
ence in  the  quantity  of  fluid  contained  in  them.t 

519.  The  Erectile  tissues  constitute  another  curious  modification  of 
ordinary  vascular  apparatus.     The  chief  of  these  are  the  Corpora  Cavernoss 

*  Edinburgh  Medico-Chirurgical  Transactions,  vol.  i. 

+  The  results  of  the  more  recent  experiments  of  Dr.  G.  Burrows  (Med.  Gaz.,  April 
May,  1843)  fully  confirm  the  views  stated  above. 


388  ON  RESPIRATION. 

in  the  penis  of  the  male,  and  in  the  clitoris  of  the  female ;  the  collection  of 
similar  tissues  round  the  vagina,  and  in  the  nymphae  of  the  female  ;  and  the 
nipple  in  both  sexes.  In  all  these  situations,  erection  may  be  produced  by  local 
irritation ;  or  it  may  take  place  as  a  result  of  certain  emotional  conditions  of 
the  mind;  the  influence  of  which  is  probably  transmitted  through  the  sympa- 
thetic nerve,  as  it  may  be  experienced  even  in  cases  of  paraplegia.  The  erectile 
tissue  appears  essentially  to  consist  of  a  plexus  of  varicose  veins,  enclosed  in 
a  fibrous  envelop.  According  to  Gerber,*  this  plexus  is  traversed  by  numerous 
contractile  fibres,  which  are  analogous  to  those  that  form  the  dartos  ;  and  to  the 
contraction  of  these  is  probably  to  be  attributed  that  obstruction  to  the  return 
of  blood  by  the  veins,  which  is  the  occasion  of  the  turgescence.  The  proxi- 
mate cause  of  the  erection  of  the  penis,  has  been  stated  by  some  to  be,  the 
action  of  the  ischio-cavernosi  muscles  ;  and  by  others  it  has  been  attributed  to 
the  compression  of  the  vena  dorsalis  penis  against  the  symphysis  pubis.  But 
it  is  obvious  that  nothing  analogous  to  this  can  apply  to  the  other  erectile  organs, 
especially  to  the  nipple.  In  the  penis,  according  to  Miiller,  there  are  two  sets 
of  arteries ;  of  which  one,  destined  for  the  nutrition  of  the  tissues,  communi- 
cates with  the  veins  in  the  usual  way,  through  a  capillary  network  ;  whilst  the 
others  pass  off  as  large  branches  and  penetrate  the  cavernous  substance  in  a 
helicine  manner,  communicating  abruptly  with  the  venous  cells.  It  would 
seem  not  improbable,  that  these  last  are  not  ordinarily  pervious  to  blood ;  but 
that  the  same  change  in  the  contractile  fibres  which  impedes  the  return  of  the 
blood  by  the  veins,  may  also  permit  it  to  enter  more  freely  from  the  helicine 
arteries.  This  double  communication,  however,  is  denied  by  Valentin,  who 
gives  a  different  explanation  of  the  appearances  described  by  Miiller.  The 
arteries  are  protected  in  such  a  manner,  that,  even  when  the  veins  are  most 
compressed  and  the  erection  most  complete,  they  are  still  quite  pervious. 


CHAPTER    X. 

ON    RESPIRATION. 

I.  Nature  of  the  Function;  and  Provisions  for  its  Performance. 

520.  IT  is  obvious  that  the  Nutritive  fluid,  in  its  circulation  through  the 
capillaries  of  the  system,  must  undergo  great  alterations,  both  in  its  physical 
constitution,  and  in  its  vital  properties.  It  gives  up  to  the  tissues  with  which 
it  is  brought  into  contact,  some  of  its  most  important  elements ;  and,  at  the 
same  time,  it  is  made  the  vehicle  of  the  removal,  from  these  tissues,  of  ingre- 
dients which  are  no  longer  in  the  state  of  combination,  that  fits  them  for  their 
offices  in  the  Animal  Economy.  To  separate  these  ingredients  from  the 
general  current  of  the  circulation,  and  to  carry  them  out  of  the  system,  is  the 
great  object  of  the  Excretory  organs;  and  it  is  very  evident  that  the  importance 
of  the  respective  functions  of  these  will  vary  with  the  amount  of  the  ingredient 
which  they  have  to  separate,  and  with  the  deleterious  influence  which  its 

*  Op.  cit.,  p.  298. 


ON  RESPIRATION  IN  GENERAL.  389 

retention  would  exert  on  the  welfare  of  the  system  at  large.  Of  all  these 
injurious  ingredients,  Carbonic  Acid  is  without  doubt  the  most  abundantly 
introduced  into  the  nutritive  fluid ;  and  it  is  also  most  deleterious  in  its  etiects 
on  the  system,  if  allowed  to  accumulate.  One  of  the  most  important  changes 
which  result  from  its  retention,  is  the  stagnation  of  the  blood,  both  in  the  sys- 
temic and  pulmonary  capillaries  ;  for  there  is  evidence  that,  if  the  process  of 
aeration,  by  which  the  venous  blood  brought  to  the  lungs  is  converted  into 
arterial,  be  in  any  way  checked,  the  flow  of  blood  through  the  pulmonary 
capillaries  speedily  ceases ;  and  that  if  venous  blood  be  propelled  through  the 
system,  in  place  of  arterial,  it  is  transmitted  with  difficulty  through  the  sys- 
temic vessels.  The  cause  is  the  same  in  both  instances; — the  normal  changes, 
which  the  blood  ought  to  undergo  in  these  vessels,  are  prevented ;  and  there 
is  consequently  a  cessation  of  that  capillary  power  which  has  been  shown  to 
be  one  of  the  most  important  of  the  forces  by  which  the  blood  is  kept  in 
motion  (§  511). 

521.  We  find,  accordingly,  that  the  provision  for  the  removal  of  carbon 
from  the  blood,  surpasses  in  extent  that  which  is  made  for  any  other  excretion. 
The  two  largest  glands  in  the  body — the  Liver  and  the  Lungs — are  designed 
for  this  purpose ;  but  their  operation  is  made  subservient,  in  each  case,  to  other 
objects.     By  the  Liver,  the  carbon  is  excreted,  with  other  elements,  in  the 
form  of  a  fluid,  which  has  important  uses  in  the  digestive  function ;  whilst  by 
the  Lungs  (which  will  be  presently  seen  to  have  in  all  essential  points  a  glan- 
dular structure)  it  is  thrown  off  in  a  gaseous  form,  and  thus  is  made  subser- 
vient, according  to  the  laws  of  the  mutual  diffusion  of  gases,  to  the  introduction 
of  oxygen  into  the  system,  and  consequently  to  the  maintenance  of  the  animal 
temperature,  as  well  as  of  the  stimulating  properties  of  the  blood.     It  is  evi- 
dent, then,  that  any  circumstances  which  check  the  excretion  of  carbonic  acid 
by  the  lungs,  will  have  an  immediately  injurious  effect  upon  the  system  at 
large;  by  causing  the  accumulation,  in  the  fluid  upon  which  it  is. dependent 
for  the  performance  of  its  vital  actions,  of  an  agent  that  so  seriously  injures  its 
vivifying  properties.     But  this  is  not  the  only  mode  in  which  the  cessation 
of  this  function  becomes  injurious.     The  exclusion  of  a  constant  supply  of 
oxygen  from  the  blood,  even  though  the  removal  of  the  carbonic  acid  were 
provided  for  by  other  means,  deprives  it  of  its  due  power  of  nourishing  and 
exciting  to  action  the  tissues  and  organs  to  which  it  is  afterwards  distributed ; 
for  it  would  appear  that  this  element  is,  throughout  animated  nature,  a  stimu- 
lant as  essential  to  the  energy  of  its  operations,  as  caloric  is  to  all,  and  light  to 
many  of  these.     Further,  in  those  animals  in  which  (as  in  Man)  the  whole 
current  of  blood  passes  through  the  Respiratory  apparatus,  any  stagnation  in 
its  capillaries  must  derange,  and  soon  check,  the  systemic  circulation.    There 
are  some  animals,  however,  (such  as  Reptiles,)  in  which  only  a  portion  of  the 
blood  that  has  returned  from  the  system  is  transmitted  to  the  lungs  by  each 
impulse  of  the  heart;  so  that  their  pulmonary  circulation  is  in  some  respects 
upon  the  footing  of  the  portal  circulation  in  other  animals:  in  such,  therefore, 
the  interruption  of  the  pulmonary  circulation  will  not  immediately  suspend 
the  movement  of  the  blood  through  the  systemic  vessels;  and  in  the  Batrachia, 
whose  soft  moist  skin  allows  the  air  to  act  with  tolerable  freedom  upon  the 
blood  contained  in  its  vessels,  life  may  be  prolonged  for  a  considerable  time, 
even  after  the  complete  removal  of  the  lungs,  provided  the  temperature  be 
low.*     But  if,  under  these  circumstances,  the  skin  be  covered  with  any  unc- 
tuous substance,  preventing  the  transmission  of  air,  death  speedily  ensues. 

522.  The  necessity  for  the  Aeration  of  the  Circulating  fluid,  is  most  remark- 

*  See  Edwards  on  the  Influence  of  Physical  Agents  on  Life  (Translation  by  Hudgkin), 
p.  32. 

33* 


390  ON  RESPIRATION. 

ably  exemplified,  in  the  provision  which  is  made  for  it  in  every  living  being; 
such  provision  being  more  universally  found  than  that  for  any  other  function, 
except  for  the  ingestion  of  aliment,  and  for  the  perpetuation  of  the  race.  Even 
in  Plants,  a  true  Respiration  is  continually  going  on,  although  its  effects  are 
sometimes  obscured  by  those  of  a  converse  change,  which  is  subservient  to  a 
different  purpose.  It  has  been  ascertained,  that  the  absorption  of  oxygen,  and 
the  extrication  of  carbonic  acid  never  cease  during  the  life  of  the  plant,— 
taking  place  under  all  conditions,  by  day  and  by  night,  in  sunshine  and  in 
shade.  This  is  their  true  Respiration.  But  Plants  obtain  from  the  atmo- 
sphere a  large  proportion  of  the  carbon  which  they  require  as  food ;  and  this 
they  procure,  by  decomposing  the  carbonic  acid  of  the  air,  absorbing  or  fixing 
its  carbon,  and  setting  free  its  oxygen.  Now  to  this  process,  which  is  only 
performed  by  the  green  parts  of  plants,  and  under  the  influence  of  light,  the 
name  Digestion  has  not  improperly  been  given.  A  healthy  Plant  will  fix  in 
this  manner  much  more  carbon  than  it  sets  free  by  Respiration ;  so  that  its 
effect  upon  the  atmosphere  is,  on  the  whole,  to  aid  in  purifying  it  from  the 
deleterious  ingredient  so  largely  imparted  to  it  by  Animal  Respiration,  Com- 
bustion, &c.  The  Fungi,  however,  derive  their  support,  like  Animals,  only 
from  matter  which  has  been  previously  organized:  and  their  respiration  is 
uncompensated  by  the  fixation  of  carbon  from  the  atmosphere.  The  same  is 
the  case,  during  the  processes  of  flowering  and  germination  in  the  higher 
Plants ;  for  certain  chemical  conversions  are  then  taking  place,  which  involve 
the  liberation  of  a  large  amount  of  carbonic  acid,  and  a  corresponding  absorp- 
tion of  oxygen,  without  any  counterbalancing  change.*  In  no  Plants  is  there 
any  distinct  respiratory  circulation ;  since  the  nutritious  fluid  can  be  brought 
into  close  relation  with  the  air,  in  almost  every  part  of  its  course.  There  is, 
however,  a  rudiment  of  an  internal  respiratory  apparatus,  in  a  system  of  air- 
vessels,  or  tracheae,  composed  of  membranous  tubes  kept  pervious  by  an 
elastic  spiral  fibre  which  winds  within  them,  and  closely  resembling  the  air- 
tubes  of  Insects. 

523.  In  the  Animal  kingdom  we  almost  universally  find  distinct  organs 
for  the  aeration  of  the  blood ;  these  are  always  formed  upon  the  same  general 
plan,  being  essentially  composed  of  a  membranous  prolongation  of  the  external 
surface,  adapted  by  its  vascularity  and  permeability,  to  bring  the  blood  into 
close  relation  with  the  surrounding  medium.  But  as  this  medium  may  be 
either  air  or  water,  we  find  two  principal  forms  of  the  apparatus  ;  one  of  them 
adapted  for  each  kind  of  respiration.  In  aquatic  animals,  the  membrane  is 
usually  prolonged  externally  into  tufts  or  fringes,  which  are  so  arranged  as  to 
expose  the  greatest  amount  of  surface  to  the  water ;  each  filament  of  which 
these  are  composed  includes  an  afferent  and  efferent  capillary  vessel ;  and  it 
is  whilst  the  fluid  is  passing  through  them,  that  its  aeration  is  accomplished. 
The  collection  of  tufts  or  fringes  constitutes  what  are  known  as  gills;  and 
though  their  arrangement  varies  considerably,  their  essential  character  is 
but  little  different  throughout  the  classes  of  animals  that  possess  them.  On 
the  other  hand,  in  air-breathing  Animals,  the  aerating  surface  is  reflected  in- 
wardly, forming  passages  or  chambers,  into  which  the  air  is  received,  and  on 
the  walls  of  which  the  blood  is  distributed  in  a  minute  capillary  network. 
Such  a  conformation  is  found  even  among  some  of  the  lower  Articulata,  which 
have  a  series  of  air-sacs  disposed  along  each  side  of  the  body,  one  for  every 
segment.  In  Insects  we  find,  instead  of  these  sacs,  a  system  of  prolonged 
tubes,  ramifying  through  the  body,  and  carrying  air  into  its  minutest  portions. 
Even  in  some  Mollusca,  such  as  the  Snail  and  other  terrestrial  Gasteropods, 
we  find  a  provision  for  aerial  respiration ;  a  large  cavity  being  formed  in  the 

*  See  Principles  of  General  and  Comparative  Physiology,  §  440  etseq. 


NATURE  OF  THE  FUNCTION.  391 

back,  communicating  with  the  air,  and  having  a  beautifully-reticulated  plexus 
of  blood-vessels  on  its  walls.  In  none  of  the  Invertebrata,  however,  does  the 
respiratory  apparatus  communicate  with  the  mouth  ;  which  is  an  organ  solely 
appropriated,  in  them,  to  the  ingestion  of  food.  In  the  Mollusca,  indeed,  the 
channel  through  which  the  water,  that  has  passed  over  the  aerating  surface, 
leaves  the  chamber  (formed  by  a  fold  of  the  mantle  or  general  envelop)  that 
contains  the  gills,  is  the  same  as  that  through  which  the  excrementitious 
matter  is  discharged  from  the  intestine ;  and  the  gills  themselves  are  very 
commonly  situated  in  the  neighbourhood  of  the  anal  orifice.  This  fact  is  inte- 
resting, in  regard  to  the  character  of  the  temporary  respiratory  apparatus  of 
the  Human  embryo.  In  Fishes  and  the  larvae  of  Batrachia,  which  are  the 
highest  animals  that  breathe  by  gills,  these  organs  are  so  disposed  in  connection 
with  the  cavity  of  the  mouth,  that  fresh  currents  of  water  are  continually  being 
forced  over  them  by  its  muscles  ;  and  thus  the  energy  of  their  action  is  greatly 
increased.  Moreover,  the  whole  blood  which  is  propelled  from  the  heart, 
proceeds  first  to  the  respiratory  organs,  instead  of  passing  through  them  on  its 
return  from  the  systemic  circulation,  as  in  most  of  the  aquatic  Invertebrata. 
Still,  as  the  quantity  of  oxygen  which  the  blood  can  obtain  in  this  manner  is 
very  small,  being  limited  to  that  contained  in  the  atmospheric  air  dissolved  in 
the  water,  the  amount  of  aeration  must  be  considered  as  low. 

524.  In  the  lowest  Vertebrata  that  possess  any  thing  like  a  pulmonary 
cavity,  this  has  a  structure  as  simple  as  that  of  the  air-sac  of  the  Snail.  This 
is  the  case  in  many  Fishes,  where  it  is  known  as  the  air-bladder ;  it  is  fre- 
quently single  in  this  class,  and  communicates  with  the  intestinal  canal  near 
the  stomach,  or  is  altogether  destitute  of  outlet.  In  others,  however,  it  is 
double,  and  its  duct  opens  into  the  oesophagus  near  the  mouth ;  so  that  its 
analogy  to  the  lungs  of  higher  animals  is  very  evident.  The  Batrachia  begin 
life  as  fishes,  breathing  by  gills  during  their  tadpole  state ;  but  at  the  time 
that  the  legs  are  developed  and  the  tail  has  decreased,  the  pulmonary  organs 
also  are  evolved,  and  the  course  of  the  blood  is  altered,  so  that  it  is  no  longer 
transmitted  through  the  gills,  which  speedily  shrivel  and  disappear  (§  42). 
There  are  some  species,  however,  whose  metamorphosis  is  checked,  so  that 
in  their  permanent  condition  both  lungs  and  gills  are  present ;  but  the  former 
are  then  present  in  a  very  rudimentary  form,  not  being  more  developed  than 
the  air-sacs  of  many  Fishes.  The  lungs  of  Reptiles  are,  almost  universally, 
simple  sacs  with  little  subdivision  into  cells.  Where  such  subdivision  exists, 
it  is  usually  at  the  upper  part  of  each  lung,  the  rest  being  one  undivided  bag, 
on  the  walls  of  which  the  pulmonary  vessels  are  distributed.  They  afford  us, 
therefore,  a  good  opportunity  of  studying  the  distribution  of  these  vessels  ;  and 
the  accompanying  figures  represent  the  course  of  the  circulation  as  observed 
in  them.  It  will  be  seen  that  the  trunk  of  the  pulmonary  artery  runs  along 
one  side  of  the  sac,  and  that  of  the  pulmonary  vein  along  the  other  (Fig.  93) ; 
and  that  numerous  branches  arise  from  the  former,  which  subdivide  into 
capillaries  that  ramify  over  the  whole  surface,  and  then  reunite  into  small 
veins  which  terminate  in  the  latter.  The  islets  of  parenchyma  left  between 
the  capillary  vessels,  are  seen  to  be  much  smaller  than  those  which  are  usually 
to  be  observed  in  the  systemic  circulation  (Figs.  94,  95) ;  so  that  the  mem- 
brane is  more  copiously  traversed  by  vessels  than  any  other  that  is  known. 
The  walls  of  the  capillaries,  moreover,  are.  much  less  distinct  than  those  of  the 
systemic  circulation.  These  two  conditions  are  obviously  favourable  to  the 
exposure  of  the  largest  possible  quantity  of  blood  to  the  influence  of  the  air ; 
but  as  the  surface  is  not  an  extensive  one,  the  amount  which  can  be  thus 
exposed  at  any  one  time  is  very  limited ;  and  the  pulmonary  artery  is  in  fact 
one  of  the  smaller  branches  of  the  aorta,  which  conveys  a  mixed  fluid  to  the 
system  at  large. 


392 


ON  RESPIRATION, 


Fig.  93. 


Fig.  04. 


Lung  of  Triton  cri&tatus,  magnified  about  3  dia- 
meters ;  a,  pulmonary  artery ;  6,  pulmonary  vein. 


Portion  of  the  lung  of  the  same  animal,  more 
highly  magnified ;  the  vessels,  finely  injected  with 
size  and  vermilion,  form  a  network  so  minute  that 
the  parenchyma  is  only  seen  in  small  islets  in  its 
interstices.  (After  Wagner.) 


Fis.  95. 


Portion  of  the  lung  of  a  living  Triton,  as  seen  under  the  microscope  wilh  a  power  of  150  diameters:  a, 
pulmonary  vein,  receiving  blood  from  the  large  trunk  c,  and  a  smaller  vessel  d.    (After  Wagner.) 


PROVISIONS  FOR  THE  FUNCTION.  393 

525.  In  the  warm-blooded  Vertebrata,  which  Fig.  96. 
have   a   complete   double   circulation, — namely, 

birds  and  mammalia,— a  much  larger  extent  of 
surface  is  provided  for  the  aeration  of  the  blood; 
the  whole  current  of  which  is  transmitted  to  the 
lungs,  before  circulating  again  through  the  sys- 
tem. This  increase  is  provided  in  birds,  partly 
by  the  more  minute  subdivision  of  the  lungs  into 
cells,  and  partly  by  the  addition  of  a  number  of 
large  air-sacs,  which  are  disposed  in  various  parts 
of  the  body,  and  even  in  the  interior  of  the  long 
bones.  Hence  it  happens,  that  the  amount  of  Potion  of  the  Lung  of  a  p/^,  the 

...  I'll-  terminal  vessels  being  filled   with 

respiration  is  greater  m  this  class  than  in  any    mercury.  A,natural  8ize.  B)  mode. 
other,  although  the  form  of  the  apparatus  is  not     rateiy  magnified.  (After  Wagner.) 
nearly  so  concentrated  as  in  the  mammalia ;  nor  is 
the  mechanism  of  the  chest  so  well  adapted  to  a 

constant  exchange  of  the  air  contained  in  its  cavities  (§  48).  In  mammalia 
the  lungs  are  proportionally  smaller,  and  the  whole  respiratory  apparatus  is 
restricted  to  the  thorax ;  but  the  minute  subdivision  of  their  cavity,  and  the 
mechanism  by  which  a  continual  interchange  of  air  is  provided  for,  render 
them  very  efficient  for  their  designed  purpose.  In  regard  to  the  intimate 
structure  of  the  lungs  of  man  and  of  the  mammalia,  it  is  difficult  to  speak  with 
confidence.  It  was  maintained  by  Reissessen,  and  has  been  repeated  by  other 
anatomists,  that  the  air-cells  of  the  lungs  are  in  reality  the  globular  dilatations 
of  the  extremities  of  the  ultimate  ramifications  of  the  bronchial  tubes,  analogous 
to  the  milk-cells  of  the  mammary  gland  (Fig.  161) ;  but  it  has  been  objected, 
that  they  are  much  more  numerous  than  these  ramifications  can  be  supposed 
to  be  ;  and  there  seems  much  reason  to  believe  that  every  tube  leads  to  a  clus- 
ter of  cells,  communicating  with  each  other.  The  recent  inquiries  of  Mr. 
Addison*  have  shown  that  Reissessen's  account  is  true  of  the  foetal  lung ;  in 
which  the  ultimate  subdivisions  of  the  bronchial  tubes  terminate  without  anas- 
tomosis in  closed  extremities.  But  when  an  animal  has  respired,  these  termi- 
nations undergo  a  great  change  ;  for  the  membrane  composing  each  of  them 
offers  but  a  feeble  resistance  to  the  pressure  of  the  air,  and  is  pushed  forwards 
and  distended  laterally  into  rounded  inflations,  forming  a  series  of  cells,  which 
are  moulded  by  mutual  pressure  into  various  angular  forms,  and  which  com- 
municate freely  with  one  another  by  large  oval  apertures.  The  passages  thus 
formed  do  not  communicate  with  each  other,  otherwise  than  by  their  connec- 
tion with  the  same  bronchial  tube ;  and  the  blood-vessels  lie  between  the  con- 
tiguous walls  of  each  two  of  them,  so  that  the  capillary  stream  is  exposed  to 
air  on  either  side.  It  appears  from  the  researches  of  M.  Bourgery,t  that  the 
development  of  the  air-cells  continues  in  the  human  subject  up  to  the  age  of 
thirty,  at  which  time  the  capacity  for  respiration  is  the  greatest ;  it  subsequently 
decreases,  especially  in  persons  who  suffer  from  cough, — the  violence  of  which 
expiratory  effort  frequently  causes  rupture  of  the  air-cells,  and  thus  gradually 
produces  that  emphysematous  state  of  the  lungs  which  is  so  common  in  elderly 
persons.  The  power  of  increasing  the  volume  of  air  taken  in,  by  a  forced 
inspiration,  is  much  less  in  the  old  person  than  in  the  child,  though  the  average 
amount  of  air  inspired  may  be  the  same  ;  hence  the  young  person  possesses  a 
greater  capacity  of  respiration,  as  it  were,  in  reserve  ;  whilst  the  old  man  has 
little,  and  is  therefore  unfit  for  great  exertion. 

526.  The  lungs  are  developed,  in  the  first  instance,  as  diverticula  from  the 

*  Philosophical  Transactions,  1842. 

j-  Archives  Generates  de  Medecine,  Mars,  1843. 


394 


ON  RESPIRATION. 


Fig.  97.  cesophageal  tube.     In  the  chick,  about 

the  fourth  day,  a  little  sacculus  is  de- 
scribed as  shooting  forth  at  its  posterior 
and  inferior  part ;  and  this  soon  sub- 
divides at  its  lower  part  into  two,  at  the 
same  time  becoming  more  separated 
from  the  tube  by  a  constriction  around 
the  neck,  which  soon  elongates  so  as  to 
form  the  trachea.  On  the  fifth  or  sixth 
day,  the  lung  of  one  side  is  completely 
distinct  from  that  of  the  other,  and  each 
is  attached  to  the  common  pedicle  by 
a  peculiar  branch,  the  future  bronchus.  The  upper  portion  has  much  thicker 
walls  than  the  lower,  and  these  appear  to  contain  a  large  quantity  of  vesicular 
parenchyma,  in  which  the  ramifications  of  the  bronchial  tubes  subsequently 
extend  themselves.  About  the  tenth  or  eleventh  day  of  incubation,  these  rami- 
fications possess  nearly  their  permanent  character  and  situation.  The  first 
trace  of  the  glottis  appears  about  the  fifth  day ;  it  is  then  a  mere  slit  in  the 
walls  of  the  ossophagus,  resembling  that  by  which  the  ductus  pneumaticus  of 
some  fishes  opens  into  the  alimentary  canal.  The  formation  of  the  cartilaginous 

[Fig.  98. 


First  appearance  of  the  Lungs ;  a,  in  a  Fowl  at 
four  days ;  b,  in  a  Fowl  at  six  days;  c.  termination 
of  bronchus  in  very  young  Pig.  (After  Rathke.) 


The  Larynx,  Trachea  and  Bronchiae,  deprived  of  their  fibrous  covering,  and  with  the  outline  of  the 
Lungs;  1,  1,  outline  of  the  upper  lobes  of  the  lungs;  2,  outline  of  the  middle  lobe  of  the  right  lung;  3,  3, 
outline  of  the  inferior  lobes  of  both  lungs;  4,  outline  of  the  ninth  dorsal  vertebra,  showing  its  relation  to 
the  lungs  and  the  vertebral  column;  5,  thyroid  cartilage;  6,  cricoid  cartilage;  7,  trachea;  8,  right  bronchus; 
9,  left  bronchus;  10,  crico-thyroid  ligament;  11, 12,  rings  of  the  trachea;  13,  first  ring  of  the  trachea;  14, 
1  ast  ring  of  the  trachea,  which  is  corset-shaped;  15, 16,  a  complete  bronchial  cartilaginous  ring;  17,  one 
which  is  bifurcated;  18,  double  bifurcated  bronchial  rings;  19, 19,  smaller  bronchial  rings;  20,  depressions 
for  the  course  of  the  large  blood-vessels.] 


NATURE  OF  THE  FUNCTION. 

[Fig.  99. 


395 


A  view  of  the  Bronchise  and  Blood- Vessels  of  the  Lungs  as  shown  by  dissection,  as  well  as  the  relative 
position  of  the  Lungs  to  the  Heart;  1,  end  of  the  left  auricle  of  the  heart;  2,  the  right  auricle  ;  3,  the  left 
ventricle  with  its  vessels;  4,  the  right  ventricle  with  its  vessels;  5,  the  pulmonary  artery;  6,  arch  of  the 
aorta;  7,  superior  vena  cava;  8,  arteria  innominata;  9,  left  primitive  carotid  artery;  10,  left  sub-clavian 
artery;  11,  the  trachea;  12,  the  larynx;  13,  upper  lobe  of  the  right  lung;  14,  upper  lobe  of  the  left  lung; 
15,  trunk  of  the  right  pulmonary  artery ;  16,  lower  lobes  of  the  lungs.  The  distribution  of  the  bronchia  and 
of  the  arteries  and  veins,  as  well  as  some  of  the  air-cells  of  the  lungs,  are  also  shown  in  this  dissection.] 

rings  of  the  trachea  does  not  commence  until  after  the  twelfth  day,  when  they 
first  appear  as  transverse  striae  on  the  median  line  of  the  front  only ;  they 
gradually  become  solid,  and  extend  themselves  on  either  side,  until  they  nearly 
meet  at  last  on  the  median  line  on  the  back  or  vertebral  side  of  the  tube. — The 
history  of  the  process  in  the  human  embryo,  appears  to  be  very  nearly  the 
same.  The  first  appearance  of  the  lungs  takes  place  about  the  sixth  week, 
at  which  time  they  are  simple  vesicular  prolongations  of  the  oesophageal  mem- 
brane. Their  surface,  however,  soon  becomes  studded  with  numerous  little 
wart-like  projections,  and  these  are  caused  by  the  formation  of  corresponding 
enlargements  of  their  cavity.  These  enlargements  soon  become  prolonged, 
and.  develop  corresponding  bud-like  enlargements  from  their  sides ;  and  in 
this  manner  the  form  of  the  organ  is  gradually  changed,  a  progressive  increase 
in  their  bulk  taking  place  from  above  downwards,  in  consequence  of  the  exten- 
sion of  the  bronchial  ramifications  from  the  single  tube  at  the  apex.  At  the 
same  time,  however,  a  corresponding  increase  in  the  amount  of  the  parenchy- 
matous  tissue  of  the  lung  is  taking  place ;  for  this  is  deposited  in  all  the  inter- 
stices between  the  bronchial  ramifications,  and  might  be  compared  with  the 
soil  filling  up  the  spaces  amongst  the  roots  of  a  tree.  It  is  in  this  parenchyma 
that  the  pulmonary  vessels  are  distributed,  and  the  portion  of  it  which  extends 
beyond  the  terminations  of  the  bronchial  tubes,  seems  to  act  as  the  nidus  for 
their  further  extension.  It  can  be  easily  shown  that,  up  to  a  late  period  of  the 


396  ON  RESPIRATION. 

development  of  the  lungs,  the  dilated  terminations  of  the  bronchi  constitute  the 
only  air-cells  (Fig.  97,  c) :  but,  as  already  mentioned,  the  parenchyma  subse- 
quently has  additional  cavities  formed  within  it.  It  is  a  fact  of  some  interest, 
as  an  example  of  the  tendency  of  certain  diseased  conditions  to  produce  a  return 
to  forms  which  are  natural  to  the  foetal  organism,  or  which  present  themselves 
in  other  animals,  that  up  to  a  late  period  in  the  development  of  the  human  em- 
bryo, the  lungs  do  not  nearly  fill  the  cavity  of  the  chest,  and  the  pleura  of  each 
side  contains  a  good  deal  of  serous  fluid. 

527.  The  network  of  vessels  on  the  walls  of  the  air-cells  is  described  by 
Reissessen  as  so  minute,  that  the  diameter  of  the  meshes  is  scarcely  so  great 
as  that  of  the  capillary  vessels  which  form  it.  According  to  Mr.  Addison,  the 
capillaries  in  the  lung  of  a  Toad  admit,  in  their  natural  state,  no  more  than 
one,  or  at  most  two  rows  of  blood-corpuscles ;  and  the  islets  of  tissue  between 
them  are  comparatively  large  :  whilst,  if  the  lung  be  congested  or  inflamed, 
five  or  six  rows  of  corpuscles  are  seen  in  the  vessels ;  and  the  islets  of  tissue 
are  almost  entirely  obliterated.  The  diameter  of  the  pulmonary  vesicles  is 
about  twenty  times  greater  than  that  of  the  capillaries  which  are  distributed 
upon  their  parietes  ;  varying  (according  to  the  measurement  of  Weber)  from 
the  -nf  ¥th  to  the  g\th  of  an  inch.  There  is  no  evidence  that  the  alteration  in 
the  size  of  the  air-cells,  which  takes  place  during  the  respiratory  process,  is 
due  to  any  other  cause  than  the  simple  elasticity  of  their  walls ;  but  the  bron- 
chial tubes  certainly  possess  a  considerable  amount  of  contractility,  which  can 
scarcely  be  regarded  as  otherwise  than  muscular.  From  the  experiments  of 
Dr.  C.  B.  Williams,*  it  appears  that  all  the  air-tubes  are  endowed  with  a  con- 
siderable amount  of  irritability,  which  may  be  excited  by  electrical,  chemical, 
or  mechanical  stimuli,  applied  to  themselves,  but  not  readily  (if  at  all)  excitable 
through  their  nerves.  This  contractility  resembles  that  of  the  intestines  or 
arteries  more  than  that  of  the  voluntary  muscles  or  heart ;  the  contraction  and 
relaxation  being  more  gradual  than  that  of  the  latter,  though  less  tardy  than 
that  of  the  former.  It  is  chiefly  manifested  in  the  smaller  bronchial  tubes ; 
since,  in  the  trachea  and  the  larger  bronchi,  the  cartilaginous  rings  prevent 
any  decided  diminution  in  the  calibre  of  the  tube.  Wedemeyer  did  not  succeed 
in  producing  any  distinct  contraction  of  the  fibres  of  the  trachea  and  larger 
bronchi ;  but  he  states  that  tubes  of  less  than  a  line  in  diameter  could  be  per- 
ceived to  contract  gradually  under  the  stimulus  of  galvanism,  until  their  cavity 
was  nearly  obliterated.  It  is  remarked  by  Dr.  Williams,  that  the  irritability 
of  the  bronchial  muscles  is  soon  exhausted  by  the  action  of  a  stimulus ;  but 
that  it  may  in  some  degree  be  restored  by  rest,  even  when  the  lung  is  removed 
from  the  body.  When  the  stimulation  is  long  continued,  however,  as  by 
intense  irritation  of  the  mucous  membrane  during  life,  the  contractile  tissue 
passes  into  a  state  which  resembles  that  of  the  tonic  contraction  of  muscular 
fibre  (§  390).  The  contractility  is  greatly  affected  by  the  mode  of  death,  and 
is  remarkably  diminished  by  the  action  of  vegetable  narcotics,  particularly 
stramonium  and  belladonna ;  whilst  it  seems  to  be  scarcely  at  all  affected  by 
hydrocyanic  acid.  These  facts  are  very  important,  as  throwing  light  upon  cer- 
tain diseased  conditions.  It  has  long  been  suspected,  that  the  dyspnoea  of  Spas- 
modic Asthma  depends  upon  a  constricted  state  of  the  smaller  bronchial  tubes, 
excited  through  the  nervous  system,  frequently  by  a  stimulating  cause  at  some 
distance  ;  and  there  can  now  be  little  doubt  that  this  is  the  case.  That  they 
should  not  be  readily  excited  to  contraction  by  a  galvanic  stimulus  applied  to 
their  nerves,  is  no  valid  argument  against  this  view ;  as  it  was  long  held  that 
the  muscular  coat  of  the  alimentary  canal  also  was  completely  removed  from 
nervous  influence,  which  is  now  well  known  to  be  not  by  any  means  the  case. 

*  Athenaeum  Report  of  the  Meeting  of  the  British  Association,  1840,  p.  802. 


NATURE  OF  THE  FUNCTION.  397 

The  peculiar  influence  of  stramonium  and  belladonna,  in  diminishing  the 
contractility  of  these  fibres,  harmonizes  remarkably  with  the  well-known  fact 
of  the  relief  frequently  afforded  by  them  in  this  distressing  malady. 

528.  Notwithstanding  the  high  degree  of  contractility  which  the  bronchial 
tubes  have  been  shown  to  possess,  there  is  no  valid  reason  for  the  belief,  that 
they  contribute  by  any  rhythmical  movement  to  the  exchange  of  the  contained 
air,  which,  in  the  healthy  state,  is  continually  taking  place.     For  it  can  be 
scarcely  imagined  that  they  should,  by  any  power  of  their  own,  contract  and 
dilate  uniformly  with  the  contraction  and  expansion  of  the  chest,  unless  their 
muscles  were  equally  subject  with  those  of  the  thorax,  to  the  influence  of  the 
nervous  system ;  which  all  experiments  concur  in  showing  not  to  be  the  case. 
The  lungs  themselves,  then,  are  to  be  regarded  as  quite  passive  in  the  move- 
ments of  respiration ;  the  renewal  of  their  contained  air  being  accomplished 
by  the  action  of  the  muscles  external  to  the  thorax,  or  partly  forming  its  pari- 
etes.     The  lung  completely  fills  the  cavity  of  the  pleura,  in  the  healthy  state 
at  least ;  so  that,  when  this  is  enlarged,  a  vacuum  is  produced,  which  can  only 
be  filled  by  a  corresponding  enlargement  of  the  lung ;  and  to  produce  this,  the 
air  rushes  down  the  trachea,  and  passes  to  the  remotest  air-cells.     The  dis-' 
tension  of  the  whole  tissue  of  the  lung,  which  is  effected  in  this  manner,  is 
much  more  complete  than  that  which  could  be  occasioned  by  simple  insuffla- 
tion from  the  trachea  ; — a  fact  of  which  it  has  been  proposed  to  take  advantage 
in  juridical  inquiries  in  regard  to  suspected  cases  of  Infanticide,  where  the 
lungs  are  found  to  float,  and  the  defence  is  set  up  that  the  child  was  still-born, 
and  that  air  was  blown  into  the  chest  for  the  purpose  of  resuscitating  it.     It 
has  been  ascertained  by  the  experiments  of  Mr.  Jennings,*  that  if  a  piece  of 
lung,  which  has  been  filled  with  air  by  insufflation,  be  exposed  to  great  pres- 
sure, the  air  may  be  expelled  from  it  sufficiently  to  cause  it  to  sink  in  water ; 
but  that  no  pressure  can  produce  the  same  effect  upon  that  which  has  been  filled 
by  a  natural  inspiratory  effort.     It  is  a  serious  objection  to  the  use  of  this  test 
in  juridical  investigations,  however,  that  the  early  inspiratory  efforts  of  the 
infant  are  often  so  feeble  as  to  produce  but  a  very  imperfect  dilatation  of  the 
air-cells  ;  so  that  the  lung  of  an  infant  which  has  naturally  inspired  cannot, 
by  such  means,  be  distinguished  from  one  that  has  been  artificially  inflated. 
The  fact  ascertained  by  Mr.  J.,  however,  is  one  of  much  physiological  interest. 
Owing  to  the  freedom  with  which  the  air  enters  the  lungs,  when  there  is  no 
abnormal  obstruction,  the  external  surface  is  always  in  contact  with  the  walls 
of  the  chest,  so  that  the  pulmonary  and  costal  pleura  glide  over  one  another 
with  every  inspiration  and  expiration.     The  smooth  and  moistened  character 
of  their  surface  prevents  the  movement  from  producing  any  sound  ;  but  it 
becomes  evident  when  the  friction  is  increased,  either  by  the  dryness  that  is 
commonly  one  of  the  early  changes  produced  by  inflammation,  or  by  the  rough 
deposit  that  subsequently  appears. 

529.  The  complete  dependence  of  the  expansion  of  the  Lungs  upon  the 
production  of  a  vacuum  in  the  chest,  is  well  shown  by  the  effect  of  admission 
of  air  into  the  pleural  cavity.     When  an  aperture  is  made  on  either  side,  so 
that  the  air  rushes  in  at  each  inspiratory  movement,  the  expansion  of  the  lung 
on  that  side  is  diminished,  or  entirely  prevented,  in  proportion  to  the  size  of 
the  aperture.     If  air  can  enter  through  it  more  readily  than  through  the 
trachea,  an  entire  collapse  of  the  lung  takes  place ;  and  by  making  such  an 
aperture  on  each  side,  complete  asphyxia  is  produced.     But  if  it  be  too  small 
to  admit  the  very  ready  passage  of  air,  the  vacuum  produced  by  the  inspira- 
tory movement  is  more  easily  filled  by  the  distension  of  the  lungs  than  by  the 
rush  of  air  into  the  pleural  cavity ;  so  that  a  sufficient  amount  of  change  takes 

*  Transactions  of  the  Provincial,  Medical  and  Surgical  Association,  vol.  n. 
34 


ON  RESPIRATION. 


place  for  the  maintenance  of  life.  This  is  frequently  observed  in  the  case  of 
penetrating  wounds  of  the  thorax,  in  the  surgical  treatment  of  which  it  is  of 
great  importance  to  close  the  aperture  as  completely  as  possible ;  when  this 
has  been  accomplished,  the  air  that  had  found  its  way  into  the  cavity  is  soon 
absorbed,  and  the  lung  resumes  its  full  play.  Where  one  lung  is  obstructed 
by  tubercular  deposit,  or  is  prevented  in  any  other  way  from  rightly  dis- 
charging its  function,  an  opening  that  freely  admits  air  into  the  pleural  cavity 
of  the  other  side,  is  necessarily  attended  with  an  immediately  fatal  result ;  an'd 
in  this  manner  it  not  unfrequently  happens,  that  chronic  pulmonary  diseases 
suddenly  terminate  in  Asphyxia, — a  communication  being  opened  by  ulcera- 
tion,  between  a  bronchial  tube  and  the  cavity  of  the  thorax. 

530.  The  dilatation  of  the -chest  during  Inspiration,  is  chiefly  accomplished 
by  the  contraction  of  the  Diaphragm,  which,  from  the  high  arch  that  it  pre- 
viously formed,  becomes  nearly  plane ;  in  this  change  of  figure,  it  presses  on 
the  abdominal  viscera,  so  as  to  cause  them  to  protrude,  which  they  are  enabled 
to  do  by  the  relaxation  of  the  abdominal  muscles.      In  ordinary  tranquil 
breathing,  the  action  of  the  diaphragm  is  alone  nearly  sufficient  to  produce 
the  necessary  exchange  of  air ;  but,  when  a  full  inspiration  is  required,  the 
cavity  of  the  chest  is  dilated  laterally,  as  well  as  inferiorly.     This  is  accom- 
plished by  the  Intercostal  muscles,  the  Scaleni,  Serrati,  and  others ;  which,  by 
elevating  the  ribs,  bring  them  and  their  •  cartilages  more  nearly  into  the  same 
direction,  and  thus  separate  them  more  widely  from  the  median  line.     Expi- 
ration is  chiefly  effected  by  the  contraction  of  the  abdominal  muscles,  which  at 
the  same  time  force  up  the  diaphragm  by  their  pressure  on  the  viscera,  and 
depress  the  ribs ;  in  the  latter  movement  they  are  aided  by  the  Longissimus 
Dorsi,  Sacrolumbalis,  &c.,  and  also  by  the  elasticity  of  the  cartilages  of  the 
ribs,  with  that  of  the  air-cells  and  air-tubes  themselves. — It  is  difficult  to  form 
an  estimate,  by  observations  on  one's  self,  of  the  usual  number  and  degree  of 
the  respiratory  movements;    since  the  direction  of  the  attention  to  them  is 
certain  to  increase  their  frequency  and  amount.     In  general  it  may  be  stated 
that  from  14  to  18  alternations  usually  occur  in  a  minute ;  of  these,  the  ordi- 
nary inspirations  involve  but  little  movement  of  the  thorax;  but  a  greater 
exertion  is  made  at  about  every  fifth  recurrence.     The  average  numerical 
proportion  of  the  respiratory  movements,  to  the  pulsations  of  the  heart,  is 
about  1  to  5  or  4£ ;  and  when  this  proportion  is  widely  departed  from,  there 
is  reason  to  suspect  some  obstruction  to  the  aeration  of  the  blood,  or  some 
disorder  of  the  nervous  system.     Thus  in  Pneumonia,  in  which  a  greater  or 
less  amount  of  the  lung  is  unfit  for  its  office,  the  number  of  respirations  in- 
creases in  a  more  rapid  proportion  than  the  acceleration  of  the  pulse ;  so  that 
the  ratio  becomes  as  1  to  3,  or  even  1  to  2,  in  accordance  with  the  degree  of 
engorgement.*     In  Hysterical  patients,  however,  a  similar  increase,  or  even  a 
greater  one,  may  take  place  without  any  serious  cause ;  thus  Dr.  Elliotsont 
mentions  a  case,  in  which  the  respiratory  movements  of  a  young  female, 
through  nervous  affection,  were  98  or  even  106,  whilst  the  pulse  was  104. 
On  the  other  hand,  the  respirations  in  certain  typhoid  conditions  and  in  nar- 
cotic poisoning  become  abnormally  slow,  owing  to  the  torpid  condition  of  the 
nervous  centres,  the  proportion  being  1  to  6,  or  even  1  to  8;  and  in  such 
cases,  the  lungs  not  unfrequently  become  oedematous,  from  the  cause  formerly 
mentioned  (§§231  and  232). 

531.  The  amount,  also,  of  the  Respiratory  Movements  is  affected  by  various 
morbid  conditions ;  thus  when  dislocation  of  the  spine  takes  place  above  the 

*  See  a  paper  by  Dr.  Hooker,  on  the  Relation  between  the  Respiratory  and  Circulating 
Functions,  in  the  Boston  (N.  E.)  Medical  and  SurgicalJournal;  an  abstract  of  which  will 
be  found  in  the  British  and  Foreign  Medical  Review,  vol.  vi.  p.  263. 

f  Physiology,  p.  215,  note. 


NATURE  OF  THE  FUNCTION.  399 

origin  of  the  intercostal  nerves,  but  below  that  of  the  phrenic,  so  that  the 
former  are  paralyzed,  the  respiratory  movement  is  confined  to  the  diaphragm ; 
and  as  this  is  insufficient,  serum  is  effused  into  the  lungs,  and  a  slow  Asphyxia 
supervenes,  which  usually  proves  fatal  in  from  three  to  seven  days.  Even 
where  the  muscles  and  nerves  are  all  capable  of  action,  the  full  performance 
of  the  inspiratory  movements  is  prevented  by  the  solidification  or  engorgement 
of  any  part  of  the  lung,  which  interferes  with  its  free  distension ;  or  by  adhe- 
sions between  the  pleural  surfaces,  which  offer  a  still  more  direct  impediment. 
When  these  adhesions  are  of  long  standing,  they  are  commonly  stretched  into 
bands,  by  the  continual  tension  to  which  they  are  subjected.  If  the  impeding 
cause  affect  both  sides,  the  movements  of  both  will  be  alike  interfered  with;  but 
if  one  side  only  is  affected,  its  movements  will  be  diminished,  whilst  those  of 
the  other  remain  natural ;  and  the  physician  hence  frequently  derives  an  indi- 
cation of  great  value,  in  regard  to  the  degree  in  which  the  lung  is  incapable 
of  performing  its  functions.  It  is  to  be  remembered,  however,  that  the  action 
both  of  the  diaphragm  and  of  the  elevators  of  the  ribs  may  be  prevented,  by 
pain  either  in  the  muscles  themselves  or  in  the  parts  which  they  move ;  thus  the 
descent  of  the  diaphragm  is  checked  by  inflammation  of  the  abdominal  viscera 
or  of  the  peritoneum;  and  that  of  the  intercostals  by  rheumatism,  pleuritis, 
pericarditis,  or  other  painful  disorders  of  the  parts  forming  the  parietes  of  the 
thorax. 

532.  In  regard  to  the  capacity  of  the  Lungs,  the  quantity  of  air  introduced 
and  expelled  at  each  ordinary  respiratory  movement,  and  the  amount  that 
remains  after  expiration,  great  discrepancy  exists  in  the  statements  of  the  vari- 
ous experimenters  who  have  endeavoured  to  ascertain  them.  This  discrepancy 
has  doubtless  arisen  in  part  from  the  circumstance  already  mentioned, — that 
attention  to  the  respiratory  movements  will  render  them  fuller  and  more  fre- 
quent :  and  in  part,  also,  from  the  degree  of  effort  that  is  required,  to  draw  air 
from  any  kind  of  apparatus  adapted  to  afford  a  measurement  of  the  quantity 
inhaled;  which  effort  will  of  itself  cause  the  distension  of  the  chest  to  be 
much  greater  than  natural.  The  experiments  of  Messrs.  Allen  and  Pepys 
seemed  to  give  16£  cubic  inches  as  the  average  quantity  taken  in  at  each 
inspiration  :  whilst  those  of  Menzies  (who  is  followed  by  Dr.  Bostock)  caused 
him  to  rate  it  at  40  cubic  inches.  The  most  recent  experiments  on  the  subject 
are  those  of  Mr.  Coathupe,*  in  which  the  Author  has  much  reason  to  feel  con- 
fidence. According  to  his  estimate,  about  286£  cubic  feet,  or  460,224  cubic 
inches  of  air,  pass  through  the  lungs  in  24  hours ;  reckoning  the  average 
number  of  inspirations  at  16  per  minute,  this  would  give  20  cubic  inches  as 
the  amount  inhaled  at  each.  According  to  the  experiments  of  Allen  and 
Pepys,  the  quantity  of  air  remaining  in  the  lungs  of  a  stout  full-grown  man 
after  death,  is  about  100  cubic  inches ;  this  is  probably  less  than  the  amount 
that  remains  after  ordinary  expiration.! 

*  Athenaeum  Report  of  Meeting  of  the  British  Association,  1839,  p.  702. 

j-  [  Many  very  interesting  and  practically  important  results  have  been  obtained  by  Mr. 
Hutchinsori,t  with  his  spiromefer,  an  instrument  by  which  the  capacity  of  respiration  is 
measured  by  the  quantity  of  air  expired  in  a  full  and  forcible  expiration.  Among  these 
the  chief  is  the  fact  of  the  existence  of  an  intimate  relation  between  this  capacity  and 
the  height  of  the  individual  examined.  In  1088  healthy  men  from  five  to  more  than  six 
feet  in  height,  he  found  the  capacities  of  respiration  as  follows:  in  men  of  5  feet,  135 
cubic  inches;  of  5  feet  1  in.,  177  c.  i.;  of  5ft.  2  in.,  173  c.  in.;  of  5  ft.  3  in.,  184  c.  i.;  of 
5  ft.  4  in.,  193  c.  in.;  of  5  ft.  5  in.,  208  c.  in.;  of  5  ft.  6  in.,  204  c.  in.;  of  5  ft.  7  in.,  224 
c.  i.;  of  5  ft.  8  in.,  220  c.  i.;  of  5  ft.  9  in.,  229  c.  i.;  of  5  ft.  10  in.,  246  c.  i.;  of  5  ft.  1 1  in., 
254  c.  i.;  of  6  ft.,  255  c.  i.;  of  upwards  of  6  ft.,  260  c.  i.  These  numbers  are  such  that 
it  may  be  generally  stated  that  for  every  additional  inch  of  height  from  5  to  6  feet,  eight 
additional  cubic  inches  of  air,  at  60°,  are  given  out  by  a  forced  expiration.  And  the 

[*  Lancet,  July  27  and  Aug.  3,  1844.] 


400  ON  RESPIRATION. 


II.  Chemical  Phenomena  of  Respiration. 

533.  We  naturally  pass  from  the  foregoing  inquiries  to  those  that  relate  to 
the  alterations  in  the  air,  which  are  effected  by  Respiration.     It  was  formerly 
supposed  that  the  blood  arrived  at  the  lungs  charged  with  Carbon, — that  this 
carbon  was  united  in  their  cells  to  the  Oxygen  of  the  atmosphere, — and  that 
in  this  manner  a  certain  amount  of  the  Oxygen  of  the  inspired  air  was  being 
continually  converted  into  Carbonic  acid,  which  thus  replaced  it  in  the  expired 
air.     Subsequent  researches,  however,  appear  to  have  satisfactorily  proved, 
that  this  is  not  a  true  account  of  the  changes  which  take  place  in  the  Lungs  ; 
and  that  it  would  be  more  correct  to  say,  that  the  blood  comes  to  the  lungs 
charged  with  Carbonic  acid,  formed  by  the  union  of  carbon  and  oxygen  in  the 
systemic  capillaries ;    this  it  imparts  to  the  inspired  air,  at  the  same  time 
abstracting  from  it  a  volume  of  Oxygen  which  is  always  as  large,  and  usually 
greater.     Hence  it  is  not  correct  to  speak  of  a  certain  quantity  of  the  inspired 
oxygen  as  being  converted  into  carbonic  acid  in  the  lungs  ;  but  it  should  rather 
be  said,  that  a  certain  quantity  of  oxygen  is  absorbed,  and  a  certain  quantity 
(generally  less  than  the  equivalent  bulk)  of  carbonic  acid  exhaled.     The  pro- 
portion of  these  quantities  is  by  no  means  constant ;  varying  with  different 
species,  and  with  the  same  animal  at  different  ages  and  at  different  periods  of 
the  year.     According  to  Dr.  Edwards,  the  quantity  of  oxygen  which  entirely 
disappears  from  the  air  is  sometimes  as  much  as  one-third  of  the  whole ;  it  is 
greatest  in  the  young  animal,  and  is  sometimes  almost  imperceptible  in  the 
adult. — It  appears  probable  that  a  part  of  this  Oxygen  is  made  to  combine  with 
Hydrogen  set  free  in  the  systemic  capillaries ;  and  that  the  water  thus  gene- 
rated forms  part  of  that  exhaled  from  the  lungs. — A  sort  of  combustion  of 
Hydro-Carbon  thus  appears  to  be  continually  going  on  in  the  body  at  large,  the 
products  of  which  are  got  rid  of  by  the  lungs;  and  this  process  is  mainly,  if 
not  solely,  instrumental  in  the  maintenance  of  Animal  Heat.  (See  Chap,  xm.) 

534.  The  quantity  of  Carbonic  Acid  excreted  by  the  lungs  has  been  esti- 
mated by  some  experimenters  at  as  much  as  39,600  cubic  inches  in  twenty- 
four  hours;  this  amount  of  gas  would  contain  5,148  grains,  or  11  ounces 
(Troy)  of  solid  carbon.     This  estimate  was  formed  upon  the  results  of  an  expe- 
riment continued  during  a  short  time ;  in  which,  from  the  nature  of  the  appa- 
ratus employed,  the  respirations  were  to  a  certain  degree  laborious,  and  the 
quantity  of  air  renewed  at  each  movement  was  therefore  greater ;  and  there 
are  several  reasons  for  regarding  it  as  much  too  high.     In  Mr.  Coathupe's 
experiments,  great  care  was  taken  to  render  the  inspiration  as  free  as  possible 
from  effort ;  and  the  measuring  process  was  continued  for  a  much  longer  time. 
According  to  his  statement,  the.  quantity  of  Carbonic  acid  generated  in  twenty- 
four  hours  is  about  17,856  cubic  inches  ;  this  will  contain  2,616  grains,  or  5| 
ounces  of  solid  carbon, — a  quantity,  which  we  may  very  well  imagine  to  be 
thus  excreted,  and  which  corresponds  very  closely  with  the  results  obtained 
by  MM.  Prevost  and  Dumas.*     The  proportion  of  carbonic  acid  contained  in 

results  of  the  examinations  are  so  nearly  uniform  that  disease  may  be  suspected  in  any 
man  who  cannot  blow  out  nearly  so  many  cubic  inches  as  the  average  of  those  of  ihe 
same  height,  even  when,  by  external  measurement,  his  chest  appears  to  be  of  full  size. 
Indeed,  in  general,  the  size  of  the  chest  affords  no  good  indication  of  the  capacity  of  expi- 
ration. The  only  exceptions  among  healthy  men"  to  the  general  rule  of  the  direct  pro- 
portion between  the  height  of  the  body  and  the  capacity,  are  in  the  cases  of  fat  men 
whose  capacity  is  always  low. — M.  C.] ' 

*  M  M.  Andral  and  Gavarret  state  the  following  as  the  results  of  experiments  made  on 
seventy-two  persons  (thirty-six  males  and  thirty-six  females),  to  determine  the  quantity 
of  carbonic  acid  exhaled  in  breathing.  These  experiments  were  made  as  nearly  as  pos- 
sible under  the  same  circumstances,  as  regards  health,  time  of  the  day,  amount  of  exer- 


CHEMICAL  PHENOMENA  OF  RESPIRATION.  401 

the  expired  air  appears  from  these  estimates  to  be  about  4  per  cent,  on  the 
whole  ;  but  single  experiments  give  a  much  higher  estimate.  Thus,  in  one 
of  those  made  by  Allen  and  Pepys,  in  which  fresh  air  was  taken  in  at  every 
inspiration,  the  proportion  was  8  parts  in  every  100.  They  found,  however, 
that  if  the  air  be  already  charged  in  some  degree  with  carbonic  acid,  the  quan- 
tity excreted  is  much  less ;  for  when  300  cubic  inches  were  respired  for  three 
minutes,  only  28£  cubic  inches  of  carbonic  acid  were  found  in  it,  although  the 
rate  of  its  production  in  a  parallel  experiment  was  32  cubic  inches  in  a  minute. 
Knowing,  then,  the  necessity  of  a  free  excretion  of  carbonic  acid,  we  are  led 
by  this  fact  to  perceive  the  high  importance  of  ventilation ;  for  it  is  not  suf- 
ficient for  health,  that  a  room  should  contain  the  quantity  of  air  requisite  for 
the  support  of  its  inhabitants  during  a  given  time  ;  since  after  they  have 
remained  in  it  but  a  part  of  that  time,  the  quantity  of  carbonic  acid  which  its 
atmosphere  will  contain,  will  be  large  enough  to  interfere  greatly  with  the  due 
aeration  of  their  blood,  and  thus  to  cause  oppression  of  the  brain  and  the  other 
morbid  affections  that  result  from  the  accumulation  of  carbonic  acid  in  the  cir- 
culating fluid. — On  the  other  hand,  it  has  been  ascertained  by  the  recent  expe- 
riments of  Dr.  Boswell  Reid  that,  if  the  carbonic  acid  be  removed  as  fast  as  it 
is  formed,  an  animal  may  remain  in  a  limited  quantity  of  air,  without  much 
inconvenience,  until  nearly  the  whole  of  its  oxygen  is  exhausted ; — thus 
showing  that  the  respirability  of  air  does  not  depend  so  much  upon  the  pro- 
portion of  oxygen  it  contains,  as  upon  its  freedom  from  contamination  with 
carbonic  acid  or  other  poisonous  gases. 

535.  Although  the  statements  just  given  may  be  regarded  as  representing 
the  average  amount  of  carbonic  acid  evolved  during  the  twenty-four  hours, 

tion,  &c. ;  and  were  repeated  several  times  on  each  individual.  1.  At  all  ages  beyond 
eight  years,  the  exhalation  is  greater  in  males  than  in  females.  2.  In  mules,  it  regularly 
increases  in  quantity  from  eight  to  thirty  years  of  age ;  from  thirty  to  forty  it  is  stationary, 
or  diminishes  a  little;  from  forty  to  fifty  the  diminution  is  greater;  and  from  fifty  to 
extreme  age,  it  goes  on  diminishing,  till  it  scarcely  exceeds  the  quantity  at  ten  years. 

3.  The  quantity  of  carbonic  acid  exhaled  in  one  hour  by  males  of  different  ages,  is  as 
follows; — at  eight  years,  77-5  grains;  at  fifteen,  135  grains;  at  twenty,  176-7   grains; 
between  thirty  and  forty,  189  grains;  between  forty  and  sixty,  156  grains;  between  sixty 
and  eighty,  142-5  grains;  and  in  a  man  of  a  hundred  and  two,  it  was  only  91  5  grains. 

4.  In  females,  nearly  the  same  proportionate  increase  goes  on  to  the  time  of  puberty ; 
when  the  quantity  abruptly  ceases  to  increase,  and  remains  stationary  so  long  as  they 
continue  to  menstruate.     When,  however,  menstruation  has  ceased,  the  exhalation  of  car- 
bonic acid  begins  again  to  augment,  and  then,  again,  in  advancing  years,  decreases  as  it 
does  in  men.    Thus  before  puberty  the  quantity  of  carbon  exhaled  by  girls  in  an  hour  is 
99  grains;  and  so  it  remains  during  the  continuance  of  menstruation;  afterwards,  from 
thirty-eight  to  forty-nine  years  of  age,  it  increases  to  130  grains:  from  fifty  to  sixty  it 
again  falls  to  1 13  grains ;  from  sixty  to  eighty  it  is  reduced  to  105  grains  ;  and  in  a  woman 
of  eighty-two,  it  was  only  93  grains.     5.  Should  menstruation  temporarily  cease  at  any 
time,  the  exhalation  of  carbonic  acid  immediately  undergoes  an  increase, — precisely  as 
at  the  final  cessation  of  the  function.     6.  In  pregnancy,  the  exhalation  is  equal  to  that 
which  is  natural  soon  after  cessation  of  the  menstruation.     7.  The  more  robust  the  indi- 
vidual, cseteris  paribus,  the  more  carbonic  acid  is  exhaled;  but  the  differences  are  not  con- 
stant.    8.  The  influences  of  the  weights  of  individuals,  of  the  capacities  of  their  chests, 
and  of  the  extent  of  the  respiratory  movements,  are  not  great.     9.  The  maximum  observed 
was  in  a  strong  man  of  twenty-six,  who  exhaled  at  the  rate  of  21ci-5  grains  of  carbon  per 
hour.     Another  robust  man  of  sixty  years  of  age  exhaled  at  the  rate  of  209  grains  per 
hour;  another,  of  similar  constitution,  and  sixty-three  years  of  age,  exhaled  at  the  rate  of 
190  grains  per  hour;  and  an  old  man  of  ninety-two,  who  preserved  an  uncommon  degree 
of  energy,  and  who,  in  his  younger  days,  had  boasted  of  uncommon  muscular  powers, 
still  consumed  at  the  rate  of  151  grains  per  hour.    On  the  other  hand,  a  slender  man  of 
forty-five,  in  the  enjoyment  of  good  health,  only  consumed  139-5  grains  per  hour.  These 
facts  demonstrate  the  influence  of  individual  constitution  on  the  amount  of  carbonic  acid 
generated. — Interesting  as  these  results  undoubtedly  are,  they  require  to  be  confirmed  by 
a  more  extensive  series  of  experiments,  before  they  can  be  received  as  physiological  truths. 

24* 


402  ON  RESPIRATION. 

the  amount  is  subject  to  great  variation  under  particular  circumstances.  Thus, 
during  a  state  of  muscular  activity  it  is  greatly  increased.  Mr.  Newport  has 
noticed  that  in  Insects  the  difference  is  enormous, — their  respiration  being  as 
feeble  as  that  of  cold-blooded  animals  when  they  are  at  rest,  and  more  energetic 
(the  quantity  of  oxygen  consumed  in  proportion  to  their  size  being  greater) 
than  that  of  any  other  animals,  when  they  are  in  active  movement.  In  Man 
the  difference  is  not  so  great,  and  its  exact  amount  cannot  be  readily  estimated ; 
but  it  is  unquestionable  that  an  increase  does  take  place.  It  has  been  ascer- 
tained by  Dr.  Prout,  however,  that,  if  the  exercise  be  prolonged  so  as  to  occa- 
sion fatigue,  a  diminished  consumption  of  oxygen  takes  place ;  he  also  states 
that  the  exhilarating  passions  increase,  whilst  the  depressing  passions  (as  also 
the  use  of  alcohol  and  tea)  diminish,  the  quantity  of  carbonic  acid  exhaled. 
There  is  little  doubt  that  there  is  a  great  diminution,  also,  during  sleep  ;  this 
may  be  partly  due  to  the  total  cessation  of  muscular  exertion,  and  partly  to  the 
greater  retention  of  the  heat  which  is  the  consequence  of  it.  For  it  appears 
that  the  amount  of  carbonic  acid  produced  is  greatly  influenced  by  the  tem- 
perature ;  in  the  Guinea-pig,  according  to  Crawford,  the  quantity  exhaled  at 
104°  is  only  half  that  which  is  generated  at  55°.*  The  final  cause  or  purpose 
of  this  connection  will  be  evident,  when  we  consider  the  subject  of  Animal 
Heat. 

536.  It  has  been  supposed,  until  recently,  that  the  azote  of  the  air  undergoes 
no  change  through  Respiration ;  but  the  experiments  of  Dr.  Edwards  have 
shown  that,  although  its  quantity  may  remain  nearly  the  same,  there  is  a  con- 
tinual absorption  and  a  continual  exhalation  of  the  gas.     If  the  absorption  be 
the  more  active,  there  will  be  a  disappearance  of  azote  from  the  air ;  if  exha- 
lation predominate,  the  proportion  of  this  gas  will  be  increased.     Even  in  the 
same  animal,  there  may  be  a  variation  in  this  respect  at  different  periods  of 
the  year,  and  even  at  different  parts  of  the  day.    Thus  in  nearly  all  the  lower 
animals  on  which  he  experimented,  there  was  an  augmentation  in  the  quantity 
of  azote  during  the  summer,  sometimes  equaling-,  in  the  course  of  the  day,  the 
whole  bulk  of  the  animal.     On  the  other  hand,  towards  the  end  of  October, 
he  found  that  a  diminution  of  the  nitrogen  began  to  be  apparent ;  and  this, 
continued  until  the  following  spring. 

537.  The  reaction  which  takes  place  between  the  air  and  the  blood,  is  easily 
explained  upon  physical  principles.     If  the  Blood  come  to  the  Lungs  charged 
with  Carbonic  acid,  and  is  exposed  in  their  cells  to  the  influence  of  atmo- 
spheric air,  which  is  a  mixture  of  Oxygen  and  Nitrogen,  an  endosmose  and 
exosmose  of  gases  will  take  place,  according  to  certain  fixed  laws.t    The  Car- 
bonic acid  of  the  blood  will  pass  out,  to  be  replaced  by  Oxygen  and  Nitrogen ; 
and  the  quantity  of  the  former  which  enters  will  be  much  greater  than  that  of 
the  latter,  on  account  of  the  superior  facility  with  which  oxygen  passes  through 
porous  membranes.     If  the  venous  blood  also  contain  Nitrogen  as  well  as  car- 
bonic acid,  this  also  will  pass  out,  to  be  replaced  by  the  Oxygen  of  the  air. 
Thus,  there  will  be  a  continual  Exosmose  of  Carbonic  acid  and  Nitrogen,  and 
a  continual  Endosmose  of  Oxygen  and  Nitrogen ;  and  the  relative  quantities 
of  these  gases  exhaled  and  absorbed  will  be  subject  to  continual  variation  from 

*  The  experiments  of  Dr.  Malcolm  (Edinb.  Monthly  Journal,  Jan.,  1843),  appear  to 
show  that  the  proportion  of  carbonic  acid  exhaled  is  greatly  diminished  in  typhus  fever. 
According  to  Dr.  Prom's  experiments,  the  average  proportion  generated  in  healthy  respi- 
ration, between  11  A.  M.  and  1  P.  M.,  is  about  3-96  per  cent,  of  the  whole  inspired  air. 
But  in  some  severe  cases  of  fever,  the  proportion  was  as  little  as  1-18  per  cent.;  but  in 
general  it  was  about  2-50.  The  proportion  did  not  seem  to  be  much  influenced  by  the 
number  of  respirations;  being  about  the  same  when  they  were  only  20  as  when  48  per 
minute. 

f  See  Principles  of  General  and  Comparative  Physiology,  §§  437—9. 


EFFECTS  OF  RESPIRATION  ON  THE  BLOOD.  403 

secondary  causes. — It  appears  that,  in  general,  even  in  herbivorous  animals, 
the  Exhalation  of  Nitrogen  predominates  over  the  absorption  ;  but  nrrni 
inquiries  have  shown,  that  their  food  ordinarily  contains  a  supply  of  azotized 
matter  amply  sufficient  for  their  wants.  It  is  yet  a  matter  of  doubt,  however, 
whether  the  Absorption  would  not  predominate,  when  there  is  a  deficiency  of 
azotized  matter  in  the  aliment.  Such  we  may  imagine  to  be  the  case  in  Insects 
which  feed  upon  the  saccharine  juices  of  plants  ;  the  waste  of  their  muscular 
tissue  being,  from  the  activity  of  their  movements,  excessively  rapid. 

III.  Effects  of  Respiration  on  the  Blood. 

538.  That  an  important  change  is  effected  in  the  character  of  the  Blood,  by 
exposure  to  atmospheric  air  in  the  lungs,  has  been  known,  from  the  time 
when  it  was  first  ascertained  that  it  is  regularly  transmitted  to  those  organs. 
The  most  obvious  part  of  this  change  is  the  alteration  in  its  colour,  from  the 
dark  purple  of  the  venous  fluid,  to  the  rich  crimson  of  the  arterial.     But  this 
alteration  is  only  the  index  of  changes  far  more  important  which  occur  in  its 
chemical  constitution.     Respecting  the  nature  of  these  changes,  there  has 
been,  as  formerly  stated,  much  difference  of  opinion ;  some  maintaining  that 
the  carbonic  acid  exhaled  is  formed  in  the  lungs ;  and  others,  that  it  is  con- 
tained in  the  venous  blood,  and  is  truly  excreted  from  it.     The  latter  opinion, 
which  was  long  since  brought  forwards  by  La  Grange  and  Hassenfratz,  has 
recently  obtained  such  full  confirmation  from  the  experiments  of  Spallanzani, 
Edwards,  Miiller,  Bischoff,  Magnus,  and  others,  as  to  have  a  full  claim  for 
adoption  as  a  physiological  truth.    These  experiments  are  of  two  kinds  ;  first, 
those  which  show  that  an  exhalation  of  carbonic  acid  may  continue  for  a  long 
time,  when  the  animal  is  breathing  an  atmosphere  in  which  no  oxygen  exists  ; 
and,  secondly,  those  which  prove  that  much  more  carbonic  acid  exists  in  an 
uncombined  state  in  venous  blood  than  in  arterial,  whilst  more  oxygen  exists 
in  a  similar  condition  in  arterial  blood  than  in  venous.     The  results  of  these 
will  now  be  briefly  stated. 

539.  It  was  stated,  Jong  since,  by  Spallanzani,  that  Snails  might  be  kept 
for  a  long  period  in  Hydrogen,  without  apparent  injury  to  them ;  and  that 
during  this  period  they  disengaged  a  considerable  amount  of  Carbonic  acid. 
Dr.  Edwards  subsequently  ascertained  that,  when  frogs  were  kept  in  hydrogen 
for  several  hours,  the  quantity  of  carbonic  acid  exhaled  was  fully  as  great  as 
it  would  have  been  in  atmospheric  air,  or  even  greater ;  this  latter  fact,  if 
correct,  may  be  accounted  for,  by  the  superior  displacing  power,  which  (on 
the  laws  of  the  diffusion  of  gases),  hydrogen  possesses  for  carbonic  acid.     Col- 
lard  de  Martigny  repeated  this  experiment  in  nitrogen,  with  the  same  results. 
In  both  sets  of  experiments,  the  precaution  was  used  of  compressing  the  flanks 
of  the  animal,  previously  to  immersing  it  in  the  gas,  so  as  to  expel  from  the 
lungs  whatever  mixture  of  oxygen  they  might  contain.     These  experiments 
have  been  since  repeated  by  Miiller  and  Bergemann,  who  took  the  additional 
precaution  of  removing,  by  means  of  the  air-pump,  all  the  atmospheric  air  that 
the  lungs  of  the  frog  might  previously  contain,  together  with  the  carbonic  acid 
that  might  exist  in  the  alimentary  canal.     They  found  in  one  of  their  experi- 
ments, that  the  quantity  of  carbonic  acid  exhaled  in  hydrogen  was  nearly  a 
cubic  inch  in  6£  hours ;  and  in  another,  that  nearly  the  same  amount  was 
given  off  in  nitrogen,  but  this  required  rather  a  longer  period.    It  appears  from 
the  table  of  their  results,*  that  the  amount  was  not  ordinarily  greater  in  the 
experiments  which  were  prolonged  for  twelve  or  fourteen  hours  than  in  those 
which  were  terminated  in  half  the  time ;  hence  it  may  be  inferred,  that  the 

*  Miiller's  Physiology,  p.  338. 


404 


ON  RESPIRATION. 


quantity  which  the  blood  is  itself  capable  of  disengaging  is  limited,  and  that 
the  absorption  of  oxygen  is  necessary  to  enable  carbon  to  be  set  free  from  the 
tissues.  An  exception  may  be  taken  to  all  these  experiments,  on  the  ground 
that  they  were  made  upon  cold-blooded  animals  ;  and  that  in  the  warm-blooded 
tribes  the  character  of  the  change  may  be  different.  It  is  scarcely  probable, 
however,  that  the  uniformity  of  Nature  should  be  thus  violated.  There  is  no 
difference  in  kind  between  the  alterations  effected  in  the  air  by  the  respiration 
of  warm-blooded,  and  by  that  of  cold-blooded  animals  ;  the  only  variation  is  in 
degree.  Nor  is  there  any  appreciable  difference  in  the  character  of  the 
changes  effected  upon  their  venous  blood,  by  the  action  of  oxygen  or  of  other 
gases.  It  is  impossible,  however,  for  an  adult  Bird  or  Mammal  to  sustain  life 
for  any  considerable  time,  in  an  atmosphere  deprived  of  oxygen ;  since  the 
greatly  increased  rapidity  and  energy  of  all  their  vital  operations,  necessitates 
a  much  more  constant  supply  of  this  vivifying  agent  than  is  needed  by  the 
inferior  tribes  ;  and,  as  we  shall  presently  see,  the  capillary  action  necessary 
for  the  passage  of  the  blood  through  the  lungs  will  not  take  place  without  it. 
But  Dr.  Edwards  has  shown,  that  young  Mammalia  can  sustain  life  in  an 
atmosphere  of  hydrogen  or  nitrogen,  for  a  sufficient  length  of  time  to  exhale  a 
sensible  amount  of  carbonic  acid  ;  so  that  the  character  of  the  process  is  clearly 
proved  to  be  the  same  in  them  as  in  Reptiles  and  Invertebrata. 

540.  That  the  change  which  Venous  Blood  undergoes  in  the  lungs  is  to  be 
explained  upon  principles  of  a  purely  chemical  and  physical  nature,  is  evi- 
dent from  the  fact,  that  the  same  changes  will  take  place  when  it  is  exposed 
to  the  air  out  of  the  body,  even  through  the  medium  of  a  thick  membrane, 
such  as  a  bladder.  Such  changes,  however,  only  affect  the  surface  of  the 
fluid ;  but  this  is  exactly  what  we  should  expect,  since  the  air  has  no  access 
to  the  part  beneath.  The  Blood,  whilst  circulating  through  the  capillaries  of 
the  Lungs,  is  divided  into  an  innumerable  multitude  of  minute  streamlets, 
each  so  small  as  to  admit  but  a  single  layer  of  its  corpuscles  ;  and  in  these, 
therefore,  the  surface  which  is  placed  in  contact  with  the  air  is  so  enormously 
extended,  as  to  be  almost  beyond  calculation.  Hence,  then,  we  can  at  once 
understand  how  a  change  may  be  instantaneously  effected  in  it ;  which  would 
occupy  several  hours,  when  the  blood  is  less  advantageously  exposed  to  the 
influence  of  oxygen.  The  ultimate  comparative  analysis  of  Venous  and  Arte- 
rial blood  indicates  the  predominance  of  Carbon  in  the  former,  and  of  Oxygen 
in  the  latter  ;  and  it  would  appear,  from  the  experiments  of  Michaelis,  that  it  is 
in  the  composition  of  the  Red  particles,  that  the  principal  difference  exists.* 


Venous  Blood. 
Carbon.  Nitrogen. 

Albumen 52-650  15-505 

Cruor 53-231  17-392 

Fibrin 50-440  17-267 


Hydrogen. 
7-359 
7-711 

8-228 


Oxygen. 
24-486 
21-666 
24-065 


Total  in  300  parts  .     .156-321  50-164         23-298  70-217 

Jlrterial  Blood. 

Carbon.  Nitrogen.       Hydrogen. 

Albumen 53-009  15-562  6-993 

Cruor 51-382  17-253 


Fibrin 
Total  in  300  parts 


51-374 
155-765 


8-354 
7-254 

22-601 


Oxygen. 
24-436 
23-011 
23-785 

71-232 


Mailer's  Physiology,  p.  323. 


EFFECTS  OF  RESPIRATION  ON  THE  BLOOD.  405 

The  analysis  of  Marcet  gives  a  more  decided  predominance  of  Carbon  in 
Venous  blood  and  of  Oxygen  in  Arterial;  according  to  him,  venous  blood 
contains  55«7  per  cent,  of  carbon,  and  only  21-7  per  cent,  of  oxygen;  whilst 
arterial  blood  contains  only  50-2  per  cent,  of  carbon,  but  as  much  as  26-3  per 
cent,  of  oxygen.  The  discrepancy  between  these  results  is  probably  to  be 
accounted  for  by  the  fact  to  be  presently  noticed,  regarding  the  facility  with 
which  important  changes  are  effected  in  the  gaseous  contents  of  the  blood,  by 
a  short  exposure  of  it  to  the  atmosphere.  The  analysis  of  Dr.  Marcet  proba- 
bly over-states  the  difference  between  arterial  and  venous  blood,  as  that  of 
Michaelis  underrates  it ;  but  from  these  and  other  data,  the  general  fact  of  the 
predominance  of  oxygen  in  the  former,  and  of  carbon  in  the  latter,  may  be 
confidently  stated.  Here,  then,  we  have  an  important  confirmation  of  the 
doctrine,  that  there  is  an  absolute  removal  of  oxygen  from  the  air,  during  the 
process  of  respiration ;  and  not  a  mere  conversion  of  this  gas  into  carbonic  acid. 
541.  In  what  precise  form  the  variable  amount  of  these  bodies  is  contained 
in  the  Blood,  has  not  yet  been  clearly  shown.  That  they  must  be  partly  com- 
bined with  its  other  ingredients,  and  not  merely  dissolved  in  the  fluid,  is  clear, 
from  the  changes  which  they  produce  in  its  aspect  and  properties;  these 
changes  are  the  most  evident  in  the  red  corpuscles ;  but  they  are  also  con- 
siderable in  the  fibrinous  portion  of  the  blood.  Indeed,  as  the  Invertebrata  do 
not  possess  red  corpuscles,  it  can  only  be  upon  the  Liquor  Sanguinis  that  their 
respiration  operates.  There  seems  good  reason  to  believe,  that  the  red  Cor- 
puscles are  the  chief  carriers  of  oxygen  from  the  lungs  to  the  tissues,  and  of 
carbonic  acid  from  the  tissues  to  the  lungs;  whether  or  not  we  hold  with 
Liebig,  that  they  possess  this  power  in  virtue  of  the  iron  which  enters  into 
their  composition. — The  numerous  experiments  of  Scudamore,  Clanny,Bischoff 
and  others,  have  shown  that  a  small  quantity  of  these  gases  may  be  removed 
from  fresh-drawn  blood  by  exposing  it  to  a  vacuum.  But  the  amount  thus 
obtained  is  small  in  proportion  to  that  which  may  be  procured  by  treating  it 
with  hydrogen  or  nitrogen :  for  these  gases  possess,  according  to  the  laws  of 
mutual  diffusion  already  referred  to,  a  much  greater  power  of  displacing  the 
carbonic  acid  and  oxygen  diffused  through  the  blood,  than  is  exerted  by  a 
vacuum.  Carbonic  acid,  however,  may  be  obtained  from  venous  blood  in  con- 
siderable amount,  by  agitating  it  with  atmospheric  air,  the  oxygen  and  nitrogen 
of  which  have  a  powerful  displacing  influence  upon  it;  and  it  is  probable  that 
a  large  quantity  is  thus  removed,  during  the  flow  of  blood  from  the  vein  in 
ordinary  bleeding,  especially  when  the  fluid  does  not  spout  forth  in  a  full 
stream,  but  trickles  down  the  arm  in  a  shallow  current.  Hence,  in  all  experi- 
ments upon  the  gaseous  contents  of  the  blood,  it  is  essential  that  it  should  flow 
direct  from  the  orifice  into  the  gas  which  is  to  operate  upon  it  ;*  and  to  the 
neglect  of  this  precaution  may  be  traced  much  of  the  discrepancy  that  has 
prevailed  among  the  several  results  which  have  been  made  public.  The 
quantity  of  carbonic  acid  that  may  be  obtained  from  venous  blood  by  continued 
agitation  of  it  with  atmospheric  air,  is  stated  by  Miiller  at  half  a  cubic  inch 
from  seven  cubic  inches  of  the  fluid;  but  when  it  is  agitated  with  hydrogen, 
the  quantity  of  carbonic  acid  obtained  is  sometimes  as  much  as  one-sixth  of  the 
volume  of  the  blood.  Hence  we  understand  the  mode  in  which  the  respira- 
tion of  hydrogen  is  a  powerful  cause  of  the  extrication  of  carbonic  acid  from 
the  lungs  of  those  animals  which  can  support  life  for  some  time  without  oxy- 
gen. The  most  important  and  satisfactory  experiments  that  have  been  hith- 
erto made  upon  the  gases  of  the  blood,  are  those  of  Magnus.  He  has  shown 
that  carbonic  acid,  oxygen,  and  nitrogen,  may  be  extracted  both  from  arterial 

*   An  apparatus  contrived  for  this  purpose  by  Dr.  Stevens,  is  described  by  him  m 
the  Phil.  Trans.,  1834. 


406  ON  RESPIRATION. 

and  venous  blood,  but  in  varying  proportion.  The  amount  of  oxygen  in  arte- 
rial blood  equals  at  least  one-third,  and  frequently  almost  one-half  that  of  the 
carbonic  acid ;  whilst  in  venous  blood  the  oxygen  is  scarcely  ever  more  than 
one-fourth,  and  often  less  than  one-fifth,  of  the  carbonic  acid.  The  proportion 
of  nitrogen  seems  to  be  continually  varying,  without  any  fixed  law  ;  it  is  some- 
times as  little  as  one-twelfth  of  the  whole  quantity  of  gas  extracted  from  the 
blood;  and  sometimes  nearly  a  fourth. 

542.  That  the  change  of  the  colour  of  Venous  blood  to  that  of  Arterial,  is 
principally  due  to  the  replacement  of  its  carbonic  acid  by  oxygen,  is  very 
easily  shown.  The  simple  removal  of  the  carbonic  acid  by  hydrogen  will  not 
produce  the  alteration  ;  it  has  been  observed  by  Magnus,  however,  that  a  slight 
change  of  colour  takes  place  in  blood  under  the  vacuum  of  an  air-pump, 
although  it  does  not  nearly  acquire  the  arterial  tint.  This  falls  in  with  what 
is  known  of  the  influence  of  carbonic  acid  on  the  blood :  in  common  with 
other  acids  it  has  a  blackening  effect  upon  it,  so  that  arterial  blood  when  ex- 
posed to  it  becomes  venous,  and  venous  blood  is  rendered  still  darker  ;  but  the 
simple  removal  of  it  is  not  sufficient  to  restore  the  original  hue.  This  restora- 
tion may  be  effected  in  two  ways,— -either  by  the  addition  of  saline  matter  to 
the  blood, — or  by  exposing  the  fluid  to  oxygen.  The  presence  of  a  certain 
amount  of  saline  matter  appears,  from  the  experiments  of  Dr.  Stevens,  to  be  a 
condition  necessary  for  the  due  influence  of  oxygen  upon  the  colouring  matter 
of  the  blood ;  since,  if  it  be  deficient,  the  contact  of  oxygen  will  not  produce 
its  usual  effect.  On  the  other  hand,  the  addition  of  saline  matter  (especially 
nitre)  will  occasion  a  decided  change  of  hue,  without  any  extrication  of  car- 
bonic acid  or  absorption  of  oxygen.  Hence  it  appears  that  the  presence  of 
saline  matter  in  the  blood  is  an  essential  condition  for  the  due  effect  of  the 
process  of  oxygenation ;  and  that  the  change  of  colour  may  be  regarded  as 
resulting  from  the  conjoint  operation  of  the  removal  of  carbonic  acid,  and  the 
absorption  of  oxygen.* 

*  [Some  experiments  by  Schererf  both  confirm  the  opinion  of  Nasse,  that  the  change 
from  the  arterial  to  the  venous  colour  of  the  blood  depends  in  great  measure  on  the  form, 
of  the  blood-corpuscles,  and  explain  most  of  the  observations  of  Dr.  Sievens  on  the  effects 
of  distilled  water  and  salts  upon  the  blood.    Their  general  conclusions  are:  1.  That 
when  fresh-stirred  and  bright-red  ox-blood  is  mixed  with  distilled  water,  it  acquires  a 
dark-red  colour,  and  its  corpuscles,  by  imbibing  water,  become  spherical,  and  at  last 
vanish.     But,  2.  That  if,  after  the  change  has  begun,  and  not  gone  far,  a  concentrated 
solution  of  a  neutral  salt  be  added,  the  blood-corpuscles  again  acquire  their  natural  form, 
and  the  bright-red  colour  is  restored.     3.  That  when  oxygen  is  passed  through  blood 
darkened  by  the  addition  of  distilled  water,  it  is  not  changed  in  colour,  and  the  blood- 
corpuscles  do  not  reappear;  but  that  the  same  kind  of  blood,  mixed  with  a  small  quan- 
tity of  milk,  or  oil,  or  finely-powdered  chalk,  or  gypsum,  soon   regains  its  bright  red 
colour.     4.  Again,  by  the  long-continued  contact  of  concentrated  saline  solutions  with 
the  blood-corpuscles,  they  become  jagged  and  decomposed, and  the  blood  becomes  black; 
and  those  which  have  been  reddened  by  the  action  of  salts,  become  black  again  on  being 
expanded  by  the  imbibition  of  water.     5.  By  adding  carbonic  acid  to  bright-red  blood,  its 
corpuscles  change  their  biconcave  for  a  biconvex  form,  and  at  the  same  time  its  colour 
changes  from  red  to  black.     So  that  there  are  always  changes  in  the  shape  of  the  blood- 
corpuscles,  coincident  with  the  changes  in  the  colour  of  the  mass  of  blood ;  whenever 
they  are  dilated,  as  by  distilled  water  or  carbonic  acid,  the  dark  colour  is  produced; 
whenever  they  are  contracted  into  the  biconcave  form,  the  bright-red  colour  is  restored. 

Mulder,  also,t  espouses  the  opinion  of  the  changes  of  colour  in  the  blood  being  im- 
mediately due  to  physical  rather  than  to  chemical  changes  of  the  corpuscles,  and  has 
added  many  facis  to  those  just  quoted  in  disproof  of  the  opinion  of  Liebig.that  the  changes 
are  due  to  the  alternate  production  of  the  carbonate  of  the  protoxyde,  and  of  the  peroxyde, 

f  [  Henle  and  Pfeufler,  Zeitschrift,  &c.,  and  Oesterr.  Medic.  Wochenschrift,  Nov.  4, 
1843.— B.  &  F.  Med.  Rev.,  vol.  xix,  p.  253.] 

*  [  Verslag  van  de  Vertiende  Vergadering  van  het  Nederlandsche  Instituut  in  '  Het  In- 
stituut,'    1844,  No.  iv,  and  Physiologische  Scheikunde,  pp.  361-77.— Lond.  Med.  Gaz., 
No.  13,  Dec.  1844.] 


EFFECTS  OF  RESPIRATION  ON  THE  BLOOD.  407 

543.  The  aeration  of  the  blood  may  take  place,  not  only  by  means  of  the 
lungs,  but  also  through  the  medium  of  the  cutaneous  surface.  In  some  of  the 
lower  tribes  of  animals,  indeed,  this  is  a  very  important  part  of  their  respira- 
tory process  ;  and  even  in  some  Vertebrata,  the  cutaneous  respiration  is  capa- 
ble of  supporting  life  for  a  considerable  time.  This  is  especially  the  case  in 
the  Batrachia,  whose  skin  is  soft,  thin,  and  moist ;  and  the  effect  is  here  the 
greater,  since  the  blood  which  circulates  through  the  system  is,  from  the  small 
proportion  of  it  that  has  passed  through  the  lungs,  very  imperfectly  arterial- 
ized.  By  the  experiments  of  Bischoff  it  was  ascertained  that,  even  after  the 
lungs  of  a  Frog  had  been  removed,  a  quarter  of  a  cubic  inch  of  carbonic  acid 
was  exhaled  from  the  skin,  during  eight  hours.  Experiments  which  have 
been  made  on  the  Human  subject  leave  no  room  for  doubt,  that  a  similar  pro- 
cess is  effected  through  the  medium  of  his  general  surface ;  for,  when  a  limb 
has  been  enclosed  for  some  hours  in  an  air-tight  vessel  containing  atmospheric 
air  freed  from  carbonic  acid,  a  sensible  amount  of  this  gas  has  been  found  to 

of  iron  in  the  blond-corpuscles,  as  they  pass  alternately  through  the  systemic  and  the 
pulmonary  capillaries.  His  chief  facts'  are— 1.  That  the  elementary  composition  of  the 
colouring  matter  is  the  same,  whether  obtained  from  arterial  or  from  venous  blood,  viz., 
C.  44,  H.  44,  N.  6,  O.  6,  Fe.  2.  That  the  change  from  dark  to  bright  blood  is  effected  as 
completely  by  the  agency  of  a  neutral  salt  as  by  oxygen.  3.  That  if  the  iron  were  present 
in  the  blood  as  an  oxyde  (and  especially  as  a  peroxyde),  it  should  be  easily  extracted  by 
weak  acids;  but  he  has  found  that  well-prepared  hsamatine  may  be  digested  in  diluted 
hydrochloric  or  sulphuric  acid  for  several  days  without  the  iron  in  it  being  in  the  least 
diminished.  After  being  so  treated,  he  has  obtained,  after  incineration,  the  regular  pro- 
portion of  9-49  per  cent,  of  oxyde.*  If  strong  sulphuric  acid  be  poured  on  dried  blood, 
or  dried  pure  haematine,and  kept  on  it  for  some  days,  and  then  water  be  added,  hydrogen 
is  evolved,  and  sulphate  of  peroxyde  of  iron  is  found  in  the  solution,  which  could  not 
happen  if  the  iron  had  been  at  first  in  the  form  of  peroxyde.j-  5.  The  iron  may  thus 
be  all  extracted  from  the  blood,  or  from  haematine,  (though  not,  as  some  say,  without 
affecting  the  colour,)  and  the  other  constituents  may  be  obtained  in  a  separate  form. 
Numerous  analyses  of  this  constituent,  by  Van  Goudoever,  regularly  yielded  the  same 
equivalents  of  the  elements,  viz.,  C.  44,  H.  44,  N.  6,  O.  6;  but  if  the  iron  had  been  united 
with  this  in  the  form  of  Fe.  2,  O.  3,  and  in  the  proportion  of  one  equivalent  to  two,  there 
should  have  remained  only  four  and  a  half  equivalents  of  oxygen. 

Mulder  concludes,  therefore,  that  iron  is  present  in  hsematine,  as  iodine  is  in  sponge, 
or  sulphur  in  cystine,  or  arsenic  in  cacodyl.  His  notion  of  the  mode  in  which  the  changes 
of  colour  are  effected  is,  that  when  the  corpuscles  of  the  venous  blood  are  exposed  in  the 
lungs,  oxy-proteine  is  formed  by  the  oxydation  of  the  fibrin  proteine  of  the  liquor  san- 
guinis,  or  perhaps,  by  the  oxydation  of  the  outer  layer  of  the  cell  membrane  of  the 
corpuscles.  If  formed  in  the  liquor  sanguinis,  its  peculiar  plasticity  would  lead  to  its 
being  deposited  in  a  thin  layer  on  the  corpuscles.  In  either  such  case,  the  dark  corpus- 
cles would,  after  respiration,  be  invested  by  a  thin  layer  of  white  and  imperfectly  trans- 
parent oxy-proteine,  or  buffy  coat,  through  which  they  would  look  bright-red,  as  dark 
blood  does  when  contained  in  a  vessel  of  milk-white  glass.  But,  in  the  systemic  capil- 
laries, the  oxy-proteine  may  be  consumed  in  nutrition,  and  the  darkness  of  the  corpuscles 
will  then  again  appear  unveiled. 

Moreover,  since  it  appears  that,  in  the  biconcave  form,  the  corpuscles,  by  reflecting 
more  light,  are  always  bright,  and  in  the  biconvex  form  always  dark,  it  may  be  that  in 
the  arterial  blood  they  are  not  only  buffed,  but  also  cupped,  by  the  oxy-proteine,  by  the 
plastic  properties  of  which,  moreover,  it  is  easy,  on  this  pretty  theory,  to  explain  the 
ready  adhesion  of  the  corpuscles  in  inflammatory  blood.  Diluted  acids,  which  make 
bright  blood  dark,  may  do  so  by  making  the  outer  layer  of  the  corpuscles  transparent,  as 
they  do  fibrin  before  dissolving  it;  and  concentrated  solutions  of  neutral  salts  may 
make  it  bright  by  making  the  same  layer  contract. — M.  C.] 

*  [Liebig  adduces  the  possibility  of  extracting  iron  from  dried  blood  as  one  of  the  proofs 
of  its  being  in  an  oxydized  state;  but  Mulder  says  this  iron  must  have  been  extracted 
from  some  other  constituent  of  the  blood;  for  others,  besides  the  globules,  even  pure 
serum,  contain  iron.] 

f  [When  the  blood  or  its  colouring  matter  has  been  exposed  to  the  air  prepared  in  it, 
the  iron  must  always,  according  to  Liebig's  view,  be  in  the  state  in  which  he  supposed 
it  to  be  in  arterial  blood.] 


408  ON  RESPIRATION. 

be  generated.  Moreover,  it  has  been  observed  not  unfrequently,  that  the  livid 
tint  of  the  skin  which  supervenes  in  Asphyxia,  owing  to  the  non-arterialization 
of  the  blood  in  the  lungs,  has  given  place  after  death  to  the  fresh  hue  of  health, 
owing  to  the  reddening  of  blood  in  the  cutaneous  capillaries  by  the  action  of 
the  atmosphere  upon  them.  (See  also  §  726.) 

544.  We  have  no  means  of  ascertaining  the  usual  amount  of  carbonic  acid 
excreted  through  the  skin,  except  by  determining  the  whole  quantity  disen- 
gaged from  the  body,  and  subtracting  the  portion  exhaled  from  the  lungs. 
This  determination  has  been  attempted  in  various  ways.     By  Liebig  the  total 
quantity  of  carbon  in  the  food  consumed  by  a  certain  number  of  soldiers,  was 
compared  with  that  excreted  in  the  faeces  and  urine ;  and  an  excess  of  13-9 
oz.  daily  for  each  man  was  found  in  the  former  ;  which  excess  is  regarded  by 
him  as  the  amount  disengaged  in  the  form  of  carbonic  acid,  by  the  lungs  and 
skin.     The  experiment,  however,  was  far  from  being  exactly  conducted ;  as 
many  items  among  the  ingesta  are  set  down  by  guess  merely ;  and  no  exact 
estimate  was  made  of  the  quantity  of  carbon  in  the  urine.     The  amount  con- 
tained in  the  solid  matter  excreted  from  the  skin,  too,  was  altogether  neglected. 
The  estimate  is  in  all  probability  much  too  high. — Another  mode  of  deter- 
mining the  total  amount  of  carbon  thrown  off  in  the  form  of  carbonic  acid,  in 
the  twenty-four  hours,  has  been  recently  tried  by  Professor  Scharling.     He 
constructed  an  air-tight  chamber,  of  dimensions  sufficient  to  allow  an  indi- 
vidual to  remain  in  it  for  some  time  without  inconvenience  ;  and  so  arranged 
that  he  could  eat  and  drink,  read,  or  sleep,  within  it.     This  was  connected 
with  an  apparatus,  by  which  the  air  was  continually  renewed ;  and  the  air 
drawn  off  was  carefully  analyzed,  In  order  to  determine  the  quantity  of  car- 
bonic acid  contained  in  it.     The  following  are  the  principal  results  deduced 
from  his  experiments.     The  amount  given  off  during  sleep  and  when  fasting, 
was  the  least ;  and  after  a  meal  it  was  always  the  highest.     (It  may  be  re- 
marked, however,  that  the  construction  of  the  apparatus  did  not  admit  of  active 
exercise,  which  would  probably  increase  the  quantity  of  carbonic  acid  gene- 
rated, to  a  still  higher  proportion.)     Children  exhaled  more  carbonic  acid,  in 
proportion  to  their  weight,  than  adults.     The  total  quantity  of  carbon  thus 
extricated  in  the  twenty-four  hours,  allowing  seven  hours  for  sleep  in  the 
adult,  and  nine  hours  for  the  child,  appears  to  be  as  follows  : — In  the  adult 
male,  from  7  oz.  to  7£  ;  in  the  adult  female,  about  5d  oz. ;  and  in  the  child  of 
ten  years  old,  from  4  oz.  to  4£  oz.*     These  comparative  results  accord  well 
with  those  of  Dr.  Prout,  and  of  MM.  Andral  and  Gavarret,  upon  the  exhalation 
of  carbonic  acid  by  the  Lungs  alone  (§  534,  note,  §  535) :  and  also  with  that 
already  given  of  the  actual  quantity  of  carbon  thrown  off  by  them  ;  for  if  this 
be  estimated  at  5<|  oz.,  the  remaining  2  oz.  may  very  fairly  be  supposed  to  be 
exhaled  from  the  Skin  in  a  similar  form. 

545.  From  the  facts  which  have  been  stated,  and  from  many  others  of  the 
same  kind,  the  conclusion  seems  indisputable,  that  the  changes  produced  by 
Respiration  are  of  the  following  nature.     The  Arterial  blood  propelled  from 
the  heart  to  the  System  contains  a  large  proportion  of  oxygen,  either  free  or 
in  loose  combination  with  it ;  and  also  a  certain  amount  of  carbonic  acid. — 
During   its  passage  through  the  systemic  capillaries,  it  loses  a  part  of  its 
oxygen,  and  acquires  a  great  increase  in  its  amount  of  carbonic  acid,  together 
with  some  addition  to  its  water;  and  it  returns  to  the  heart  in  the  state  of 
Venous  blood,  its  colour  having  been  darkened  by  the  loss  of  its  oxygen,  and 
by  the  influence  of  the  acid.     In  the  Lungs,  to  which  it  is  then  transmitted,  it 
undergoes,  by  exposure  to  the  atmosphere,  the  converse  change  to  that  which 
took  place  in  the  systemic  capillaries ;  a  large  part  of  its  carbonic  acid  and 

*  Annalen  der  Cheinie  und  Pharmacie,  xlv.  p.  214. 


EFFECTS  OF  RESPIRATION  ON  THE  BLOOD.  409 

water  being  removed,  and  a-  considerable  addition  being  made  to  the  amount 
of  oxygen  which  it  contains :  its  arterial  hue  and  character  are  thus  restored. 
It  may  be  observed,  then,  that  the  blood,  by  its  alternate  passage  through  the 
systemic  and  pulmonary  capillaries,  serves  to  bring  the  two  into  close  rela- 
tion ;  and  that  in  this  manner,  the  oxygen  of  the  air  is  enabled  to  act  upon  the 
minutest  portions  of  those  tissues  of  the  body  that  are  most  distant  from  the 
lungs,  as  completely  as  it  can  do  by  being  directly  introduced  into  their  sub- 
stance, as  it  is  in  Insects.  It  is  interesting  to  remark  that  these  are  the  only 
Invertebrata  in  which  there  is  an  active  respiration ;  and  it  would  seem  as  if 
the  universal  permeation  of  their  tissues  by  tracheae  is  a  compensating  struc- 
ture, making  up  for  that  deficiency  in  the  carrying  power  of  the  blood,  which 
may  be  attributed  to  the  absence  of  red  corpuscles  (§  576). 

546.  We  have  now  to  consider  the  results  of  the  cessation  of  the  Respiratory 
function,  and  the  consequent  retention  of  carbonic  acid  in  the  blood.  If  this 
be  sufficiently  prolonged,  a  condition  ensues  to  which  the  name  of  Asphyxia 
has  been  given ;  the  essential  character  of  which  is  the  cessation  of  muscular 
movement,  and  shortly  afterwards  of  the  circulation ;  with  an  accumulation  of 
blood  in  the  venous  system.  The  time  which  is  necessary  for  life  to  be  de- 
stroyed by  asphyxia  varies  much,  not  only  in  different  animals,  but  in  different 
states  of  the  same.  Thus,  Warm-blooded  animals  are  much  sooner  asphyxiated 
than  Reptiles  or  Invertebrata;  on  the  other  hand,  a  hybernating  Mammal 
supports  life  for  many  months,  with  a  respiration  sufficiently  low  to  produce 
speedy  asphyxia  if  it  were  in  a  state  of  activity.  And  among  Mammalia  and 
Birds,  there  are  many  species  which  are  adapted,  by  peculiarities  of  conforma- 
tion, to  sustain  a  deprivation  of  air  for  much  more  than  the  average  period.* 
Excluding  these,  it  may  be  stated  as  a  general  fact,  that,  if  a  warm-blooded 
animal,  in  a  state  of  activity,  be  deprived  of  respiratory  power,  its  muscular 
movements  (with  the  exception  of  the  contraction  of  the  heart)  will  cease 
within  five  minutes,  often  within  three ;  and  that  the  circulation  generally 
fails  within  ten  minutes.  Many  persons,  however,  are  capable  of  sustaining 
a  deprivation  of  air  for  three,  four,  or  even  five  minutes,  without  insensibility 
or  any  other  injury ;  but  this  power,  which  seems  possessed  to  the  greatest 
degree  by  the  divers  of  Ceylon,  can  only  be  acquired  by  habit.  The  period 
during  which  remedial  means  may  be  successful  in  restoring  the  activity  of 
the  vital  and  animal  functions,  is  not,  however,  restricted  to  this.  Cases  are 
not  unfrequent,  of  the  revival  of  drowned  persons  after  a  submersion  of  half 
an  hour;  and  more  than  one  has  been  credibly  recorded,  in  which  above 
three-quarters  of  an  hour  had  elapsed.  It  is  not  improbable,  however,  that  in 
some  of  these  cases  a  state  of  Syncope  had  come  on  at  the  moment  of  immer- 
sion, through  the  influence  of  fear  or  other  mental  emotion,  concussion  of  the 
brain,  &c, ;  so  that,  when  the  circulation  was  thus  enfeebled,  the  deprivation 
of  air  would  not  have  the  same  injurious  effect  as  when  this  function  was  in 
full  activity.  The  case  would  then  closely  resemble  that  of  a  hybernating 
animal ;  for  in  both  instances  the  being  might  be  said  to  live  very  slowly,  and 
would  therefore  not  require  the  usual  amount  of  vital  stimuli.  The  condition 
of  the  still-born  infant  is  in  some  respects  the  same ;  and  re-animation  has  been 
successfully  attempted,  when  nearly  half  an  hour  had  intervened  between 

*  Thus,  the  Cetacea  contain  far  more  blood  in  their  vessels  than  do  any  other  Mamma- 
lia; and  these  vessels  are  so  arranged,  that  both  arteries  and  veins  are  in  connection 
with  large  reservoirs  or  diverticula.    The  reservoirs  belonging  to  the  former  are  usually 
full;  but  when  the  Whale  remains  long  under  water,  the  blood  which  they  contain  is 
gradually  introdiBed  into  the  circulation,  and,  after  becoming  venous,  accumulates  i 
the  reservoirs  connected  with  the  venous  system.    By  means  of  this  provision,  the  Whale 
can  remain  under  water  for  more  than  an  hour. 
35 


410  ON  RESPIRATION. 

birth  and  the  employment  of  resuscitating  means,  and  when  probably  a  much 
longer  time  had  elapsed  from  the  period  of  the  suspension  of  the  circulation. 

547.  It  has  now  been  sufficiently  proved,  both  by  experiment  and  by  patho- 
logical observation,  that  the  first  effect  of  the  non-arterialization  of  the  blood  in 
the  lungs,  is  the  retardation  of  the  fluid  in  their  capillaries ;  of  which  the 
accumulation  in  the  venous  system,  and  the  deficient  supply  to  the  arterial, 
are  the  necessary  consequences.     It  is  some  time,  however,  before  a  complete 
stagnation  takes  place  from  this  cause :  since,  as  long  as  the  proportion  of 
oxygen  which  remains  in  the  air  in  the  lungs  is  considerable,  and  that  of  the 
carbonic  acid  is  small,  so  long  will  some  imperfectly  arterialized  blood  find  its 
way  back  to  the  heart,  and  be  transmitted  to  the  system.     This  blood  will 
have  a  depressing  influence  upon  the  functions  of  the  brain  and  of  the  mus- 
cular system ;  which  influence  is  aided  by  the  diminution  that  gradually  takes 
place  in  the  quantity  of  blood  propelled  through  the  aorta;  and  the  actions  of 
the  respiratory  muscles  and  of  the  heart  will  therefore  soon  be  enfeebled.   .  The 
cessation  of  the  heart's  contraction^  due  to  two  distinct  causes,  acting  on  the 
two  sides ;  for  on  the  right  side  it  is  the  result  of  the  over-distension  of  the  walls 
of  the  ventricle,  owing  to  the  accumulation  of  venous  blood;  and  on  the  left  to 
deficiency  of  the  stimulus  necessary  to  excite  the  movement.     The  property, 
of  contractility  is  not  finally  lost  nearly  as  soon  as  the  movements  cease;  for: 
the  action  of  the  right  ventricle  may  be  renewed,  for  some  time  after  it  has 
ceased,  by  withdrawing  a  portion  of  its  contents, — either  through  the  pulmo- 
nary artery,  their  natural  channel, — or,  more  directly,  by  an  opening  made  in , 
its  own  parietes,  in  the  auricle,  or  in  the  jugular  vein  (§  489).     On  the  other 
hand,  the  left  ventricle  may  be  again  set  in  action,  by  renewing  its  appropriate 
stimulus  of  arterial  blood.     Hence,  if  the  stoppage  of  the  circulation  have  not 
been  of  too  long  continuance,  it  may  be  renewed  by  artificial  respiration  ;  for 
the  replacement  by  oxygen  of  the  carbonic  acid  in  the  air-cells  of  the  lungs, 
restores  the  circulation  through  the  pulmonary  capillaries ;  and  thus  at  the 
same  time  relieves  the  distension  of  the  right  ventricle,  and  conveys  to  the  left 
the  due  stimulus  to  its  actions. 

548.  Of  the  mode  in  which  the  pulmonary  circulation  is  stagnated  by  the 
want  of  oxygen,  and  renewed  by  its  ingress  into  the  lungs,  no  other  explana- 
tion can  be  given,  than  that  which  has  been  heretofore  offered  of  the  capillary 
circulation  in  general; — namely,  that  the  performance  of  the  normal  reaction 
between  the  blood  and  the  surrounding  medium  (whether  this  be  air,  water, 
or  solid  organized  tissue),  is  a  condition  necessary  to  the  regular  movement  of 
the  blood  through  the  extreme  vessels.*     This  view  has  recently  obtained 
additional  support  from  the  experiments  of  Dr.  J.  Reid  on  the  Respiration  of 
Azote.t     He  found  that,  when  the  ordinary  respiration  of  an  animal  is  inter- 
rupted, and  the  Asphyxia  is  proceeding  to  the  stage  of  insensibility,  the  first 
effect  upon  the  arterial  system  is  an  increased  distension  (as  indicated  by  the 
hsemadynamometer),  even  although  the  blood  is  at  that  time  nearly  venous 
in  its  character ;  this  indicates  that  the  fluid,  now  so  perverted,  is  unable  to 
pass  with  facility  through  the  systemic  capillaries,  in  consequence  of  its  not 
being  in  a  state  fit  for  the  performance  of  its  normal  actions.     As  the  stagna- 
tion in  the  pulmonary  capillaries  becomes  more  complete,  however,  less  and 
less  blood  is  returned  from  the  lungs  to  the  heart ;  and,  the  systemic  arteries 
being  gradually  unloaded  without  being  refilled,  the  pressure  of  the  blood 
upon  their  walls  diminishes,  and  at  last  is  no  longer  experienced.     Its  dimi- 
nution is  not  arrested  by  causing  the  animal  to  breathe  nitrogen,  although  the 
respiratory  movements  are  renewed, — thus  proving  that  the  stagnation  of  the 

*  For  a  fuller  discussion  of  the  Pathology  of  Asphyxia,  see  the  Author's  essay  on  the 
subject  in  the  Library  of  Practical  Medicine,  vol.  iii. 
f  Edinb.  Med.  and  Surg.  Journal,  April,  1841. 


EXHALATION  AND  ABSORPTION  BY  THE  LUNGS.  411 

blood  in  the  capillaries  of  the  lungs  is  not  due  (as  some  have  supposed)  to  a 
mechanical  impediment:  but  the  pressure  is  immediately  increased  by  the 
admission  of  atmospheric  air,  which  occasions  the  renewal  of  the  pulmonary 
circulation,  and  the  consequent  increase  in  the  supply  of  aerated  blood  to  the 
systemic  arteries. — It  has  been  recently  shown  by  Mr.  Wharton  Jones,*  that 
the  capillary  circulation  in  a  frog's  foot  is  retarded  or  even  checked  by  the 
direction  of  a  stream  of  carbonic  acid  gas  against  the  membrane ;  and  he  attri- 
butes this  stagnation  to  the  disposition  thus  produced  in  the  red  corpuscles,  to 
aggregate  together  and  to  adhere  to  the  walls  of  the  vessel  so  as  to  choke  up 
its  calibre. 

IV.  Exhalation  and  Absorption  by  the  Lungs. 

549.  The  alteration  in  the  proportions  of  its  usual  gaseous  ingredients,  is 
by  no  means  the  only  change  which  the  blood  undergoes  in  the  Lungs.  It 
parts,  also,  with  a  considerable  amount  of  water,  in  the  form  of  vapour;  this 
usually  contains  a  certain  proportion  of  animal  matter;  and  it  is  sometimes 
charged  with  volatile  substances,  which  have  been  elsewhere  introduced  into 
the  blood,  or  which  have  been  formed  during  its  assimilation.  It  may  also 
absorb  from  the  atmosphere  volatile  matter  diffused  through  it.  Both  these 
changes  are  probably  to  be  explained  upon  simple  physical  principles ;  bein^ 
dependent  on  the  exposure  of  the  blood  to  the  atmosphere,  with  a  very  exten- 
sive surface,  and  through  a  membrane  of  great  permeability.  Of  the  fluid 
ordinarily  exhaled  with  the  breath,  a  part  doubtless  proceeds  from  the  moist 
'lining  of  the  nostrils,  fauces,  &c. ;  but  it  is  indisputable  that  the  greater  pro- 
portion of  it  comes  from  the  lungs ;  since,  when  the  respiration  is  entirely 
performed  through  a  canula  introduced  into  the  trachea,  the  amount  of  watery 
vapour  which  the  breath  contains  is  still  very  considerable.  The  quantity 
which  thus  passes  off  is  by  no  means  trifling ;  probably  between  16  and  20 
ounces  in  the  twenty-four  hours.  It  is  not  so  liable  to  variation  under  the 
influence  of  temperature,  the  movement  of  the  surrounding  air,  and  other 
similar  causes,  as  is  the  cutaneous  transpiration ;  for  air,  which  has  found  its 
way  into  the  air-cells  of  the  lungs,  will,  under  almost  all  circumstances,  be 
nearly  the  same  in  regard  to  such  conditions,  and  will,  therefore,  dissolve  an 
equal  amount  of  watery  vapour.  It  is  considered  by  Dr.  Prout,  that  the  prin- 
cipal source  of  this  vapour  is  not  the  blood  properly  so  called,  but  the  chyle 
and  lymph  which  have  just  been  introduced  into  it  from  the  thoracic  duct ;  a 
loss  of  a  portion  of  their  fluid  being  required  to  give  them  sufficient  concentra- 
tion. A  process  very  analogous  takes  place  in  Plants ;  for  a  very  large  pro- 
portion of  the  water  taken  up  in  the  crude  sap,  is  parted  with  in  the  leaves. 
But  it  is  probable  that  a  part,  at  least,  of  the  water  thrown  off  by  the  lungs  is 
generated  by  the  union  of  Oxygen  and  Hydrogen,  during  the  course  of  the 
Circulation  (§  533).  The  fluid  thrown  off  from  the  Lungs  is  not  pure  water.  It 
holds  in  solution,  as  might  have  been  expected,  a  considerable  amount  of  car- 
bonic acid,  and  also  some  animal  matter;  the  exact  nature  of  the  latter,  which, 
according  to  Collard  de  Martigny,  constitutes  about  3  parts  in  1000,  has  not 
been  ascertained.  If  the  fluid  be  kept  in  a  closed. vessel,  and  be  exposed  to 
an  elevated  temperature,  a  very  evident  putrid  odour  is  exhaled  by  it.  Every 
one  knows  that  the  breath  itself  has,  occasionally  in  some  persons,  and  con- 
stantly in  others,  a  fetid  taint ;  when  this  does  not  proceed  from  carious  teeth, 
ulcerations  in  the  air-passages,  disease  in  the  lungs,  or  other  similar  causes,  it 
must  result  jfzm  the  excretion  of  the  odorous  matter,  in  combination  with 
watery  vapour,  from  the  pulmonary  surface.  That  this  is  the  true  account  of 

*  Brit,  and  For.  Med.  Rev.,  vol.  xiv.  p.  600. 


412  ON  RESPIRATION. 

it  seems  evident,  from  the  analogous  phenomenon  of  the  excretion  of  turpen- 
tine, camphor,  alcohol,  and  other  odorous  substances,  which  have  been  intro- 
duced into  the  venous  system,  either  by  natural  absorption,  or  by  direct  injection ; 
and  also  from  the  suddenness  with  which  it  manifests  itself,  when  the  diges- 
tive apparatus  is  slightly  disordered. 

550.  The  Lungs  are  capable,  under  peculiar  circumstances,  of  absorbing  fluid 
from  the  atmosphere."  Thus  Dr.  Madden*  has  shown  that,  if  the  vapour  of  hot 
water  be  inhaled  for  some  time  together,  the  loss  by  exhalation  is  found  to  be 
so  much  less  than  usual  as  to  indicate  that  the  cutaneous  transpiration  is  partly 
counterbalanced  by  pulmonary  absorption ;  the  pulmonary  exhalation  being  at 
the  same  time  entirely  checked.     It  it  probable  that,  if  the  quantity  of  fluid  in 
the  blood  had  been  previously  diminished  by  excessive  sweating,  or  by  other 
copious  fluid  secretions,  the  pulmonary  absorption  would  have  been  much 
greater.     Still,  in  the  cases  formerly  mentioned  (§465),  in  which  a  large  in- 
crease in  weight  could  only  be  accounted  for  on  the  supposition  of  absorption 
of  water  from  the  atmosphere,  it  seems  probable  that  the  cutaneous  surface 
was  chiefly  concerned ;  for  it  can  only  be  when  the  air  introduced  into  the 
lungs  is  saturated  with  watery  vapour  that  the  usual  exhalation  will  be  checked, 
or  that  any  absorption  can  take  place.     That  absorption  of  volatile  matter  dif- 
fused through  the  air  is,  however,  continually  taking  place  by  the  lungs,  is 
easily  demonstrated.     A  familiar  example  is  the  effect  of  the  inhalation  of  the 
vapour  of  turpentine  upon  the  urinary  excretion.     It  can  only  be  in  this 
manner  that  those  gases  act  upon  the  system  which  have  a  noxious  or  poison- 
ous effect,  \vhen  mingled  in  small  quantities  in  the  atmosphere.     Of  these, 
sulphuretted  hydrogen  is  one  of  the  most  powerful  in  its  action ;  for  it  has 
been  found  that  air  impregnated  with  TIL-Qth  part  of  it  will  kill  a  bird  in  a  very 
short  time,  and  that  a  quantity  but  little  more  than  double,  namely  ¥^th  part, 
will  soon  kill  a  dog.     This  gas  is  exhaled  in  large  quantities  from  many  forms 
of  decomposing  animal  and  vegetable  matter,  and  it  has  recently  been  shown 
(by  Professor  Daniell)  to  be  absorbed  by  the  water  of  the  estuaries  of  those 
African  rivers,  whose  mouths  are  regarded  as  among  the  most  pestilential  spots 
upon  the  surface  of  the  globe.     Carburetted  hydrogen  is  another  gas  whose 
effects  are  similar,  but  a  larger  proportion  is  required  to  destroy  life. 

551.  Carbonic  acid  gas  also  appears  to  be  absorbed  by  the  lungs,  when  a 
large  proportion  of  it  is  contained  in  the  atmosphere.     The  accumulation  of 
this  gas  in  the  blood,  when  the  respired  air  is  charged  with  it  even  to  a  mode- 
rate amount,  might  be  attributed  to  the  impediments  thus  offered  to  its  ordinary 
exhalation ; — but  the  following  experiment  appears  to  prove,  that  it  may  be 
actually  absorbed  into  the  blood,  and  that  it  will  thus  exert  a  real  poisonous 
influence,  and  not  merely  produce  an  asphyxiating  effect.     It  was  found  by 
Rolando,  that  the  air-tube  of  one  lung  of  the  land  tortoise  may  be  tied  without 
apparently  doing  any  material  injury  to  the  animal,  as  the  respiration  performed 
by  the  other  is  sufficient  to  maintain  life  for  some  time  ;  but,  having  contrived 
to  make  a  tortoise  inhale  carbonic  acid  by  one  lung  whilst  it  breathed  air  by 
the  other,  he  found  that  the  animal  died  in  a  few  hours .t     Cyanogen  is  another 
gas  which  has  an  actively  poisonous  influence  upon  animals  when  absorbed 
into  the  lungs  ;  its  agency,  also,  is  of  a  narcotic  character.     It  is  singular  that 
the  effects  of  the  respiration  of  pure  oxygen  should  not  be  dissimilar.     At 

*  Prize  Essay  on  Cutaneous  Absorption,  p.  55. 

f  The  fatal  result  of  breathing  the  fumes  of  charcoal  is,  therefore,  not  simple  asphyxia, 
such  as  would  result  from  breathing  hydrogen  or  nitrogen.  Other  volatile  products  are 
set  free  in  the  combustion  of  charcoal,  besides  carbonic  acid.  Mr.  Cd|thupe  (loc.  cit.) 
states  these  to  be  Carbonate,  Muriate  and  Sulphate  of  Ammonia,  Carbonic  Oxide,  Oxygen, 
Nitrogen,  Watery  vapour,  and  Empyreumatic  Oil:  to  these  Sulphurous  Acid  may  appear 
to  be  properly  added. 


ORGANIZABLE  PRINCIPLES.  413 

first,  the  rapidity  of  the  pulse  and  the  number  of  the  respirations  are  increased, 
and  the  animal  appears  to  suffer  little  or  no  inconvenience  for  an  hour ;  but 
symptoms  of  coma  then  gradually  develop  themselves,  and  death  ensues  in 
six,  ten,  or  twelve  hours.  If  the  animals  are  removed  into  the  air  before  the 
insensibility  is  considerable,  they  then  quickly  recover.  When  the  body  is 
examined,  the  heart  is  seen  beating  strongly,  while  the  diaphragm  is  motion- 
less ;  the  whole  blood  in  the  veins,  as  well  as  in  the  arteries,  is  of  a  bright 
scarlet  colour ;  and  several  of  the  membranous  surfaces  have  the  same  tint. 
The  blood  is  observed  to  coagulate  with  remarkable  rapidity ;  and  it  is  to  the 
alteration  in  its  properties,  occasioned  by  the  hyper-arterialization,  and  indicated 
by  this  condition,  that  we  are  probably  to  attribute  the  fatal  result.  There  can 
be  no  doubt  that,  in  this  instance,  an  undue  amount  of  oxygen  is  absorbed. — 
Death  is  also  caused  by  the  inhalation  of  several  gases  of  an  irritant  character, 
such  as  sulphurous,  nitrous  and  muriatic  acids  ;  but  it  is  doubtful  how  far  they 
are  absorbed,  or  how  far  their  injurious  effects  are  due  to  the  abnormal  action 
which  they  excite  in  the  lining  membrane  of  the  air-cells  and  tubes.  It  cannot 
be  doubted,  that  miasmata  and  other  morbific  agents  diffused  through  the  at- 
mosphere, are  more  readily  introduced  into  the  system  through  the  pulmonary 
surface  than  by  any  other ;  and  our  aim  should  therefore  be  directed  to  the 
discovery  of  some  counteracting  agents,  which  can  be  introduced  in  the  same 
manner.  The  pulmonary  surface  affords  a  channel  for  the  introduction  of  cer- 
tain medicines  that  can  be  raised  in  vapour  when  it  is  desired  to  affect  the 
system  with  them  speedily  and  powerfully  ;  such  are  iodine,  mercury,  tobacco, 
stramonium,  &c. 


CHAPTER    XI 


OF    NUTRITION. 

551.  THE  Function  of  Nutrition  essentially  consists  of  the  conversion  of  the 
fluid  alimentary  materials, — prepared  by  the  digestive  process,  and  introduced 
into  the  system  by  absorption, — into  organized  tissue,  possessed  of  certain  pro- 
perties which  inorganic  matter  never  exhibits,  and  which,  being  neither  phy- 
sical nor  chemical,  are  termed  Vital.     We  shall  hereafter  see  reason  to  believe 
that  the  manifestation  of  these  vital  properties,  which  gives  rise  to  the  various 
phenomena  of  life,  is  to  be  considered  as  the  result  of  the  process  of  organiza- 
tion, to  which  matter  is  subjected  in  the  living  body  (§  560). 

I.   Organizable  Principles. 

552.  It  has  been  shown  (§  467)  that  the  Chyle  taken  up  by  the  lacteals  is 
composed  of  water  holding  albumen  and  saline  matter  in  solution,  and  having 
oily  particles  suspended  in  it.     Albumen  may  be  regarded  as  the  proximate 
element,  at  the  expense  of  which,  in  conjunction  with  fatty  matter  (which 
never  itself  undergoes  organization  as  such,  §  16),  all  the  tissues  of  the  animal 
body  are  ultimately  formed.     In  this  assumption  we  seem  justified  by  two  very 
obvious  considerations.     First,  in  the  egg  of  a  bird,  (or  any  other  oviparous 


35 


414  OF  NUTRITION. 

animal,)  we  find  that,  putting  aside  the  fatty  matter  of  the  yolk,  albumen  is  the 
sole  organic  compound,  at  the  expense  of  which  all  its  tissues  are  to  be  formed  ; 
so  that,  by  the  wonderful  processes  of  chemical  and  vital  transformation,  which 
take  place  during  the  period  of  incubation,  the  albumen  which  it  contained  at 
first  is  metamorphosed  into  bone,  cartilage,  nerve,  muscle,  tendon,  ligament, 
membrane,  areolar  tissue,  gelatinous  matter,  horny  substance,  feathers,  &c.,  &c. 
Secondly,  a  similar  metamorphosis  appears  to  be  continually  taking  place  in 
the  body  of  the  adult  animal;  for  every  protein  compound  employed  as  food 
appears  to  be  reduced  to  the  form  of  albumen  in  the  digestive  process  ;  so  that 
this  becomes  the  essential  constituent  of  whatever  fluid  is  absorbed  for  the 
nutrition  of  the  tissues.  It  ,is  true  that  gelatin  taken  in  as  food  may  be  absorbed 
and  carried  into  the  current  of  the  circulation ;  but  there  is  no  doubt  that  it  is 
incapable  of  being  applied  to  the  re-construction  of  any  but  the  gelatinous 
tissues ;  and  it  seems  questionable  whether,  even  in  these,  it  exists  in  a  con- 
dition that  can  rightly  be  termed  organized.  Moreover,  as  it  is  clear  that  the 
gelatinous  tissues  may  be  formed  at  the  expense  of  albumen,  we  are  justified 
in  regarding  this  substance  as  the  common  pabulum  for  all.  Hence  albumen 
seems  to  hold  very  much  the  same  position  in  the  animal  economy,  with  gum 
in  the  vegetable.  As  long,  however,  as  albumen  remains  in  the  state  regarded 
by  chemists  as  characteristic  of  it,  it  exhibits  no  tendency  to  become  organized ; 
and  it  is  only  when  it  has  been  subjected  to  certain  peculiar  vital  influences, 
and  perhaps  undergone  a  change  in  its  chemical  constitution, — or,  in  other 
words,  has  become  converted  into  fibrin, — that  any  such  tendency  manifests 
itself.  The  properties  of  albumen  may  be  studied  in  the  white  of  egg,  or  in 
the  serum  of  blood,  from  both  of  which  situations  it  may  be  obtained  in  a  pure 
state  by  very  simple  means.  In  the  animal  fluids  it  exists  in  a  soluble  state  ; 
and  even  when  it  has  been  dried  (at  a  temperature  of  126°),  it  is  readily  dis- 
solved again  in  water,  forming  a  glairy,  colourless,  and  nearly  tasteless  fluid. 
In  this  condition  it  is  always  combined  with  a  small  quantity  of  free  soda ;  to 
the  separation  of  which  (whether  by  the  agency  of  heat  or  acids),  its  coagula- 
tion is  thought  by  many  chemists  to  be  due.  On  this  view,  pure  albumen  is 
not  soluble  in  water ;  its  solution  being  only  accomplished  by  union  with  an 
alkali.  When  dissolved  in  water  it  coagulates  at  158°  ;  a  very  dilute  solution, 
however,  does  not  become  turbid  until  it  is  boiled.  When  the  coagulation  of 
albumen  takes  place  rapidly,  a  coherent  mass  is  formed  which  shows  no  trace 
whatever  of  organization ;  but,  when  the  process  is  more  gradual,  minute 
granules  present  themselves,  which  do  not,  however,  exhibit  any  tendency 
towards  a  higher  form  of  structure.  It  is  thrown  down  from  its  solution,  in  a 
coagulated  state,  by  alcohol,  creosote,  and  by  most  acids  (particularly  nitric) 
with  the  exception  of  the  acetic.  These  precipitates  are  definite  compounds  of 
the  acids  with  the  albumen,  which  here  acts  the  part  of  a  base.  On  the  other 
hand,  coagulated  albumen  dissolves  in  caustic  alkalies,  and  neutralizes  them  ; 
so  that  it  must  here  act  as  an  acid.  A  solution  of  albumen  in  water  is  precipi- 
tated by  acetate  of  lead,  and  by  many  other  metallic  solutions :  and  insoluble 
compounds  are  formed,  of  which  one — the  albuminate  of  the  chloride  of  mer- 
cury— is  of  much  interest,  as  being  that  which  is  produced  by  the  mixture  of 
a  solution  of  albumen  with  one  of  corrosive  sublimate.  Albumen,  both  in  its 
soluble  and  insoluble  state,  always  contains  a  certain  amount  of  sulphur  (§  458), 
which  blackens  metallic  silver.  Soluble  albumen  dissolves  phosphate  of  lime  ; 
and  about  two  per  cent,  of  this  salt  may  be  separated  from  it  in  its  coagulated 
state. 

553.  Subsequently  to  its  introduction  into  the  living  system,  Albumen  under- 
goes a  very  peculiar  modification,  by  which  it  is  converted  into  Fibrin.  As 
already  mentioned  (§  457)  it  appears  from  the  analyses  of  Mulder  and  Scherer, 
that  the  ultimate  composition  of  these  two  substances  is  the  same ;  but  their 


ORGANIZABLE  PRINCIPLES.  415 

properties  are  widely  different:  according  to  Dumas,  however,  there  is  a 
marked  difference  in  composition  between  Fibrin  and  the  various  forms  of 
Albumen, — the  former  having  less  Carbon,  and  more  Nitrogen,  than  the  latter. 
The  following  are  the  results  of  his  analyses. 


From  serum.  From  egs:s. 

Carbon 58-32  53-37             53-50             52-78 

Hydrogen 7-29  7-10               7-05               <HH> 

Nitrogen 15-70  15-77             15-77             10-78 

Oxygen ~) 

Sulphur I  23-69  23-76            23-68            21-48 

Phosphorus       .     .     .     .J 

100-00  100-00          100-00          100-00 


It  is  not,  perhaps,  of  any  great  moment  whether  this  difference  has  a  real 
existence  or  not ;  for  the  conversion  of  Albumen  into  Fibrin  is  unquestionably 
a  process  much  more  of  vital  than  of  chemical  transformation.  We  shall 
presently  see,  that  Fibrin  may  be  regarded  as  Albumen  in  which  the  process 
of  Organization  has  begun  ;  its  molecules  being  ready  to  assume  the  peculiar 
arrangement  that  is  so  designated :  this  arrangement  takes  place  most  com- 
pletely, when  the  fibrinous  mass  is  in  contact  with  a  living  tissue,  and  is, 
therefore,  to  a  certain  degree,  under  its  influence.  Fibrin,  like  albumen,  may 
exist  in  a  soluble  or  in  a  coagulated  state ;  its  soluble  form  only  occurs, 
however,  in  the  living  Animal  Fluids, — the  chyle,  lymph,  and  blood ; — and 
it  seems  to  be  the  intermediate  condition  between  the  soluble  albumen,  and  the 
solid  organized  substances  which  are  formed  from  it.  When  withdrawn  from 
the  blood-vessels,  the  Blood  soon  coagulates  (as  do  also  the  Chyle  and  Lymph, 
when  they  contain  sufficient  fibrin,  §§  564  and  565) ;  and  this  coagulation  is 
entirely  due  to  a  change  in  the  condition  of  the  Fibrin,  the  particles  of  which 
have  a  tendency  to  aggregation.  The  Fibrin  may  be  obtained  in  a  separate 
form,  by  stirring  fresh-drawn  blood  with  a  stick,  to  which  it  adheres  in  threads  ; 
these  contain  some  fatty  matter  which  is  to  be  washed  out  with  alcohol.  In 
this  condition  it  possesses  the  softness  and  elasticity  which  characterize  the 
flesh  of  animals,  and  contains  about  three-fourths  of  its  weight  of  water.  It 
may  be  deprived  of  this  water  in  dry  air,  and  then  becomes  a  hard  and  brittle 
substance ;  but,  like  flesh,  it  imbibes  water  again  when  moistened,  and  recovers 
its  original  softness  and  elasticity.  When  burned,  it  always  leaves,  like  albu- 
men, a  portion  of  phosphate  of  lime.  Fibrin  is  insoluble  in  alcohol  and  ether, 
and  also,  under  ordinary  circumstances,  in  water;  but  when  long  boiled  in 
water,  especially  under  pressure,  its  nature  is  altered,  and  it  becomes  soluble. 
This  is  also  the  case  with  coagulated  albumen.  Fibrin,  like  albumen,  unites 
with  acids  as  a  base,  forming  definite  compounds  ;  and  with  bases  as  an  acid. 
Its  correspondence  with  albumen  has  been  recently  proved  by  the  fact  (first 
stated  by  M.  Denis),  that  it  may  be  entirely  dissolved  in  a  solution  of  nitrate 
of  potash ;  and  that  this  solution  is  coagulated  by  heat,  and  greatly  resembles 
a  solution  of  albumen.  This  is  only  true,  however,  of  the  ordinary  Fibrin  of 
Venous  blood ;  for  that  which  is  obtained  from  arterial  blood  or  from  the  buffy 
coat,  or  which  has  been  exposed  for  some  time  to  the  air,  is  not  thus  soluble. 
This  is  an  important  and  interesting  circumstance.  The  difference  appears 
to  depend  upon  the  larger  quantity  of  oxygen  contained  in  the  latter ;  for  a 
solution  of  Venous  Fibrin  in  nitre,  contained  in  a  deep  cylindrical  jar,  allows 
a  precipitate  in  fine  flocks  to  fall  gradually,  provided  the  air  have  access  to 
the  surface,  but  not  if  it  be  prevented  from  coming  in  contact  with  the  fluid ; 


416  OF  NUTRITION. 

this  precipitate  is  insoluble  in  the  solution  of  nitre,  and  possesses  the  properties 
of  arterial  fibrin.*  Hence  it  may  be  inferred,  that  the  Fibrin  of  Venous  blood 
most  nearly  resembles  albumen  ;  whilst  that  of  Arterial  blood,  and  of  the  Buffy 
coat,  contains  more  oxygen,  and  is  more  highly  animalized.  It  is  evident, 
from  this  circumstance,  that  the  matter  of  the  Red  Corpuscles  is  by  no  means 
the  only  constituent  of  the  Blood,  which  undergoes  a  change  in  the  respiratory 
process  (§  540)  .t  When  decomposition  commences  in  a  coagulum  of  Fibrin 
withdrawn  from  the  body  (and  even  in  the  greatly  debilitated  living  body,  in 
which  the  fibrin  appears  to  be  imperfectly  formed),  a  granular  mode  of  Aggre- 
gation is  evident  in  the  particles  of  the  mass, — thus  showing  its  affinity  to 
Albumen,  when  its  peculiar  vital  characters  have  departed,  or  are  possessed 
by  it  in  an  inferior  degree. 

554.  It  appears  to  be  in  the  Fibrin  of  the  Blood  that  all  the  organized 
constituents  of  the  body  have  their  immediate  origin ;  and  it  may  hence  be 
designated  as  the  plastic  or  organizable  constituent  of  the  nutritious  fluid. — 
To  use  a  rather  homely  illustration,  Albumen,  Fibrin,  and  Organized  tissue, 
stand  in  much  the  same  relation  to  each  other,  with  raw  cotton,  spun  yarn, 
and  the  woven  fabric.  That  the  particles  of  perfectly  elaborated  Fibrin  are 
capable,  in  solidifying,  of  spontaneously  assuming  a  definite  arrangement, 
cannot  now  be  questioned.  In  the  ordinary  Crassamentum  of  healthy  Blood 
(§  582),  this  arrangement  can  be  seen,  by  examining  thin  slices  under  the 
microscope ;  especially  after  the  clot  has  been  hardened  by  boiling.  A  num- 
ber of  fibres,  more  or  less  distinct,  may  be  seen  to  cross  one  another ;  forming, 
by  their  interlacement,  a  tolerably  regular  network,  in  the  meshes  of  which  the 
red  corpuscles  are  entangled-.  This  fact  was  known  to  Haller ;  but  it  has 
been  generally  overlooked  by  subsequent  physiologists,  until  attention  was 
drawn  to  it  by  the  inquiries  of  Messrs.  Addison,  Gulliver,  and  others. — It  is 

*  Scherer,  Chemisch-physiologische  Untersuchungen ;  Annalen  der  Chemie,  Oct.,  1841; 
quoted  in  Graham's  Chemistry,  p.  1025. 

t  It  appears,  from  the  recent  inquiries  of  Mulder,  that  the  Protein-base  of  Fibrin  may 
exist  in  different  states  of  definite  combination  with  Oxygen.  When  Fibrin  is  long 
boiled,  so  that  part  of  it  is  dissolved,  the  soluble  portion  is  found  to  consist  of  Triioxide 
of  Protein,-  whilst  the  insoluble  residue  is  in  the  state  of  Deutoxf.de.  When  Albumen  is 
boiled  for  a  sufficient  length  of  time,  a  Tritoxide  of  Protein  is  formed  and  dissolved  in 
like  manner;  but  the  residue  is  simple  Albumen.  Tritoxide  of  Protein  may  be  further 
produced,  by  exposing  Fibrin  to  Oxygen  gas.  It  is  found  in  small  quantity  in  healthy 
blood;  its  amount  being  greater  in  arterial  than  in  venous:  but  it  forms  a  much  larger 
proportion  of  the  Buffy  coat,  of  which  14  per  cent,  may  be  dissolved  by  a  quarter  of  an 
hour's  boiling.  This  soluble  matter  has  been  mistaken  for  Gelatin  ;  but  its  composition 
is  altogether  different;  and  it  is  slated  by  Mulder  to  agree  exactly  with  that  which  Dumas 
has  analyzed  as  Fibrin.  These  Oxides  of  Protein  are  regarded  by  Mulder  as  formed  at 
the  expense  of  the  Fibrin  during  its  passage  through  the  Lungs;  and  as  being  the  real 
materials  of  the  nutritive  process  ;  and  he  denies  that  any  other  constituent  of  the  blood 
undergoes  oxidation  in  the  pulmonary  capillaries.  In  this  view  he  is  probably  as  much 
in  error,  as  are  those  who  deny  that  any  element  but  the  Red  Corpuscles  is  concerned  in 
the  respiratory  process.  How  far  he  is  correct  in  asserting,  that  the  oxides  of  Protein 
alone  are  the  materials  of  the  nutritive  processes,  further  researches  alone  can  deter- 
mine. It  appears  to  the  Author,  however,  that  the  doctrine  is  inconsistent  with  known 
facts  in  regard  to  the  organizability  of  true  Fibrin.  And  it  may  be  remarked,  that  the 
differences  of  opinion  which  prevail  amongst  the  most  eminent  Chemists,on  topics  which 
lie  at  the  foundation  of  Physiological  Chemistry,  should  lead  us  to  hesitate  before  ad- 
mitting the  novelties  continually  put  forth  by  one  or  other  of  them  as  the  basis  of  our 
deductions.  To  him  it  appears,  that  the  direct  observation  of  Vital  phenomena,  about 
which  there  can  be  little  or  no  difference  of  opinion,  is  a  much  surer  basis  for  theorizing 
than  those  Analyses  of  the  Chemist  in  which  the  utmost  delicacy  of  manipulation  is 
required  to  insure  even  tolerably  accurate  results,  and  as  to  the  details  of  which,  a  new 
set  of  statements  is  put  forth  from  some  of  the  great  Continental  Laboratories,  almost 
every  month.— For  the  detailed  account  of  Mulder's  researches,  see  the  Annalen  der 
Chemie  und  Pharmacie,  Band  xlvii. 


ORGANIZABLE  PRINCIPLES.  417 

in  the  Buffy  Coat  (§  588),  however,  that  the  fibrous  arrangement  is  best  seen; 
on  account,  as  it  would  appear,  of  the  stronger  attraction  which  the  particles 
of  fibrin  have  for  one  another,  when  its  vitality  has  been  raised  by  the  increased 
elaboration  to  which  it  has  been  subjected.  That  there  are  varieties  of  plastic!  I  \/ 
in  the  substance,  which,  on  account  of  its  power  of  spontaneously  coagulating, 
we  must  still  calljibrin,  appears  from  this  fact  among  others, — that,  in  tuber- 
culous subjects,  the  quantity  of  fibrin  in  the  blood  is  higher  than  usual  (Andral 
and  Gavarret),  although  its  plasticity  is  certainly  below  par.  It  is  easy  to 
understand,  that  its  plasticity  may  be  increased  as  that  it  may  be  diminished ; 
and  this  either  in  the  general  mass  of  the  blood,  or  in  a  local  deposit.  In 
fact,  the  adhesions  which  are  formed  by  the  consolidation  of  coagulable  lyrnph, 
or  in  other  words,  of  liquor  sanguinis,  whose  plasticity  has  been  heightened 
by  the  vital  actions  in  the  capillaries  of  the  part  on  which  it  has  been  effused, 
often  acquire  very  considerable  firmness,  before  any  vessels  have  penetrated 
them ;  and  this  firmness  must  depend  upon  that  mutual  attraction  of  the  par- 
ticles for  one  another,  which,  in  aplastic  deposits,  is  altogether  wanting,  and 
which,  in  cacoplastic  deposits,  is  deficient. — A  very  interesting  example  of  a 
structure  entirely  composed  of  matted  fibres,  and  evidently  originating  in  the 
simple  consolidation  of  Fibrin,  has  lately  been  discovered  by  the  writer.  This 
is  found  in  the  membrane  adherent  to  the  interior  of  the  Egg-shell  (Membrana 
putaminis) ;  and  also  in  that  which  forms  the  basis  of  the  Egg-shell  itself. 
Between  the  two,  there  is  no  essential  difference ;  as  may  be  seen  by  examin- 
ing "  an  egg  without  shell,"  as  it  is  commonly  termed,  (or  rather  one  in  which 
the  shell-membrane  has  been  unconsolidated  by  the  deposition  of  calcareous 
matter) ;  or  by  treating  the  egg-shell  with  dilute  acid,  so  as  to  remove  the 
particles  of  carbonate  of  lime,  which  are  deposited  in  the  interstices  of  jhe 
network.  The  place  of  the  shell  is  then  found  to  be  occupied  by  a  membrane 
of  considerable  firmness,  closely  resembling  that  which  surrounds  the  albumen 
of  the  egg,  but  thicker  and  more  spongy.  After  maceration  for  a  few  days, 
either  of  these  membranes  may  be  separated  into  a  number  of  laminae ;  each 
of  which  (if  sufficiently  thin)  will  show  a  beautiful  arrangement  of  reticulated 
fibres.  It  is  impossible  to  refuse  to  such  a  structure  the  designation  of  an 
organized  tissue,  although  it  contains  no  vessels,  and  must  be  formed  by  the 
simple  consolidation  of  Fibrin,  poured  out  from  the  lining  membrane  of  the 
oviduct  of  the  bird.  It  is  probably  in  the  same  manner  that  the  Chorion  of 
the  Mammiferous  animal  originates;  since  this  is  a  new  envelop,  formed 
around  the  ovum,  during  its  passage  along  the  Fallopian  tube.  In  the  latter, 
for  an  ulterior  purpose,  vessels  are  afterwards  developed,  by  extension  from 
the  contained  ovum ;  and  by  the  nutrition  they  supply,  its  size  is  increased, 
and  changes  take  place  in  its  texture.  But  in  the  Egg-membrane  of  the  Bird 
there  is  no  need  of  vessels ;  because  no  subsequent  change  in  its  texture  is 
required,  and  its  duration  is  sufficient  for  the  purpose  it  has  to  answer. 

555.  The  completeness  of  the  transformation  of  Fibrin  into  simple  Fibrous 
Tissue,  appears  to  depend  upon  two  circumstances  in  particular ; — the  perfect 
elaboration  of  the  Fibrin  itself,  and  the  vitality  of  the  surface  upon  which  the 
concretion  takes  place.  When  the  Fibrin  is  highly  elaborated,  it  will  coagu- 
late in  the  form  of  a  definite  network  of  minute  fibrillaB,  even  upon  a  dead 
surface,  as  a  slip  of  glass;  this  is  the  case,  for  instance,  with  the  Fibrin  of  the 
buffy  coat  of  the  Blood,  or  with  that  of  the  Liquor  Sanguinis  (coagulable 
lymph),  poured  out  for  the  reparation  of  an  injured  part.  But  in  the  ordinary 
Fibrin  of  the  blood,  the  fibrillation  is  less  distinct  when  the  concretion  takes 
place  upon  a  dead  surface.  When  it  occurs  in  contact  with  a  living  surface, 
however,  the  coagulation  takes  place  more  gradually ;  and  it  seems  as  if  the 
particles,  having  more  time  to  arrange  themselves,  become  aggregated  into 
more  definite  forms,  so  that  a  more  regular  tissue  is  produced— just  as  crystals 


418  OF  NUTRITION. 

are  most  perfectly  formed  when  the  crystalline  action  takes  place  slowly.  It 
was  formerly  imagined,  that  the  Muscular  tissue  is  the  only  one  produced  at 
the  expense  of  the  Fibrin  of  the  blood ;  the  other  tissues  being  formed  from 
its  Albumen.  This,  however,  is  unquestionably  erroneous/  There  is  no 
proof  whatever  that  Albumen,  as  long  as  it  remains  in  that  condition,  ever 
becomes  organized ;  whilst,  on  the  other  hand,  there  is  abundant  evidence 
that  the  plasticity  of  any  fluid  deposit — that  is,  its  capability  of  being  meta- 
morphosed into  organized  tissue — is  in  direct  relation  with  the  quantity 'of 
Fibrin  which  it  contains.  Thus  the  Liquor  Sanguinis  or  Coagulable  Lymph, 
thrown  out  for  the  reparation  of  injuries,  contains  a  large  amount  of  Fibrin; 
and  this  substance  is  converted,  not  at  first  into  muscular  fibre,  but  (whatever 
may  be  the  tissue  to  be  ultimately  produced  in  its  place),  into  a  fibrous  net- 
work, which  fills  up  the  breach,  and  holds  together  the  surrounding  structure. 
This  may  be  regarded  as  a  simple  form  of  areolar  tissue ;  which  gradually 
becomes  more  perfectly  organized,  by  the  extension  of  vessels  and  nerves  into 
its  substance;  and  in  \vhich  other  forms  of  tissue  may  subsequently  make 
their  appearance.  This  process  will  be  more  particularly  described  here- 
after; it  is  at  present  noticed  here  as  an  illustration  of  the  general  fact,  that 
fibrin  is  to  be  regarded  as  the  plastic  element  of  the  nutritive  fluids. — The 
change  from  Albumen  to  Fibrin  is,  therefore,  the  first  important  step  in  the 
process  of  Assimilation.  It  commences  in  the  Absorbent  system,  (§  564), 
and  it  continues  in  the  Blood ;  for  the  quantity  of  Fibrin  it  contains  is  always 
kept  up,  in  health,  to  a  certain  standard,  although  there  must  be  a  continual 
withdrawal  of  it  for  the  nutritive  processes,  without  a  correspondingly  regular 
supply  from  the  chyle ;  and  we  find  it,  moreover,  undergoing  a  sudden  and 
remarkable  increase,  under  the  influence  of  local  agencies.  The  mode  in 
which  this  conversion  is  effected,  will  be  better  discussed  hereafter ;  when 
the  chief  circumstances  under  which  it  occurs,  have  been  inquired  into 
(§  579). 

II.  Formation  of  Cells. 

556.  A  very  large  proportion  of  the  Vegetable  Organism  (in  the  simplest 
Plants,  the  entire  structure)  is  made  up  of  cells  or  vesicles;  wnich  are  minute 
closed  sacs,  whose  walls  are  composed  in  the  first  instance  of  a  delicate  mem- 
brane, frequently  strengthened,  at  a  period  long  subsequent  to  their  first 
formation,  by  some  internal  deposit.  The  form  of  these  cells  is  extremely 
variable,  and  depends  chiefly  upon  the  degree  and  direction  of  the  pressure, 
to  which  they  have  been  subjected  at  the  period  of  their  origin,  and  subse- 
quently to  it.  Sometimes  they  are  spheroidal ;  sometimes  cubical  or  prismatic ; 
sometimes  cylindrical ;  and  sometimes  very  much  prolonged.  These  cells  may 
undergo  various  transformations. — One  of  the  most  common,  is  the  conversion 
of  several  into  a  continuous  tube  or  Duct.  This  is  principally  seen  in  the 
vessels  through  which  the  sap  ascends  the  stem ;  these  appear  to  have  been 
formed  by  the  breaking  down  of  the  transverse  partitions,  between  a  regular 
series  of  cylindrical  cells  laid  end  to  end ;  and  the  remains  of  such  partitions 
may  frequently  be  seen  in  them.  The  ducts  which  convey  the  ascending 
sap  do  not  inosculate  with  each  other,  their  purpose  being  merely  to  carry  it 
direct  to  the  leaves ;  but  the  vessels  through  which  the  descending  or  elabo- 
rated sap  flows,  are  of  very  different  character;  for  their  purpose  is  to  distribute 
the  nutritious  fluid  through  the  tissues  (§  497) ;  and  they  anastomose  very 
freely,  just  as  do  the  capillaries  of  Animals.  The  network  which  they  form, 
however,  can  be  as  clearly  traced  to  an  origin  in  cells  whose  cavities  were 
originally  distinct,  as  can  the  bundles  of  straight  non-communicating  ducts. — 
Another  important  transformation  of  the  original  cells,  is  that  by  which  the 


FORMATION  OF  CELLS.  419 

Woody  Fibres,  which  compose  nearly  all  the  fibrous  textures  of  Vegetables, 
are  produced.  These  fibres  are  still  cells,  but  their  form  is  very  much  elon- 
gated ;  they  have  a  fusiform  or  spindle  shape,  being  tubes  drawn  to  a  point  at 
each  end;  at  first  they  are  quite  pervious,  like  ordinary  cells;  but  in  the  older 
wood,  their  cavity  is  filled  up  by  interior  deposit.  There  seerns  reason  to 
believe,  that  fasciculi  of  these  fibre-cells  originate  within  certain  of  the  ordi- 
nary cells  of  the  primary  cellular  tissue ;  for  in  the  young  Plant,  the  latter 
alone  can  be  detected ;  and  it  is  not  until  the  operation  of  the  leaves  has  fairly 
commenced,  that  any  true  woody  structure  is  formed.  Thus,  cells  or  vesicles 
may  be  regarded  as  the  primordia  of  all  the  Vegetable  tissues.  The  next 
question  is, — how  are  Cells  formed  ? 

657.  Cells  appear  to  originate  in  two  modes ;  either  in  the  midst  of  an 
organizable  fluid,  under  the  influence  of  a  living  solid  tissue  with  which  it  is  in 
contact,  or  in  the  interior  of  previously-formed  cells.  Both  these  modes  may 
be  observed  in  the  Animal  as  well  as  in  the  Vegetable  organism  ;  and  the  right 
comprehension  of  them  is  of  the  utmost  importance.  It  has  been  already 
remarked,  that  Gum  holds  the  same  rank  in  the  economy  of  the  Plant  as 
Albumen  does  in  that  of  the  Animal ;  and  the  glutinous  compound  which  exists 
in  the  elaborated  sap,  and  which  is  especially  abundant  in  parts  where  organ- 
ization is  taking  place  with  rapidity,  may  be  compared  with  fibrin.  This  glu- 
tinous sap  undergoes  a  sort  of  coagulation  when  withdrawn  from  the  vessels, 
and  it  may  be  sometimes  perceived  to  resolve  itself  into  distinct  organic  forms. 
The  process  of  organization  may  be  observed  with  the  greatest  facility  in  the 
embryonal  sac,  previously  to  fecundation.  This  contains,  when  first  developed, 
a  consistent  gummy  fluid,  slightly  wanting  in  transparency,  but  not  exhibiting 
any  distinguishable  granules  ;  the  addition  of  tincture  of  iodine  produces  a  sort 
of  granular  coagulum,  of  a  pale  yellow.  The  first  perceptible  stage  of  organ- 
ization is  the  appearance  in  this  fluid  of  a  number  of  extremely  minute  granules, 
which  render  it  opalescent  and  almost  opaque.  The  fluid  then  takes  from 
iodine  a  somewhat  darker  tinge,  and  the  granules,  when,  their  small  size  per- 
mits their  colour  to  be  distinguished,  seem  to  become  of  a  dark  brownish-yellow. 
Single,  larger,  and  more  sharply-defined  granules  are  next  evident  in  the  mass, 
and  these  soon  present  a  regular  form,  and  increase  in  size1  apparently  from 
the  coagulation  of  the  minuter  granules  around  the  larger  ones.  These  bodies 
usually  assume  a  flattened  disc-like  form,  with  a  circular  or  oval  outline  ;  and 
as  they  speedily  become  subservient  to  the  formation  of  cells,  they  have  been 
termed  cytoblasts  or  cell-germs.  From  the  surface  of  each  of  these,  a  delicate 
transparent  membrane  is  seen  to  project,  as  a  watch-glass  does  from  the  dial ; 
and  this  is  the  commencement  of  the  cell.  The  membrane  gradually  projects 
more  and  more,  and  extends  beyond  the  cytoblast,  which  is  at  last  seen  as  a 
mere  spot  upon  its  walls.  It  is  some  time  in  acquiring  consistence  ;  for  even 
after  the  cell  has  arrived  at  nearly  its  full  size,  it  may  be  made  to  dissolve  by 
agitation  in  the  surrounding  fluid.  In  fact,  a  disappearance  not  unfrequently 
takes  place,  as  a  part  of  the  natural  course  of  vital  phenomena  ;  the  cell-walls 
melting  away  before  they  have  acquired  consistence  enough  to  be  permanent. 
When  the  cell  is  complete,  the  granular  cytoblast  commonly  disappears  ;  some- 
times, however,  it  remains  in  the  wall  of  the  cell,  where  (in  the  orders  Orchideas 
and  Cactese)  it  was  long  since  described  by  Dr.  R.  Brown,  under  the  name  of 
the  nucleus.  By  Schleiden,  the  original  observer  of  these  phenomena,*  it  is 
considered  that  the  function  of  the  cytoblast  is  complete  with  the  formation 
of  the  primordial  cell ;  but  there  is  strong  reason  to  believe,  that  the  granules 
of  which  it  is  composed  are  the  germs  of  new  cells  afterwards  to  be  developed 

*  See  Muller's  Archiv.,  1808,  p.  137,  Taylor's  Scientific  Memoirs,  vol.  ii.,  and  the  Brit. 
and  For.  Med.  Rev.,  vol.  ix.  p.  499. 


420  OF  NUTRITION'. 

within  the  parent  vesicle  ;  and  that,  even  when  it  disappears,  it  is  by  a  resolu- 
tion into  its  component  granules,  which  may  act  as  well  separately  as  in  appo- 
sition. It  is  not  to  be  inferred  from  the  preceding  account,  that  cells  are  ever 
formed  by  the  mere  apposition  of  particles,  at  all  in  the  manner  of  the  aggre- 
gation of  molecules  in  a  crystal ;  since  there  appears  sufficient  reason  to  believe 
that  in  this  instance,  as  in  all  others,  germs  are  present  in  the  fluid,  which 
were  prepared  by  previously  existing  cells,  and  which  grow  and  develop 
themselves  in  virtue  of  their  peculiar  inherent  powers. 

558.  We  are  thus  brought  to  the  second  mode  in  which  Cells  may  be  de- 
veloped, which  is  within  the  parent  vesicles  or  primordial  cells ;  the  granules 
contained  in  these  being  apparently  the  germs  from  which  they  originate. — 
This  is  probably  the  mode  which  is  always  followed  when  a  tissue  previously 
existing  has  to  be  extended  or  partially  renewed ;  the  former  one  being  adopted 
where  a  structure  entirely  new  has  to  be  evolved,  which  is  normally  the  case 
in  certain  phases  of  Vegetable  life,  but  is  less  common  in  Animals.     The 
secondary  cells  developed  within  a  parent  vesicle,  originating  in  the  granular 
germs  which  it  includes,  at  first  grow  at  the  expense  of  the  fluid  it  contains, 
and  afterwards  by  absorbing  nutrient  materials  through  its  walls.    When  they 
have  undergone  great  increase  in  size,  they  distend  the  original  vesicle  in  such 
a  manner  that  its  limits  are  no  longer  apparent.     The  pressure  to  which  they 
are  subjected  during  their  development,  determines  their  form,  as  in  the  pre- 
vious case.     If  the  original  cell  be  spherical,  and  the  pressure  be  equal  on  all 
sides,  they  also  will  be  spherical  until  their  sides  are  flattened  against  each 
other,  when  they  will  become  rhomboidal  dodecahedrons.     If,  on  the  other 
hand,  the  pressure  be  predominant  in  one  direction,  or  there  be  any  traction  in 
another,  the  newly-forming  cells  will  be  elongated  in  the  direction  of  least  re- 
sistance ;  and  this  elongation  may  be  carried  to  such  an  extent  as  to  impart  to 
them  the  fibrous  character.     The  development  of  cells  within  cells  is  most 
distinctly  seen  in  the  case  of  the  spore  or  pollen-grain  ;  the  granules  contained 
in  which  are  clearly  the  germs  of  the  cells  that  compose  the  tissue  of  the  em- 
bryonic structure.     These  cells,  when  fully  evolved,  in  their  turn  produce 
others  in  their  interiors  ;  and  in  this  manner  a  complex  and  extensive  organism 
may  be  developed  from  a  single  cell-germ.     This,  in  fact,  is  what  takes  place 
in  the  lowest  plants,  in  which  the  cell-germs  or  reproductive  granules  are  set 
free  from  the  parent  vesicle,  before  they  are  themselves  developed  into  cells  ; 
and  each  one  of  them,  imbibing  nutriment  from  the  air  and  moisture  around, 
may  ultimately  evolve  itself  into  a  complete  individual.    In  the  higher  Crypto- 
gamic  Plants,  on  the  contrary,  the  parent  vesicle  or  spore  does  not  rupture,  but 
the  new  cells  of  the  embryo  are  developed  within  it,  at  last  distending  its  walls 
so  much  that  they  can  be  no  longer  traced ;  and  it  would  seem  as  if  it  served 
to  elaborate  for  them,  from  the  surrounding  elements,  the  nutriment  they  re- 
quire.    In  the  flowering  plants,  a  further  supply  of  this  nutriment  is  provided 
in  the  ovule,  where  materials  previously  elaborated  are  stored  up,  to  be  absorbed 
through  the  wall  of  the  parent  cell,  and  to  be  subservient  to  the  development 
of  its  contained  germs.     This  process,  although  forming  a  part  of  the  function 
of  reproduction,  is  in  reality  essentially  the  same  with  the  ordinary  nutritive 
operations ;  for  in  these  the  circulating  fluid  supplies  the  pabulum  or  organiza- 
ble  matter ;  whilst  the  cells  already  formed  contain  the  germs,  which,  with  the 
assistance  of  this,  evolve  themselves  into  new  cells,  and  thus  become  the  means 
of  the  extension  of  the  original  structure. 

559.  The  Animal  body  exhibits  phenomena  of  a  character  essentially  the 
same.  Even  in  the  fully-formed  organism,  many  parts  may  be  found,  which 
are  composed,  more  or  less  evidently,  of  isolated  cells  or  vesicles,  analogous 
to  those  of  Plants  ;  and  it  has  been  clearly  proved  that,  in  its  early  condition, 
the  whole  fabric  has  this  character.  In  fact,  it  has  been  shown  by  the  re- 


FORMATION  OF  CELLS.  421 

searches  of  Barry,  Schwann,  and  Valentin,  that  the  whole  structure  originates 
in  a  single  cell ;  that  this  cell  gives  birth  to  others  analogous  to  itself,  and  these 
again  to  many  future  generations ;  and  that  all  the  varied  tissues  of  the  Animal 
body  are  developed  from  these,  although  no  difference  can  be,  in  the  first 
instance,  observed  among  them.  The  multiplication  of  cells  appears  to  take 
place  upon  the  plan  just  stated,  two  or  more  being  produced  within  the  parent 
vesicle ;  and  this  alike  in  the  earliest  condition  of  the  embryo,  and  in  the  more 
advanced  stages  of  the  formation  of  its  tissues.  (See  Plate  I.,  Figs.  9 — 12, 
and  Explanation.)  The  organizable  fluid,  then,  prepared  by  the  digestive 
process,  is  converted  into  organized  tissue,  by  supplying  the  materials  for  this 
continual  reproduction;  the  formation  itself  is  dependent  upon  the  powers  of 
the  solid  texture. 

560.  This  is  not,  however,  the  only  mode  in  which  new  cells  are  produced 
in  the  Animal  body ;  for  they  may  originate  in  Fibrin,  from  nuclei  or  cyto- 
blasts,  which  are  formed  by  the  aggregation  of  minute  granules ;  just  as  do 
those  of  the  Plant  in  the  organizable  gummy  fluid  of  the  ovule.  Both  require 
for  their  perfect  performance,  that  the  fluid  should  be  in  contact  with  a  living 
tissue ;  and,  when  this  condition  is  supplied,  there  seems  to  be  no  necessity 
for  any  further  assistance ;  but  traces  of  cellular  organization  may  often  be 
discovered  in  Fibrin,  even  after  it  has  been  drawn  from  the  vessels  of  the 
living  body,  though  more  frequently,  perhaps,  in  that  which  has  coagulated 
within  the  vessels  after  death.*  The  cells,  where  they  present  themselves, 
possess  nuclei,  and  have  all  the  characters  of  being  in  progress  of  development ; 
and  frequently  the  nuclei  can  be  distinguished  when  no  cells  yet  appear. — 
It  is,  however,  when  Fibrin  is  effused,  in  the  form  of  Coagulable  Lymph,  on  a 
cut  surface,  or  on  an  inflamed  membrane,  that  this  process  of  organization  most 
unequivocally  displays  itself.  Soon  after  the  coagulation,  a  number  of  granular 
bodies  may  be  seen  in  the  mass  ;  and  these  soon  present  appearances  which 
indicate  that  they  serve  as  nuclei  for  the  formation  of  cells.  In  this  condition 
they  are  known  as  Exudation-Corpuscles.  The  layers  of  these  soon  acquire 
such  a  consistence,  that  they  may  be  peeled  off  in  cohering  shreds  from  the 
membranes  to  which  they  are  attached ;  and  the  cells  when  first  formed  present 
a  ruddy  yellow  colour,  which  corresponds  with  that  of  the  Chyle-globules. 
The  Exudation-Cells  are  laid  flat  over  one  another,  forming  many  super- 
imposed layers,  which  unite  into  membranous  expansions,  bearing  a  strong 
resemblance  to  the  layers  of  flat  cells  of  which  Epithelium  is  composed ;  their 
margins  are  at  first  rounded,  and  they  are  united  by  a  connecting  medium, 
which  gradually  disappears,  leaving  the  sides  coherent  to  each  other,  so  that 
the  figure  of  the  disk  is  changed  into  a  polygon.  These  cells  afterwards  give 
place  to  the  various  forms  of  tissue  that  are  to  present  themselves  in  the  new 
fabric,  by  a  series  of  changes  which  will  be  hereafter  more  fully  described. 
If  the  general  principle  be  correct,  that  no  Cell  can  be  produced,  save  from  a 
germ  prepared  by  a  pre-existing  cell,  it  is  obvious  that  such  germs  must  be 
contained  in  the  Liquor  Sanguinis,  and  must  escape  from  the  blood-vessels 
which  pour  it  forth.  When  their  extreme  minuteness  is  considered,  this  may 
not  be  deemed  improbable.  The  formation  of  similar  cells  in  the  Clot  of  Blood 
drawn  directly  from  the  vessels,  and  even  in  that  which  has  coagulated  within 
them,  seems  to  add  weight  to  this  idea.  We  have  reason  to  believe  that  such 
granules  are  being  continually  set  free  by  the  rupture  of  the  White  Corpus- 
cles of  the  Blood  (§  577) ;  and  reasons  will  hereafter  be  given  for  the  belief, 
that  they  may  be  the  germs  of  the  Epithelial  Cells,  to  which  the  layers  o 
Exudation  Cells  bear  so  strong  a  resemblance. — It  is  well  known,  that 
character  of  organisms  of  a  low  grade  is  very  much  influenced  by  the  circum- 

*  See  Mr.  Gulliver's  Appendix  to  Gerber's  General  Anatomy,  p.  31. 
30 


422  OF  NUTRITION. 

stances  under  which  they  are  developed ;  hence  there  is  no  a  priori  objection 
to  the  belief  (which  other  circumstances  seem  to  favour),  that  Pus  Corpuscles, 
and  Tubercular  matter,  are  abnormal  forms  of  the  same  elements,  as  those 
which  would  otherwise  produce  a  well-formed  layer  of  Exudation  Cells 
(§§  609,  610). 

561.  From  what  has  been  stated,  it  appears  evident  that  the  process  of 
Nutrition  mainly  consists  in  the  growth  of  the  individual  cells  composing  the 
fabric ;  and  that  these  derive  their  support  from  the  organic  compounds  with 
which  they  are  supplied  by  the  blood,  just  as  the  cells  composing  the  simplest 
Plants  derive  theirs  from  the  inorganic  elements  which  surround  them :  and 
as  different  species  of  the  latter  select  and  combine  these,  in  such  modes  and 
proportions,  as  to  give  rise  to  organisms  of  very  diversified  forms  and  proper- 
ties, so  it  is  easily  intelligible  that  the  different  parts  of  the  fabric  of  the  highest 
Animals  should  exercise  a  similar  selective  power,  in  regard  to  the  materials 
with  which  the  blood  supplies  them.     The  structure  composing  every  separate 
portion  of  the  body  has  (what  may  be  termed)  a  special  affinity  for  some  par- 
ticular constituents  of  the  blood ;  causing  it  to  abstract  from  that  fluid,  and  to 
convert  into  its  own  substance  certain  of  its  elements.     The  conversion  is 
termed  Assimilation.     The  property  by  which  the  cells  of  the  Animal  or 
Vegetable  structure  are  enabled  to  perform  it,  is  one  of  which  we  are  not  likely 
ever  to  know  more.     It  will  probably  long  remain  an  ultimate  fact  in  Physio- 
logy, that  cells  have  the  power  of  growing  from  germs,  of  undergoing  certain 
transformations,  and  of  producing  germs  that  will  develop  other  cells  similar 
to  themselves  ; — just  as  it  is  an  ultimate  fact  in  Physics,  that  masses  of  matter 
attract  each  other ;  or  in  Chemistry,  that  the  molecules  of  different  substances 
have  a  tendency  to  unite  so  as  to  form  a  compound  different  from  either  of  the 
elements.     It  is  of  such  ultimate  facts  as  these  that  the  science  of  Vitality 
essentially  consists  ;  since  the  Physical  and  Chemical  phenomena  which  occur 
in  living  bodies  are  not  strictly  removable  from  the  laws  of  Inorganic  Nature. 
The  conditions  under  which  this  Assimilating  power  operates,  however,  are 
freely  open  to  our  investigation ;  and  it  is  a  great  step  in  the  progress  of  the 
inquiry,  to  become  aware  that  these  are  so  closely  conformable  throughout  the 
organized  world,  as  they  have  been  shown  to  be.     It  may  be  stated  as  a  general 
fact,  that  in  assimilating,  or  converting  into  its  own  substance,  matter  which 
was  previously  unable  to  exhibit  any  of  the  manifestations  of  life,  every  cell 
thereby  participates  in  the  process  of  organization  and  vitalization ;  for,  by 
the  new  circumstances  in  which  the  matter  is  placed,  its  properties  undergo  a 
change, — or,  to  speak  more  correctly,  properties  which  were  previously  dor- 
mant are  caused  to  manifest  themselves.     No  matter  that  is  not  in  a  state  of 
Organization  can  exhibit  those  properties  which,  from  their  being  peculiar  to 
living  bodies,  and  altogether  different  from  Physical  and  Chemical,  are  termed 
Vital;  and  it  may  also  be  asserted  that  no  matter  which  exhibits  perfect 
organization,  is  destitute  of  the  peculiar  vital  properties  belonging  to  its  kind 
of  structure.*     As  a  corollary  to  this  general  fact,  it  may  be  stated  that  no 
organism  can  be  produced  by  any  fortuitous  combination  of  inorganic  matter ; 
since,  even  for  the  generation  of  the  simplest  cell,  there  is  required  a  cell 
previously  existing,  to  furnish  the  germ. 

562.  But  this  view  also  leads  us  to  admit  greater  probability  to  the  idea 
that  beings  of  the  highest  degree  of  organization  may,  by  a  perversion  of  their 
assimilating  processes,  give  origin  to  structures  of  a  lower  grade ;  and  it  is 
difficult  to  say  that  this  is  not  the  case  in  certain  diseases  with  which  the 

*  For  a  fuller  consideration  of  this  question,  and  the  grounds  upon  which  this  view  is 
supported,  the  reader  is  referred  to  the  Article  Life  in  the  Cyclopaedia  of  Anatomy  and 
Physiology ;  and  to  the  Chapter  on  the  «  Nature  and  Causes  of  Vital  Actions,"  in  his 
Principles  of  General  and  Comparative  Physiology. 


ELABORATION  OF  CHYLE  AND  LYMPH.  423 

medical  man  is  familiar.  Thus,  in  the  various  forms  of  Cancer,  it  has  been 
shown  by  Miiller  and  others,  that  the  new  growth  consists  of  a  mass  of  cells ; 
which,  like  the  Vegetable  Fungi,  develop  themselves  with  great  rapidity ; 
and  which  destroy  the  surrounding  tissues  by  their  pressure,  as  well  as  by 
abstracting  from  the  blood  the  nourishment  which  was  destined  for  them. 
These  parasitic  masses  have  a  completely  independent  power  of  growth  and 
reproduction ;  and  it  seems  difficult  to  refuse  them  the  title  of  distinct  exist- 
ences. They  can  be  propagated  by  inoculation,  which  conveys  into  the 
tissues  of  the  animal  operated  on  the  germs  of  the  peculiar  cells  that  constitute 
this  morbid  growth  ;  and  these  soon  develop  themselves  into  a  new  mass. 
It  seems  to  be  by  the  diffusion  of  the  germs  produced  in  one  part  through  the 
whole  fabric,  by  the  circulating  current,  that  the  tendency  to  re-appearance 
(which  is  one  great  feature  in  the  malignant  character  of  these  diseases)  is 
occasioned.  Yet  there  is  no  evidence  that  the  first  production  of  a  Cancerous 
growth  is  due  to  germs  introduced  from  without ;  in  fact,  as  it  appears  to  the 
Author,  the  history  of  its  origin,  as  well  as  the  analogy  of  similar  cases,  makes 
it  far  more  probable  that  the  Cancer-cell  is  but  a  degenerated  form  of  the  ordi- 
nary tissue  of  the  body, — being,  in  fact,  a  cell  which  possesses,  to  an  unusual 
degree,  the  power  of  reproduction  instead  of  undergoing  those  transformations 
by  which  it  would  be  converted  into  other  kinds  of  tissue  (§  645).  Several 
instances  have  been  recently  published  of  the  occurrence  of  Vegetable  organ- 
isms as  parasites  upon  the  Animal  body  ;  that  in  some  of  these  a  true  Plant, 
possessing  a  regular  apparatus  of  nutrition  and  reproduction,  has  arisen  from 
a  germ  introduced  from  without,  there  can  be  little  question ;  but  in  other 
instances  (as  in  the  case  of  the  crusts  of  Porrigo  favosa]  it  has  been  assumed 
that  the  organization  is  Vegetable,  because  it  consists  of  a  mass  of  cells  capable 
of  extending  themselves  by  the  ordinary  process  of  multiplication.  But  it 
must  be  remembered  that  the  cellular  organization  is  common  to  Animals  as 
well  as  to  Plants ;  being  the  only  form  that  manifests  itself  at  an  early  period 
of  development  in  either  kingdom ;  and  remaining  throughout  life  in  those 
parts,  which  have  .not  undergone  a  metamorphosis  for  special  purposes. , 
Hence  to  speak  of  Porrigo  favosa,  or  any  similar  disease,  as  produced  by  the 
growth  of  a  Vegetable  within  the  Animal  body,  appears  to  the  Author  a  very 
arbitrary  assumption ;  the  simple  fact  being,  in  regard  to  this  and  many  other 
structures  of  a  low  type,  that  they  present  the  simplest  or  most  general  kind 
of  organization.*  Their  nature  must  generally  be  decided  by  their  Chemical 
constitution  (§  16)  ;  and  this,  in  the  case  of  the  Porrigo  favosa,  appears  to  be 
unquestionably  Animal. 

III.  Elaboration  of  Chyle  and  Lymph. 

563.  The  Chyle,  as  first  absorbed  in  the  Lacteals,  is  very  different,  both  in 
its  physical  and  chemical  characters,  from  that  which  may  be  obtained  from 
the  larger  absorbent  trunks,  and  from  the  Thoracic  Duct ;  for  during  its  pas- 
sage through  these  vessels,  and  their  ganglia  or  glands,  it  undergoes  important 
alterations,  which  gradually  assimilate  it  to  Blood.  The  chyle  drawn  from 
the  lacteals  that  traverse  the  intestinal  walls,  contains  Albumen  in  a  state  of 
complete  solution  (§  467) ;  and  it  is  entirely  destitute  of  the  power  of  coagula- 
tion, no  fibrin  being  present  in  it.  The  Salts,  also,  are  completely  dissolved ; 
but  the  Oily  matter  presents  itself  in  the  form  of  globules  of  variable  size.t  It 

*  The  Author  is  strongly  inclined  to  bel'ieve  that  the  propagation  of  many  diseases  by 
inoculation,  essentially  consists  in  the  implanting  of  cell-germs  from  one  animal  in  the 
body  of  another.  The  structure  of  the  Vaccine  Vesicle  appears  to  him  to  point  clearly 
to  such  a  view. 

f  These  oily  globules  are  more  abundant  in  the  Chyle  of  Man  and  of  the  Carnivora, 


424  OF  NUTRITION. 

is  generally  supposed  that  the  milky  colour  of  the  chyle  is  owing  to  these ;  but 
Mr.  Gulliver  has  recently  pointed  out*  that  it  is  really  due  to  an  immense  mul- 
titude of  far  more  minute  particles,  which  he  describes  as  forming  the  mole- 
cular base  of  the  chyle.  These  molecules  are  most  abundant  in  rich,  milky, 
opaque  chyle ;  and  in  poorer  chyle,  which  is  semi-transparent  or  opaline,  the 
particles  float  thinly  or  separately  in  the  transparent  fluid,  and  often  exhibit 
the  vivid  motions  common  to  the  most  minute  molecules  of  various  substances. 
Such  is  their  minuteness,  that,  even  with  the  best  instruments,  it  is  impossible 
to  form  an  exact  appreciation  either  of  their  form  or  their  dimensions.  They 
seem,  however,  to  be  generally  spherical ;  and  their  diameter  may  be  estimated 
at  between  1 -36,000th  and  1 -24,000th  of  an  inch.  Their  chemical  nature  is 
as  yet  uncertain :  they  are  remarkable  for  their  unchangeableness,  when  sub- 
jected to  the  action  of  numerous  other  re-agents,  which  quickly  affect  the 
proper  Chyle-corpuscles ;  and  they  are  readily  soluble  in  Ether,  the  addition 
of  which  causes  the  whole  molecular  base  instantly  to  disappear,  not  a  particle 
of  it  remaining ;  whence  it  may  be  inferred  that  they  consist  of  oily  or  fatty 
matter.  The  milky  colour,  which  the  serum  of  blood  sometimes  exhibits,  is 
due  to  an  admixture  of  this  molecular  base ;  it  is  most  common  in  young  ani- 
mals that  are  suckling;  but  it  is  not  uncommon  in  adults,  and  is  not  to  be 
attributed  to  an  absorption  of  milk  into  the  chyle,  as  the  physical  properties  of 
the  two  are  quite  different.. 

564.  During  the  passage  of  the  Chyle  through  the  absorbents  on  the  intes- 
tinal edge  of  the  Mesentery,  towards  the  Mesenteric  Glands,  its  character 
changes  in  several  important  particulars.  The  presence  of  Fibrin  begins  to 
manifest  itself,  by  the  slight  coagulability  of  the  fluid  when  withdrawn  from 
the  vessels ;  and  while  this  ingredient  increases,  the  Albumen  and  the  Oil- 
globules  gradually  diminish  in  amount.  The  Chyle  drawn  from  the  neigh- 
bourhood of  the  mesenteric  glands  exhibits  the  Corpuscles  regarded  as  charac- 
teristic of  that  fluid ;  these  are  peculiarly  abundant  in  the  fluid  drawn  from 
the  glands  themselves ;  and  they  are  constantly  found  in  it,  through  its  whole 
subsequent  course.  The  Chyle-corpuscles  are  much  larger  than  the  molecules 
just  described,  and  an  examination  of  their  characters  presents  no  difficulty. 
The  diameter  varies  from  1-71 10th  to  l-2600th  of  an  inch;  the  average  being 
about  l-4600th.  They  are  usually  minutely  granulated  on  ths  surface,  seldom 
exhibiting  any  nuclei,  even  when  treated  with  acetic  acid;  but  sometimes 
three  or  four  central  particles  may  be  distinguished  within  them.  During  the 
passage  of  the  Chyle  through  the  mesenteric  glands,  a  further  increase  in  the 
proportion  of  Fibrin  takes  place ;  and  the  resemblance  of  the  fluid  to  blood 
becomes  more  apparent.  The  Chyle  drawn  from  the  vessels  intermediate 
between  these  and  the  central  duct,  possesses  a  pale  reddish-yellow  colour ; 
and,  when  allowed  to  stand  for  a  time,  undergoes  a  regular  coagulation,  sepa- 
rating into  dot  and  serum.  The  former  is  a  consistent  gelatinous  mass,  which, 
when  examined  with  the  microscope,  is  found  to  include  the  Chyle-corpuscles, 
each  of  them  being  surrounded  by  a  delicate  film  of  oil:  the  Fibrin  of  which 
it  is  principally  composed,  differs  remarkably  from  that  of  the  blood,  in  its  infe- 
rior tendency  to  putrefaction ;  whence  it  may  be  inferred  that  it  has  not  yet 
undergone  its  complete  vitalization.  The  serum  contains  the  Albumen  and 
Salts  in  solution,  and  a  proportion  of  the  Chyle-corpuscles  suspended  in  it.  It 
is  curious,  however,  that  considerable  differences  in  the  perfection  of  the  coagu- 
lation, and  in  its  duration,  should  present  themselves  in  different  experiments. 
Sometimes  the  chyle  sets  into  a  jelly-like  mass,  which,  without  any  separation 
into  coagulum  and  serum,  liquefies  again  at  the  end  of  half  an  hour,  and 

than  in  that  of  the  Herbivora;  their  diameter  has  been  observed  to  vary  from  l-25,000th 
to  l-2000th  of  an  inch. 
*  Dublin  Medical  Press,  Jan.  1,  1840,  and  Gerber's  General  Anatomy,  Appendix,  p.  88. 


ELABORATION  OF  CHYLE  AND  LYMPH.  425 

remains  in  this  state.  This  change  takes  place  in  the  true  coagulum  also,  if  it 
be  kept  moist  for  a  sufficient  length  of  time.  The  Chyle  from  the  Recepta- 
culum  and  Thoracic  Duct  coagulates  quickly,  often  almost  instantaneously ; 
and  few  or  none  of  the  corpuscles  remain  in  the  serum. 

565.  It  is  to  be  remembered  that  the  Lacteals  are  the  Lymphatics  of  the 
intestinal  walls  and  mesentery ;  performing  that  function  of  Interstitial  Absorp- 
tion, which  is  elsewhere  accomplished  by  vessels  that  are  not  concerned  in  the 
introduction  of  alimentary  substances  from  without.  During  the  intervals  of 
digestion,  they  contain  a  fluid  which  is  in  all  respects  conformable  to  the 
Lymph  of  the  Lymphatic  trunks. — The  aspect  of  the  Lymph  greatly  differs 
from  that  of  the  Chyle,  the  former  being  nearly  transparent,  whilst  the  latter 
is  opaque  or  opalescent ;  and  this  difference  is  readily  accounted  for,  when  the 
assistance  of  the  microscope  is  sought,  by  the  entire  absence  from  the  Lymph 
of  that  molecular  base  which  is  so  abundant  in  the  Chyle,  A  considerable 
number  of  corpuscles  are  generally  present  in  it ;  and  these  seem  to  corre- 
spond in  all  respects  with  the  white  or  colourless  corpuscles  of  the  Blood  (§  577). 
Their  amount,  however,  is  extremely  variable  ;  as  is  also  that  of  the  oil-glob- 
ules, which  sometimes  occur,  whilst  in  other  instances  none  can  be  discovered. 
Lymph  coagulates  like  chyle ;  a  colourless  61ot  being  formed,  which  encloses 
the  greater  part  of  the  corpuscles. 

560.  The  nature  and  source  of  the  peculiar  globules  of  the  Chyle,  are  as  yet 
matters  of  doubt;  some  light,  however,  has  been  thrown  on  their  history,  by 
recent  investigations ;  and  much  may  be  said  of  them,  which,  if  not  absolutely 
proved,  can  scarcely  be  regarded  as  improbable.  The  process  of  their  forma- 
tion bears  a  striking  analogy  to  that  of  the  cytoblasts  of  Plants,  as  observed  by 
Schleiden  (§  557).  They  appear  in  the  midst  of  a  fluid  crowded  with  minute 
granules,  and  appear  to  be  themselves  at  first  composed  of  an  aggregation  of 
smaller  particles.  Various  stages  of  development  present  themselves,  how- 
ever, in  these  bodies ;  and  the  larger  ones,  which  are  chiefly  to  be  met  with 
in  the  Thoracic  Duct,  are  evidently  cells,  bearing  a  strong  resemblance  to  the 
Lymph-corpuscles,  and  to  the  Colourless  corpuscles  of  the  blood.  Like  the 
latter,  they  contain  three  or  four  large  central  particles,  which  are  distinctly 
brought  into  view,  when  they  are  treated  with  acetic  acid.  Their  diameter, 
too,  is  about  the  same ;  being  usually  between  the  1 -2600th  and  the  1 -2900th 
of  an  inch,  or  rather  larger  than  the  Red  corpuscles  of  Human  blood.  It  will 
be  hereafter  pointed  out,  that  there  is  strong  reason  to  believe  their  functions 
to  be  the  same  (§  578). 

567.  The  changes  which  the  Chyle  is  observed  to  undergo,  in  its  passage 
from  the  Intestinal  villi  to  the  Thoracic  Duct,  suggest  some  inferences  in  regard 
to  the  possible  transformation  of  Fatty  matter  into  a  Protein-compound.  That 
the  Chyle-corpuscles  are  not  identical  in  chemical  composition  with  the  Mole- 
cular base  is  quite  certain,  from  the  completely  different  effects  of  re-agents 
upon  the  two  respectively;  but  it  maybe  surmised  that,  as  they  appear  to 
consist  of  an  altered  form  of  Albumen,  the  soluble  Albumen  and  the  Fatty 
matter  are  both  concerned  in  their  production.  It  has  been  stated  that,  whilst 
the  Fibrin  increases,  the  Oil-globules  undergo  an  evident  diminution  (§  564), 
and  that  the  quantity  of  Albumen  lessens.  It  is  not  conceivable  that  the 
Fibrin  should  be  at  once  formed  at  the  expense  of  the  Oil-globules ;  since 
Albumen,  which  is  a  mere  chemical  compound,  ready  to  undergo  organization 
and  vitalization,  is  always  the  preceding  grade.  The  Fibrin  must,  therefore, 
be  produced  at  the  expense  of  the  Albumen ;  whilst  new  Albumen  is  elabo- 
rated from  the  Oily  matter.  Of  the  process  by  which  the  latter  important 
change  is  accomplished,  we  are  yet  entirely  ignorant ;  but  the  evident  altera- 
tion which  takes  place  in  the  proportion  of  azotized  ingredients  would  seem  to 
show,  that  Nitrogen  is  in  some  manner  communicated  to  the  Chyle  during  its 

36* 


426  OF  NUTRITION. 

progress  along  the  Lacteals.  No  source  for  this  nitrogen  can  be  suggested 
except  the  Blood:  and  the  influence  of  the  blood  upon  the  contents  of  the 
absorbent  vessels,  must  be  in  part  communicated  through  the  vasa  vasorum 
distributed  upon  their  walls,  (since  in  the  cold-blooded  Vertebrata  there  are  no 
lymphatic  glands,)  but  chiefly  in  the  Lymphatic  Glands,  where  the  blood-ves- 
sels and  absorbents  come  into  extremely  close  relation.  The  idea  that  the 
Blood  is  deprived,  in  the  Mesenteric  vessels,  of  fcome  of  its  azote,  seems  to 
derive  important  confirmation  from  the  fact,  that  the  secretion  of  the  Liver, 
which  is  chiefly  formed  from  blood  that  has  returned  from  these  vessels,  con- 
sists almost  entirely  of  unazotized  ingredients  (Chap.  xn.).  It  may  be  con- 
ceived, then,  that  whilst  the  Albuminous  matter  originally  present  in  the  Chyle 
is  being  converted  into  Fibrin,  new  Albumen  is  being  formed  at* the  expense  of 
the  Fatty  matter.  The  same  account  is  applicable  to  the  Lymphatics,  a  part  of 
whose  functions  it  is,  to  bring  the  oily  matter  stored  up  in  the  Adipose  tissue 
within  the  sphere  of  the  nutritive  operations  (§  468) ;  and  the  variation  in  the 
circumstances  which  may  render  this  necessary,  fully  accounts  for  the  varia- 
tion in  the  amount  of  Oily  and  Albuminous  matter  presenting  itself  in  this 
fluid.— It  must  be  acknowledged,  however,  that  the  views  here  offered  are  in 
great  part  hypothetical.  They  derive  some  confirmation,  however,  from  the 
circumstance— recently  pointed  out  by  Mr.  G.  Ross,*— -that  the  constituents  of 
fatty  matter,  added  to  those  of  uric  acid,  would  very  nearly  give  the  atomic 
constituents  of  albumen;  whence  it  might  be  surmised  that,  when  there  is  a 
demand  for  Protein-compounds  in  the  system,  azotized  matter,  which  would 
otherwise  be  excreted,  may  be  united  with  non-azotized  compounds  taken  in 
as  food,  in  order  to  supply  its  wants.  The  fact,  which  constitutes  an  important 
feature  in  the  Physiology  of  Secretion  (§  648),  that  a  separation  of  Protein- 
compounds  into  two  such  classes  of  bodies  is  continually  taking  place  in  the 
living  economy,  would  seem  to  render  the  possibility  of  their  union  greater. — 
An  important  source  of  fallacy,  however,  attends  all  deductions  founded  upon 
the  differences  observed  in  the  Chyle  in  the  several  parts  of  its  course  through 
the  Lacteals;  viz.,  that  we  cannot  be  at  all  sure  how  far  this  is  dependent  upon 
an  actual  interchange  of  ingredients  with  the  Blood,  taking  place  by  Imbibition 
or  Endosmose  through  the  very  thin  parietes  of  the  contiguous  vessels.  The 
whole  question  offers  a  very  wide  scope  for  further  inquiry. 

568.  The  fluid  drawn  from  the  Thoracic  Duct,  and  from  the  Absorbent  ves- 
sels which  empty  their  contents  into  it,  is  frequently  observed  to  present  a 
decided  red  tinge,  which  increases  on  exposure  to  the  air.  This  tinge  is  due 
to  the  presence  of  true  Blood-corpuscles ;  but  these  are  somewhat  modified  in 
form  and  size,  being  a  little  smaller  than  the  ordinary  Blood-discs,  and  fre- 
quently angular,  granulated,  or  indented  at  the  edges.  By  Mr.  Lanet  it  is 
stated  that  this  intermixture  is  accidental ;  and  that  it  results  from  the  absorp- 
tion of  Blood-particles  into  the  Lymphatics,  at  the  points  where  the  latter  are 
divided,  in  making  the  sections  necessary  to  expose  the  centres  of  the  Absorbent 
system :  and  he  mentions  a  striking  fact  in  illustration  of  his  view.  He  con- 
siders that  the  alteration  in  the  character  of  the  corpuscles  is  due  to  the  action 
of  the  Chyle  on  the  Blood,  since  many  other  fluids  will  produce  analogous 
effects ;  and  he  states  that  shortly  after  a  flow  of  chyle  into  the  blood,  a  large 
number  of  such  altered  discs  may  be  seen  in  the  circulating  fluid.  On  the 
other  hand,  Mr.  Gulliver  and  several  eminent  observers,  regard  these  blood- 
discs  as  true  constituents  of  the  fluid  of  the  absorbents  ;  and  suppose  that  they 
are  in  process  of  formation.  Reasons  will  hereafter  be  given,  however,  for 
the  belief  that  the  red  Blood-discs  are  not  formed  from  the  Chyle-corpuscles ; 

*  Lancet,  1842-3,  vol.  i. 

f  Cyclopaedia  of  Anatomy  and  Physiology,  vol.  iii.  p.  220. 


PROPERTIES  OF  THE  BLOOD.  427 

so  that  Mr.  Lane's  view  is  probably  the  correct  one.  Even  if  the  Blood-discs 
are  not  introduced  into  the  Lymphatics  during  the  operation  of  exposing  tha 
Thoracic  Duct,  it  may  not  be  considered  as  improbable  that,  in  those  animals 
in  which  the  Lymphatics  have  several  communications  with  the  Veins,  they 
should  naturally  obtain  an  entrance  in  various  parts  of  the  system.  Such 
communications,  according  to  Gerber,  decidedly  exist  in  the  Horse  ;  and  it  is 
in  the  Chyle  of  that  animal,  that  the  rosy  tint,  and  the  Blood-corpuscles  which 
occasion  it,  have  been  chiefly  observed. 

509.  The  following  table,  slightly  modified  from  that  of  Gerber,  presents 
in  a  concise  form,  a  view  of  the  relative  proportions  of  the  three  chief  ingre- 
dients in  the  Chyle,  in  different  parts  of  the  absorbent  system,  and  thus  gives 
an  idea  of  its  advance  in  the  process  of  assimilation. 

In  the  afferent  or  periphe-  ("Fat,  in  maximum  quantity  (numerous  fat  or  oil 

ral  Lacteals  (from  the  In-J      globules> 

xi v    T./T  •  <  Albumen  m  minimum  quantity. 

SET)  Few  or  no  chyle-COTP«scks- 

In  the  efferent  or  central 
LacteaJs  (from  the  Me- 
senteric  glands  to  the 
Thoracic  Duct). 


In  the  Thoracic  Duct. 


JFibrin,  almost  entirely  wanting. 

"Fat,  in  medium  quantity  (fewer  oil-globules). 

Albumen,  in  maximum  quantity. 

Chyle-corpuscles  very  numerous,  but  imperfectly 
developed. 

_Fibrin,  in  medium  quantity. 

"Fat,  in  minimum  quantity  (fewer  or  no  oil- 
globules). 

Albumen,  in  medium  quantity. 

Chyle-corpuscles  numerous,  and  more  distinctly 
cellular. 

_Fibrin,  in  maximum  quantity. 


IV.  Physical  and  Vital  Properties  of  the  Blood. 

570.  The  Blood,  whilst  circulating  in  its  vessels,  is  composed  of  a  fluid,  in 
which  a  large  number  of  corpuscles  or  particles  of  a  red  colour  are  suspended. 
The  fluid  portion,  which  is  known  under  the  name  of  Liquor  Sanguinis, 
essentially  consists  of  Fibrin  and  Albumen,  with  Saline  matter,  dissolved  in 
water ;  and  this,  when  effused  without  an  intermixture  of  corpuscles,  is  known 
under  the  name  of  Coagulable  Lymph.  The  red  Blood-particles  (commonly, 
but  erroneously,  termed  globules]  are  flattened  discs,  which,  in  Man  and  most 
of  the  Mammalia,  have  a  distinctly  circular  outline.  In  the  discs  of  Human 
blood,  when  examined  in  its  natural  condition,  the  sides  are  somewhat  con- 
cave ;  and  there  is  a  bright  spot  in  the  centre,  which  has  been  regarded  by 
many  as  indicating  the  existence  of  a  nucleus,  although  it  is  in  reality  due 
simply  to  the  greater  thinness  of  the  disc  at  that  part.  The  form  of  the  disc 
is  very  much  altered  by  various  reagents ;  for  the  membrane  which  composes 
its  exterior  is  readily  permeable  by  fluids ;  so  that,  if  the  discs  be  put  into 
water,  a  powerful  endosmose  takes  place  towards  the  interior,  causing  the 
particles  to  assume  a  globular  form ;  whilst,  if  they  be  treated  with  syrup,  or 
with  a  thick  solution  of  albumen,  they  will  be  more  or  less  completely  emptied, 
so  as  to  present  a  shrunken  appearance.  Hence,  in  examining  the  Blood,  it  is 
necessary  to  dilute  it  with  a  fluid  as  nearly  as  possible  of  the  same  character 
with  ordinary  serum.*  In  regard  to  the  existence  of  a  nucleus  in  the  corpus- 

*  By  Wagner,  the  filtered  serum  of  frog's  blood  is  recommended  for  this  purpose. 
Weak  solutions  of  salt  or  sugar,  and  urine,  answer  tolerably  well ;  but  Mr.  Gulliver  re- 
marks that  all  addition  must  be  avoided  when  it  is  intended  to  measure  the  corpuscles, 


428 


OF  NUTRITION. 


Fig.  100. 


Corpuscles  of  Human  Blood,  magnified  about  500 
diameters;  A,  single  red  particles;  1,  1,  their  flattened 
face;  2,  a  particle  seen  edgeways,  three-quarter  view; 
B,  aggregation  of  particles  in  a  columnar  form;  c,  co- 
lourless corpuscles.  (After  Wagner.) 


Fig.  101. 


cles  of  Mammalia,  there  has  been 
considerable  difference  of  opinion 
amongst  microscopists ;  some  main- 
taining that  it  can  be  brought  into 
view  by  treating  them  with  acetic 
acid,  whilst  others  deny  that  any  de- 
finite appearance  is  thus  produced. 
The  researches  of  Mr.  Gulliver  and 
Mr.  Wharton,  however,  appear  to 
the  Author  quite  conclusive  as  to 
the  non-existence,  in  the  red  parti- 
cles of  Mammalia  (even  in  the  oval 
discs  of  the  Camelidas),  of  any  thing 
at  all  analogous  to  the  nucleus, 
which  is  to  be  seen  in  the  blood- 
discs  of  Oviparous  Vertebrata.  The 
corpuscles,  when  emptied  of  their  coloured  contents  by  the  action  o'f  water, 
exhibit  no  trace  of  it  in  Mammalia ;  though  the  same  process  brings  them 
clearly  into  view  in  the  oval  blood-discs  of  all  other  Vertebrata.  The  central 
matter  in  the  Mammiferous  blood-disc,  which  undergoes  coagulation  under  the 
influence  of  acetic  acid,  is  therefore  not  to  be  regarded  as  a  true  cell-nucleus, 
which  is  evidently  the  character  of  the  central  spot  on  other  blood-discs ;  but 
is  rather  a  collection  of  albuminous  particles,  which  are  coagulated  by  the 
action  of  the  acid  upon  them,  just  as  they  would  be  in  the  liquor  sanguinis  or 
in  the  serum  of  the  blood. 

571 .  In  all  Oviparous  Vertebrata, 
without  any  known  exception,  the 
red  corpuscles  are  oval,  the  propor- 
tion between  their  long  and  short 
diameters,  however,  being  much 
subject  to  variation  ;  and  their  nu- 
clei may  always  be  brought  into 
view  by  treatment  with  acetic  acid, 
when  not  at  first  visible.  In  the 
red  particles  of  the  Frog,  which  are 
far  larger  than  those  of  Man,  a  nu- 
cleus can  be  observed  to  project 
somewhat  from  the  central  portion 
of  the  oval,  even  during  their  circu- 
lation, and  it  is  rendered  extremely 
distinct  by  the  action  of  acetic  acid ; 
this  dissolves  away  the  remainder  of  the  particle  and  gives  an  increased 
opacity  to  the  nucleus,  which  is  then  seen  to  consist  of  a  granular  substance. 
In  the  still  larger  blood-disc  of  the  Proteus  and  Siren,  this  appearance  is  yet 
more  distinct ;  the  structure  of  the  nucleus  being  so  evident,  without  the  addi- 
tion of  acetic  acid,  that  its  granules  can  be  counted.* 

or  to  ascertain  their  true  forms;  as  the  serum  of  one  Mammal  reacts  injuriously  on  the 
blood  of  another.     See  Philos.  Magaz.,  Jan.  and  Feb.,  1840. 

*  As  Professor  Owen's  interesting  account  of  the  blood-discs  of  the  Siren  may  not  be 
generally  accessible  (Penny  Cyclopedia,  Art.  Siren'),  the  leading  facts  in  it  will  be  here 
stated.  This  animal  agrees  with  the  Proteus  and  other  species  in  being  perenni branchi- 
ate (§43);  and,  as  in  all  its  congeners  yet  examined,  the  blood-discs  are  of  very  large 
dimensions.  They  are  usually  of  an  oval  form,  the  long  diameter  being  nearly  twice  the 
short;  and  the  nucleus  projects  slightly  from  each  of  the  flattened  surfaces.  Considera- 
ble variety  in  the  form  of  the  disc  presented  itself,  some  of  the  corpuscles  being  much 
less  oval  than  others;  but  the  nucleus  did  not  partake  of  these  variations  in  nearly  the 


Particles  of  Frogs  Blood;  1. 1.  their  flattened  face; 
2,  particle  turned  nearly  edgeways  ;  3,  lymph-globule  ; 
4,  blood-corpuscles,  altered  by  dilute  acetic  acid.  Mag- 
nified 500  diameter.  (After  Wagner.) 


PROPERTIES  OF  THE  BLOOD.  429 

572.  The  form  of  the  Red  Corpuscles  is  not  unfrequently  seen  to  change 
during  their  circulation  ;  but  this  is  generally  in  consequence  of  pressure,  from 
the  effects  of  which,  however,  they  quickly  recover  themselves.  In  the  narrow 
capillary  vessels,  they  sometimes  become  suddenly  elongated,  twisted,  or  bent, 
through  a  narrowing  of  the  channel ;  and  this  may  take  place  to  such  a  degree 
as  to  enable  the  disc  to  pass  through  an  aperture  which  appears  very  minute 
in  proportion  to  its  diameter.*  When  undergoing  spontaneous  decomposition, 
the  blood-discs  become  granulated,  and  sometimes  (as  long  ago  noticed  by 
Hewson),even  mulberry-shaped  ;  and  particles  in  which  these  changes  appear 
to  be  commencing  may  be  found  in  the  blood  at  all  times.  It  has  been  ascer- 
tained that  bile  and  urea  exert  a  peculiar  solvent  power  on  the  blood-corpuscles ; 
and  hence  we  can  understand  one  of  the  modes  in  which  a  retention  of  these 
substances  in  the  circulating  fluid  (§  649)  proves  so  injurious.  The  size  of  the 
blood-discs  is  liable  to  considerable  variation,  even  in  the  same  individual ;  and 
this  is  at  once  understood  when  they  are  considered  as  cells  in  different  stages 
of  growth.  There  are,  however,  limits  to  this  variation  for  each  species  ;  and 
the  blood-discs  of  one  tribe  of  Mammalia  can  rarely  be  confounded  with  those 
of  another.  The  diameter  of  the  corpuscles  bears  no  constant  relation  to  the 
size  of  the  animal,  even  within  the  limits  of  the  same  class ;  thus,  although 
those  of  the  elephant  are  the  largest  among  Mammalia  (as  far  as  is  hitherto 
known),  those  of  the  Mouse  tribe  are  far  from  being  the  smallest,  being  in  fact 
more  than  three  times  the  diameter  of  those  of  the  Musk  Deer,  there  is, 
however,  a  more  uniform  relation  between  the  size  of  the  animal  and  that  of 
its  blood-discs,  when  the  comparison  is  made  within  the  limits  of  the  same 
order.  In  man,  the  diameter  varies  from  about  l-4000th  to  l-2800th  of  an 
inch ;  the  average  diameter  is  probably  about  1 -3400th. 

a.  The  following  measurements  of  the  blood-discs  of  various  animals,  are  chiefly 
given  on  the  authority  of  Mr.  Gulliver. — The  diameter  of  the  corpuscles  in  the  Quad- 
rumana  is  generally  about  the  same  with  that  of  the  Human  blood-discs;  there  is,  how- 
ever, a  slight  diminution  among  the  Lemurs,  and  there  is  more  variation  among  them, 
than  among  the  Monkeys.  Among  the  Cheiroptera,  the  diameter  of  the  corpuscles  is 
somewhat  less  than  in  the  preceding  order,  the  average  being  about  l-4300th  of  an  inch. 
The  blood-discs  of  the  Mole  are  still  smaller,  averaging  only  the  l-4750th  of  an  inch; 
those  of  the  Hedge-hog,  however,  are  larger,  being  about  l-4100th.  Among  the  Planti- 
grade Carnivora,  the  average  is  about  l-3800th,  and  from  this  none  depart  very  widely: 
but  among  the  Digitigrade  species  there  is  a  considerable  range;  in  the  Weasel  tribe, 
the  average  is  about  l-4800th ;  in  the  Feline,  it  is  about  l-4400th ;  in  the  Dog  tribe,f  there 
is  a  range  of  averages  from  l-3400th  to  l-4100th ;  and  in  the  Seal,  the  average  is  about 
l-3300th.  Observations  on  the  blood-discs  of  the  Cetacea  are  much  required.  Among 
the  Pachyderrnata,  the  average,  excluding  the  Elephant  (the  diameter  of  whose  blood- 
same  degree.  The  nucleus  is  clearly  seen  to  consist  of  a  number  of  moderately-bright 
spherical  granules,  of  which  from  20  10  30  could  be  seen  in  one  plane  or  focus,  the  total 
number  being  of  course  much  greater.  When  removed  from  the  capsule,  the  nuclei  are 
colourless,  and  the  component  granules  have  a  high  refracting  power.  Viewed  in  situ, 
they  present  a  tinge  of  colour  lighter  than  that  of  the  surrounding  fluid,  and  dependent 
upon  the  thin  layer  of  that  fluid  interposed  between  the  nucleus  and  the  capsule.  As  the 
fluid  contents  of  the  blood-disc  in  part  evaporate  during  the  process  of  desiccation,  the 
capsule  falls  into  folds  in  the  interspace  between  the  nucleus  and  the  outer  margin;  these 
folds  generally  take  the  direction  of  straight  lines,  three  to  seven  in  number,  radiating 
from  the  nucleus. 

*  "  Blood-corpuscles  are  repeatedly  found,  quite  unaltered  in  appearance,  on  the  mucous 
surfaces,  when  no  solution  of  continuity  whatever  can  be  detected  in  the  vessels."  Gul- 
liver, in  Gerb.  Gen.  Anat.,  p.  78. 

f  Two  facts  of  much  interest  in  Zoology  have  been  brought  to  light  by  Mr.  Gulliver's 
examination  of  the  diameter  of  the  blood-corpuscles  of  this  tribe.  The  difference  between 
those  of  the  Dog  and  Wolf  is  not  greater  than  that  which  exists  among  the  varieties  of 
the  Dog,  whilst  the  discs  of  the  Fox  are  much  smaller.  The  discs  of  the  Hyaena  are  far 
more  approximate  to  those  of  the  Canidae  than  they  are  to  those  of  the  Felidae. 


430  OF  NUTRITION. 

discs  is  about  l-2745th  of  an  inch),  and  the  Rhinoceros  (in  which  they  are  about  l-3765th), 
may  be  stated  at  about  l-4200th;  and  there  is  les*  variation  than  might  have  been  ex- 
pected, from  the  different  size  and  conformation  of  the  several  species  examined.  Among 
the  Ruminantia,  the  corpuscles  are  for  the  most  part  smaller  than  in  other  orders;  and 
there  is  more  relation  between  their  diameter  and  the  size  of  the  animal,  than  is  else- 
where observable.  Excluding  the  Camelidae  (which  are  zoologically  intermediate 
between  the  Ruminantia  and  Pachydermata),  we  find  a  range  of  sizes  extending  from  the 
l-3777th  to  the  l-12325th  of  an  inch;  the  former  is  the  diameter  in  one  of  the  larger 
Deer:  the  latter  in  the  Musk  Deer,  which  is  the  smallest  of  the  whole  order.  In  the 
Camel  tribe,  the  average  of  the  long  diameter  of  the  oval  corpuscles  is  l-3400th  of  an 
inch:  whilst  that  of  the  short  diameter  is  l-6300th;  and  this  is  no  where  widely  departed 
from:  the  length  of  the  discs  is,  therefore,  not  quite  twice  their  breadth.  Among  the 
Rodentia,  the  discs  are  rather  large,  especially  considering  the  small  size  of  most  of  the 
species.  In  the  Capybara,  which  is  the  largest  animal  of  the  order,  they  average  l-3216ih  ; 
and  in  the  Mouse  family  (the  smallest  of  Mammalia)  they  are  as  much  as  l-3800th.  In 
the  Squirrels,  the  diameter  is  rather  less;  but  in  scarcely  any  of  the  whole  order  is  it 
under  l-4000th.  Among  the  Edentata,  the  only  species  yet  examined,  is  one  of  the  Arma- 
dillos, in  which  the  diameter  of  the  corpuscles  is  about  the  same  as  in  the  Quadrumana. 
In  the  Marsupialia  the  range  is  nearly  the  same  as  among  the  Rodentia. 

b.  In  BIRDS,  according  to  the  observations  of  Mr.  Gulliver,  the  long  and  short  diameters 
of  the  corpuscles  usually  bear  to  each  other  the  proportion  of  1£  or  2,  to  1  ;  and  this  is 
the  general  relation  among  Oviparous  Vertebrata,  with  the  exception  of  some  of  the 
Crocodile  tribe,  in  which  the  length  is  sometimes  three  times  the  breadth.     The  size  of 
the  corpuscles  of  Birds  has  generally  more  relation  to  that  of  the  species,  than  in  Mam- 
malia.   No  instance  has  yet  been  detected,  of  the  occurrence  of  comparatively  small 
corpuscles  in  the  larger  species,  and  of  large  corpuscles  among  smaller  animals,  which 
has  been  seen  to  be  common  among  the  former  class;  the  blood  of  the  Humming-birds, 
however,  has  not  yet  been  examined.     The  largest  discs  are  found  among  the  Cursores  ; 
those  of  the  Ostrich  have  an  average  long  diameter  of  l-1649th  of  an  inch,  and  a  short 
diameter  of  l-3000th ;  and  among  the  larger  Raptures,  Grallatores,  and  Natatores,  the 
dimensions  are  but  little  inferior.     The  least  dimensions  hitherto  observed  are  among  the 
small  Passerine  birds;  in  which  the  corpuscles  have  a  long  diameter  of  about  l-2400th 
of  an  inch,  and  a  transverse  diameter  of  from  l-3800th  to  l-4800th.     Circular  discs  may 
be  occasionally  observed  in  some  species,  agreeing  with  the  others  in  every  particular 
but  their  form;  and  every  gradation  may  be  noticed  between  these  and  the  regular  oval 
corpuscles. 

c.  The  large  size  of  the  blood-discs  in  REPTILES,  especially  in  Batrachia,  and  above 
all,  in  the  Perennibranchiate  species  of  the  latter,  has  been  of  great  service  to  the  Phy- 
siologist; by  enabling   him   to   ascertain   many  particulars  regarding  their  structure, 
which  could  not  have  been  otherwise  determined  with  certainty.     Among  other  facilities 
which  this  occasions,  is  that  of  procuring  their  separation  from  the  other  constituents  of 
the  blood  ;  for  they  are  too  large  to  pass  through  the  pores  of  ordinary  filtering-paper, 
and  are  therefore  retained  upon  it,  after  the  liquor  sanguinis  has  flowed  through.    The 
blood-discs  of  the  warm-blooded  Vertebrata  cannot  be  thus  separated.      The  oval  cor- 
puscles of  the  Frog  have  a  long  diameter  of  about  l-1000th,  and  a  transverse  diameter 
of  about  l-lSOOth^of  an  inch;  those  of  the  Salamander  or  Water-newt,  are  rather  smaller. 
The  long  diameter  of  the  corpuscles  of  the  Proteus  is  staled  by  Wagner  at  l-337th  of  an 
inch ;  that  of  the  Siren  is  about  l-435th,  the  short  diameter  being  about  1-SOOth  of  an 
inch;  the  extremes  of  variation,  however,  are  very  wide.    The  long  diameter  of  the 
nuclei  is  about  l-1000th  or  l-l  100th,  and  the  short  diameter  about  l-2000th;  hence  it  is 
about  three  times  as  long,  and  nearly  twice  as  broad,  as  the  entire  Human  blood-disc, 
thus  having  six  times  its  superficies;  its  thickness  is  about  l-3800th  of  an  inch. 

573.  In  regard  to  the  Chemical  constitution  of  red  Blood-corpuscles,  it  is 
difficult  to  speak  with  defmiteness  ;  since  there  are  three  parts  in  each  disc 
which  are  essentially  different  in  character,  and  which  may  have  a  very  dif- 
ferent composition.  These  parts, — the  capsule,  the  nucleus,  and  the  con- 
tained matter,  cannot  be  separated  without  the  use  of  chemical  reagents,  which 
must  alter  their  respective  properties.  Two  proximate  principles  have  been 
obtained  from  the  blood-discs  :  these  are  designated  as  hssmatosine  and  globu- 
line. — To  the  h&matosin  the  red  colour  of  the  blood  is  due,  although  it  con- 
stitutes not  more  than  a  20th  or  25th  part  of  the  whole  mass  of  dried  globules. 
When  separated  from  the  globulin,  it  is  of  a  dark-brown  hue,  and  is  tasteless 
and  insoluble  in  water,  alcohol,  and  ether ;  but  is  readily  soluble  in  water  or 


PROPERTIES  OF  THE  BLOOD.  431 

alcohol  that  contain  alkalies  or  acids,  whence  it  may  be  supposed  to  unite  with 
these,  like  albumen,  as  an  acid  or  a  base.  In  composition,  however,  it  differs 
considerably  from  both  protein  and  albumen ;  its  formula  being  44  c,  22  H,  :J 
N,  6  o,  with  a  single  proportional  of  iron.  When  burned,  it  yields  a  notable 
quantity  of  peroxide  of  iron  ;  and  one  atom  of  this  is  considered  to  be  present 
in  combination  with  one  of  the  animal  compound,  which  is  analogous  to  protein. 
The  red  colour  is  not  due,  however,  as  formerly  supposed,  to  the  presence  of 
this  peroxide ;  for  M.  Scherer  has  recently  found,  that  the  metal  may  be 
entirely  dissolved  away  by  the  agency  of  acids,  and  that  the  animal  matter, 
afterwards  boiled  in  alcohol,  colours  the  spirit  intensely  red. — The  globulin, 
which  is  the  principal  constituent  of  the  corpuscles,  has  not  yet  been  isolated  ; 
but  from  its  properties  in  combination,  it  is  inferred  to  differ  but  little  from 
protein. — It  may  perhaps  be  doubted,  whether  these  two  principles  have  a 
separate  existence  ;  or  whether  they  are  not  rather  results  of  the  chemical 
processes  employed  to  obtain  them.  When  the  blood-discs  are  separated  from 
the  other  constituents  of  the  fluid,  and  are  immersed  in  water,  they  soon  absorb 
so  much  as  to  become  globular ;  and  the  continuance  of  the  endosmose  occa- 
sions the  diffusion  of  their  contents  (by  the  rupture  of  the  capsule)  through 
the  water,  in  which  the  greater  part  dissolves.  This  solution  exhibits  the 
same  changes  of  colour  under  the  influence  of  oxygen,  acids,  saline  matter, 
&c.,  as  the  blood  undergoes  in  similar  circumstances  (§  542).  When  it  is 
heated,  the  matter  of  the  globules  is  coagulated  and  forms  an  insoluble  pre- 
cipitate ;  both  in  its  soluble  and  coagulated  states,  it  exhibits  similar  effects 
with  reagents,  as  does  albumen  in  the  same  conditions. 

574.  The  question  of  the  origin  of  the  red  Blood-corpuscles  is  a  very  in- 
teresting one,  and  cannot  yet  be  regarded  as  completely  determined.  That 
they  are  to  be  regarded  as  nucleated  cells, — conformable  in  general  character 
with  the  isolated  cells,  which  constitute  the  whole  of  the  simplest  Plants 
(§  555),  and  having  each  an  independent  life  of  its  own,  there  can  now  be  no 
reasonable  doubt.  From  this  we  should  infer  that  they  have  the  power  of 
reproducing  themselves ;  and  the  recent  observations  of  Dr.  Barry  and  other 
Microscopists  have  confirmed  the  statement  long  ago  made  to  that  effect  by 
Leeuwenhoek.  The  first  change  which  takes  place  is  the  appearance  of 
delicate  radiating  lines  between  the  nucleus  and  the  periphery ;  dividing  the 
disc  into  several  segments,  usually  six  in  number  (Fig.  22,  Plate  I.).  The 
margin  is  soon  observed  to  become  crenated,  by  indentations  at  corresponding 
points ;  and  these  indentations  become  deeper,  until  a  complete  separation 
takes  place,  forming  six  young  cells  or  discs  («,  b,  c,  d,  e).  It  is  next  to  cer- 
tain that  these  are  developed  within  the  parent  cell  or  disc,  from  some  of  the 
granules  on  the  margin  of  its  nucleus ;  just  in  the  same  manner  as  rings  of 
cells  will  be  hereafter  described  (§  745)  as  arising  from  the  Germinal  Spot. 
From  this  fact,  connected  with  what  has  been  already  stated  of  the  continual 
decomposition  of  the  blood-discs  (§  572),  we  may  infer  that  each  cell  has  a 
determinate  period  of  existence  ;  and  that  whilst  some  are  decaying  from  age, 
their  place  is  being  supplied  by  young  ones  in  process  of  growth.  Between 
the  small  newly-generated  disc,  and  the  full-sized  corpuscle,  we  should  expect 
to  find  every  intermediate  size  ;  and  this  is  exactly  what  presents  itself.  That 
the  corpuscles  may  be  generated  with  great  rapidity  under  peculiar  circum- 
stances, will  hereafter  appear  (§  594) ;  and  their  amount  may  undergo  a  rapid 
diminution  also,  without  any  evident  abstraction  of  them  from  the  circulating 
fluid.  Appearances  have  been  seen  by  Wagner,  Gulliver  and  others,  in  the 
blood  of  Batrachia,  which  seem  to  indicate  that  the  Colourless  corpuscles 
(§  577)  serve  as  the  nuclei  of  cells,  which,  when  fully  developed,  may  become 
Red  blood-discs  ;  but  in  the  Mammalia  it  is  scarcely  possible  to  imagine  that 
this  can  occur ;  since  the  diameter  of  the  colourless  corpuscles  is  very  con- 


432  OF  NUTRITION. 

slant ;  whilst  that  of  the  blood-discs  is  so  variable,  that  the  former,  though 
sometimes  the  smaller,  are  in  other  instances  far  larger  than  the  latter.  If  it 
be  admitted  that  the  red  corpuscles  have  the  power  of  reproduction,  like  other 
isolated  cells,  it  does  not  seem  necessary  to  seek  elsewhere  for  the  source  of 
their  constant  renewal ;  and  various  facts,  hereafter  to  be  stated,  appear  to  the 
Author  strongly  indicative  of  the  entire  functional  as  well  as  structural  differ- 
ence, between  the  red  and  the  colourless  corpuscles  of  the  blood  of  Vertebrata. 
575.  That  the  red  Blood-discs,  when  first  formed  in  the  embryo,  have  an 
origin  common  to  that  of  all  other  tissues,  cannot  be  doubted.  They  are  pro- 
duced, in  the  embryo  of  the  Bird,  in  the  portion  of  the  germinal  membrane 
which  afterwards  becomes  the  area  vasculosa ;  this  consists  of  delicate  cells 
very  uniformly  disposed ;  and  whilst  capillary  vessels  are  being  formed  by 
the  union  of  the  cavities  of  these,  blood-discs  seem  to  be  developed  from  the 
granules  or  cell-germs  they  contain.  These  changes  take  place  about  the 
second  or  third  day  of  incubation ;  but  it  is  not  until  some  days  afterwards 
that  the  discs  assume  their  characteristic  form.*  As  at  this  period  no  special 
organs  exist  in  the  embryonic  structure,  it  is  evident  that  the  blood  must  be 
formed  by  the  cells  of  the  germinal  membrane,  at  the  expense  of  the  albumi- 
nous alimentary  materials  which  they  absorb  from  the  yolk ;  hence  we  may 

Fig.  102. 


& 


Production  of  Blood-Corpuscles  in  Chick,  on  the  fourth  day  of  incubation ;  a,  particles  fully  formed :  b. 
particles  in  progress  of  formation ;  c,  similar  particles,  altered  by  dilute  acetic  acid  so  as  to  display  their 
nuclei.  (After  Wagner.) 

infer  that  no  special  organ  can  be  needed  for  this  purpose  in  the  adult,  and 
that  the  assignment  of  the  manufacture  of  blood-corpuscles  by  some  physiolo- 
gists to  the  Spleen,  by  others  to  the  Thymus,  must  be  incorrect.  The  cor- 

*  Mr.  Macleod  gives  the  following  history  of  the  development  of  the  blood-corpuscles 
in  the  Chick.  In  blood  withdrawn  from  the  heart,  on  the  third  day,  and  diluted  with 
serum,  or  from  the  germinal  membrane  or  allantois,  and  diluted  with  fluid  albumen, — 
*'  a  number  of  small  granules  are  seen  floating  about  the  field :  these  enlarge  and  become 
clearer  in  the  centre ;  this  enlargement  goes  on  very  rapidly,  and  when  they  have  gained 
to  about  twice  their  original  size,  the  central  clear  part  becomes  dull.  This  dullness 
slightly  increases,  and  in  a  short  time  it  is  seen  to  be  distinctly  granular:  whilst  the 
borders  are  observed  to  be  well-defined,  smooth,  and  clearer  than  the  central  part.  The 
enlargement  of  these  bodies,  with  the  granular  appearance  of  their  centre,  seems  not  to 
depend  on  the  aggregation  of  granules  round  a  central  one,  but  on  a  property  which 
they  have  in  themselves  of  enlarging  and  presenting  that  figure.  During  all  this  time 
they  are  quite  spherical  and  of  good  consistence,  as  they  do  not  lose  their  form  by  con- 
siderable pressure.  In  the  second  stage,  the  central  portion  gradually  becomes  less 
opaque,  and  ceases  to  appear  granular,  the  external  portion  at  the  same  separating  in 
some  degree  from  the  central  part.  The  blood-corpuscle,  in  this  stage  of  development, 
has  the  appearance  of  a  slightly  flattened  round  cell,  formed  of  a  somewhat  delicate  but 
elastic  membrane,  with  a  nucleus  in  the  centre.  At  this  time  a  number  of  these  bodies, 
being  close  together  in  the  field,  present  a  yellowish  colour.  The  cell  is  disc-like,  rather 
concave,  but  the  nuclus  convex.  In  the  third  stage,  one  side  of  the  corpuscle  gradually 
elongates,  giving  it  a  pear-shaped  appearance;  the  opposite  side  then  elongates  itself  in 
a  similar  manner,  and  to  the  same  degree.  The  concavity  between  the  nucleus  and 
border  disappears,  and  the  whole  becomes  slightly  convex.  The  hue  at  the  same  time 
gradually  becomes  redder."  (London  and  Edinburgh  Monthly  Journal,  September,  1842.) 


PROPERTIES  OF  THE  BLOOD.  433 

puscles  are  generally  larger  in  the  embryo  than  in  the  adult,  especially  soon 
after  the  period  of  their  first  formation  ;  it  was  remarked  by  M.  Prevost  that 
in  the  foetal  goat  they  were  at  first  twice  the  size  of  those  of  the  mother.  Mr. 
Gulliver  has  observed  however,  that  at  a  later  period  of  utero-gestation  they 
are  sometimes  smaller  than  the  average  dimension  of  the  adult :  but  perhaps 
all  such  observations  are  to  be  received  with  hesitation,  owing  to  the  fact 
mentioned  by  him,  that  the  variety  in  the  magnitude  of  the  foetal  corpuscles  is 
much  greater  than  in  the  full-grown  animal. 

576.  In  regard  to  the  uses  of  the  red  Blood-corpuscles  in  the  animal  econ- 
omy, it  appears  to  the  Author  that  a  definite  conclusion  may  be  now  arrived 
at.  Their  existence  in  the  circulating  fluid  is  confined  to  the  Vertebrated 
classes ;  the  corpuscles  which  are  seen  in  the  blood  of  the  Invertebrata  being 
analogous  rather  to  the  colourless  corpuscles,  presently  to  be  described  as 
present  in  the  blood  of  the  higher  animals.  Hence  the  inference  appears 
irresistible,  that  they  are  not  essentially  necessary  to  the  production  of  the 
organizable  elements  of  the  blood,  or  of  the  organized  tissues.  The  red  cor- 
puscles are  most  abundant  in  those  classes  among  Vertebrata,  which  maintain 
the  highest  temperature ;  thus,  they  are  somewhat  more  numerous,  in  propor- 
tion to  the  whole  bulk  of  the  blood,  in  Birds  than  in  Mammalia ;  and  far  more 
in  the  latter  than  in  Reptiles  and  Fishes.  As  it  is  evident  that  they  undergo 
very  important  changes  in  the  pulmonary  and  systemic  capillaries,  their 
colour  being  changed  from  purple  to  red  in  the  former,  and  from  red  to  purple 
in  the  latter;  it  seems  highly  probable  that  they  have  for  their  principal 
office  the  introduction  of  oxygen  into  the  blood  that  circulates  through  the 
systemic  capillaries,  and  the  removal  of  the  carbonic  acid  set  free  there ; — 
to  serve  as  the  medium,  in  fact,  for  bringing  the  tissues  into  relation  with  the 
air,  the  influence  of  which  is  necessary  for  the  maintenance  of  their  vital 
activity.  In  the  Invertebrata  generally,  whose  respiration  is  very  feeble,  this 
end  will  be  sufficiently  answered  by  the  fluid  plasma  of  the  blood ;  the  altera- 
tions in  which,  under  the  influence  of  the  air,  have  been  already  noticed  (§  540 
and  553).  And  in  Insects, — the  only  class  whose  respiration  is  at  all  active, 
we  find  the  air  directly  conveyed  into  the  tissues;  the  circulating  fluid  not 
being  employed  as  its  carrier.  By  Liebig  it  is  supposed,  that  the  iron  in  the 
red  corpuscles  is  the  real  agent  in  the  respiratory  process ;  for  if  its  original 
state  be  the  protoxide,  it  may  become  the  peroxide  by  uniting  with  an 
additional  atom  of  oxygen,  or  the  protocarbonate  by  the  addition  of  an  atom  of 
carbonic  acid.  The  former  change  is  supposed  by  him  to  take  place  in  the 
lungs,  to  which  the  blood  comes  charged  with  carbonic  acid ;  the  carbonic 
acid  is  given  up  by  the  iron,  and  replaced  by  an  equivalent  of  oxygen  taken 
in  from  the  air;  whilst  in  the  systemic  capillaries,  the  converse  change 
takes  place, — the  oxygen  being  imparted  to  the  tissues,  and  being  replaced 
by  carbonic  acid  which  is  given  up  by  them  to  be  conveyed  out  of  the  system. 
It  is  stated  by  Liebig  that  there  is  far  more  than  sufficient  iron  in  the  whole 
mass  of  the  blood,  to  convey  in  this  manner  all  the  oxygen  and  carbonic  acid, 
which  are  interchanged  between  the  pulmonary  and  systemic  capillaries. 
The  speculation  is  certainly  an  ingenious  one ;  but  it  can  scarcely  be  yet 
received  as  a  physiological  fact.  In  addition  to  their  uses  in  the  respiratory 
process,  it  would  not  seem  unlikely  that  the  red  corpuscles  may  be  of  impor- 
tant assistance  in  promoting  the  movement  of  the  fluid  in  which  they  are 
suspended ;  for,  if  it  be  true  that  this  partly  depends  upon  the  chemical  con- 
dition of  the  blood  in  respect  to  the  tissues  which  it  supplies,  any  attractions 
or  repulsions  arising  out  of  this  may  be  more  powerfully  exercised  upon  a 
solid  corpuscle  than  upon  the  constantly-shifting  particles  of  the  fluid.  Hence, 
perhaps,  the  local  congestions  of  anaemic  patients. 

577.  Besides  the  red  particles  of  the  Blood,  there  are  others  which  possess 
37 


434 


OF  NUTRITION. 


no  colour,  and  which  seem  to  have  a  function  altogether  different ;  these  are 
known  as  the  white  or  colourless  corpuscles.  Their  existence  has  long  been 
recognized  in  the  blood  of  the  lower  Vertebrata,  where,  from  being  much 
smaller  than  the  red  corpuscles,  they  could  be  readily  distinguished.  But  it 
is  only  of  late, — chiefly  through  the  researches  of  Gulliver,  Addison,*  and 
others, — that  they  have  been  recognized  in  the  blood  of  Man  and  other  Mam- 
malia; their  size  being  nearly  the  same  with  that  of  the  red  corpuscles;  and 
the  general  appearance  of  the  two  (owing  to  the  circular  form  of  the  latter, 
and  the  absence  of  a  proper  nucleus,)  being  less  distinct.  It  is  remarkable 
that,  notwithstanding  the  great  variations  in  the  size  of  the  red  corpuscles  in 
the  different  classes  of  Vertebrata,  the  dimensions  of  the  colourless  corpuscles 
are  extremely  constant  throughout;  their  diameter  seldom  being  much  greater 
or  less  than  l-3000th  of  an  inch.  This  has  been  observed  even  in  those  ani- 
mals,— the  Musk-Deer,  and  the  Proteus, — which  present  the  widest  departure 
from  the  general  standard  in  the  size  of  their  red  corpuscles  ;  so  that  the 
colourless  corpuscle  is  as  much  as  four  times  the  diameter  of  the  red  in  one 
instance;  whilst  it  is  not  one-eighth  of  the  long  diameter  of  the  red  in  the 
other.  Hence  it  would  seem  very  improbable  that  the  red  can  ever  be  con- 
verted into  the  white,  or  the  white  into  the  red.  The  aspect  of  the  two,  under 
the  Microscope,  is  very  different.  Instead  of  presenting  a  distinct  central 
nucleus,  like  the  red  corpuscles  of  the  Oviparous  Vertebrata, — or  being  en- 
tirely destitute  of  granular  contents,  as  are  those  of  Mammalia  when  unaffected 
by  reagents,— the  colourless  corpuscles  are  studded  with  minute  granules, 
which  may  be  occasionally  seen  in  active  motion  within  them,  and  which  are 
discharged  when  the  corpuscles  are  .treated  with  liquor  potassse.  They  possess, 
moreover,  a  higher  refracting  power  than  the  red  corpuscles;  and  are  further 

distinguished  from  them  by  their  greater 
firmness,  and  by  the  absence  of  any  dis- 
position to  adhere  to  each  other ;  so  that, 
when  a  drop  of  recent  blood  is  placed 
between  two  strips  of  glass,  and  these 
are  gently  moved  over  one  anoher,  the 
white  corpuscles  may  be  at  once  recog- 
nized by  their  solitariness,  in  the  midst 
of  rows  and  irregular  masses  formed  by 
the  aggregation  of  the  red.  These  white 
corpuscles  of  the  blood  correspond  so 
closely,  in  all  their  characters,  with  the 
Lymph-corpuscles,  that  it  is  difficult  to 
regard  them  as  otherwise  than  identical ; 
and,  as  already  pointed  out  (§  566),  the 
corpuscles  of  the  Chyle  appear  to  be  of 
"the  same  character,  though  less  perfectly 
formed.  The  colourless  corpuscles  may 
be  readily  distinguished  in  the  circulat- 
ing Blood,  in  the  capillaries  of  the  Frog's 
foot ;  and  it  is  then  observable,  that  they 
occupy  the  exterior  of  the  current,  where 
the  motion  of  the  fluid  is  slow,  whilst  the 
red  corpuscles  move  rapidly  through  the 
centre  of  the  tube.  The  colourless  cor- 
puscles, indeed,  often  show  a  disposition 
to  adhere  to  the  walls  of  the  vessels ;  which  is  manifestly  increased  on  the 


A  small  venous  trunk  a,  from  the  web  of  the 
Frog's  loot,  magnified  350  diameters;  b.  b,  cells  of 
pavement-epithelium,  containing  nuclei.  In  the 
space  between  the  current  of  oval  blood-corpus- 
cles and  the  walls  of  the  vessels,  the  round, 
transparent,  white  corpuscles  are  seen.  (After 
Wagner.) 


*  Transactions  of  the  Provincial  Medical  Association,  1842  and  1843. 


PROPERTIES  OF  THE  BLOOD.  435 

application  of  an  irritant.  Hence  the  idea  naturally  arises,  that  (to  use  the 
words  of  Mr.  Wharton  Jones)  "there  is  some  reciprocal  relation  between  the 
colourless  corpuscles,  and  the  parts  outside  the  vessels,  in  the  process  of 
nutrition."  What  that  relation  is,  we  shall  now  proceed  to  inquire. 

578.  In  regard  to  the  purpose  of  the  colourless  corpuscles  in  the  animal 
economy,  a  view  has  been  brought  forward  by  the  Author,*  which  increased 
consideration  has  only  served  to  strengthen  ;  and  which  he  advances  here  with 
some  degree  of  confidence  that  it  will  be  found,  on  attentive  examination,  war- 
ranted by  a  large  number  of  physiological  analogies,  though  not  capable  of 
being  directly  proved.  That  it  may  be  rightly  understood,  a  general  sketch 
of  certain  known  operations  of  cells  in  Plants  and  Animals  will  be  first  given. 
— It  is  not  difficult,  on  taking  a  comprehensive  survey  of  the  assimilating  pro- 
cesses, to  find  a  number  of  examples  in  which  cells  are  developed  in  a  tempo- 
rary manner ;  growing,  arriving  at  maturity,  and  then  disappearing,  apparently 
without  having  performed  any  particular  function.  In  the  albumen  of  the 
seed,  for  instance,  this  often  takes  place  to  a  remarkable  extent.  In  the  Yolk 
of  the  Egg  there  is  a  similar  transitory  development  of  cells,  of  which  several 
generations  succeed  each  other,  without  any  permanent  structure  being  the 
result.  In  the  Germinal  Vesicle,  again  (according  to  Dr.  Barryt),  several  annuli 
of  cells  are  seen  to  occupy  its  cavity,  when  it  is  prepared  for  fecundation;  and 
the  oldest  and  largest  of  these  contain  another  generation :  yet  all  these  dis- 
appear by  liquefaction,  as  soon  as  the  two  permanent  cells  begin  to  be  developed 
in  the  centre  (§  746).  Further,  in  the  subsequent  development  of  all  the  cells 
which  are  descended  from  these,  and  form  the  "  mulberry  mass,"  the  same 
process  is  repeated ;  a  great  number  of  temporary  cells  being  produced,  only 
to  liquefy  again  as  soon  as  the  two  permanent  central  cells  make  their  appear- 
ance. It  can  scarcely  be  imagined  by  the  well-judging  physiologist,  that  all 
this  cell-life  comes  into  existence  without  some  decided  purpose ;  and  if  we 
can  assign  to  it  an  object,  the  fulfilment  of  which  is  consistent  with  the  facts 
supplied  by  analogy  elsewhere,  this  may  be  reasonably  considered  as  having 
a  fair  claim  to  be  received  as  a  physiological  induction. — In  all  these  instances, 
and  in  many  more  which  might  be  quoted,  the  crude  alimentary  materials  are 
being  prepared  to  undergo  conversion  into  permanent  and  regularly-organized 
structures.  The  very  first  union  of  the  inorganic  elements  into  the  simplest 
proximate  principles,  is  effected  by  the  cell-life  of  plants.  The  change  of 
these  principles  into  the  peculiar  compounds  which  form  the  characteristic 
secretions  of  plants,  is  another  result  of  their  cell-life.  And  there  seems  equal 
ground  for  the  belief,  that  the  change  of  these  proximate  principles  into  the 
peculiar  glutinous  sap,  which  is  found  wherever  a  formation  of  new  tissue  is 
taking  place,  is  equally  dependent  upon  the  agency  of  cells.  Thus,  the  starchy 
fluid  which  is  contained  in  the  ovule,  previously  to  its  fecundation,  is  probably 
not  in  the  state  in  which  it  can  be  immediately  rendered  subservient  to  the 
nutrition  of  the  embryo ;  and  the  development  of  successive  generations  of 
cells,  which  exert  upon  it  their  vitalizing  influence,  may  be  reasonably  regarded 
as  the  means  by  which  the  requisite  change  is  effected.  Exactly  the  same 
may  be  said  of  the  albuminous  matter  contained  in  the  yolk  of  the  egg,  which 
is  certainly  not  in  a  condition  in  which  it  can  be  immediately  applied  to  the 
purposes  of  nutrition ;  and  its  conversion  may  be  regarded  as  commencing 
with  the  development  of  transitory  cells  within  its  own  substance,  and  as  being 
completed  by  means  of  the  cells  forming  the  inner  layer  of  the  germinal  mem- 
brane, by  which  it  is  subsequently  taken  up  and  introduced  into  the  current  of 

*  Report  on  Cells,  in  British  and  Foreign  Medical  Review,  Jan.,  1843. 
f  Euibryological  Researches.    Third  Series. 


436  OF  NUTRITION. 

blood  flowing  through  the  vascular  area  (§  761).  A  similar  purpose  is  proba- 
bly answered  by  the  transitory  cells  developed  within  the  germinal  vesicle,  and 
by  those  which  appear  at  a  similar  period  in  the  evolution  of  the  descendants 
of  the  "twin  cells"  produced  in  it. — Many  similar  examples  have  been  else- 
where adduced.* — We  have  thus  a  class  of  facts,  which  indicates  that  the  con- 
version of  the  Chemical  compound  into  the  Organizable  principle — the  aplastic 
into  the  plastic  material — is  effected  in  the  particular  situations  where  it  is  most 
wanted,  by  the  vital  agency  of  transitory  cell-life  ;  that  is,  by  the  production  of 
cells  which  are  not  themselves  destined  to  form  an  integral  part  of  any,  perma- 
nent structure,  but  which,  after  attaining  a  certain  maturity,  reproduce  them- 
selves and  disappear ;  successive  generations  thus  following  one  another  until 
the  object  is  accomplished,  after  which  they  altogether  vanish.  We  shall  now 
consider  another  class  of  facts,  which  seems  to  indicate  that  a  change  of  this 
kind  is  being  continually  effected  in  the  nutritious  fluids  of  Animals,  during 
their  circulation  through  the  body :  by  Cells,  which  are  either  carried  about 
with  them,  or  which  are  developed  for  the  purpose  in  particular  situations,  as 
in  plants.  The  former  is  the  more  common  occurrence  ;  since  the  conditions  of 
animal  life,  usually  involving  a  general  movement  of  the  body,  require  also  a 
general  reparation  of  its  parts,  and  an  adaptation  of  the  circulating  fluid  there- 
fore to  the  wants  of  the  whole  fabric. 

579.  It  has  been  already  shown,  that  Cells,  which  seem  identical  with  the 
white  corpuscles  of  the  Blood,  are  to  be  met  with  in  the  Chyle  and  Lymph, — 
fluids  in  which  the  elaboration  of  plastic  fibrin  is  going  on  (§564) ;  and  that 
such  an  elaboration  must  be  continually  taking  place  in  the  blood  itself,  to 
supply  the  plastic  material  which  is  being  as  continually  drawn  off  by  the 
nutritive  processes.  Hence  there  would  seem  reason  for  attributing  this  im- 
portant function  to  these  floating  cells ;  the  number  of  which  present  in  the 
fluids  seems  to  bear  a  very  close  relation  with  the  energy  of  this  elaborating 
process.  It  is  a  fact  of  great  physiological  interest  and  importance,  that,  whilst 
the  colourless  corpuscles  are  to  be  met  with  in  the  nutritious  fluids  of  all  ani- 
mals which  possess  a  distinct -circulation,  the  red  corpuscles  are  restricted  to 
the  blood  of  Vertebrata.  This  observation,  which  was  first  put  forth  by  Wag- 
ner,t  has  been  confirmed  by  the  Author,  who  had  been  previously  struck  with 
the  very  close  analogy  between  the  floating  cells  carried  along  in  the  current  of  the 
circulation  in  some  of  the  very  transparent  aquatic  larvae  (especially  those  of  the 
Culicidae),  and  the  lymph-corpuscles  of  the  frog.  Now  it  is  evident  from  this 
fact,  that,  as  the  blood  of  Vertebrata  is  distinguished  from  their  chyle  chiefly  by 
the  presence  of  red  corpuscles  in  the  former  and  by  their  absence  in  the  latter, 
the  nutritious  fluid  of  invertebrated  animals  is  rather  analogous  (as  Wagner  has 
remarked)  to  the  Chyle  and  Lymph,  than  to  the  blood  of  Vertebrata.  Or,  to  put 
the  same  idea  in  another  form,  the  presence  of  the  colourless  corpuscles  in  the 
nutritious  fluid  appears  to  be  the  most  general  fact  in  regard  to  its  character 

*  There  are  probably  cases,  however,  in  which  cells  are  very  rapidly  called  into  exist- 
ence, without  that  preparatory  elaboration  of  their  nutrient  materials,  which  we  regard 
as  due  to  the  vital  operations  of  a  preceding  generation.  Thus  the  Bovista  giganteum, 
a  large  fungus  of  the  puff-ball  tribe,  has  been  known  to  increase,  in  a  single  fright,  from 
a  mere  point  to  the  size  of  a  huge  gourd,  estimated  to  contain  47,000,000,000  cellules.  In 
such  a  case  it  is  difficult  to  suppose  than  any  but  the  most  rapid  mode  of  generating  cells 
can  have  been  in  operation;  and  the  idea  that  these  could  not  have  been  developed  by 
any  such  elaborate  process  as  that  just  alluded  to,  is  borne  out  by  the  fact  of  their  ex- 
tremely transitory  character,  the  decay  of  such  a  structure  being  almost  as  rapid  as  its 
production.  The  same  may  be  remarked  of  those  fungous  growths  in  the  animal  body, 
which  sprout  forth  most  rapidly.  Hence  the  apparent  exception  assists  in  proving  the 
rule. 

|  Physiology,  by  Willis,  Part  ii. 


PROPERTIES  OF  THE  BLOOD.  437 

throughout  the  whole  animal  scale  ;  whilst  the  presence  of  red  corpuscles  in 
that  fluid  is  limited  to  the  vertebrated  classes.  Hence  it  would  not  be  wrong 
to  infer,  that  the  function  of  the  colourless  corpuscles  must  be  of  a  general 
character,  and  intimately  connected  with  the  nutritious  properties  of  the  circu- 
lating- fluid ;  whilst  the  function  of  the  red  corpuscles  must  be  of  a  limited 
character,  being  only  required  in  one  division  of  the  animal  kingdom.  Fur- 
ther, it  has  been  noticed  by  Mr.  Gulliver,  that  in  the  very  young  embryo  of 
the  Mammalia,  the  white  globules  are  nearly  as  numerous  as  the  red  particles  : 
this,  Mr.  Gulliver  has  frequently  noticed  in  foetal  deer  of  about  1£  inches  long. 
In  a  still  smaller  foetus,  the  blood  was  pale  from  the  preponderance  of  the  white 
corpuscles.  It  is,  therefore,  a  fact  of  much  interest  that,  even  in  the  Mam- 
miferous  embryo,  at  the  period  when  growth  is  most  rapid,  the  circulating 
fluid  has  a  strong  analogy  to  that  of  the  Invertebrata.  It  then,  too,  bears  in 
other  respects  the  most  striking  analogy  to  chyle  ;  since  it  consists  of  the  fluid 
elaborated  from  the  organizable  matter  supplied  by  the  parent,  and  directly 
introduced  into  the  current  of  the  circulation.  The  function  of  the  placental 
vessels  may  be  regarded  as  double  :  for  they  are  at  the  same  time  the  channel 
through  which  the  alimentary  materials  supplied  by  the  parent  are  introduced 
into  the  circulating  system  of  the  foetus,  and  the  medium  of  aerating  the  fluid 
which  has  traversed  the  foetal  system.  Hence  the  placenta  may  be  regarded 
as  at  once  the  digestive  and  the  respiratory  apparatus  of  the  foetus ;  and  the 
fluid  circulating  through  the  cord,  as  at  once  chyle  and  blood.  It  is  not  until 
the  pulmonary  and  lacteal  vessels  of  the  embryo  have  commenced  their  inde- 
pendent operation,  that  the  distinction  between  the  blood  and  the  chyle  of  the 
foetus  becomes  evident ;  and  we  should  expect,  therefore,  to  find  that  the  circu- 
lating fluid,  up  to  the  time  of  birth,  contains  a  large  proportion  of  white  cor- 
puscles,— which  is  actually  the  case.  There  is  a  gradual  decrease,  however, 
in  their  proportional  number,  from  the  earlier  to  the  later  stages  of  embryonic 
life,  in  accordance  with  the  diminishing  energy  of  the  formative  processes. — 
It  has  been  also  observed  by  Wagner,*  that  the  number  of  colourless  corpuscles 
is  always  remarkably  great  in  the  blood  of  well-fed  frogs  just  caught  in  the 
summer  season ;  and  that  it  is  very  small  in  those  that  had  been  kept  long 
without  food,  and  in  those  examined  during  the  winter. — The  most  remarka- 
ble evidence,  however,  of  the  connection  between  the  generation  of  white  cor- 
•  puscles  in  the  blood  and  the  production  of  fibrin,  is  derived  from  the  pheno- 
mena of  Inflammation.  A  decided  increase  in  the  normal  proportion  of  fibrin 
in  the  blood  (from  2£  to  3£  parts  in  1000),  may  probably  be  looked  upon  as 
the  essential  indication  of  the  existence  of  the  inflammatory  condition  (§  591  a}. 
That  this  production  of  fibrin  is  due  to  a  local  change  can  scarcely  be  doubted, 
since  it  is  frequently  observed  to  commence  before  any  constitutional  symp- 
toms manifest  themselves ;  and  it  may  be  regarded,  in  fact,  as  one  cause  of 
these  symptoms.  Now  the  recent  microscopic  observations  of  Mr.  Addisont 
and  Dr.  Williams,;};  which  were  made  independently  of  each  other,  have 
established  the  important  fact,  that  a  great  accumulation  of  white  corpuscles 
takes  place  in  the  vessels  of  an  inflamed  part:  this  seems  to  be  caused  at  first 
by  a  determination  of  those  already  existing  in  the  circulating  fluid  towards 
the  affected  spot ;  but  partly  by  an  actual  increase  or  generation  of  these  bodies, 
which  appear  to  have  the  power  of  very  rapidly  multiplying  themselves. — 
The  accumulation  of  white  corpuscles  may  be  easily  seen,  by  applying  irri- 
tants to  the  web  of  a  frog's  foot.  Mr.  Addison  has  noticed  it,  in  the  human 

*  Op.  cit.  p.  245. 

f  Medical  Gazette,  Dec.,  1840;  Jan.  and  March,  1841. 

t  Medical  Gazette,  July,  1841;  and  Principles  of  Medicine,  [Amer.  ed.  by  Dr.  Clymer, 
pp.  214,  215.] 


438  OF  NUTRITION. 

subject,  in  blood  drawn  by  the  prick  of  a  needle  from  an  inflamed  pimple,  the 
base  of  a  boil,  the  skin  in  scarlatina,  &c.  And  the  Author,  without  any  know- 
ledge of  these  observations,  had  remarked  a  very  obvious  difference  between 
the  proportions  of  white  corpuscles,  in  blood  drawn  from  a  wound  in  the  skin 
of  a  frog  immediately  upon  the  incision  being  made,  and  in  that  drawn  a  few 
minutes  after  ;  and  had  been  led,  like  the  observers  just  quoted,  to  refer  this 
difference  to  a  determination  of  white  corpuscles  to  a  part  irritated.  The  ab- 
solute increase,  sometimes  to  a  very  considerable  amount,  in  the  quantity  of 
white  corpuscles  in  the  blood  of  an  inflamed  subject,  has  been  verified  by  Mr. 
Gulliver  and  several  other  observers.  These  facts,  therefore,  afford  strong 
ground  for  the  belief,  that  the  production  of  fibrin  in  the  blood  is  closely  con- 
nected with  the  development  of  the  white  corpuscles ;  and  when  we  consider 
them  in  connection  with  the  facts  previously  urged,  there  scarcely  appears  to 
be  a  reasonable  doubt,  that  the  elaboration  of  fibrin  is  a  consequence  of  this 
form  of  cell-life,  and  is,  in  fact,  its  express  object. — This  view  derives  further 
confirmation  from  the  following  recent  experiment  of  Mr.  Addison's.*  "Pro- 
vide six  or  eight  slips  of  glass,  such  as  are  usually  employed  for  mounting 
microscopical  objects  :  and  as  many  smaller  pieces.  Having  drawn  blood  from 
a  person  with  rheumatic  fever,  or  any  other  inflammatory  disease,  place  a  drop 
of  the  colourless  liquor  sanguinis,  before  it  fibrillates,  on  each  of  the  large  slips 
of  glass ;  cover  one  immediately  with  one  of  the  smaller  slips,  and  the  others 
one  after  another  at  intervals  of  thirty  or  forty  seconds :  then,  on  examining 
them  by  the  microscope,  the  first  will  exhibit  colourless  blood  corpuscles  in 
various  conditions,  and  numerous  white  molecules  distributed  through  a  more 
or  less  copious  fibrous  net-work ;  and  the  last  will  be  a  tough,  coherent,  and 
very  elastic  membrane,  which  cannot  be  broken  to  pieces  nor  resolved  into 
smaller  fragments,  however  roughly  or  strongly  the  two  pieces  of  glass  be  made 
to  rub  against  each  other.  This  is  a  *  glaring  instance'  of  a  compact,  tough, 
elastic,  colourless,  and  fibrous  tissue,  forming  from  the  colourless  elements  of 
the  blood;  and  the  several  stages  of  its  formation  may  be  actually  seen  and 
determined.  Numerous  corpuscles  may  be  observed,  in  all  these  preparations, 
•  to  have  resolved  themselves,  or  to  have  fallen  down  into  a  number  of  minute 
molecules,  which  are  spread  out  over  a  somewhat  larger  area  than  that  occu- 
pied by  the  entire  corpuscles ;  and  although  still  retaining  a  more  or  less  per- 
fectly circular  outline,  yet  refracting  the  light  at  their  edges,  in  a  manner  very 
different  from  that  in  which  the  corpuscles  themselves  are  seen  to  do.  It  is 
from  these  and  various  other  larger  and  more  irregular  masses  of  molecules  or 

*  Transactions  of  the  Provincial  Medical  Association,  1843. 

j-  A  different  view  of  the  cause  of  the  production  of  fibrin,  however,  has  been  enter- 
tained by  some  eminent  physiologists;  and  it  does  not  seem  right  to  allow  the  opinions  of 
Wagner,  Henle,  and  Wharton  Jones,  to  pass  without  notice,  even  though  they  appear  to 
the  Author  to  be  easily  set  aside.  By  these  observers,  the  elaboration  of  fibrin  has  been 
attributed  to  the  red  corpuscles,  and' has  been  regarded  as  one,  at  least,  of  their  special 
functions.  Nearly  all  the  arguments,  however,  which  have  led  us  to  assign  this  duty  to 
the  white  corpuscles,  tell  equally  against  the  doctrine  now  under  consideration.  The  pre- 
sence of  fibrin  in  the  circulating  fluid  may  be  regarded  as  a  universal  fact;  but  the  red 
corpuscles  are  restricted  to  vertebrated  animals:  how,  then,  is  the  plastic  element  elabo- 
rated in  the  invertebrata!  The  number  of  the  red  corpuscles  in  the  blood  of  different 
classes  bears  an  obvious  relation  to  their  amount  of  respiratory  power,  and  to  the  func- 
tional activity  of  the  several  organs,  which  is  closely  connected  with  the  amount  of  oxygen 
introduced  into  the  system;  but  it  does  not  bear  the  same  relation  with  the  activity  of  the 
formative  processes,  which  may  be  taking  place  energetically,  (as  in  the  development  of 
the  embryo,  or  in  the  reparation  of  parts  in  the  adult),  in  a  state  of  functional  quiescence. 
—The  pathological  evidence  that  the  red  corpuscles  are  not  the  elaborators  of  the  fibrin, 
appears  to  the  Author  to  be  quite  conclusive.  Whilst  the  quantity  of  fibrin  is  so  remark- 
ably increased  in  inflammation,  the  number  of  red  corpuscles'  undergoes  no  decided 


PROPERTIES  OF  THE  BLOOD.  439 

disintegrated  corpuscles,  that  the  fibrinous  filaments  shoot  out  on  all  sides,  as 
from  so  many  centres ;  or  frequently  the  filaments  are  more  copious  in  two 
opposite  directions."! 

580.  Besides  the  red  corpuscles  and  the  colourless  globules,  it  is  stated  by 
Mr.  Gulliver,*  that  the  blood  obtained  from  Mammals  after  death  not  unfre- 
quently  contains  an  abundance  of  white  matter,  generally  presenting  the  form 
of  spherules,  having  a  diameter  of  from  l-4000th  to  1-1 750th  of  an  inch. 
They  frequently  seem  to  have  a  semi-fluid  consistency,  especially  in  the  blood 
of  the  rnesenteric  veins,  in  which  the  white  matter  is  found  most  abundantly. 
The  appearance  of  these  globules  (which  appear  to  be  the  same  with  the 
fibrinous  globules  of  Mandl)  is  probably  to  be  attributed  to  Pathological  changes, 
and  especially  to  the  existence  of  Tubercular  disease ;  a  large  proportion  of 
the  granular  matter  of  caseous  tubercles  consists  of  similar  corpuscles. — The 
milky  serum,  which  sometimes  occurs  when  patients  are  bled  not  long  after  a 
meal,  and  which  is  seen  not  unfrequently  in  the  blood  drawn  from  young  ani- 
mals, is  usually  found,  by  the  highest  powers  of  the  microscope,  to  present  the 
granular  base,  which  has  been  already  described  in  the  account  of  chyle 
(§  563].    The  appearance  seems  due,  however,  in  some  instances,  to  the  diffu- 
sion 01  oily  matter,  in  a  less  finely  divided  state  than  usual,  through  the  fluid ; 
in  some  of  these  cases,  a  very  large  amount  of  fat  has  been  shown,  by  chemical 
analysis,  to  exist  in  it.t — The  only  visible  constituents  of  ordinary  blood  which 
remain  to  be  noticed,  are  the  corpuscles  of  the  Spleen  (§  708)  and  of  the  Supra- 
Renal  capsules  (§  711)  which  may  be  frequently  observed  in  the  Splenic  and 
Supra  Renal  veins  respectively. — According  to  Schultz,  the  red  corpuscles  of 
the  Portal  vein  differ  from  those  of  the  rest  of  the  vascular  system,  in  their 
tendency  to  decay;  their  colouring  matter  is  soluble  in  the  liquor  sanguinis, 
which  is  not  the  case  elsewhere ;  and  they  seem  to  have  lost  a  portion  of  their 
contractility. 

581.  Having  now  separately  considered  the  chief  Organic  Elements  which 
enter  into  the  composition  of  the  Blood,  we  are  prepared  to  inquire  into  the 
characters  of  this  fluid  as  a  whole.     The  analysis  of  M.  LecanuJ  is  usually 
regarded  as  the  most  complete  and  satisfactory.     The  following  is  his  account 
of  the  composition  of  the  fluid,  obtained  from  two  stout  and  healthy  Men. 

Water 780-145  785-590 

Fibrin 2-100  3-565 

Albumen 65-090  69-415 

Colouring  matter  (globules)         ....  133-000  119-626 

Fatty  crystallizable  matter           ....  2-430  4-300 

change.  Again,  the  augmentation  of  the  fibrin  is  not  incompatible  with  a  chlorotic  state 
of  the  blood;  the  peculiar  characteristic  of  which  is  a  great  diminution  in  the  proportion 
of  red  corpuscles.  By  such  alterations,  the  normal  proportions  between  the  fibrin  and 
the  red  corpuscles,  which  may  be  stated  as  A:  B,  may  be  so  much  altered, as  to  become,  in 
inflammation,  3  A  :  B,  in  chlorisis,  A  :  £  B.  Again,  in  fever,  the  characteristic  alteration  in 
the  condition  of  the  blood  appears  to  be  an  increase  in  the  amount  of  red  corpuscles, 
with  a  diminution  in  the  quantity  of  fibrin  ;  yet  if  a  local  inflammation  should  establish 
itself  during  the  course  of  the  fever,  the  proportion  of  fibrin  will  rise;  and  this  without 
any  change  in  the  amount  of  corpuscles.  Lastly,  the  effect  of  loss  of  blood  has  been 
shown  by  Andral's  investigations  to  be  a  marked  diminution  in  the  number  of  red  cor- 
puscles, with  no  decided  reduction  in  the  quantity  of  fibrin,  even  when  this  is  much 
above  its  normal  standard;  and  in  this  condition  of  the  blood,  it  has  been  observed  by 
Remak  that  the  colourless  corpuscles  are  very  numerous. 

*  Gerber's  Anatomy,  Appendix,  p.  21. 

f  For  some  very  interesting  observations  lately  made  on  this  subject,  see  §  711,  note. 

i  Journal  de  Pharmacie,  Nos.  ix.  and  x.,  1831. 


440 


OF  NUTRITION. 


Oily  matter        ...... 

Extractive  matter  soluble  in  water  and  aleohol 
Albumen  combined  with  soda 
Chloride  of  sodium 


potassium 


Carbonates 

Phosphates    I.  of  potash  and  soda 

Sulphates     J 

Carbonates  of  lime  and  magnesia 

Phosphates  of  lime,  magnesia,  and 

Peroxide  of  iron 

Loss          ..... 


iron  L 


1-310 
1-790 
1-265 

8-370 


2-100 
2-400 


2-270 
1-920 
2-010 

7-304 


1-414 

2-586 


100-000         100-000 


Hence  it  is  seen  that  the  proportion  of  the  elements  of  Blood  is  subject  to  con- 
siderable variation  within  the  limits  of  ordinary  Health ;  we  shall  hereafter 
find  that,  in  Disease,  these  variations  are  far  more  decided,  and  that  they  have 
a  constant  and  evident  connection  with  the  morbid  condition  of  the  system. 
The  amount  of  solid  matter  in  the  Blood  appears  to  be  in  general  greater  in 
the  Male  than  in  the  Female.  The  following  table  exhibits  the  general  results 
of  the  inquiries  of  Denis  on  this  head:  it  represents  the  Maximum  and  Mini- 
mum of  each  of  the  chief  constituents  of  the  Blood ;  and  it  will  be  seen  that, 
whilst  the  Water  predominates  in  the  Female,  the  other  elements  (with  a 
slight  exception  in  favour  of  the  albumen)  are  in  largest  amount  in  the  Male. 


Water 
Albumen 
Globules  . 
Fibrin      . 

MALE. 

FEMALE. 

Maximum. 

Minimum. 

Maximum. 

Minimum. 

805 
63 
186 
4 

732 

48-5 
110-5 

2 

848 
68 
167 
3-1 

753 
50 
71-4 

2 

The  Specific  Gravity  of  course  varies  with  the  amount  of  solid  matter  contained 
in  it ;  in  the  Human  subject,  the  average  is  probably  about  1050.  The  esti- 
mate formerly  given  (§  490)  of  the  proportional  amount  of  Blood  in  the  body, 
has  recently  been  confirmed  by  a  very  ingenious  experiment  of  Valentin's,  in 
which  the  calculation  was  based  on  Specific  Gravity.  A  certain  quantity  of 
blood  was  taken  away  from  the  jugular  vein  of  an  animal  of  known  weight ; 
and  a  known  measure  of  blood-warm  distilled  water  was  slowly  injected,  by 
the  orifice  of  the  vein,  towards  the  heart.  Some  minutes  afterwards,  another 
portion  of  the  blood  was  withdrawn,  and  carefully  weighed.  The  two  quan- 
tities were  then  evaporated  in  dry  air,  until  the  residue  no  longer  lost  weight ; 
and  the  whole  amount  of  the  previously-contained  mass  of  blood  could  then  be 
calculated,  by  a  simple  mathematical  formula,  from  the  degree  of  attenuation 
in  the  fluid,  produced  by  the  injected  water.  This  was  found  to  be  between 
one-third  and  one-fourth,  or  about  two-sevenths,  of  the  whole  weight  of  the 
body. 

582.  When  the  Blood  is  drawn  from  the  body,  and  left  to  itself,  its  organic 
elements  speedily  undergo  a  new  arrangement.     The  Fibrin  coagulates,  and 


PROPERTIES  OF  THE  BLOOD.  441 

separates  itself  from  the  fluid  in  which  it  was  previously  dissolved  ;  and  during 
its  coagulation  it  attracts  the  red  particles ;  these  are  included  in  areoke  or 
meshes  of  the  Clot,  the  substance  of  which  has  a  tendency  to  assume  a  fibrous 
arrangement  (§  554) ;  and  they  usually  group  themselves  together  in  columnar 
masses,  resembling  piles  of  money  (Fig.  100,  B).  The  Coagulum  or  clot  be- 
comes dense  in  proportion  to  the  amount  of  Fibrin  it  contains ;  and  the  Albu- 
minous and  Saline  matter  still  dissolved  in  the  water  are  separated  from  it, 
constituting  what  is  called  the  Serum.  This  separation  will  not  occur,  how- 
ever, if  the  coagulation  takes  place  in  a  shallow  vessel ;  nor  if  the  amount  of 
Fibrin  should  be  small,  or  its  vitality  low.  A  homogeneous  mass,  deficient  in 
firmness,  presents  itself  under  such  circumstances ;  though  the  solid  part  of 
this  may  pass  into  a  state  of  more  complete  condensation,  after  the  lapse  of  a 
certain  time.  That  the  coagulation  is  due  to  the  Fibrin,  and  that  the  Red 
particles  are  merely  passive  in  the  process,  appears  from  several  considera- 
tions. A  microscopical  examination  of  the  Clot  shows  that  it  has  the  same 
texture  with  Fibrin  when  coagulating  by  itself;  the  Corpuscles  clustering 
together  in  the  interspaces  of  the  network,  and  not  being  uniformly  diffused 
through  the  whole  mass.  Their  Specific  Gravity  being  greater  than  that  of 
the  Fibrin,  they  are  usually  most  abundant  at  the  lower  part  of  the  clot ;  and 
the  upper  surface  is  sometimes  nearly  colourless,  especially  when  the  coagu- 
lation has  taken  place  slowly ;  yet  this  upper  part  is  much  firmer  than  the 
under,  showing  that  the  Fibrin  alone  is  the  consolidating  agent.  This  has 
been  proved  to  demonstration  by  an  experiment  of.  Muller's.  He  placed  the 
blood  of  a  Frog,  diluted  with  water  (or  still  better  with  a  very  thin  syrup)  on 
a  paper  filter,  of  sufficiently  fine  texture  to  keep  back  the  Corpuscles ;  and 
the  Liquor  Sanguinis,  having  passed  through  the  filter  completely  unmixed 
with  them,  presented  a  distinct  coagulum,  although  from  the  diluted  state  of 
the  fluid,  this  did  not  possess  much  consistency.  Owing  to  the  more  minute 
size  of  the  Blood-discs  of  warm-blooded  animals,  this  experiment  cannot  be 
performed  with  their  blood  ;  but  there  is  no  reason  to  believe  its  constitution 
to  be  different.  In  fact,  the  sole  agency  of  the  Fibrin  in  coagulation  is  very 
easily  proved  in  another  way.  If  fresh-drawn  blood  be  continually  stirred 
with  a  stick,  the  Fibrin  will  adhere  to  it  in  strings  during  its  coagulation ; 
and  the  red  particles  will  be  left  suspended  in  the  serum,  without  the  slightest 
tendency  to  coagulate.  Moreover,  if  a  solution  of  any  salt,  that  has  the  pro- 
perty of  retarding  the  coagulation  (such  as  carbonate  of  potash  or  sulphate  of 
soda),  be  added  to  the  blood,  the  Corpuscles  will  have  time  to  sink  to  the 
lower  stratum  of  the  fluid,  before  the  clot  is  formed ;  the  greater  part  of  the 
Coagulum  is  then  entirely  colourless,  and  is  found  by  the  microscope  to  con- 
tain few  or  no  red  particles.* 

583.  That  the  coagulation  of  the  Fibrin  is  not,  as  some  have  supposed,  a 
proof  of  the  death  of  the  blood,  but  is  rather  an  act  of  vitality,  appears  evident 
from  what  has  been  already  stated  (§  554)  of  the  incipient  organization  which 
may  be  detected  even  in  an  ordinary  clot ;  and  still  more  from  the  fact  that,  if 
the  effusion  of  Fibrin  takes  place  upon  a  living  surface,  its  coagulation  is  the 

*[M.  Figuierj-  has  suggested  an  easy  method  for  the  rough  analysis  of  the  blood.  By 
adding  to  one  volume  of  defibrinated  blood,  two  volumes  of  a  solution  of  sulphate  of 
soda,  of  sp.  gr.  making  16°  to  18°  in  Baume's  areometer,  the  corpuscles  will  separate 
(as  Berzelius  showed),  and  may,  with  hardly  an  exception,  be  all  collected  on  a  filter. 
Thus  their  quantity  may  be  estimated,  as  that  of  the  fibrine  may  very  roughly  by  what 
is  obtained  by  whipping.  The  quantity  of  albumen  may  be  estimated  by  boiling  the 
serum  ;  and  the  water,  by  evaporating  a  separate  portion  of  blood. — M.  C.] 

f  Report  of  the  Academie  des  Sciences  du  8,  Juillet  1844;  and,  in  full,  in  the  Ann.  de 
Chimie  et  de  Physique,  Aout,  1844. 


442  OF  NUTRITION. 

first  act  of  its  conversion  into  solid  tissues  possessing  a  high  degree  of  vitality. 
It  is  absurd  to  suppose  that  the  blood  dies,  in  order  to  assume  a  higher  form. 
When  withdrawn  from  the  body,  however,  the  Coagulation  of  the  Blood  is  the 
last  act  of  its  life ;  for,  if  not  within  the  influence  of  a  living  surface,  it  soon 
passes  into  decomposition.  Instances  occasionally  present  themselves  in  which 
the  Blood  does  not  coagulate  after  death ;  and  in  most  of  these  there  has  been 
some  sudden  and  violent  shock  to  the  Nervous  system,  which  has  destroyed 
the  vitality  of  solids  and  fluids  alike.  This  is  generally  the  case  in  men  and 
animals  killed  by  lightning,  or  by  strong  electric  shocks ;  and  in  those  poisoned 
by  prussic  acid,  or  whose  life  has  been  destroyed  by  a  blow  on  the  epigastrium. 
It  has  also  been  observed  in  some  instances  of  rupture  of  the  heart,  or  of  a 
large  aneurism  near  it ;  and  a  very  interesting  phenomenon  then  not  unfre- 
quently  presents  itself, — the  coagulation  of  the  Blood  which  has  been  effused 
into  the  pericardium  (the  effusion  having  taken  place  during  the  last  moments 
of  life),  whilst  that  in  the  vessels  has  remained  fluid.  In  several  of  the  in- 
stances in  which  the  blood  has  been  found  uncoagulated  in  the  vessels,  many 
hours  after  death,  a  portion  withdrawn  from  the  body  has  clotted  ;  this  would 
seem  to  indicate  that  there  is  some  absolutely  depressing  influence  exercised 
by  the  surrounding  tissues  under  such  circumstances, — an  influence  of  which 
manifest  evidence  is  afforded,  by  the  sudden  destruction  of  the  muscular  con- 
tractility, the  arrestment  of  the  capillary  circulation,  and  other  phenomena  of 
like  nature.  It  appears,  however,  that  simple  arrestment  of  Nervous  influence 
favours  the  coagulation  of  the  blood  in  the  vessels ;  clots  being  found  in  their 
trunks  within  a  few  minutes  after  the  Brain  and  Spinal  marrow  have  been 
broken  down. 

584.  The  length  of  time  which  elapses  before  Coagulation,  and  the  degree 
in  which  the  Clot  solidifies,  vary  considerably ;  in  general,  they  are  in  the 
inverse  proportion  to  each  other.  Thus,  if  a  large  quantity  of  blood  be  with- 
drawn from  the  vessels  of  an  animal  at  the  same  time,  or  within  short  inter- 
vals, the  portions  that  last  flow  coagulate  much  more  rapidly,  but  much  less 
firmly,  than  those  first  obtained.  In  Blood  drawn  during  Inflammatory  states, 
again,  the  coagulation  is  usually  slow,  but  the  clot  is  preternaturally  firm; 
especially  at  its  upper  part,  where  the  Buffy  coat  (§  588)  or  colourless  stratum 
of  Fibrin,  gradually  contracts,  and  produces  the  cup,  which  is  usually  regarded 
as  indicative  of  a  high  degree  of  Inflammation.  Except,  under  the  peculiar 
circumstances  just  stated,  the  Blood  withdrawn  from  the  body  always  coag- 
ulates;* whether  it  be  kept  at  rest  or  in  motion;  whether  its  temperature  be 
high  or  low ;  and  whether  it  be  excluded  from  the  air,  or  be  admitted  to  free 
contact  with  the  atmosphere.!  The  Coagulation  may  be  accelerated  or  retarded, 
however,  by  variation  in  these  conditions.  Thus,  if  the  Blood  be  continually 

*  Some  diseases  may,  perhaps,  be  an  exception;  non-coagulation  of  the  Blood  is  said 
to  be  characteristic  of  the  Scurvy,  but  this  is  erroneous.  In  very  severe  forms  of  Typhus, 
the  same  has  been  stated  to  occur. 

f  f[An  inexplicable  case,  in  which  the  complete  coagulation  of  the  blood  did  not  take  place 
till  fifteen  days  after  its  abstraction,  has  been  published  by  Dr.  Pollit,  who  adduces  this 
case  in  proof  that  there  is  no  blood  which  becomes  putrid  before  it  has  coagulated.  The 
patient  was  a  man  37  years  old,  with  acute  pneumonia.  The  blood  of  a  first  bleeding  was 
drawn  into  a  block-tin  vessel,  and  set  in  a  temperature  between  46°  and  52°.  It  remained 
liquid  for  eight  days,  the  blood-corpuscles  having  settled  to  the  bottom,  with  the  liquor  san- 
guinis  floating  above  them,  exactly  like  serum  pressed  from  a  clot.  On  the  ninth  day,  a 
membranous  pellicle  began  to  form  on  the  surface  of  the  fluid,  and  this  becoming  thicker, 
and  increasing  in  tenacity  and  consistence,  acquired  at  last- all  the  characters  of  the  most 
genuine  bufify  coat.  The  serum  began  to  ooze  from  the  clot  on  the  fifteenth  day  :  and  on 


Gazzetia  Medica  di  Milano,Gennaio  20,  1844. 


PROPERTIES  OF  THE  BLOOD.  443 

gitated  in  a  bottle,  its  coagulation  is  delayed,  though  it  will  at  last  take  place 
in  shreds  or  insulated  portions ;  but  that  rest  is  not  the  cause  of  its  coagula- 
tion (as  some  have  supposed),  is  proved  by  the  fact  that,  if  a  portion  of  blood 
be  included  between  two  ligatures  in  a  living  vessel,  it  will  remain  fluid  for  a 
long  time.  Again,  the  Coagulation  is  accelerated  by  moderate  heat,  and 
jetarded  by  cold ;  but  it  is  not  prevented  by  even  extreme  cold ;  for,  if  blood 
be  frozen  immediately  that  it  is  drawn,  it  will  coagulate  on  being  thawed. 
Moreover  it  is  accelerated  by  exposure  to  air,  but  it  is  not  prevented  by  com- 
plete exclusion  from  it,  as  is  proved  by  its  taking  place  in  a  vacuum,  or  in  a 
shut  sac  within  the  dead  body:  complete  exclusion  from  the  air,  however, 
retards  the  change ;  as  has  been  shown  by  causing  Blood  to  flow  into  a  vessel 
containing  oil,  which  will  form  an  impervious  coating  on  its  surface,  and  will 
occasion  the  coagulation  to  take  place  so  slowly,  that  the  Red  particles  have 
time  to  subside,  and  the  upper  stratum  of  the  clot  is  colourless.*  An  extrica- 
tion of  Carbonic  acid  usually  takes  place  to  a  slight  degree  during  coagula- 
tion ;  but  this  is  not  a  constant  occurrence  ;  and  the  process  is  not  prevented, 
even  by  agitating  Carbonic  acid  with  the  Blood. 

585.  The  proportions  of  Serum  and  Clot  which  present  themselves  after 
coagulation  are  liable  to  great  variation,  independently  of  the  amount  of  the 
several  ingredients  characteristic  of  each ;  for  the  Coagulum  may  include  not 
only  the  Fibrin  and  Red  particles,  but  also  a  large  proportion  of  the  Serum, 
entangled  as  it  were  in  its  substance.  This  is  particularly  the  case  when  the 
coagulation  is  rapid ;  and  the  clot  then  expels  little  or  none  of  it  by  subsequent 
contraction.  On  the  other  hand,  if  the  coagulation  be  slow,  the  particles  of 
Fibrin  seem  to  become  more  completely  aggregated,  the  coagulum  is  denser 
at  first,  and  its  density  is  greatly  increased  by  subsequent  contraction.  When 
a  firm  fresh  clot  is  removed  from  the  fluid  in  which  it  is  immersed,  its  concre- 
tion is  found  to  continue  fqr  24  or  even  48  hours,  serum  being  squeezed  out 
in  drops  upon  its  surface ;  and  in  order,  therefore,  to  form  a  proper  estimate 
of  the  relative  proportions  of  Crassamentum  and  Serum,  the  former  should  be 
cut  into  slices,  and  laid  upon  bibulous  paper,  that  the  latter  may  be  pressed 
from  it  as  completely  as  possible. — According  to  the  experiments  of  Mr. 
Thackrah,  Coagulation  takes  place  sooner  in  metallic  vessels  than  in  those  of 
glass  or  earthenware,  and  the  quantity  of  Serum  separated  is  much  less ;  in 
one  instance  the  proportion  of  Serum  to  Clot  was  as  10  to  24£,  when  the  blood 
coagulated  in  a  glass  vessel;  whilst  a  portion  of  the  same  Blood,  coagulating 
in  a  pewter  vessel,  gave  only  10  of  Serum  to  175  of  Clot.  The  Specific 
Gravity  of  Blood  is  no  measure  of  its  coagulating  power;  for  a  high  specific 
gravity  may  be  due  to  an  excess  in  the  amount  of  globules,  which  form  the 
heaviest  part  of  the  blood;  and  may  be  accompanied  by  a  diminution  in  the 
quantity  of  fibrin,  which  is  the  coagulating  element. 

586.  The  Serum,  when  completely  separated  from  the  Crassamentum,  may 
be  said  to  contain  all  the  Albumen  and  Saline  matter  of  the  Blood ;  together 
with  a  portion  of  the  Fatty  matter  (of  which  some  adheres  to  the  Fibrin),  and 
those  "  ill  defined  animal  principles"  which  are  included  under  the  designa- 

the  clot  being  now  taken  out  of  the  vessel,  it  was  found  that  the  upper  four-fifths  of  it 
consisted  of  buffy  coat,  and  only  the  lower  fifth  clot  coloured  with  corpuscles.  The  serum 
which  continued  to  be  expressed  was  perfectly  transparent,  and  the  blood  did  not  show 
signs  of  putrefaction  till  a  month  after  it  had  been  drawn  from  the  body.  A  small 
quantity  drawn  from  another  pneumonic  patient,  and  placed  under  the  same  circum- 
stances, was  completely  coagulated  in  two  hours,  and  was  quite  putrid  in  fifteen  days. 
In  fifteen  bleedings  of  the  same  patient  in  the  following  eight  days,  the  blood  drawn 
gradually  lost  its  indisposition  to  coagulate,  the  whole  process  being  completed  each  time 
in  twelve  hours  or  less.  The  patient  recovered.— M.  C.] 
*  Babington  in  Medico-Chirurgical  Transactions,  vol.  xvi. 


444  OF  NUTRITION. 

tion  "  extractive  matter."  Its  Specific  Gravity  may  be  stated  at  about  1030 
in  health;  and  it  contains  about  9^  per  cent,  of  solid  matter.  When  it  is 
heated  to  160°,  its  Albumen  coagulates  and  the  remaining  fluid  may  be  sepa- 
rated by  pressure.  This  fluid  still  contains  some  Albumen,  which  is  held  in 
solution  by  free  alkali ;  for  if  the  latter  be  neutralized  by  Acetic  acid,  a  further 
precipitation  takes  place  on  the  application  of  heat.  The  fatty  matter,  which 
may  be  separated  by  ether,  seems  to  be  nearly  allied  to  the  several  fatty  sub- 
stances formed  in  the  body  ;  for  some  chemists  have  determined  it  to  consist 
of  Oleine,  Margarine,  and  Stearine,  the  constituents  of  ordinary  fat ;  whilst  others 
regard  it  as  analogous  to  Cerebrine,  the  fatty  matter  of  the  brain ;  and  others, 
again,  consider  it  to  bear  a  closer  resemblance  to  Cholesterine,  the  fatty  matter 
of  the  bile.  The  Extractive,  matter  partly  consists  of  Lactic  acid,  partly  of  a 
substance  called  Osmazome  ;  it  is  believed  by  Berzelius  that  this  portion  of 
the  blood  contains  the  resultants  of  the  acts  of  decomposition  continually  taking 
place  in  the  body  ;  and  that  it  is  chiefly,  therefore,  from  this  that  the  excre- 
tions are  formed. 

587.  It  cannot  be  doubted  that,  upon  the  due  admixture  in  the  Blood  of  all 
these  elements,  the  regular  performance  of  its  actions  is  dependent.     In  regard 
to  its  physical  properties  merely,  it  is  easily  shown  that  a  slight  alteration  may 
produce  the  most  injurious  consequences ;  for  a  certain  degree  of  viscidity  has 
been  found  (by  the  experiments  of  Poisseuille)  to  favour  the  passage  of  fluid 
through  capillary  tubes;  and  thus,  if  the  viscidity  of  the  blood  be  diminished 
by  a  loss  of  part  of  its  Fibrin,  stagnation  of  the  current,  and  extravasation  of 
a  portion  of  the  contents  of  the  vessels,  will  be  the  result.     This  has  been 
fully  proved  by  the  numerous  experiments  of  Magendie ;  and  the  fact  is  one 
of  very  important  Pathological  applications  (§  592  6).     In  regard  to  the  effect 
of  alterations  in  the  amount  of  the  Red  Particles,  our  information  is  less  satis- 
factory, since  it  is  almost  impossible  to  deprive  Blood  of  these,  without  at  the 
same  time  defibrinizing  it.     It  appears,  however,  from  the  experiments  of 
Dieffenbach  on  transfusion,  that  they  are  more  effectual  as  stimuli  to  the 
Heart's  action,  than  is  any  other  constituent  of  the  blood ;    and,  if  the  hypo- 
thetical account  of  their  use  already  offered  (§  576)  have  any  correctness,  they 
must  be  important  agents  in  the  maintenance  of  the  Capillary  Circulation  also. 
The  rapidity  with  which  they  may  be  decomposed  and  reconstituted,  is  made 
remarkably  evident  by  the  experiments  of  Magendie,  who  found  that,  when 
the  Blood  of  one  animal  was  injected  into  the  veins  of  another  having  discs  of 
very  different  size  and  form  (care  being  taken  to  prevent  the  coagulation  of 
the  Fibrin  during  the  operation),  the  original  Red  particles  soon  disappeared, 
and  were  replaced  by  those  characteristic  of  the  species,  in  whose  veins  the 
fluid  was  circulating.     The  Albumen  of  the  Blood  seems  to  be  chiefly  of  im- 
portance as  the  material  from  which  Fibrin  is  elaborated.     The  continual 
drain  upon  the  Fibrin,  which  is  taking  place  in  the  capillaries  of  the  system, 
is  made  evident  by  the  remarkable  fact,  that  Arterial  blood  contains  a  much 
larger  proportion  of  it  than  Venous, — the  excess  being  usually  about  one-fifth. 

588.  The  Crassamentum  not  unfrequently  exhibits,  in  certain  disordered 
conditions  of  the  Blood,  a  layer  of  Fibrin  nearly  free  from  colour;  and  this  is 
known  as  the  Buffy  coat.     The  presence  of  this  has  been  frequently  regarded 
as  a  sign  of  the  existence  of  Inflammation,  occasioning  an  undue  predominance 
of  Fibrin ;    but  this  idea  is  far  from  being  correct,  since,  as  will  presently 
appear,  (589),  it  may  result  from  a  very  opposite  condition  of  the  Blood.     A 
similar  colourless  layer  of  Fibrin  is  always  observable,  when  the  Coagulation 
of  the  blood  is  retarded  by  the  addition  of  agents  that  have  the  power  of  delay- 
ing it  ( §  582) ;  and  since,  in  Inflammatory  states  of  the  system,  the  blood  is 
generally  long  in  coagulating,  it  has  been  supposed  that  the  separation  of  the 


PROPERTIES  OF  THE  BLOOD.  445 

red  particles  is  due  to  this  cause  alone.  Dr.  Alison,*  however,  maintains 
that  there  must  be  an  absolute  tendency  to  separation  between  the  two  compo- 
nents of  the  clot,  in  order  to  account  for  the  phenomena  sometimes  presented 
by  it;  and  he  adduces  the  two  following  reasons  in  support  of  this  view. 
"  1,  The  formation  of  the  Buffy  coat,  though  no  doubt  favoured  or  rendered 
more  complete  by  slow  coagulation,  is  often  observed  in  cases  where  the 
coagulation  is  more  rapid  than  usual;  and  the  colouring  matter  is  usually 
observed  to  retire  from  the  surface  of  the  fluid  in  such  cases,  before  any  coagu- 
lation has  commenced.  2.  The  separation  of  the  Fibrin  from  the  colouring 
matter  in  such  cases  takes  place  in  films  of  blood  so  thin  as  not  to  admit  of  a 
stratum  of  the  one  being  laid  above  the  other ;  they  separate  from  each  other 
laterally,  and  the  films  acquire  a  speckled  or  mottled  appearance,  equally 
characteristic  of  the  state  of  the  blood  with  the  buffy  coat  itself."  It  appears 
from  the  observations  of  Mr.  Wharton  Jones,  that  the  red  corpuscles  of  Inflam- 
matory Blood  have  an  unusual  attraction  for  each  other,  which  occasions  their 
coalescence  in  piles  and  masses ;  so  that  by  this  character,  the  state  of  the 
Blood  may  be  detected,  from  the  examination  of  no  more  than  a  single  drop  of 
the  fluid.  Now  if  we  consider,  in  connection  with  this  increase  in  the  mutual 
attraction  of  the  Blood  discs,  the  increase  in  the  mutual  attraction  of  the  par- 
ticles of  Fibrin  (which  causes  the  coagulation  of  Inflammatory  blood  to  be  so 
much  firmer  and  more  decidedly  fibrous  than  that  of  the  healthy  fluid),  we 
have  a  cause  sufficient  to  explain  the  phenomena  noticed  by  Dr.  Alison ; 
without  the  necessity  of  resorting  to  the  idea  of  an  absolute  repulsion  being 
present  between  the  two  constituents. — It  is  in  the  Buffy  Coat  of  Inflammatory 
Blood,  that  we  see  the  clearest  indications  of  organization  ever  presented  by 
the  circulating  fluid.  The  fibrous  network  is  frequently  extremely  distinct; 
and  it  commonly  includes  a  large  number  of  white  corpuscles  in  its  meshes. 
589.  When  the  Buff  arises  from  other  causes,  however,  its  appearance  is 
less  characteristic.  It  appears  from  the  researches  of  Andral,  that  the  essen- 
tial condition  of  its  production  is  an  increase  in  the  quantity  of  Fibrin  in 
proportion  to  the  Red  Corpuscles;  and  not  a  simple  increase  of  Fibrin. 
When  the  Blood  contains  an  excessive  quantity  of  Fibrin,  it  coagulates  slowly; 
thus  the  blood  of  a  patient  labouring  under  Rheumatism  coagulates  more 
slowly  than  that  of  one  affected  with  Typhoid  fever.  The  increase  may 
occur  in  two  ways ;  either  by  an  absolute  increase  in  the  Fibrin,  the  amount  of 
the  corpuscles  remaining  unchanged,  or  not  being  augmented  in  the  same 
proportion;  or  \>y  a  diminution  of  the  Corpuscles,  the  quantity  of  Fibrin 
remaining  the  same,  or  not  diminishing  in  the  same  proportion.  Hence  in 
severe  Chlorosis,  in  which  the  latter  condition  is  strongly  developed,  the  buffy 
coat  may  be  as  well  marked  as  in  the  severest  Inflammation.  Unless  the 
composition  of  the  blood  be  altered  in  one  of  these  two  ways,  it  is  stated  by 
Andral  that  the  buffy  coat  is  never  formed ;  the  influence  of  circumstances 
which  favour  it  not  being  sufficient  to  produce  it  when  acting  alone.  The 
absence  of  these  circumstances  may  prevent  it,  however,  when  it  would 
otherwise  have  been  formed ;  thus,  when  the  Blood  flows  slowly,  the  buff  is 
not  properly  produced  ;  because  the  slow  discharge  gives  one  portion  time  to 
coagulate  before  another ;  and  only  the  blood  last  drawn  furnishes  the  Fibrin 
at  the  upper  part  of  the  vessel.  Again,  in  a  deep  narrow  vessel,  the  buff  will 
form  much  more  decidedly  than  in  a  broad  shallow  one  ;  because  the  thickness 
of  the  Fibrinous  crust  will  be  greater.  If  the  blood  be  agitated  during  its  co- 
agulation, the  Corpuscles  are  mixed  up  with  the  Fibrin,  and  the  crust  is 
imperfect  and  soft.  The  process  of  the  formation  of  the  Buffy  coat  may  be 
best  studied  by  treating  ordinary  Blood  with  some  of  those  agents  which  re- 

*  Outlines  of  Physiology,  3d  edition,  p.  89. 

38 


446  OF  NUTRITION. 

tard  its  coagulation.  Of  these,  the  Sulphate  of  Soda  is  stated  by  Andral  to  be 
the  best,  producing  no  alteration  in  the  character  of  the  elements,  but  simply 
delaying  their  change  of  state ;  and  the  following  is  his  account  of  the  appear- 
ances observed.  After  a  few  minutes  the  blood  separates  into  two  parts ;  the 
lower  one  contains  the  globules  collected  together  into  a  soft  mass ;  the  upper 
one  is  at  first  transparent  and  resembles  serum,  but  soon  becomes  opaque.  At 
this  period  a  number  of  globular  white  corpuscles  may  be  seen  in  it  with  the 
microscope;  and  these  form  the  first  degree  of  solidification  of  the  fibrin. 
After  48  hours,  the  fluid  contains  numerous  flocci  like  spiders'-webs ;  which 
flocci  are  chiefly  composed  of  the  Fibrin  set  free  from  the  white  corpuscles  : 
this  is  the  second  stage  of  solidification.  After  96  hours,  the  fluid  recovers 
its  transparency  and  contains  no  trace  of  separate  corpuscles ;  but  the  flocci 
are  more  numerous,  more  firm,  and  constitute  an  irregular  web  composed  of 
fibres  arranged  in  various  directions.  Where  the  web  is  thickest,  several 
reticulated  layers  may  be  seen,  the  one  placed  over  the  other ;  and  in  the 
midst  of  the  distinct  fibres,  several  strings  of  corpuscles,  still  retaining  their 
globular  character,  are  perceived.  This  state  of  organization  is  intermediate 
between  that,  in  which  the  Corpuscles  are  altogether  separate,  and  that  in 
which  a  firm  coagulation  of  the  Fibrin  takes  place  ;  and  it  may  be  seen  to  be 
that,  through  which  the  buffy  coat  passes  in  the  progress  of  its  formation 

• 

V.  Pathological  Changes  in  the  Blood. 

590.  From  the  part  which  the  Blood  performs  in  the  ordinary  processes  of 
Nutrition,  it  cannot  be  doubted  that  it  undergoes  important  alterations,  when 
these  processes  take  place  in  an  abnormal  manner.  These  alterations  must 
be  sometimes  the  causes,  and  sometimes  the  effects,  of  the  morbid  phenomena, 
which  constitute  what  we  term  the  Disease.  Thus,  when  some  local  cause, 
affecting  the  solid  tissues  of  a  certain  part  of  the  body,  produces  Inflammation 
in  them,  their  normal  relation  to  the  blood  is  altered ;  the  consequence  is,  that 
the  blood,  in  passing  through  them,  undergoes  a  different  set  of  changes  from 
those,  for  which  it  is  originally  adapted ;  and  thus  its  own  character  undergoes 
a  change,  which  soon  becomes  evident  throughout  the  whole  mass  of  the  cir- 
culating fluid,  and  is,  in  its  turn,  the  cause  of  morbid  phenomena  in  remote 
parts  of  the  system.  On  the  other  hand,  the  strong  analogy  between  many 
Constitutional  diseases,  and  the  effects  of  poisonous  agents  introduced  into  the 
blood,  appears  clearly  to  point  to  the  inference,  that  these  diseases  are  due  to 
the  action  of  some  morbific  matter,  which  has  been  directly  introduced  into 
the  current  of  the  circulating  fluid,  and  which  has  affected  both  its  physical 
and  its  vital  properties.*  Here,  then,  is  a  wide  field  for  investigation,  of 
which  the  surface  can  scarcely  be  said  to  be  yet  broken  up,  and  which  must 
yield  an  abundant  harvest  to  those  who  shall  cultivate  it  with  intelligence  and 
zeal.  The  only  connected  researches  which  have  been  yet  published,  on  the 
changes  which  the  blood  undergoes  in  disease,  are  those  of  MM.  Andral  and 
Gavarret  ;t  and  these  are  confined  to  the  alterations  which  take  place  in  the 

*  This  doctrine  has  been  recently  brought  prominently  for  ward  §/  in  a  Paper  on  Sym- 
metrical Diseases,  read  by  Dr.  William  Budd  before  the  Medico-Chirurgical  Society, 
Dec.  16,  1841.  The  Author  ingeniously  proves,  that  the  symmetry  of  many  diseases 
(such  as  certain  forms  of  cutaneous  eruptions,' rheumatism,  &c.)  which  do  riot  imme- 
diately depend  upon  external  causes,  necessarily  involves  the  idea  of  the  conveyance  of 
the  morbific  agent  in  the  circulating  fluid;  the  palsy  produced  by  lead  is  a  very  interest- 
ing example,  in  which  the  agent  is  known  to  be  mingled  with  the  blood,  and  to  be  depo- 
sited in  the  parts  affected,  which  are  generally,  if  not  always,  symmetrical. 

f  An  account  of  these  inquiries  will  be  found  in  the  Provincial  Medical  and  Surgical 
Journal  for  May,  June,  and  July,  1841;  in  the  Annales  des  Sciences  Naturelles,  Dec. 
1840,  and  March  1841 ;  and  in  the  Ann.  de  Chimie,  Tom.  Ixxv.  They  have  since  been 
published  in  a  separate  form,  under  the  title  of  "Essai  d'Hematologie  Pathologique." 


PATHOLOGICAL  CHANGES  IN  THE  BLOOD.  447 

proportions  of  the  Organic  elements  of  the  fluid.  It  is  of  course  necessary  to 
determine,  in  the  first  instance,  what  are  the  usual  or  normal  proportions ; 
and  the  following  is  estimated  by  them,  from  numerous  analyses,  as  the  ordi- 
nary quantity*  of  each  element  in  1000  parts  of  healthy  blood. 

Fibrin 3 

Globules 127 

Solid  matter  of  serum 80 

Water 790 

The  proportion  of  Fibrin  may  vary,  within  the  limits  of  health,  from  2£  to  3£, 
or  even  from  2  to  4:  but  these  last  extremes  are  rarely  met  with  in  perfect 
health ;  and  must  be  considered,  when  they  occur,  as  exceptions  dependent 
on  idiosyncrasy.  The  extremes  in  the  proportion  of  Globules,  in  the  physio- 
logical condition  of  the  system,  are  fixed  at  110  and  140;  the  latter  converging 
towards  the  condition  of  the  blood  characteristic  of  Plethora. 

591.  The  inquiries  which  have  been  made  by  Andral,  in  regard  to  the 
alterations  which  these  proportions  undergo  in  various  states  of  Disease,  have 
already  led  to  results  of  great  interest  and  value ;  and  there  can  be  no  doubt 
that  these  will  be  greatly  extended,  when  this  simple  analytical  process  shall 
have  been  more  generally  employed.  As  an  instance  of  the  erroneous  conclu- 
sions into  which  we  may  be  led,  by  merely  attending  to  the  size  of  the  crassa- 
rnentum,  it  may  be  remarked  that  the  existence  of  a  large  Clot  does  not  by 
any  means  necessarily  imply  the  presence  of  an  increased  amount  of  Fibrin ; 
since  it  may  depend  upon  the  retention  within  it  of  a  large  proportion  of 
Serum,  consequent  upon  the  deficient  contractile  power  of  the  clot,  which 
results  from  a  diminution  in  the  proportion  of  Fibrin.  When  the  clot  is  dense 
and  contains  but  little  Serum,  it  may  be  judged  to  contain  a  full  proportion  of 
Fibrin,  even  though  it  may  itself  be  small. — Before  entering  upon  the  con- 
sideration of  the  alterations  in  the  Blood  which  are  affected  by  particular  mor- 
bid states,  Andral  notices  two  extraneous  causes,  usually  operating  in  disease, 
which  may  affect  the  result.  These  are,  abstinence  from  food,  and  loss  of 
blood  by  venesection.  It  has  been  commonly  stated,  that  they  have  a  tendency 
to  diminish  the  proportion  of  all  the  solid  elements  of  the  blood;  but  this  is  not 
the  case ;  for  they  seem  especially  to  act  upon  the  Globules,  the  quantity  of 
Fibrin  remaining  nearly  the  same, — unless  the  hemorrhage  have  been  very 

*  The  analysis  of  the  Blood  with  reference  to  the  quantity  of  the  chief  proximate  ele- 
ments which  it  may  contain,  is  very  easily 'accomplished;  and  as  the  determination  of 
this  is  the  point  of  most  practical  importance,  the  method  adopted  in  the  inquiries  of 
MM.  Andral  and  Gavarret  will  be  here  detailed. — The  blood  is  caused  to  flow  into  two 
different  vessels;  into  one  vessel,  the  first  and  last  quarters  of  the  blood  are  received; 
and  into  the  other,  the  second  and  third  quarters:  in  this  manner,  the  similarity  of  the 
two  quantities  is  secured  as  far  as  possible.  The  blood  in  one  vessel  is  allowed  to  coag- 
ulate spontaneously;  that  in  the  other  is  beaten  with  a  small  rod,  in  order  to  separate  the 
fibrin.  When  the  first  portion  is  completely  coagulated,  the  serum  is  carefully  separated 
from  the  crassamentum;  and  there  are  then  dried  and  weighed, — 1.  The  Fibrin  obtained 
by  the  rod; — 2.  The  whole  Crassamentum; — 3.  The  Serum.  The  weight  of  the  sepa- 
rated fibrin  gives  us  the  quantity  of  it  contained  in  the  clot.  The  weight  of  the  serum 
after  complete  desiccation,  gives  us  the  proportional  quantity  of  solid  matter  contained 
in  its  water.  The  quantity  of  water  driven  off"  from  the  clot  in.  drying,  gives  us  the 
amount  of  serum  it  contained;  from  which  may  be  estimated  the  proportion  of  the  solid 
matter  of  the  serum  that  the  crassamentum  included.  Hence,  by  deducting  from  the 
weight  of  the  whole  dried  clot,  first,  that  of  the  fibrin  separated  by  agitation,  and  then  that 
of  the  solid  elements  of  the  serum,  ascertained  by  calculation,  we  obtain  the  weight  of 
the  globules.  In  order  to  ascertain  the  whole  amount  of  solid  matter  in  the  serum,  that 
which  was  ascertained  by  calculation  to  exist  in  the  fibrin,  is  added  to  that  which  was 
obtained  from  the  separate  serum.  The  proportion  of  organic  and  of  inorganic  matter  in, 
this  solid  residuum,  is  ascertained  by  incinerating  it  in  a  crucible;  by  which  the  whole 
of  the  former  will  be  driven  off,  and  the  latter  will  be  left. 


448  OF  NUTRITION. 

severe,  in  which  case  the  Fibrin  and  the  solid  matter  of  the  Serum  are  also 
reduced  in  amount.  The  extreme  variations  of  each  ingredient  noticed  by 
Andral  were,— Fibrin,  from  0-9  to  10-0  in  every  1000  parts  of  Blood;  the 
Globules,  from  21  to  185;  the  solid  parts  of  the  Serum,  from  57  to  104:  and 
the  Water  from  725  to  915.  The  smallest  proportion  of  Globules,  and  the 
largest  amount  of  Water,  were  presented  in  a  case  of  severe  uterine  hemor- 
rhage. 

a  The  most  important  fact  substantiated  by  Andral  is  one  that  had  been  previously 
suspected,— the  invariable  increase  in  the  quantity  of  Fibrin  during  acute  Inflammatory 
affections;  the  increase  being  strictly  proportional  to  the  intensity  of  the  Inflammation, 
and  to  the  degree  of  symptomatic  Fever  accompanying  it.  "  The  augmentation  of  the 
quantity  of  Fibrin  is  so  certain  a  sign  of  Inflammation,  that,  if  we  find  more  than  5  parts 
of  fibrin  in  1000,  in  the  course  of  any  disease,  we  may  positively  affirm  that  some  local 
inflammation  exists."  Several  cases  are  mentioned,  in  which  an  increase  to  7  or  7£ 
parts  took  place,  without  any  apparent  cause;  but  in  which  it  afterwards  proved  that 
severe  local  inflammation  was  present:  and  thus  we  are  furnished  with  a  pathognomonic 
sign  of  great  importance.  The  average  augmentation  of  Fibrin  in  inflammation  may  be 
estimated  at  7;  the  minimum  at  5;  the  maximum  at  10£.  It  does  not  appear  that  in. 
robust  athletic  persons,  the  proportion  of  Fibrin  is  greater  than  in  those  of  feeble  consti- 
tution ;  in  the  latter  it  is  the  Globules  that  are  deficient ;  and  it  is  rather  from  this  dispro- 
portion, than  from,  an  absolute  excess  of  Fibrin,  that  their  greater  liability  to  Inflamma- 
tory affections  arises.  Diseases  which  commence  at  the  same  time  as  the  Inf1  ammation, 
or  co-exist  with  it,  do  not  prevent  the  characteristic  increase  of  the  Fibrin ;  thus  in 
Chlorotic  females,  the  proportion  rises  to  6  or  7,  under  this  influence.  The  augmenta- 
tion is  observed  at  the  very  outset  of  the  affection ;  the  quantity  increases  with  its 
progress;  and  a  decrease  shows  itself  when  the  disease  begins  to  abate.*  When  the 
disease  presents  alternations  of  increase  and  decline,  these  are  marked  by  precisely  cor- 
responding changes  in  the  quantity  of  Fibrin.  It  appears  that  the  rise  of  the  quantity  of 
Fibrin  above  the  normal  standard  is  not  immediately  checked  by  venesection ;  this  does 
not  prove,  however,  that  bleeding  is  useless  ;  but  only  that  it  cannot  arrest  instanter  the 
tendency  to  the  production  of  an  increased  quantity  of  Fibrin.  It  is  a  curious  fact,  that 
an  augmentation  is  commonly  observable  during  the  advanced  stage  of  Phthisis,  in  spite 
of  the  deterioration  which  the  blood  must  then  have  undergone;  this  is  probably  depend- 
ent upon  the  development  of  local  inflammation  around  the  tubercular  deposits.  Some 
experiments  performed  by  M.  Andral  on  the  blood  of  pregnant  women  seem  to  lead  to 
the  conclusion  that,  during  the  first  six  months,  the  Fibrin  is  below  the  normal  standard ; 
and  that  it  subsequently  varies,  usually  undergoing  an  augmentation  between  the  sixth 
and  seventh,  and  the  eighth  and  ninth  months.  There  is  also  a  diminution  in  the  Globules ; 
and  these  circumstances  combined  favour  the  production  of  the  buffy  coat  (§  589). 

b.  It  appears  obvious,  from  what  has  been  just  stated,  that  the  increase  in  the  quantity 
of  Fibrin  is  not  dependent  upon  the  febrile  condition,  which  is  secondary  to  the  local 
inflammation,  but  upon  the  Inflammation  itself.  This  conclusion  is  confirmed  by  the 
interesting  fact  that,  in  idiopathic  Fever,  the  proportion  of  Fibrin  is  diminished,  instead 
of  undergoing  an  increase.  This  diminution  was  constantly  observed  by  Andral  in  the 
premonitory  stage  of  Continued  Fever;  in  some  instances  the  amount  was  no  more  than 
1-6  parts  in  1000.  The  proportion  of  Globules  was  found  to  have  usually,  but  not  con- 
stantly, undergone  an  increase;  as  had  also  thatttf  the  solid  parts  of  the  Serum.  In 
ordinary  Continued  Fever,  in  which  there  was  no  evident  complication  from  local  disease, 
the  quantity  of  Fibrin  varied  from  4-2  to  2-2;  that  of  the  Globules  from  185-1  to  103  6 
(excluding  a  case  in  which  their  amount  was  only  82-5,  which  was  that  of  a  Chlorotic 
female);  that  of  the  solid  matter  of  the  Serum,  from  98-7  to  90-9;  and  that  of  the  Water 
from  725-6  to  851-9.  Hence  the  quantity  of  solid  matter  appears  to  be  usually  increased  ; 
but  the  peculiar  condition  of  the  disease  may  probably  be  stated  to  be,  an  increase  in  the 

*  By  experiments  on  animals,  M.  Andral  has  ascertained  that  no  circumstance  of  pre- 
vious debility  or  privation  prevent  this  characteristic  change.  Having  ascertained  the 
amount  of  fibrin  in  the  blood  of  three  dogs  to  be  2-3,  2-2,  and  1-6  (the  natural  range  for 
these  animals),  he  deprived  them,  completely  or  partially  of  food.  On  the  fourteenth 
day,  the  proportion  of  fibrin  had  risen,  in  the  first,  to  4-5:  and  in  the  second,  to  4:  these 
animals  had  no  food.  In  the  third  dog,  which  was  supplied  with  a  very  small  quantity 
of  food  daily,  the  same  condition  developed  itself  at  a  later  period;  the  blood  on  the  four- 
teenth day  exhibiting  only  1-8  parts  of  fibrin;  but  on  the  twenty-second  day  presenting 
3-3  parts. — In  all  these  instances,  the  elevation  in  the  proportion  of  fibrin  was  coincident 
with  Inflammatory  changes  in  the  stomach. 


PATHOLOGICAL  CHANGES  IN  THE  BLOOD.  449 

proportion  of  the  Globules  to  the  Fibrin.  When,  however,  a  local  Inflammatory  affection 
develops  itself  during  the  course  of  the  Fever,  the  amount  of  Fibrin  increases;  but  its 
augmentation  seems  to  be  kept  down  by  the  febrile  condition. — In  Typhoid  Fever,*  the 
decrease  in  the  proportion  of  Fibrin  is  much  more  decidedly  marked;  this  dues  not 
depend  upon  abstinence;  for  it  ceases  as  soon  as  a  favourable  change  occurs  in  the 
disease,  long  before  the  effect  of  food  could  show  itself.  In  the  various  cases  examined 
by  Andral,  the  blood  furnished  a  maximum  of  37  of  Fibrin,  and  a  minimum  of  0-9;  in 
this  last  case,  the  Typhoid  condition  existed  in  extreme  intensity,  yet  the  patient  recovered. 
The  proportion  of  Globules  varies  considerably;  in  an  early  stage  of  the  disease  it  is 
usually  found  to  be  absolutely  high;  and  it  always  remains  high  relatively  to  the  amount 
of  Fibrin.  In  Typhoid  Fever,  then,  the  abnormal  condition  of  the  Blood,  in  regard  to 
the  disproportion  between  the  Globules  and  the  Fibrin,  is  more  strongly  marked  than  in 
ordinary  Continued  Fever:  yet  the  usual  augmentation  of  Fibrin  will  take  place,  if  a 
local  inflammation  develops  itself.  In  the  Eruptive  Fevers,  it  does  not  appear  that  the 
proportion  between  the  Fibrin  and  the  Globules  undergoes  so  striking  a  change,  as  in 
Ordinary  continued  Fever;  but  the  number  of  cases  examined  was  too  small  to  admit 
of  decided  conclusions.  It  was  evident,  however,  that  the  specific  Inflammations  proper 
to,  and  characteristic  of,  these  Fevers,  have  not  the  same  effect  in  occasioning  an  increase 
of  the  Fibrin,  as  an  intercurrent  Inflammation  of  an  extraneous  character. — By  the  expe- 
riments of  Magendie  it  has  been  ascertained,  that  one  of  the  effects  of  a  diminution  in 
the  proportion  of  Fibrin  is  a  tendency  to  the  occurrence  of  Hemorrhage  or  of  Conges- 
tion, either  in  the  parenchymatous  tissue,  or  on  the  surface  of  membranes:  these  con- 
ditions are  well  known  to  be  of  frequent  occurrence,  as  complications  of  febrile  disorders. 
A  marked  diminution  of  Fibrin  was  noticed  also  in  many  cases  of  the  disorder  termed 
Cerebral  Congestion,  which  commences  with  headache,  vertigo,  and  tendency  to  epis- 
taxis,  and  not  unfrequently  passes  into  coma  and  apoplexy.  In  Apoplexy,  the  diminution 
of  Fibrin  was  still  more  striking;  and  in  general,  there  was  found  to  be  an  increase  of 
the  Globules.  In  one  instance,  the  quantity  of  Fibrin  on  the  second  day  of  the  attack 
was  found  to  have  fallen  to  1-9,  whilst  that  of  the  Globules  had  risen  to  175-5;  but  on  the 
third  day,  when  the  patient's  consciousness  began  to  return,  the  quantity  of  Fibrin  was 
3-5,  whilst  that  of  the  Globules  had  fallen  to  137-7.  It  would  seem,  from  the  great  change 
in  the  character  of  the  Blood,  which  was  noticed  in  this  and  in  other  instances,  that  the 
want  of  due  proportion  between  the  Fibrin  and  the  Globules  was  the  cause,  rather  than 
the  effect,  of  the  Apoplectic  attack. 

c.  The  amount  of  Globules  seems  to  be  subject  to  greater  variation  within  the  limits  of 
ordinary  health,  than  is  that  of  Fibrin.  In  the  condition  which  is  ordinarily  termed  a 
highly  sanguineous  temperament,  or  Plethora,  it  is  chiefly  the  former  that  undergoes  an 
increase.  Plethoric  persons  are  not  more  liable  to  Inflammation,  than  are  those  of 
weaker  constitution;  but,  from  the  quantity  of  Fibrin  in  their  blood  being  small  rela- 
tively to  that  of  the  Globules,  they  are  liable  to  Congestion,  especially  of  the  brain,  and 
to  apoplexy  or  other  Hemorrhage.  The  effect  of  Bleeding  in  diminishing  this  tendency 
is  now  intelligible;  since  we  know  that  loss  of  blood  reduces  the  number  of  Globules. — 
On  the  other  hand,  in  that  temperament,f  which,  when  exaggerated,  becomes  Anaemia, 
there  is  a  marked  diminution  of  the  globules;  this  temperament  may  lead  to  two  dif- 
ferent conditions  of  the  system.  In  Chlorosis,  the  Globules  are  diminished,  whilst  the 
Fibrin  remains  the  same;  so  that  the  clot,  though  small,  is  firm,  and  not  unfrequently 
exhibits  the  buffy  coat;  in  some  extreme  cases  of  this  disease,  the  Globules  have  been 
found  as  low  as  27.  The  influence  of  the  remedial  administration  of  Iron,  in  increasing 
the  quantity  of  Globules,  was  rendered  extremely  perceptible  by  Andral's  analyses;  in 
one  instance,  after  iron  had  been  taken  for  a  short  time,  the  proportion  of  Globules  was 
found  to  have  risen  from  49-7  to  64-3;  whilst  in  another,  in  which  it  had  been  longer  con- 
tinued, it  had  risen  from  46-6  to  95-7.  On  the  other  hand,  Bleeding  reduced  still  lower 
the  proportion  of  Globules;  thus,  in  one  instance,  their  amount  was  found,  on  a  second 
bleeding,  to  have  sunk  from  62-8  to  49.  The  full  proportion  of  Fibrin  in  the  blood  of 
Chlorotic  patients  accounts  for  the  infrequency  of  Hemorrhage  in  them;  whilst  it  also 
leads  us  to  perceive  that  they  may  be,  equally  with  others,  the  subjects  of  acute  Inflam- 
mation, which  we  know  to  be  the  fact.  A  diminution  of  Globules  may  also  coexist  with 
a  diminution  in  the  amount,  or  in  the  degree  of  elaboration,  of  the  Fibrin ;  and  this 
degree  seems  to  be  characteristic  of  Scrofula.  Andral  has  noticed  a  diminution  in  the 
proportion  of  Globules  in  other  Cachectic  states,  resulting  from  the  influence  of  various 
depressing  causes  on  the  nutritive  powers ; — as  in  a  case  of  Diabetes  Mellitus,  in  which 

*  M.  Andral  confines  this  term  to  the  species  characterized  by  ulceration  of  the  mucous 
follicles  of  the  intestinal  canal. 

f  The  term  lymphatic  has  been  applied  to  this  temperament;  by  which  term  was 
meant  a  predominance  of  lymph  in  the  absorbent  vessels. 

38* 


450  OF  NUTRITION. 

the  patient  was  much  exhausted; — a  case  of  Aneurismal  dilatation  of  the  Heart  inducing 
Dropsy; — and  in  several  cases  of  Cachexia  Saturnina. 

d.  The  chief  class  of  cases,  in  which  any  marked  change  has  been  observed  in  the 
amount  of  solid  matter  in  the  Serum,  is  that  of  Albuminuria,  or  Bright's  disease  of  the 
Kidney.  The  diminished  Specific  Gravity  of  the  Serum  was  long  ago  pointed  out  by  Dr. 
Christison;  but  Andral  remarks  that  this  is  not  an  accurate  criterion. since,  if  there  be  a 
diminished  amount  of  Globules  (as  is  not  unfrequenlly  the  case  in  this  disease),  the  pro- 
portion of  water  in  the  whole  will  be  increased,  and  the  specific  gravity  of  the  serum 
thus  lowered,  without  any  alteration  in  its  proper  quantity  of  solid  matter.  According  to 
Andral,  the  diminution  in  the  amount  of  Albumen  in  the  Serum  is  exactly  proportional 
to  the  quantity  contained  in  the  urine.  A  case  is  related  by  him,  under  this  head,  which 
affords  an  interesting  exemplification  of  the  general  facts,  that  have  been  already  attained 
by  his  investigations.  A  woman  who  had  been  suffering  from  Erysipelas  of  the  face, 
and  who  had  lost  blood  both  by  venesection  and  by  leeches,  became  the  subject  of  Albu- 
minuria. The  blood  drawn  at  this  time  exhibited  a  considerable  diminution  in  the  pro- 
portion of  Globules,  as  well  as  of  Albumen, — a  fact  which  the  previous  loss  of  blood 
fully  accounted  for.  After  a  short  period,  during  which  she  had  been  allowed  a  fuller 
diet,  another  experimental  bleeding  exhibited  an  increase  in  the  proportion  of  Globules. 
Some  time  afterwards,  when  the  Albumen  had  disappeared  from  the  Urine,  some  more 
blood  was  drawn ;  and  it  was  then  observed  that  the  Albumen  of  the  Serum  had  returned 
to  its  due  proportion,  but  that  the  Globules  had  again  diminished,  whilst  there  was  a 
marked  increase  in  the  quantity  of  Fibrin.  This  alteration  was  fully  accounted  for  by 
the  fact,  that,  in  the  interval,  several  Lymphatic  ganglia  in  the  neck  had  been  inflamed 
and  had  suppurated;  and  that  the  patent  had  been  again  placed  on  very  low  diet. 
"Thus,"  observes  Andral,  "we  were  enabled  to  give  a  complete  explanation  of  the 
remarkable  oscillations  which  were  presented,  in  the  proportion  of  the  different  elements 
of  the  blood  drawn  at  three  different  times  from  the  same  individual;  and  thus  it  is  that, 
the  more  extended  are  our  inquiries,  the  more  easy  does  it  become  to  refer  to  general 
principles  the  causes  of  all  those  changes  in  the  composition  of  the  blood,  which,  from 
the  frequency  and  rapidity  with  which  they  occur,  seem  at  first  sight  to  baffle  all  rules, 
and  to  take  place,  as  it  were,  at  random.  In  the  midst  of  this  apparent  disorder,  there  is 
but  the  fulfilment  of  laws,-  and  in  order  to  obtain  these,  it  is  only  necessary  to  strip  the 
phenomena  of  their  complications,  and  reduce  them  to  their  simplest  form." 

592.  That  the  Blood  is  subject  to  a  great  variety  of  other  morbid  alterations, 
which  are  sometimes  the  causes,  and  sometimes  the  results,  of  Disease,  cannot 
be  for  a  moment  doubted.  But  our  knowledge  of  the  nature  of  these  changes 
is  as  yet  very  insufficient.  The  great  amount  of  attention  which  is  being 
directed  by  Chemical  Pathologists  to  the  subject,  however,  will  doubtless  ere 
long  produce  some  important  results.  Among  the  most  frequent  causes  of 
depravation  in  the  character  of  this  fluid,  we  must  undoubtedly  rank  the  re- 
tention, in  the  Circulating  current  of  matters  which  ought  to  be  removed  by 
the  Excreting  processes.  We  have  already  seen,  that  a  total  interruption  to 
the  excretion  of  Carbonic  Acid  by  the  lungs,  will  occasion  death  in  the  course 
of  a  very  few  minutes  (§  546) ;  and  even  when  only  a  slight  impediment  is 
offered  it,  so  that  the  quantity  of  Carbonic  Acid  always  contained  in  arterial 
blood  is  augmented  to  but  a  small  degree,  a  feeling  of  discomfort  and  oppres- 
sion, increasing  with  the  duration  of  the  interruption,  is  speedily  produced. 
The  results  of  the  retention  of  the  materials  of  the  Biliary  and  Urinary  excre- 
tions will  be  hereafter  considered  (§§  661  and  670) ;  and  at  present  it  will  be 
only  remarked  that  such  retention  is  a  most  fertile  source  of  slight  disorders 
of  the  system,  that  it  is  largely  concerned  in  producing  many  severe  diseases, 
and  that  if  complete^  it  will  most  certainly  and  rapidly  produce  a  fatal  result. — 
The  most  remarkable  cases  of  depravation  of  the  Blood,  by  the  introduction  of 
matters  from  without,  are  those  in  which  these  substances  act  as  ferments, — 
exciting  such  Chemical  changes  in  the  constitution  of  the  fluid,  that  its  whole 
character  is  speedily  changed,  and  its  vital  properties  are  altogether  destroyed. 
Of  such  an  occurrence,  we  have  characteristic  examples  in  the  severe  forms 
of  Typhoid  fever,  commonly  termed  malignant;  in  Plague,  Glanders,  Pustule 
Maligne,  and  several  other  diseases  ;  in  some  of  which  we  can  trace  the  direct 
introduction  of  the  poison  into  the  blood,  whilst  in  others  we  must  infer  (from 


ORIGIN  OF  THE  SOLID  TISSUES.  451 

the  similarity  of  result)  that  it  has  been  introduced  through  some  obscure 
channel, — probably. the  lungs.  The  final  symptoms  which  are  common  to  all 
these  diseases  have  been  well  described  by  Dr.  Williams,*  under  the  title  of 
Necrsemia,  or  death  by  'depravation  of  the  blood.  "  Almost  simultaneously, 
the  heart  loses  its  power,  the  pulse  becomes  very  weak,  frequent,  and  un- 
steady :  the  vessels  lose  their  tone,  especially  the  capillaries  of  the  most  vas- 
cular organs,  and  congestions  occur  to  a  great  amount;  the  brain  becoming 
inactive,  and  stupor  ensues ;  the  medulla  is  torpid,  and  the  powers  of  respira- 
tion and  excretion  are  imperfect :  voluntary  motion  is  almost  suspended ;  se- 
cretions fail;  molecular  nutrition  ceases;  and  at  a  rate  much  more  early  than 
in  other  modes  of  death,  molecular  death  follows  close  on  somatic  death, — that 
is,  structures  die  and  begin  to  run  into  decomposition  as  soon  as  the  pulse  and 
breath  have  ceased ;  nay,  a  partial  change  of  this  kind  may  even  precede  the 
death  of  the  whole  body  ;  and  parts  running  into  gangrene,  as  in  the  carbuncle 
of  plague,  the  sphacelous  throat  of  malignant  scarlatina,  and  the  sloughy  sores 
of  the  worst  forms  of  typhus,  or  the  putrid  odour  exhaled  even  before  death 
by  the  bodies  of  those  who  are  the  victims  of  similar  pestilential  disease,  are 
so  many  proofs  of  the  early  triumph  of  dead  over  vital  chemistry." — "  The 
appearance  of  petechiae  and  vibices  on  the  external  surface,  the  occurrence  of 
more  extensive  hemorrhage  in  internal  parts,  the  general  fluidity  of  the  blood, 
and  frequently  its  unusually  dark  or  otherwise  altered  aspect,  its  poisonous 
properties  as  exhibited  in  its  deleterious  operation  on  other  animals,  and  its 
proneness  to  pass  into  decomposition,  point  out  the  Blood  as  the  first  seat  of 
disorder ;  and  by  the  failure  of  its  natural  properties  and  offices  as  the  vivifier 
of  all  structure  and  function,  it  is  plainly  the  medium  by  which  death  begins 
in  the  body." 

VI.  Origin  of  the  Solid  Tissues — Separative  Processes. 

593.  It  has  been  shown  that  the  Blood  contains  a  substance  (Fibrin),  which 
is  prepared  to  become  organized,  or  to  take  upon  itself  that  peculiar  kind  of 
molecular  arrangement,  anatomically  characterized  as  structure ;  and  which 
possesses  what  the  physiologist  terms  vital  properties ;  but  it  has  also  been 
shown,  that  the  conversion  of  this  Fibrin  into  any  higher  form  of  organized 
structure  than  simple  fibrous  tissue,  requires  the  influence  of  a  previously-ex- 
isting organism.  In  the  development  of  the  Embryo,  the  germ  of  the  first 
cell  appears  to  be  supplied  by  the  male  parent ;  whilst  the  nutriment  at  the 
expense  of  which  it  is  evolved  is  supplied  by  the  female.  In  the  subsequent 
growth  of  the  organism,  the  materials  are  derived  from  the  food  ingested  ;  and 
the  conversion  of  these  into  organized  tissue  depends  upon  the  properties  of 
the  structure  already  formed,  which,  whilst  itself  decaying,  liberates  the 
germs  of  new  cells,  and  thus  makes  preparation  for  its  renewal.  The  pro- 
cesses by  which  these  cells  are  converted  into  the  several  kinds'  of  organic 
structure,  that  compose  the  fabric  of  the  higher  animals,  are  in  many  instances 
very  complex ;  and  can  only  be  traced  by  an  attentive  examination  of  their 
several  stages.  Whether  they  are  observed,  however,  in  the  first  Develop- 
ment of  the  Embryo,  or  in  the  Reproduction  of  lost  parts,  they  seem  to  be 
essentially  the  same.  In  fact,  among  the  lowest  tribes  of  Animals,  we  find 
these  two  conditions  blended,  as  it  were,  together  ;  for  the  process  of  repara- 
tion may  be  carried  in  them  to  such  an  extent  as  to  regenerate  the  whole 
organism  from  a  very  small  portion  of  it.  In  the  Hydra,  or  Fresh-water 
Polype,  there  would  seem  to  be  scarcely  any  limit  to  this  power  ;  for,  if  the 
body  of  the  animal  be  minced  into  the  smallest  possible  fragments,  every 

*  Principles  of  Medicine,  [Am.  Ed.  by  Dr.  Clymer,  p.  373.] 


452  OF  NUTRITION. 

one  of  these  can  produce  a  new  and  perfect  being.  In  this  manner  no  less 
than  forty  have  been  artificially  generated  from  a  single  individual.  In 
ascending  the  Animal  scale,  we  find  this  reparative  power  less  conspicuous, 
because  exercised  with  regard  to  smaller  parts  only  of  the  body;  but  the 
greater  complexity  of  the  changes  involved  in  the  process,  renders  it  in  reality 
not  less  considerable  than  in  the  lower  classes.  Thus,  the  restoration  of  a  bone 
destroyed  by  Necrosis  is  a  much  more  extraordinary  operation,  than  the 
growth  of  an  entire  Polype  from  a  single  fragment ;  since  it  involves  a  far 
greater  amount  and  variety  of  actions.  Numerous  and  well-authenticated 
instances  are  on  record  of  the  reunion  of  parts  that  had  been  entirely  separated 
from  the  body,  and  of  the  restoration  of  all  their  vital  properties ;  and  this 
could  only  take  place  through  the  perfect  reproduction  of  a  large  number  of 
very  different  structures.  The  reappearance  of  Fungous  growths,  whose 
organization  is  of  a  low  character,  is  a  fact  with  which  every  surgeon  is  fami- 
liar; and  cases  occasionally,  though  rarely,  present  themselves,  in  which  re- 
production of  a  whole  member  takes'  place  even  in  the  Human  subject.* 

594.  Before  proceeding  to  describe  in  detail  the  mode  in  which  the  primor- 
dial cells  are  converted  into  the  several  varieties  of  tissue,  it  may  be  desirable 
to  take  a  general  survey  of  the  conditions  under  which  the  reparative  processes 
are  carried  on, — a  question  of  great  practical  importance,  on  which  very  mis- 
taken notions  are  prevalent.     It  is  a  general  opinion  among  British  surgeons, 
(founded  upon  what  they  believe,  but  erroneously,  to  have  been  the  doctrine  of 
Hunter),  that  inflammation  is  essential  to  the  process  of  reparation.     There  is 
no  doubt  that,  as  generally  conducted,  the  healing  of  wounds  is  attended  by  a 
greater  or  less  degree  of  inflammation  ;  but  it  does  not  thence  follow  that  this 
morbid  condition  is  essential  to  the  renewal  of  the  healthy  state  ;  and  in  fact  it 
can  be  shown  that,  in  the  majority  of  cases,  the  inflammation  is  injurious  rather 
than  beneficial.     The  following  important  conclusions  are  drawn  by  Dr.  Ma- 
cartneyt  from  a  very  philosophical  comparative  survey  of  the  operations  of 
reparation  and  inflammation,  as  performed  in  the  different  classes  of  animals : 
— "That  the  powers  of  reparation  and  reproduction  are  in  proportion  to  the 
indisposition  or  incapacity  for  inflammation ; — that  inflammation  is  so  far  from 
being  necessary  to  the  reparation  of  parts,  that,  in  proportion  as  it  exists,  the 
latter  is  impeded,  retarded,  or  prevented ; — that,  when  inflammation  does  not 
exist,  the  reparative  power  is  equal  to  the  original  tendency  to  produce  and 
maintain  organic  form  and  structure  ;— and  that  it  then  becomes  a  natural  func- 
tion, like  the  growth  of  the  individual,  or  the  reproduction  of  the  species." 

595.  Guided  chiefly  by  Dr.  Macartney's  views,  which  have  derived  impor- 
tant confirmation  from  recent  observations,  we  shall  treat  of  the  reparative  pro- 
cesses under  three  distinct  heads  : — First,  the  adhesion  of  the  sides  of  a  wound 
by  a  medium  of  coagulable  lymph,  or  of  a  clot  of  blood.     Second,  reparation 
without  any  medium  of  lymph  or  granulations,  the  cavity  of  the  wound  being 
filled  by  a  natural  process  o/  growth  from  its  walls.      Third,  reparation  by 
means  of  a  new,  vascular,  and  organized  substance,  termed  granulations. — The 
first  of  these  modes  of  reparation,  is  that  which  is  ordinarily  termed  union  by 
the  first  intention;  of  this  kind  of  adhesion,  the 'healing  of  the  incision  made 
in  venesection,  which  usually  takes  place  almost  without  consciousness  on  the 
part  of  the  patient,  and  with  scarcely  any  inflammation,  is  a  characteristic  ex- 
ample :  the  white  line  of  cicatrix  which  is  left,  marks  the  formation  of  new 
substance,  and  is  the  result  of  the  want  of  that  perfect  approximation  of  the 
lips  of  the  wound,  which  may  frequently  be  obtained  in  parts  where  pressure 

*  See,  on  the  whole  of  the  subject  of  the  comparative  powers  of  Reparation  in  the 
Animal  series,  the  Author's  Principles  of  Gen.  and  Com.  Physiol.  §§  586,  587. 
j-  Treatise  on  Inflammation,  p.  7. 


ORIGIN  OF  THE  SOLID  TISSUES.  453 

can  be  more  firmly  applied,  and  where  the  space  to  be  filled  up  is  proportion- 
ably  thinner.  This  mode  of  union  is  ordinarily  considered  by  British  surgeons 
to  be  the  result  of  an  adhesive  inflammation.  In  so  regarding  it,  they  con- 
ceive that  they  are  following  out  the  views  of  Hunter ;  but  he  expressly  states 
that  wounds  may  heal  without  any  pain  or  constitutional  disturbance,  the  re- 
union proceeding  "as  if  nothing  had  happened ;"  so  that  he  in  effect  admits 
that  reparation  of  this  kind  may  take  place  without  inflammation.  It  is  well 
known  that  if  a  slight  wound  which  is  thus  healing  be  provoked  to  an  increased 
degree  of  inflammation,  its  progress  is  interrupted ;  and  all  the  means  which 
the  surgeon  employs  to  promote  union,  are  such  as  tend  to  prevent  the  acces- 
sion of  this  state.  The  doctrine  that  the  effusion  of  lymph  for  the  reparation 
of  the  tissues  is  not  to  be  regarded  as  necessarily  a  result  of  the  inflammatory 
process,  is  not  so  novel  as  its  opponents  have  regarded  it,  since  it  has  been 
maintained  by.  many  eminent  observers,  even  from  the  earliest  times.  The 
only  case  in  which  the  occurrence  of  inflammation  can  be  regarded  as  salutary, 
is  that  in  which  there  is  a  deficiency  of  fibrin  in  the  blood,  causing  a  deficient 
organizability  of  the  lymph.  It  has  been  seen  that  the  amount  of  fibrin  is 
rapidly  increased  by  inflammation  ;  and  the  surgeon  well  knows  that  a  wound 
with  pale  flabby  edges,  in  a  depressed  state  of  the  system,  will  not  heal  until 
some  degree  of  inflammation  has  commenced. 

596.  When  the  Liquor  Sanguinis  of  the  Blood,  known  as  Coagulable  Lymph, 
is  effused  between  the  two  edges  of  a  wound,  or  upon  the  surface  of  a  membrane 
lining  a  closed  sac,  the  following  appears  to  be  the  history  of  its  organization. 
The  new  matter,  which  is  poured  out  in  a  fluid  state,  and  which  seems  to  have 
been  subjected  to  the  peculiar  influence  of  the  white  corpuscles  that  rapidly 
collect  in  large  numbers  at  the  injured  spot,  undergoes  a  Coagulation  resem- 
bling that  of  Blood ;  the  Serum,  being  set  free  by  the  concretion  of  the  Fibrin, 
is  absorbed ;  and  the  fibrino'us  coagulum  speedily  obtains  an  almost  membra- 
nous density.  If  examined  with  a  microscope  at  the  commencement  of  the 
process  of  organization,  it  is  seen  to  contain  a  large  number  of  the  exudation- 
corpuscles  already  mentioned  (§  660) ;  these  originating  probably  in  the 
granules  set  free  by  the  rupture  of  white  corpuscles.  In"a  short  time,  these 
corpuscles  present  the  appearance  of  regular  cells,  disposed  in  layers,  and 
adhering  together  by  an  intermediate  unorganized  substance ;  bearing,  in  fact, 
a  strong  resemblance  to  the  cells  of  tesselated  epithelium.  Some  hours  later, 
the  mass  exhibits  an  evidently  fibrous  character ;  which  is  probably  due  to  the 
further  elaboration  of  the  plastic  material,  by  the  cells  just  mentioned.  Between 
the  fibres,  a  considerable  amount  of  unorganized  substance  yet  remains ;  and 
they  may  be  readily  separated,  or  torn  in  any  direction.  A  vascular  rete  next 
•makes  its  appearance,  in  connection  with  the  vessels  of  the  subjacent  surface  ; 
the  first  appearance  of  this  network  is  in  the  form,  of  transparent  arborescent 
streaks,  which  push  out  extensions  on  all  sides ;  these  encounter  one  another, 
and  form  a  complete  series  of  capillary  reticulatipns,  the  distribution  of  which 
very  nearly  resembles  that  which  has  been  seen  in  the  villi  of  the  intestines 
(Fig.  60).  From  the  observations  of  Mr.  Travers*  it  appears,  that  isolated 
globules  enter  these  capillary  tubes,  and  perform  an  oscillatory  motion  in  them 
for  some  hours,  before  any  series  of  them  passes  into  it ;  so  that  we  cannot 
regard  the  new  channel  as  burrowed  out  by  a  string  or  file  of  red  corpuscles, 
pushed  out  from  the  nearest  capillary  by  vis  a  tergo,  as  some  have  maintained. 
And  he  has  further  established  two  important  facts,  in  the  history  of  the  Repara- 
tion of  Tissues,  which  correspond  with  the  observations  just  cited: — 1.  That 
the  Liquor  Sanguinis  first  effused  is  not  sufficiently  organizable  to  become  an 
entirely  new  and  permanent  tissue  ;  although  adequate  both  to  afford  nutrition 

*  Physiology  of  Inflammation  and  the  Healing  Process. 


454  OF  NUTRITION. 

to  the  old,  and  to  form  a  new  tissue  of  a  temporary  character : — and,  2.  That 
the  generation  of  the  new  tissues  is  preceded  by  the  collection  of  a  large  num- 
ber of  white  corpuscles,  in  a  nearly  stationary  condition,  in  the  blood-vessels 
immediately  subjacent ;  and  by  the  appearance  of  a  large  number  of  similar 
cells  in  the  newly-forming  tissue  ;  the  two  together  constituting  what  Mr.  T. 
has  aptly  called  "  the  new  lymph-bed  of  organization."  The  views  formerly 
advanced  (579)  respecting  the  function  of  the  Colourless  Corpuscles,  are  thus 
strikingly  confirmed. — This  process  of  Reparation  appears  to  be  conformable, 
in  all  essential  particulars,  with  that  which  has  been  observed  in  the  first 
Developement  of  new  parts, — such  as  the  toes  of  the  larva  of  the  Water-Newt. 

597.  Although  many  have  doubted  whether  effusions  of  Blood  could  thus 
become  organized,  there  seems  no  valid  reason  to  think  that  its  Fibrin  would 
comport  itself  in  any  other  way,  when  Red  particles  are  included  in  its  coagu- 
lum,  than  when  they  are  absent.     That  large  masses  of  extravasated  Blood 
should  exhibit  little  or  no  tendency  to  organization,  will  not  be  considered  sur- 
prising ;  when  it  is  remembered  that  only  their  surface  can  be  in  that  relation 
with  a  living  membrane,  which  has  been  stated  to  be  essential  to  the  further 
vitalization  of  the  effused  Fibrin  (§  555).  It  has  been  proved  in  many  instances, 
however,  that  Coagula  of  Blood  completely  enclosed  within  the  body  possess 
an  incipient  vascularity,  being  capable  of  injection  from  the  surface  beneath  ;* 
and  there  is  no  valid  reason  to  deny  that  the  thin  layer  of  Blood  which  remains 
between  the  lips  of  an  incised  wound,  when  these  are  closely  brought  together, 
is  the  medium  of  their  reunion.     It  is  unquestionable,  however,  that  the  Fibrin 
of  an  ordinary  Blood-clot  is  less  highly-elaborated,  and  consequently  less  sus- 
ceptible of  organization  than  that  of  the  Liquor  Sanguinis,  which  is  poured 
forth  after  an  injury,  and  which  has  been  subjected  to  the  local  action  that  is 
its  immediate  result. 

598.  To  the  second  mode  of  Reparation,  attention  has  recently  been  strongly 
directed  by  Dr.  Macartney ;  and  as  this,  too,  is  a  strictly  Physiological  action, 
and  is  one  which  the  surgeon  should  aim  at  producing,  it  will  be  here  dis- 
cussed somewhat  in  detail.     The  Surgeon  has,  until  recently,  regarded  the 
processes  of  Granulation  and  Suppuration,  which  are  attended  with  much 
local  inflammation,  and  with  a  considerable  amount  of  Constitutional  disturb- 
ance when  the  surface  is  large,  as  the  only  means  by  which  an  open  wound 
can  be  filled  up.     Occasional  instances,  however,  have  not  been  wanting,  in 
which  large  open  wounds  have  closed  up  under  the  dry  clot  of  blood,  by 
which  they  were  at  first  covered  over,  without  any  suppuration,  or  other 
symptom  of  inflammation  ;  and  in  these  it  has  been  found  that  the  new  surface 
much  more  nearly  resembles  the  ordinary  one,  than  does  the  Cicatrix  which 
follows  granulation.    To  Dr.  Macartney,  however,  is  due  the  merit  of  explaining 
the  rationale  of  this  action ;  which  is  precisely  analogous  to  that  which  is 
concerned  in  the  ordinary  processes  of  growth,  and  to  that  reproduction  of 
\vhole  parts  which  takes  place  in  the  lower  animals  without  inflammation.    It 
is  termed  by  him  the  modelling  process  ;  and  he  remarks  as  characteristic  of 
it  that,  when  it  goes  on  perfectly,  and  without  Inflammation,  the  patients  are 
so  completely  free  from  uneasy  sensations,  as  only  to  be  aware  of  the  extent 
of  the  injury  by  their  own  examination.     In  this  process,  the  surfaces  of  the 
wound  do  not  unite  by  vascular  connection,  even  when  they  lie  in  contact ; 
nor  is  the  space  between  them  filled  up  with  coagulable  lymph ;  but  they  are 
smooth  and  red,  moistened  with  a  fluid,  and  presenting  the  appearance  of  one 
of  the  natural  mucous  membranes.     "  It  might  be  anticipated  that,  as  this 
mode  of  reparation  bears  so  strong  a  resemblance  to  the  natural  formation  and 

*  For  well-established  cases  of  this  sort  see  communications,  by  Mr.  Dalrymple  in  the 
Medico-Chirurgical  Transactions,  Vol.  xxiii;  and  in  Lancet,  March  23,  1844. 


ORIGIN  OF  THE  SOLID  TISSUES.  ,  455 

development  of  parts,  it  is  the  slowest  mode  ;  but  this  is  of  little  account,  when 
compared  with  its  great  advantages  in  being  unattended  with  pain,  inflamma- 
tion, and  constitutional  sympathy,  and  leaving  behind  it  the  best  description 
of  cicatrix."  In  the  case  of  large  burns  on  the  trunk  in  children,  the  differ- 
ence between  the  two  modes  of  Reparation  will  frequently  be  that  of  life  and 
death ;  for  it  often  happens  that  the  patient  sinks  under  the  great  constitu- 
tional disturbance  occasioned  by  a  large  Suppurating  surface,  although  he  has 
survived  the  immediate  shock  of  the  injury. 

599.  The  most  effectual  means  of  promoting  this  kind  of  Reparative  process, 
and  of  preventing  the  interference  of  Inflammation,  vary  according  to  the  na- 
ture of  the  injury.     The  exclusion  of  air  from  the  surface,  and  the  regula- 
tion of  the  temperature  appear  the  two  points  of  chief  importance.     By  Dr. 
Macartney,  the  constant  application  of  moisture  is  also  insisted  on.*     He  states 
that  the  immediate  effects  of  injuries,  especially  of  such  as  act  severely  upon 
the  sentient  extremities  of  the  nerves,  are  best  abated  by  the  action  of  "  steam 
at  a  high  but  comfortable  temperature,  the  influence  of  which  is  gently  stimu- 
lant, and  at  the  same  time  extremely  soothing.     After  the  pain  and  sense  of 
injury  have  passed  away,  the  steam,  at  a  lower  temperature,  may  be  con- 
tinued ;"  and,  according  to  Dr.  M.,  no  local  application  can  compete  with  this, 
when  the  Inflammation  is  of  an  active  character.     For  subsequently  restraining 
this,  however,  so  as  to  promote  the  simple  Reparative  process,  Water-dressing 
will,  he  considers,  answer  sufficiently  well;    its  principal  object  being  the 
constant  production  of  a  moderate  degree  of  Cold,  which  diminishes,  whilst  it 
does  not  extinguish,  sensibility  and  vascular  action,  and  allows  the  Reparative 
process  to  be  carried  on  as  in  the  inferior  tribes  of  animals.     The  reduction 
of  the  heat  in  an  extreme  degree,  as  by  the  application  of  ice  or  iced  water,  is 
not  here  called  for,  and  would  be  positively  injurious  ;  since  it  not  only  renders 
the  existence  of  Inflammation  in  the  part  impossible,  but,  being  a  direct  seda- 
tive to  all  vital  actions,  suspends  also  the  process  of  restoration.     The  efficacy 
of  Water-dressing  in  injuries  of  the  severest  character,  and  in  those  which  are 
most  likely  to  be  attended  with  violent  Inflammation  (especially  wounds  of  the 
large  joints)  has  now  been  established  beyond  all  question ;  and  its  employ- 
ment is  continually  becoming  more  general.     Other  plans  have  been  proposed, 
however,  which  seem  in  particular  cases  to  be  equally  effectual.    To  Dr.  Green- 
how,  of  Newcastle,  for  instance,  it  was  accidentally  suggested,  a  few  years 
since,tto  cover  the  surface  of  recent  burns  with  a  liquefied  resinous  ointment; 
and  he  states  that  in  this  manner  Suppuration  may  be  prevented,  even  where 
large  sloughs  are  formed  ;  the  hollow  being  gradually  filled  up  by  new  tissue, 
which  is  so  like  that  which  has  been  destroyed  that  no  change  in  the  surface 
manifests  itself,  and  none  of  that  contraction  which  ordinarily  occurs  even 
under  the  best  management,  subsequently  takes  place.     A  plan  has,  moreover, 
been  proposed  for  preventing  suppuration,  and  promoting  reparation  by  the 
modeling  process,  which  consists  in  the  application  of  warm  dry  air  to  the 
wounded  surface.     The  experiments  made  on  this  have  not  been  entirely 
satisfactory,  but  they  seem  to  show  that  though  the  process  of  healing  is  much 
slower  under  treatment  of  this  kind,  it  is  attended  with  less  constitutional  dis- 
turbance than  is  unavoidable  in  the  ordinary  method  ;  and  it  may,  therefore, 
be  advantageously  put  in  practice  in  those  cases  in  which  the  condition  of  the 
patient  requires  every  precaution   against  such  an  additional  burthen, — as 
after  amputation  in  a  strumous  subject.     But  of  the  superiority  of  this  treat- 
ment to  the  water-dressing,  no  evidence  has  yet  been  adduced. 

600.  The  third  method  of  Reparation — that  by  Granulation — appears  to  be 

*  Treatise  on  Inflammation,  p.  178. 
f  Medical  Gazette,  Oct.  13,  1638. 


456  OF  NUTRITION. 

a  means  employed  by  Nature  for  the  purpose,  under  the  unfavourable  circum- 
stances of  Irritation  or  a  continuance  of  Inflammation ;  proving  that  parts, 
previously  in  a  healthy  state,  are  disposed  to  heal  in  despite  of  many  impedi- 
ments thrown  in  their  way.  The  Granulation-structure  is  a  special  one, 
formed  for  a  temporary  purpose.  It  is  endowed  with  higher  vascularity  and 
a  more  rapid  power  of  growth,  than  is  possessed  by  any  modification  of  ordi- 
nary tissue  ;  but  it  is  very  easily  destroyed  by  injury,  or  by  a  higher  degree 
of  inflammation.  The  existence  of  Granulations  has  been  supposed  to  be 
necessary  to  fill  up  deficiencies  ;  this,  however,  is  not  altogether  true  ;  as  we 
occasionally  find  very  considerable  vacancies  filled  with  lymph,  which  gra- 
dually becomes  organized,  without  being  converted  into  granulations  ;  and  the 
void  may  be  also  supplied  by  the  process  of  natural  growth  just  described. 
Moreover,  it  is  only  in  the  beginning  that  granulations  take  the  place  of  the 
natural  structure  ;  for  the  approximation  of  the  edges  of  a  wound  filled  with 
them,  requires  that  they  should  be  removed  by  interstitial  absorption ;  so  that 
wounds  healed  by  this  process  do  not  exhibit  any  remains  of  the  new  medium. 
This  approximation  somewhat  resembles  that  which  occurs  in  open  wounds 
that  have  never  inflamed,  being  the  result  of  the  natural  processes  of  growth, 
and  it  does  not  take  place  until  the  Inflammation  has  in  great  degree  subsided ; 
but  it  differs  from  the  modeling  processes  in  this, — that,  as  the  wound  is  oc- 
cupied by  granulations,  its  closure  takes  place  prematurely,  as  it  were ;  so 
that,  when  the  granulations  are  subsequently  absorbed  altogether,  a  contracted 
cicatrix  is  the  result. — It  will  be  presently  seen,  that  the  formation  of  the 
Granulation-structure  is  intimately  connected  with  the  elaboration  of  Pus ; 
and' this  process,  accompanied  as  it  is  with  such  great  constitutional  disturb- 
ance, and  involving  such  a  loss  of  nutritious  material,  cannot  but  be  regarded 
as  an  action  to  be  altogether  avoided,  if  possible. 

601.  We  shall  now  consider,  more  in  detail,  the  nature  of  the  process  of 
Granulation,  and  of  the  Suppuration  which  usually  accompanies  it.  Its  com- 
mencement is  exactly  conformable  to  the  first  stage  of  ordinary  reunion  by  the 
first  intention  ;  for  liquor  sanguinis  is  thrown  out,  in  \vhich  exudation-corpus- 
cles present  themselves  in  large  numbers.  According  to  Gerber,  the  trans- 
formation of  these  into  a  sort  of  imperfect  Epithelium  may  be  seen  to  take 
place  within  half  an  hour.  New  layers  are  in  the  mean  time  developed,  and 
the  most  superficial  of  the  exudation-corpuscles,  which  are  exposed  to  the 
contact  of  air,  change  their  character  fin  the  mode  to  be  presently  described 
(§  609),  and  become  Pus-Globules  ;  whilst  those  in  close  contact  with  the  subja- 
cent surface  take  a  share  in  the  process  of  reparation.  A  new  layer  of  exuda- 
tion-corpuscles is  next  deposited  over  this,  of  which  the  outer  portion  degene- 
rates as  before  into  pus-globules,  whilst  the  inner  part  gives  origin  to  a  kind  of 
areolar  tissue,  forming  Granulations.  These  Granulations  are  themselves  ex- 
tremely vascular ;  and,  as  recently  shown  by  Mr.  Listen,*  the  vessels  of  the 
subjacent  tissue  are  much  enlarged,  and  assume  a  varicose  character.  The 
bright  red  colour  of  the  Granulations,  however,  does  not  depend  on  their  vas- 
cularity alone  ;  for  the  cells  themselves,  especially  those  most  recently  evolved, 
are  of  nearly  as  deep  a  colour  as  the  blood-globules  :  and  the  superficial  bleed- 
ing which  follows  even  the  slightest  touch  of  the  granulating  surface,  does  not 
proceed  from  blood  shed  from  the  new-formed  vessels  only  ;  for  the  red  fluid 
shed  in  this  manner  contains,  besides  blood-discs,  newly-developed  red  cells, 
ruddy  cytoblasts,  pale  granules  and  reddish  serum.  It  is  a  common  property 
of  animal  cytoblasts,  that  they  present  a  red  colour  on  their  first  formation, 
when  in  contact  with  oxygen  ;  but  this  hue  they  lose  again,  whether  they  ad- 
vance to  perfect  development  and  become  integral  parts  of  a  living  tissue,  or 

*  Medico-Chirurgical  Transactions,  vol.  xxiii. 


VARYING  ACTIVITY  OF  THE  NUTRITIVE  PROCESSES.  457 

die  and  degenerate.  The  process  of  Granulation  and  Suppuration  appears  to 
differ  from  that  of  simple  Reparation  (the  modeling  process  of  Dr.  Macartney) 
in  this, — that  a  large  part  of  the  exudation-corpuscles  deposited  on  the  wounded 
surface  degenerate  into  pus  in  the  former  case,  whilst  none  are  thus  wasted  in 
the  latter ; — hut  that  the  existence  of  inflammation  occasions  a  more  copious 
supply  of  fibrin  in  the  former  case,  and  increases  its  tendency  to  become  or- 
ganized ;  the  filling-up  of  a  wound  with  granulations  being  thus  a  much  more 
rapid  process  than  that  renewal  of  the  completely-formed  Tissues  which  may 
take  place  in  the  absence  of  Inflammation.  The  imperfect  character  of  the 
granulation-structure  is  shown,  by  the  almost  complete  disappearance  of  it, 
after  the  wound  has  closed  over.  The  portion  of  it  in  immediate  contact  with 
the  subjacent  tissue,  however,  appears  to  undergo  a  higher  organization ;  for 
it  becomes  the  medium  by  which  the  Cicatrix  is  made  to  adhere  to  the  bottom 
of  the  wound.  It  is  very  liable  to  undergo  changes  which  end  in  its  disinte- 
gration ;  as  is  evident  from  the  known  tendency  to  re-opening,  in  wounds  that 
have  been  closed  in  this  manner. 

VII.    Varying  Activity  of  the  Nutritive  Processes. 

602.  Without  any  change  in  the  character  of  the  nutritive  processes  which 
we  have  been  describing,  there  may  be  considerable  variations  in  their  degree 
of  activity;  and  this,  either  as  regards  the  entire  organism,  or  individual  parts, 
though  most  commonly  the  latter.     These  variations  may  be  so  considerable 
as  to  constitute  Disease  ;  though  there  are  some  which  take  place  as  part  of  the 
regular  series  of  physiological  phenomena.     Thus,  the  Nutritive  processes 
should  have  a  degree  of  activity  more  than  sufficient  to  supply  the  waste  of 
the  body,  during  the  whole  period  of  infancy,  childhood  and  adolescence,  until, 
in  fact,  its  full  dimensions  are  attained ;  whilst,  on  the  other  hand,  they  are 
usually  less  rapid  than  the  disintegrating  processes  in  old  age,  so  that  the  bulk 
of  the  body  diminishes.     Now  as  the  waste  of  the  body,  so  far  from  being 
more  rapid  in  old  age  than  in  childhood,  is  much  less  so,  it  follows  that  the 
difference  in  the  activity  of  the  nutritive  processes  in  these  two  states  must  be 
very  considerable  ;  and  this  is  manifested,  not  only  in  the  greater  demand  for 
food  which  exists  in  the  child  (relatively  to  the  bulk  of  its  body),  but  also  in 
the  greater  quickness  and  facility  with  which  injuries  are  repaired.     Local 
variations  may  also  occur,  as  part  of  the  regular  train  of  vital  actions  in  the 
adult ;  thus  we  perceive  an  enormous  increase  in  the  amount  of  tissue  con- 
tained in  the  Uterus  and  Mammary  glands  during  pregnancy,  and  a  decrease 
in  the  bulk  of  the  Thymus  gland  after  the  first  year  of  infancy.     Now  in  these 
cases  we  see,  that  increased  nutrition  is  invariably  connected  wit'h  increased 
Functional  activity,  and  diminished  nutrition  with  diminished  functional  acti- 
vity ;  and  this  we  shall  find  to  be  the  constant  rule,  in  regard  also  to  those  vari- 
ations which  must  be  considered  as  abnormal. 

603.  Increased  Nutrition,  or  Hypertrophy,  is  never  known  to  affect  the 
whole  body,  to  a  degree  sufficient  to  constitute  disease.     It  cannot  be  produced 
as  a  consequence  of  the  ingestion  of  an  undue  supply  of  food ;  for  this  does 
not  increase  the  formative  activity  of  the  tissues,  but  merely  renders  the  blood 
richer  in  nutritive  materials ;  a  part  of  which  the  excreting  organs  are  called 
on  to  be  continually  removing,  without  its  being  rendered  subservient  to  the 
wants  of  the  body  (§  679) ;  whilst  another  part  may  be  employed  in  the  nutri- 
tion of  one  particular  tissue,  the  Adipose,  which  has  a  tendency  to  increase 
with  the  superfluity  of  non-azotized  food,  provided  that  the  requisite  amount 
of  cellular  tissue  be  generated  to  hold  the  fatty  matter  (§  433).     But  examples 
of  Hypertrophy  of  particular  tissues  or  organs  are  very  common.     Thus  any 

39 


458  OF  NUTRITION. 

particular  set  of  Muscles,  which  is  subjected  to  frequent  and  energetic  use, 
acquires  a  great  increase  in  bulk ;  as  we  s6e  in  the  arms  of  a  Blacksmith  or 
Waterman,  the  legs  of  an  Opera-dancer,  &c.  The  hypertrophy  of  these 
muscles  is  a  consequence  of  their  increased  functional  activity ;  which,  being 
produced  by  an  exertion  of  the  will,  and  unaccompanied  with  any  injurious 
effects  on  the  system,  can  scarcely  be  regarded  as  morbid.  But  there  are 
many  instances  in  which  the  involuntary  muscles  acquire  a  greatly  increased 
strength,  in  consequence  of  an  obstruction  to  their  action,  which  results  from 
•disease.  Thus  we  see  the  right  ventricle  of  the  Heart  become  hypertrophied 
(and  dilated  at  the  same  time),  where  chronic  pulmonary  disease  produces  a 
difficulty  in  the  propulsion  of  the  blood  through  the  vessels  of  the  lungs ;  the 
muscular  fibres  of  the  Bladder  become  enormously  hypertrophied,  when  stric- 
ture, diseased  prostate,  or  other  causes  produce  a  demand  for  increased  expul- 
sive force  on  the  part  of  that  organ  ;  and  those  of  the  Stomach  also  become  so, 
in  cases  of  stricture  of  the  pylorus.  As  an  instance  of  hypertrophy  of  a  Se- 
creting organ  in  consequence  of  an  undue  excitement  of  its  function,  we  may 
notice  the  enlargement  which  usually  takes  place  in  the  Kidney,  when  its 
fellow  is  incapacitated  by  disease.  And  the  Nervous  system  presents  us  with 
a  very  remarkable  case  of  hypertrophy  of  a  part,  resulting  from  over-excite- 
ment of  its  function ;  for  if  young  persons,  who  naturally  show  precocity  of 
intellect,  are  encouraged  rather  than  checked  in  the  use  of  their  brain,  the 
increased  nutrition  of  the  organ  (which  grows  faster  than  its  bony  case)  occa- 
sions pressure  upon  its  vessels,  it  becomes  indurated  and  inactive,  and  fatuity 
and  coma  are  the  result.  Local  hypertrophy  may  be  induced  also  by  local 
congestions ;  but  in  such  cases  it  will  usually  be  found  that  the  form  of  tissue 
produced  is  of  the  lowest  kind,  unless  the  functional  activity  of  the  part  be 
increased  by  the  congestion.  Thus,  when  disease  of  the  Heart  produces 
long-continued  congestion  of  the  Lungs,  Liver,  Spleen,  &c.,  the  bulk  of 
these  organs  increases  ;  but  chiefly  by  the  production  of  an  additional  amount 
of  interstitial  Areolar  tissue,  which  may  result  (as  we  .have  seen)  from  the 
simple  consolidation  of  Fibrin ;  and  partly  also  (in  the  case  of  the  spleen  espe- 
pecially)  by  the  gorging  of  their  distensible  veins  with  blood. — One  of  the 
least  explicable  cases  of  Hypertrophy,  is  that  which  takes  place  in  the  Thyroid 
gland,  causing  Bronchocele.  So  little  is  known  of  the  normal  office  of  this 
organ,  that  it  cannot  be  determined  whether  its  increased  size  be  due  to  an 
increased  activity  of  its  functional  operations,  or  to  an  unusual  formative  acti- 
vity in  its  tissue,  depending  on  some  hidden  cause.  The  connection  of  this 
disorder  with  causes  which  affect  the  whole  constitution  rather  than  individual 
parts,  would  seem  to  indicate  the  former. 

604.  When  the  Waste  of  the  Tissues  is  more  rapid  than  their  replacement 
by  Nutrition,  Atrophy  is  said  to  take  place ;  and  this  may  affect  either  the 
whole  body,  or  individual  parts.  General  Atrophy,  Marasmus,  or  emaciation, 
may  result  from  an  insufficient  supply  of  plastic  matter,  from  want  of  forma- 
tive power  in  the  tissues  themselves,  or  from  their  too  rapid  disintegration. 
The  insufficiency  of  the  supply  of  nutritive  matter  may  depend  either  on  de- 
ficiency in  the  azotized  substances  ingested  as  food,  or  on  imperfect  perform- 
ance of  those  processes  by  which  they  are  converted  into  the  plastic  element, 
— Fibrin.  Hence,  even  when  there  is  an  ample  supply  of  food,  atrophy  may 
take  place  to  a  very  severe  extent,  in  consequence  of  disordered  digestion,  or  of 
want  of  vital  power  in  the  fibrin-elaborating  cells.  Again,  we  have  reason  to 
believe  that  the  formative  power  in  the  tissues  themselves  may  be  diminished, 
so  as  to  check  the  process  of  Nutrition,  even  when  the  plastic  material  is  sup- 
plied ;  thus  there  seems  to  be  a  complete  stoppage  of  this  action  in  Fever,  and 
a  diminution  of  it  in  that  irritable  state  of  the  system  which  results  from  ex- 


VARYING  ACTIVITY  OF  THE  NUTRITIVE  PROCESSES.  459 

cessive  and  prolonged  bodily  exertion  or  anxiety  of  mind,  especially  when 
accompanied  by  want  of  sleep.  It  is  difficult  to  separate  this  cause,  however, 
from  mal-assimilation  on  the  one  hand,  or  from  too  rapid  decay  of  the  tissues 
on  the  other :  for  we  know  that,  in  such  states,  there  is  a  tendency  to  imper- 
fect elaboration  of  the  Fibrinous  element,  and  at  the  same  time  an  unusually 
rapid  disintegration  as  manifested  by  the  increased  amount  of  Urea  in  the 
urine.  The  influence  of  excessive  waste  in  causing  Atrophy  of  the  body,  is 
well  shown  in  the  cases  of  Diabetes  mellitus  and  colliquative  Diarrhoea ;  in 
both  these,  the  increase  and  depravation  of  the  secretions  are  undoubtedly  to 
be  regarded  as  the  effects,  and  not  the  causes,  of  the  textural  changes  with 
which  they  are  associated.  Colliquative  Diarrhoea  is  a  constant  occurrence 
on  the  last  day  or  two  of  life,  in  animals  reduced  by  Starvation  ;  and  is  accom- 
panied by  that  foetid  odour  of  the  body  which  indicates  that  decomposition  is 
already  going  on  throughout  the  system.  The  same  thing  occurs  as  the 
ordinary  termination  to  many  diseases  of  exhaustion ;  in  which  Inanition  is 
unquestionably  the  immediate  cause  of  death. 

605.  Partial  Atrophy  may  occur  in  consequence  of  disuse  of  the  organ 
affected,  occasioning  inactivity  in  its  formative  processes;  or  as  a  result  of  a 
deficiency  of  nutriment,  occasioned  by  an  obstruction  to  the  circulation.  Of 
the  operation  of  the  former  cause,  we  have  many  examples  in  the  ordinary 
processes  of  the  economy.  Thus  the  Uterus  is  atrophied,  relatively  to  its 
previous  condition,  as  soon  as  parturition  has  taken  place ;  and  the  Mammary 
glands,  when  lactation  has  been  discontinued.  It  is  probably  in  part  to  this 
cause,  and  in  part  to  the  diversion  of  the  blood  into  other  channels,  that  we  are 
to  attribute  the  atrophy  of  many  parts,  as  the  development  of  the  system  ad- 
vances, which  at  an  earlier  period  were  of  large  comparative  size, — such  as 
the  Corpora  Wolffiana,  the  Suprarenal  capsules,  and  the  Thymus  gland. 
Many  instances  might  be  adverted  to,  of  the  influence  of  suspension  of  func- 
tional activity,  as  a  result  of  disease  or  injury,  in  producing  local  atrophy. 
One  of  the  most  common  cases,  is  the  atrophy  of  Muscles  which  is  consequent 
upon  their  disuse.  This  disuse  will  produce  the  same  effect,  whether  it  be 
occasioned  by  paralysis,  which  prevents  the  nervous  centres  from  exciting  the 
muscles  to  contraction ;  or  by  anchylosis,  which  interposes  a  mechanical  im- 
pediment to  their  use ;  or  by  fractures  or  other  accidents,  the  reparation  of 
which  requires  the  limb  to  be  kept  at  rest.  Or  even  if,  without  having  suffered 
from  any  injury,  a  limb  be  fixed  during  some  time  in  one  posture,  its  muscles 
will  become  atrophied,  as  is  seen  in  the  case  of  the  Indian  Fakirs.  (See  §  382). 
Similar  facts  may  be  adduced,  in  regard  to  Atrophy  of  Nerves,  from  interrup- 
tion of  their  normal  function.  Thus  when  the  Cornea  has  been  rendered  so 
opaque  by  accident  or  disease,  that  no  light  can  penetrate  to  the  interior  of  the 
eye,  the  Retina  and  the  Optic  nerve  lose,  after  a  time,  their  characteristic 
structure  ;  so  that  scarcely  a  trace  of  the  peculiar  globules  of  the  former,  or  of 
the  nerve-tubes  of  the  latter,  can  be  found  in  them.  These  and  similar  facts 
are  readily  understood,  when  connected  by  the  general  principle  formerly  laid 
down, — that  every  proper  vital  operation  involves  an  act  of  nutrition  ;  in  such 
a  manner  that,  whilst  the  vital  properties  of  any  part  are  dependent  upon  its 
due  nutrition,  the  amount  of  its  nutrition  will  in  return  depend  upon  the 
degree  in  which  these  properties  are  exercised. — Partial  Atrophy  may  depend, 
however,  upon  causes  of  a  purely  mechanical  nature  ;  such,  for  example,  as 
produce  an  interruption  of  the  current  of  Blood  through  the  part.  This  may 
result  from  changes  in  the  Arteries  supplying  it ;  such  as  ossification,  or  other 
forms  of  obstruction.  Or  it  may  be  consequent  upon  disease  in  the  part  itself; 
as  when  the  deposits  produced  by  Inflammation  tend  to  contract,  and  thus  to 
press  upon  the  vascular  structure,  which  frequently  happens  in  the  lungs, 
liver,  and  kidneys  ;  or  when  the  inflammation  occurs  in  the  vessels  themselves, 


460  OF  NUTRITION. 

causing  adhesion  of  their  walls,  and  obliteration  of  their  tubes ;  or  when  a 
new  growth  absorbs  into  itself  all  the  nutritive  materials  which  the  Blood 
supplies.* 

VIII.  Abnormal  Forms  of  the  Nutritive  Process. 

606.  Under  the  preceding  head,  we  have  considered  the  chief  variations  in 
the  degree  of  activity,  that  are  witnessed  in  the  ordinary  or  normal  conditions 
of  the  Nutritive  process, — that  is,  those  conditions  in  which  the  products  are 
adapted,  by  their  similarity  of  character,  to  replace  those  which  have  been 
removed  by  disintegration.     But  we  have  now  to  consider  those  forms  of  this 
process,  in  which  the  products  are  abnormal, — being  different  from  the  tissues 
they  ought  to  replace.     We  shall  confine  ourselves  to  a  brief  examination  of 
the  two  most  important  of  these  states : — that  which  is  termed  Inflammation  ; 
and  that  which  gives  rise  to  Tubercular  deposit.     The  former  results  from  an 
excess  of  the  plastic  element  in  the  blood ;  the  latter  from  a  depraved  condition 
of  it,  whereby  its  plasticity  is  impaired  or  destroyed. — Notwithstanding  all  the 
attention  which  has  been  given  to  the  state  of  the  vessels  in  Inflammation,  a 
careful  consideration  of  its  phenomena,  with  the  light  which  recent  investiga- 
tions have  thrown  upon  these,  leads  us  to  attach  comparatively  little  importance 
to  this,  and  to  seek  for  the  essential  character  of  the  process  elsewhere.    The 
researches  of  Addison,  Williams,  Barry,  Gulliver,  Andral  and  others,  all  seem 
to  point  to  the  following  conclusions. — 1.  That  there  is  a  peculiar  afflux  or 
determination  of  the  White  Corpuscles  of  the  Blood  towards  the  inflamed 
part.     2.  That  the  total  amount  of  these  Corpuscles  in  the  circulating  blood 
undergoes  a  great  increase.     3.  That  the  quantity  of  Fibrin  in  the  Blood  aug- 
ments, in  proportion  to  the  extent  and  intensity  of  the  Inflammation ;  and  this, 
even  when  it  was  previously,  from  the  influence  of  some  other  morbid  condi- 
tion, below  the  usual  standard.     With  its  quantity,  its  plasticity,  or  tendency 
to  organization,  also  increases  in  a  healthy  subject. — Now  when  these  facts  are 
compared  together,  and  are  connected  with  those  formerly  adduced,  in  regard 
to  the  probable  function  of  the  White  Corpuscles  of  the  blood,  they  lead  almost 
irresistibly  to  the  conclusion,  that  the  process  of  Inflammation  essentially  con- 
sists in  an  undue  stagnation  of  these  Corpuscles  in  the  vessels  of  the  part,  an 
excessive  multiplication  of  them  by  the  ordinary  process  of  generation,  and  a 
consequent  over-production  of  Fibrin.     By  these  changes,  and  by  the  results 
which  follow  them,  Inflammation  may  be  distinguished  from  the  various  forms 
of  Hyperaemia  and  Congestion.     To  the  results,  then,  we  shall  next  direct  our 
attention. 

607.  It  may  be  inferred  from  various  phenomena,  that  whilst  the  formative 
power  of  the  Blood  is  increased  in  Inflammation,  that  of  the  Tissues  is  dimin- 
ished.    Certainly  this  is  the  case  in  regard  to  the  system  at  large,  when  febrile 
irritation  has  been  established ;  for,  notwithstanding  the  increased  Plasticity  of 
the  Blood,  we  see  the  body  wasting,  instead  of  increasing  in  vigour.     And  it 
may  be  inferred,  also,  in  regard  to  the  tissues  of  the  part  affected,  from  the 
tendency  to  Atrophy  and  Disintegration  which  they  exhibit ;  and  which  is 
greater  (leading  even  to  the  death  of  whole  parts)  in  proportion  as  the  inflam- 
mation is  more  intense,  and  as  the  tendency  to  the  deposit  of  new  products  is 
the  more  decided.     That  a  Stagnation  of  Blood  takes  place  in  the  vessels  of 
the  inflamed  part,  is  another  general  fact,  which  throws  some  light  upon  the 
nature  of  the  process ;  for  this  stagnation  is  obviously  favourable  to  the  trans- 
udation  of  the  fluid  Plasma  of  the  blood,  through  the  walls  of  the  vessels,  into 

*  See  on  this  subject  Dr.  Williams's  Principles  of  Medicine,  Chap,  iv.:  to  which  the 
Author  is  partly  indebted  lor  the  preceding  paragraphs. 


ABNORMAL  FORMS  OF  THE  NUTRITIVE  PROCESS.  461 

the  surrounding  tissue,  or  upon  a  neighbouring  surface.  This  deposition  of 
the  Fibrinous  element,  possessing  a  high  degree  of  plasticity,  and  capable  of 
spontaneously  passing  into  simple  forms  of  tissue  (which  may  be  gradually 
replaced  by  higher  forms,  when  penetrated  by  vessels  from  the  surrounding 
parts),  may  be  regarded  as  the  first  characteristic  result  of  Inflammation,  ft 
is  by  the  deposition,  and  subsequent  organization,  of  plastic  matter  in  the  sub- 
stance of  organs,  that  their  tissues  become  consolidated ;  and  by  its  deposition 
and  subsequent  organization  upon  their  free  surfaces,  that  false  membranes  and 
adhesions  are  formed. — It  appears  probable,  from  the  recent  inquiries  of  Mr. 
Robinson,*  that  this  deposition  may  be  attributed  to  physical  causes.  It  is  well 
known,  that  simple  Congestion  will  occasion  transudation  of  the  serous  portion 
of  the  Blood ;  and  if  the  return  of  the  Blood  by  the  veins  of  a  part  be  com- 
pletely prevented,  a  greater  or  less  proportion  of  fibrin  also  may  be  poured  forth. 
Now  when  the  quantity  of  Fibrin  in  the  blood  is  greatly  augmented,  and  the 
firmness  of  the  walls  of  the  vessels  in  the  inflamed  part  is  diminished  by  the 
alterations  taking  place  in  their  tissue,  it  is  easy  to  understand  that  the  dispo- 
sition to  the  effusion  of  Fibrin  will  be  much  increased.  Sometimes  the  Fibrin 
is  diluted  with  a  large  quantity  of  Serum  ;  and  is  poured  into  a  cavity  (as  that 
of  a  serous  sac)  in  the  form  of  a  liquid,  which  afterwards  separates  into  clot 
and  serum. 

608.  Should  the  Inflammation  increase  in  intensity,  a  complete  stagnation 
of  blood  in  the  tissue  most  affected,  or  even  in  an  entire  organ,  will  be  the 
result ;  and  this  will  occasion  its  death.     If  a  large  part  be  thus  entirely  de- 
stroyed at  once,  the  process  is  termed  Gangrene;  and  it  separates  from  the 
living  part  at  a  line  where  the  Inflammation  is  less  intense,  and  where  there 
is  a  deposit  of  Fibrin,  which  serves  the  important  purpose  of  closing  the  mouths 
of  the  blood-vessels  that  are  laid  open  by  the  process.     If  the  destruction  of 
tissue,  however,  be  interstitial,  the  dead  parts  are  not  thus  thrown  off,  but  are 
taken  up  by  the  absorbent  process  ;  and  thus  the  cavity  of  an  Jlbscess,  or  of 
an  Ulcer  is  formed.     This  cavity  is  usually  bounded  by  tissue  that  has  been 
consolidated  by  the  effusion  of  Fibrin ; — a  fact  readily  accounted  for  on  the 
principles  just  stated.     For  the  death  and  removal  of  tissue  take  place  where 
the  Inflammation  has  been  most  intense,  and  the  stagnation  most  complete ; 
which  is  in  the  centre  of  the  inflamed  spot ;   and  the  fibrinous  effusion,  the 
result  of  moderate  inflammation,  is  poured  into  the  surrounding  tissue.     The 
elements  of  Liquor  Sanguinis  are  poured  into  the  central,  as  well  as  the  peri- 
pheral, portion  of  the  inflamed  tissue  ;  but  they  assume  a  different  form — that 
of  Pus.     It  would  appear  as  if  the  influence  of  the  surrounding  death  and 
decay  produces  a  degradation  of  their  character ;  so  that  they  become  entirely 
aplastic  or  unorganizable,  although  immediately  derived  from  Blood  highly 
charged  with  Fibrin. 

609.  Between  Coagulable  Lymph  and  Purulent  effusions,  there  are  many 
degrees  of  transition ;  the  very  same  deposit  being  frequently  organizable  at 
one  part, — presenting  the  character  of  a  tough  fibrous  membrane,  interspersed 
with  corpuscles, — whilst  it  is  friable  in  another,  from  want  of  complete  fibril- 
lation in  the  fluid  portion  of  the  effusion, — and  is  entirely  destitute  of  tenacity 
in  a  third  portion,  especially  the  superficial  part,  or  free  surface,  of  the  deposit. 
When  examined  by  the  Microscope,  Pus  is  found  to  be  characterized  by  the 
presence  of  a  number  of  cells  of  a  peculiar  aspect,  having  a  very  tuberculated 
or  mulberry  surface  ;  these  are  seen  floating  in  a  fluid,  termed  liquor  puris, 
which  is  of  an  albuminous  or  low  fibrinous  character,  being  entirely  destitute 
of  organizability.     Now  the  production  of  Pus  in  an  inflamed  part,  or  in  other 
words,  the  act  of  Suppuration,  may  be  due  to  one  of  three  causes,  viz., — the 

*  Medico-Chirurgical  Transactions,  vol.  xxvi.,  p.  51. 
39* 


462  OF  NUTRITION. 

intensity  of  the  inflammation ;  the  presence  of  air,  which  becomes  a  source  of 
irritation ;  and  a  previously  vitiated  state  of  the  blood.  Various  attempts  have 
been  made  to  show,  that  the  Pus-globule  is  a  degenerated  red  or  white  corpus- 
cle of  the  Blood  ;  it  seems  more  probable,  however,  that  it  does  not  escape 
from  the  vessels  as  a  complete  cell,  but  as  a  cell-germ,  which  may  have  had 
its  origin  in  a  white  corpuscle  of  the  blood ;  and  which,  under  favourable  cir- 
cumstances, might  have  produced  an  Exudation-corpuscle  (§  560).  At  any 
rate,  it  must  be  regarded  as  a  degenerated  form  of  cell ;  and  the  liquor  puris  • 
must  be  considered  as  analogous  to  the  plasma  of  the  Blood  in  a  degenerated 
state. — In  what  manner  the  Inflammatory  process  determines  the  formation  of 
the  Pus-cell,  and  the  consequent  degradation  of  the  product,  we  are  at  present 
unable  to  state  ;  but  that  the  degree  of  irritation  in  the  part  has  an  influence 
upon  it,  is  evident  from  the  effects  of  the  contact  of  air  upon  inflamed  surfaces, 
causing  those  elements  to  take  the  form  of  Pus,  which  would  otherwise  have 
been  thrown  out  as  a  plastic  deposit.  This  circumstance  would  seem  to  indi- 
cate, beyond  all  doubt,  that  the  Exudation  and  Pus-corpuscles,  the  plastic 
Lymph  and  the  aplastic  Liquor  puris  have  the  same  origin;  but  that  their 
character  is  determined  by  local  circumstances.  There  is  great  reason  to  believe, 
that  when  Pus  is  introduced  into  the  Blood,  it  may  induce  such  a  change  in 
the  character  of  the  fluid  as  speedily  to  impair  its  vital  properties ;  so  that  the 
Pus-corpuscles  will  rapidly  propagate  themselves  in  the  Blood,  and  the  plas- 
ticity of  the  Liquor  Sanguinis  will  be  diminished.  In  this  manner  the  whole 
system  will  be  seriously  affected,  and  there  will  be  a  tendency  to  deposits  of 
Pus  in  various  organs — especially  in  those  which,  like  the  Lungs  and  Liver, 
serve  as  emunctories  to  the  system — without  any  previous  inflammatory  changes 
in  these  parts.  It  has  been  ascertained  by  Mr.  Addison,  that  if  a  drop  of  Pus 
be  treated  with  Liquor  Potassae,  it  entirely  loses  its  opaque  character,  and  be- 
comes clear  and  transparent,  like  Mucus, — with  whose  tenacity  and  elasticity 
also,  it  becomes  endowed.  If  it  be  then  treated  with  acetic  acid,  it  recovers 
somewhat  of  its  former  opacity;  and,  when  pressed  into  a  thin  film,  exhibits  a 
distinct  fibrillation. 

610.  In  persons  of  that  peculiar  constitution  which  is  termed  Scrofulous 
or  Strumous,  we  find  an  imperfectly  organizable  or  Caco-plastic  deposit,  or 
even  an  altogether  aplastic  product,  known  by  the  designation  of  Tubercular .* 
matter,  frequently  taking  the  place  of  the  normal  elements  of  Tissue ;  both 
in  the  ordinary  process  of  Nutrition,  and  still  more  when  Inflammation  is  set 
up.  From  an  examination  of  the  Blood  of  Tuberculous  subjects  it  appears, 
that  the  Fibrinous  element  is  not  deficient  in  amount,  but  that  it  is  not  duly 
elaborated ;  so  that  the  coagulum  is  loose,  and  the  red  corpuscles  are  found  to 
bear  an  abnormally  low  proportion  to  it.  We  can  understand,  therefore,  that 
such  a  constant  deficiency  in  the  Plasticity  must  affect  the  ordinary  nutritive 
process;  and  there  will  be  a  liability  to  the  deposit  of  caco-plastic  products, 
without  Inflammation,  instead  of  the  normal  elements  of  tissue.  Such  appears 
to  be  the  history  of  the  formation  of  Tubercles  in  the  lungs  and  other  organs, 
when  it  occurs  as  a  kind  of  metamorphosis  of  the  ordinary  Nutritive  process ; 
and  in  this  manner  it  may  proceed  insidiously  for  a  long  period,  so  that  a  large 
part  of  the  tissue  of  the  lungs  shall  be  replaced  by  an  amorphous  deposit, 
without  any  other  ostensible  sign  than  an  increasing  difficulty  of  respiration. 
It  is  in  the  different  forms  of  Tubercular  deposit,  that  w'e  see  the  gradation 
most  strikingly  displayed  between  the  plastic  and  the  aplastic  formations.  In 
the  semi-transparent,  milliary,  gray,  and  tough  yellow  forms  of  Tubercle,  we 
find  traces  of  organization  in  the  form  of  cells  and  fibres,  more  or  less  obvious  ; 
these  being  sometimes  almost  as  perfectly  formed  as  those  of  Plastic  Lymph, 
at  least  on  the  superficial  part  of  the  deposit,  which  is  in  immediate  relation 
with  the  living  structures  around  ;  and  sometimes  so  degenerated  as  scarcely 


FORMATION  OF  THE  TISSUES.  463 

to  be  distinguishable.  In  no  instances  do  such  deposits  ever  undergo  further 
organization;  and,  therefore,  they  must  be  regarded  as  caco-plaslic.  But  in 
the  opaque,  crude,  or  yellow  Tubercle,  we  do  not  find  even  these  traces  of 
definite  structure ;  for  the  matter  of  which  it  consists  is  altogether  granular, 
more  resembling  that  which  we  find  in  an  albuminous  coagulum.  The  larger 
the  proportion  of  this  kind  of  matter  in  a  tubercular  deposit,  the  more  is  it 
prone  to  soften,  whilst  the  semi-organized  tubercle  has  more  tendency  to  con- 
traction. This  is  entirely  aplastic.  Now  although  Tubercular  matter  may  be 
slowly  and  insidiously  deposited,  by  a  kind  of  degradation  of  the*  ordinary 
Nutritive  process,  yet  it  cannot  be  doubted  that  Inflammation  has  a  great  ten- 
dency to  favour  it ;  so  that  a  larger  quantity  may  be  produced  in  the  lungs, 
after  a  Pneumonia  has  existed  for  a  day  or  two,  than  it  would  have  required 
years  to  generate  in  the  previous  mode.  But  the  character  of  the  deposit  still 
remains  the  same ;  and  its  relation  to  the  plastic  element  of  the  blood  is  shown 
by  the  interesting  fact,  of  no  unfrequent  occurrence, — that,  in  a  Pneumonia 
affecting  a  Tuberculous  subject,  Plastic  Lymph  is  thrown  out  in  one  part, 
whilst  Tubercular  matter  is  deposited  in  another.  Now  Inflammation,  pro- 
ducing a  rapid  deposition  of  Tubercular  matter,  is  peculiarly  liable  to  arise  in 
organs,  which  have  been  previously  affected  with  chronic  Tubercular  deposits, 
by  an  impairment  of  the  process  of  textural  Nutrition  ;  for  these  deposits, 
acting  like  foreign  bodies,  may  of  themselves  become  sources  of  irritation ; 
and  the  perversion  of  the  structure  and  functions  of  the  part  renders  it  pecu- 
liarly susceptible  of  the  influence  of  external  morbific  causes.  These  views, 
at  which  several  recent  Physiologists  and  Pathologists  have  arrived  on  inde- 
pendent grounds,  seem  to  reconcile  or  supersede  all  the  discordant  opinions 
which  have  been  upheld  at  different  times  regarding  the  nature  of  Tubercle ; 
and  lead  to  the  soundest  views  with  respect  to  the  treatment  of  the  Diathesis. 

IX.  Formation  of  the  Tissues. 

611.  From  the  primordial  cells,  of  which  the  whole  fabric  of  the  embryo, 
or  the  tissue  of  a  newly-formed  part,  is  composed,  all  the  Animal  tissues,  various 
as  they  are  in  structure  and  in  properties,  are  gradually  elaborated.  Their 
variety  is  much  greater  than  that  which  exists  in  Plants  ;  and  this  is  exactly 
what  we  should  expect,  when  we  take  into  account  the  much  greater  number 
of  entirely  different  functions  to  be  performed.  When  we  contrast  the  fabric 
of  an  Animal  with  that  of  a  Plant,  we  are  struck  with  this  important  dif- 
ference in  their  conformation, — that  whilst  the  latter  is  made  up  solely  of  ele- 
ments which  are  to  perform  their  several  parts  in  the  performance  of  the 
Nutritive  and  Reproductive  operations  (the  only  exception  being  in  the  case  of 
those  more  solid  portions  of  the  fabric,  which  are  destined  to  give  mechanical 
support  to  the  remainder), — the  former  is  composed  of  a  much  greater  variety 
of  parts,  which  are  adapted  to  move  upon  each  other.  Now  this  purpose 
requires,  not  only  the  addition  of  certain  new  tissues,  to  which  nothing  ana- 
logous is  to  be  found  in  Plants,  for  creating  and  exercising  the  motor  power, 
but  also  an  adaptation  of  the  whole  structure  to  this  new  condition.  The  tissues 
of  Plants  entirely  consist  of  cells,  or  simple  modifications  of  them.  Some  of 
these  cells  being  strengthened  by  internal  deposits,  form  the  solid  woody  frame- 
work of  the  stem  and  branches  ;  which  gives  support  to  their  wide-sprsading 
foliage  and  numberless  blossoms.  Others  coalesce,  by  the  disappearance  of 
their  intervening  partitions  into  tubes ;  which  serve  for  the  conveyance  of  fluid 
between  the  most  distant  parts.  But  the  great  bulk  of  the  fabric  still  consists 
of  cells,  closely  adherent  to  each  other,  and  actively  participating  in  the  various 
operations  of  organic  life.  In  like  manner,  in  the  Animal  body,  a  certain  part 
of  the  cells  have  contributed  to  form  the  solid  Osseous  and  Cartilaginous  frame- 
work, which  not  only  gives  support  and  protection  to  the  body,  but  contributes 


464  OF  NUTRITION. 

to  its  power  of  movement,  by  affording  fixed  points  for  the  attachment  of  its 
muscles.  Others  again  have  coalesced  into  Vessels,  as  in  plants,  for  the  rapid 
conveyance  of  fluids.  Others,  too,  after  a  similar  coalescence,  have  developed 
new  and  remarkable  products  in  the  interior  of  the  tubes  thus  formed ;  and 
become  transformed  into  those  Nervous  and  Muscular  tissues,  to  which  nothing 
analogous  is  found  in  Plants,  and  which  are  the  peculiar  instruments  of  Animal 
life.  Yet  still  there  remains  a  large  number  of  unchanged  Cells  scattered 
through  the  body ;  which  perform,  as  in  Plants,  the  essential  part  in  the  func- 
tions of  Nutrition,  Reproduction,  &c.  These,  however,  could  not  be  held 
together  in  their  constantly  varying  relative  positions,  without  some  inter- 
vening substance  altogether  different  from  true  cellular  tissue.  It  must  be 
capable  of  resisting  tension  with  considerable  firmness  and  elasticity ;  it  must 
admit  free  movement  of  the  several  parts  upon  one  another ;  and  it  must  still 
hold  them  sufficiently  close  together  to  resist  any  injurious  strain  upon  the 
delicate  vessels,  nerves,  &c.,  which  pass  from  one  to  another,  as  well  as  to 
prevent  any  permanent  displacement.  Now  all  these  offices  are  performed  in 
a  remarkably  complete  degree,  by  the  Jireolar  Tissue  (§  637);  the  reason  of 
whose  restriction  to  the  Animal  kingdom,  notwithstanding  the  purely  physical 
nature  of  its  functions,  is  thus  evident.  And  as  necessity  arises,  in  certain 
parts,  for  tissues  which  shall  exercise  a  still  greater  power  of  resistance  to 
tension,  and  which  shall  thus  communicate  motion  (as  in  the  case  of  Tendons), 
or  shall  bind  together  organs  that  require  to  be  united  (as  in  the  case  of  Liga- 
ments and  Fibrous  Membranes),  so  do  we  find  peculiar  tissues  developed,  that 
shall  serve  these  purposes  in  the  most  effectual  manner.  Hence  these  tissues 
also,  although  not  endowed  with  any  properties  that  are  peculiarly  animal,  are 
nevertheless  restricted  to  the  Animal  Kingdom, — as  completely  as  are  the  Mus- 
cular and  Nervous  Tissues,  which  make  up  the  essential  parts  of  the  appara- 
tus of  Animal  Life. 

612.  That  all  the  Animal  tissues  are  in  the  first  instance  developed  from 
Cells,  was  the  doctrine  put  forth  by  Schwann,  who  first  attempted  to  generalize 
on  this  subject.  By  subsequent  research,  however,  it  has  been  shown  that 
this  statement  was  too  hasty;  and  that,  although  many  tissues  retain  their 
original  cellular  type,  through  the  whole  of  life,  and  many  more  are  evidently 
generated  from  Cells  and  are  subsequently  metamorphosed,  there  are  some  in 
which  no  other  cell-agency  can  be  traced  than  that  which  was  concerned  in 
the  preparation  of  the  plastic  material. — This  would  appear  to  be  certainly  the 
case,  in  regard  to  the  very  delicate  structureless  lamella  of  membrane,  now 
known  under  the  name  of  Basement  or  Primary  Membrane,  which  is  found 
(beneath  the  Epidermis  or  Epithelium),  on  all  the  free  surfaces  of  the  body. 
No  vestige  of  cell-structure  can  be  seen  in  this  membrane ;  and  it  would  rather 
appear  to  resemble  that,  of  which  the  walls  of  the  cells  are  themselves  con- 
stituted.* In  some  instances  it  presents  a  somewhat  granular  appearance; 
and  is  then  supposed  by  Henle  to  consist  of  the  coalesced  nuclei  of  cells,  whose 
development  has  been  arrested.  This,  however,  is  quite  hypothetical;  and 
all  we  can  say  is,  that  the  Basement  membrane  is  probably  formed  by  the  con- 
solidation of  a  layer  of  the  plastic  element,  which  may,  in  certain  cases,  include 
a  large  number  of  granules  that  may  serve  for  the  development  of  new  cells. 
Possibly  it  is  in  these  granular  germs, — sometimes  scattered  through  the  mem- 
brane, and  in  other  instances  collected  into  certain  spots,! — that  the  cells  of  the 
superjacent  Epithelium  or  Epidermis  take  their  origin;  and  if  this  be  the 

*  See  a  Paper  by  the  Author,  on  the  Microscopic  Structure  of  Shells,  &c.,  in  the  Annals 
of  Natural  History,  Dec.,  1843.  The  inner  layer  of  the  Shells  of  Mollusca,  after  treatment 
with  a  dilute  acid,  yields  specimens  of  Basement  Membrane,  in  a  form  well  adapted  for 
examination. 

j-  See  Goodsir,  in  Trans,  of  Roy.  Soc.  of  Edinb.,  1842. 


FORMATION  OF  THE  TISSUES.  465 

case,  we  must  regard  the  Basement  membrane  as  a  transitional  rather  than 
as  a  permanent  structure, — continually  disintegrating,  and  yielding  up  its  con- 
tained cell-germs  on  its  free  surface,  and  as  constantly  being  renewed  from 
the  blood  beneath.  For  the  Epidermic  structures  appear  to  constitute  an 
exception  to  the  general  rule,  that  the  Tissues  reproduce  themselves ;  since 
they  are  cast  off,  without  leaving  their  germs  behind  them;  and  the  cells 
which  replace  them  must  be  derived  from  new  germs  more  directly  supplied 
from  the  blood  than  is  elsewhere  the  case.  In  the  case  of  the  other  tissues, 
whose  disintegration  takes  place  inter stitially  (so  to  speak),  it  would  seem 
probable  that  in  the  very  act  of  the  dissolution  of  the  parent-structure,  the 
germs  of  the  new  structures  destined  to  replace  it  are  set  free ;  as  happens  in 
the  reproduction  of  the  simple  Cellular  Plants. 

013.  It  would  seem  doubtful,  also,  in  regard  to  the  simple  Fibrous  tissues, 
whether  they  are  generated  by  a  metamorphosis  of  Cells,  in  the  same  manner 
as  the  Osseous,  Muscular  and  Nervous ;  or  whether  they  are  not  produced, 
like  the  Basement  Membrane,  by  the  consolidation  of  a  plastic  fluid  which 
has  been  elaborated  by  cells.  The  latter  view  is  the  one  which  the  Author 
has  been  led  to  regard  as  most  probable,  from  the  results  of  his  own  observa- 
tions, coupled  with  those  of  Messrs.  Addison  and  Gulliver  previously  adverted 
to.  The  Membrane  of  the  Egg-shell,  whose  structure  has  been  already 
described  (§  554),  appears  to  him  to  have  essentially  the  same  constitution 
with  the  simple  Fibrous  tissues,  which  it  resembles  also  in  its  tenacity ;  whilst 
its  origin  can  scarcely  be  supposed  to  be  different  from  that  of  the  fibrous  net- 
work in  the  buffy  coat  of  the  blood,  or  in  the  bands  formed  by  the  coagulation 
of  Lymph  upon  an  inflamed  membrane.  The  appearances  which  the  Fibrous 
tissues  display,  and  which  have  been  quoted  in  proof  of  their  Cellular  origin, 
are  not  inconsistent  with  this  view.  For  in  the  reticulated  structures  just 
adverted  to,  certain  bodies  are  seen  which  appear  to  be  nuclei  or  imperfectly 
formed  cells, — originating  probably  in  germs  set  free  by  the  rupture  of  the 
white  corpuscles  of  the  blood, — and  which  closely  correspond  with  the  nuclear 
corpuscles,  which  may  be  brought  into  view  in  the  Fibrous  tissues  (§  637). 
Mr.  Addison's  observation,  too, — that  the  fibres  formed  in  the  Liquor  Sanguinis, 
during  its  coagulation,  often  seem  to  radiate  from  the  remains  of  the  white  cor- 
puscles that  have  ruptured,  or  from  the  little  aggregations  of  granules  they 
contained, — gives  the  explanation  of  several  of  the  appearances  which  have 
led  to  the  belief  in  the  production  of  Areolar  tissue  by  Cell-transformation.  As 
an  additional  argument  in  support  of  this  view,  the  appearances  presented  by 
the  semi-fibrous  Cartilages  may  be  adduced.  In  the  cartilages  of  the  ribs,  for 
instance,  a  more  or  less  distinct  fibrous  appearance  may  be  frequently  seen  in 
the  intercellular  substance ;  this  is  sometimes  so  faint,  that  it  might  be  con- 
sidered as  an  illusion  occasioned  by  the  manipulation  to  which  the  section  has 
been  subjected;  but  it  is  often  so  well-defined,  as  almost  to  present  the  appear- 
ance of  the  true  fibrous  structure.  No  indication  of  the  direct  operation  of 
cells  in  the  development  of  these  fibres  has  ever  been  witnessed ;  and  we  can 
scarcely  do  otherwise  than  regard  them  as  produced  by  the  regular  arrange- 
ment and  consolidation  of  the  particles  of  the  blastema  or  plastic  element,  in 
virtue  of  its  own  inherent  powers.  In  many  instances,  Fibres,  like  mem- 
branes, appear  to  originate  in  the  nuclei  of  cells,  whose  development  has  been 
checked;  the  fibres  which  occasionally  encircle  the  fasciculi  of  Areolar  tissue 
(§  637)  appear  to  have  this  origin. 

614.  The  transformation  of  the  elements  of  Blood  into  Organized  Tissues  is 
not  confined  to  the  form  and  structure  which  these  present,  but  extends  also 
to  their  Chemical  constitution.  In  the  greater  number  of  them,  the  Protein 
composition  prevails ;  and  there  is  reason  to  believe  that  this  is  the  case  with 
the  organized  portion  of  all  those  which  are  formed  by  the  transformation  of 


466  OF  NUTRITION. 

Cells.  Very  frequently,  however,  a  deposit  is  formed  within  these  cells, 
through  a  secreting  process  effected  by  themselves  (§  651) ;  which  may  have 
an  entirely  different  character.  Thus  the  cells  of  Adipose  tissue  elaborate 
Fatty  matter,  the  cells  of  Epidermis  appear  to  draw  off  Horny  matter,  and  the 
cells  of  the  Epithelium  fill  themselves  with  products  of  various  kinds,  which 
were  either  pre-existing  in  the  Blood,  or  are  generated  by  a  simple  transforma- 
tion of  its  elements  (§  649).  These  last  might  be  regarded,  equally  with  the 
contents  of  the  more  permanent  Tissue-cells,  as  products  of  Nutritive  action  ; 
but  it  will  be  more  convenient  to  consider  them  with  a  view  to  their  destination, 
which  is  altogether  different. 

615.  The  composition  of  the  greater  part  of  the  Fibrous  tissues,  however, 
is  very  different ;  for  they  all  yield  to  boiling  water  the  substance  called  Gela- 
tin, which  does  not  seem  capable  of  the  same  degree  of  organization  with  the 
Protein  compounds.  This  may  be  obtained  by  boiling  portions  of  Skin,  Areo- 
lar  tissue,  Serous  membrane,  Tendon,  Bone,  &c.,  in  water,  for  some  time ;  after 
which  the  decoction  is  allowed  to  cool,  when  it  solidifies  into  a  jelly  of  greater 
or  less  thickness.  Some  tissues  dissolve  readily  in  this  manner,  and  little  resi- 
dual (or  fibrinous)  substance  is  left ;  this  is  especially  the  case  with  areolar 
tissue,  serous  membranes,  and  (in  a  less  degree)  with  skin.  Others  require  a 
long  boiling  for  the  extraction  of  any  Gelatin,  and  even  then  it  is  obtained  in 
but  small  quantity ;  of  this  kind  are  the  elastic  fibrous  tissue  and  some  forms 
of  cartilage.  A  peculiar  modification  of  this  principle  exists  in  most  of  the 
permanent  cartilages ;  and  has  received  the  name  of  Chondrin.  Gelatin  is 
not  found  in  the  blood,  nor  in  any  of  the  healthy  fluids ;  and  most  Chemists 
are  of  opinion  that  it  is  rather  a  product  of  the  operation  practised  to  separate  it, 
than  a  real  constituent  of  the  living  solids.  This  idea  seems  inconsistent, 
however,  with  the  fact  that  the  gelatinous  tissues  will  exhibit,  without  any 
preparation,  the  best  marked  of  the  chemical  properties  which  are  regarded 
as  characteristic  of  Gelatin, — that,  namely,  of  forming  a  peculiar  insoluble 
compound  with  Tannin ;  and  the  Tanno-Gelatin  which  may  be  obtained  by 
precipitating  Gelatin  from  a  solution,  and  that  which  results  from  the  action 
of  Tannin  on  Animal  membrane,  appear  to  be  precisely  analogous  in  every 
respect, — save  the  presence  of  structure  in  the  latter,  and  its  absence  in  the 
former.  Gelatin  is  very  sparingly  soluble  in  cold  water ;  by  contact  with 
which,  however,  it  is  caused  to  swell  up  and  soften.  It  is  readily  dissolved 
by  hot  water ;  and  forms  so  strong  a  jelly  on  cooling,  that  1  part  in  100  of 
water  becomes  a  consistent  solid.  Its  reaction  with  Tannic  acid  is  so  distinct 
that  1  part  in  5000  of  water  is  at  once  detected  by  infusion  of  Galls.  The  fol- 
lowing are  the  results  of  four  analyses  of  Gelatin,  by  Scherer  and  Mulder. 

X 

SCHERER,  MULDER. 


Carbon     .  .  .  50-557  50-774  50-048  50-048 

Hydrogen  .  .  6-903  7-152  6.477  6-643 

Nitrogen  .  .  18-790  18-320  18-350  18-388 

Oxygen   .  .  .  23-750  23-754  25-125  24-921 

The  formula  adopted  by  the  former  is  48  C,  41  H,  7k  N,  18  O  ;  that  of  the 
latter  is  54  C,  42  H,  9  N,  20  O.  Neither  of  these  can  be  yet  regarded  as 
satisfactorily  determined  ;  and  it  is  therefore  useless  to  speculate  upon  the 
mode  in  which  Gelatin  is  produced  by  a  metamorphosis  of  Protein-compounds. 
That  it  cannot  be  converted,  in  the  living  body,  into  Albumen  or  Fibrin, 
would  appear  from  the  considerations  already  stated  (554). — A  kind  of  sugar, 
termed  Glycicoll,  may  be  obtained  from  Gelatin,  by  the  action  of  Sulphuric 
acid,  or  by  boiling  it  in  caustic  Alkali :  this  substance  crystallizes  in  large 
prisms,  which  are  colourless,  taste  sweet,  and  feel  gritty'  between  the  teeth ; 


FORMATION  OF  THE  TISSUES. PIGMENT-CELLS.  467 

it  is  soluble  in  4£  parts  of  water,  and  is  taken  up  in  small  quantity  by  alcohol. 
This  fact  is  one  of  much  interest,  in  regard  to  certain  Pathological  relations  of 
Gelatin. 

[The  following  table  presents,  perhaps,  the  best  general  view  of  the  various  tissues. 
No  satisfactory  arrangement  can  be  constructed,  based  on  any  one  principle  of  classifi- 
cation. 

TABULAR  VIEW  OF  THE  TISSUES  OF  THE  HUMAN  BODY. 

1.  Simple  membrane,  homogeneous,  or  nearly  so,    Examples. —  Posterior  layer  of  the 

employed  alone,  or  in  the  formation  of  com-        cornea.  —  Capsule  of  the   lens. 

pound  membranes.  Sarcolemma  of  muscle,  &c. 

2.  Filamentous  tissues,  the  elements  of  which  are     White  and  yellow  fibrous  tissues. 

real  or  apparent  filaments.  Areolar  tissue. 

3.  Compound  membranes,  composed  of  simple     Mucous  membrane. — Skin. — True  or 

membrane,  and  a  layer  of  cells,  of  various  secreting  glands. — Serous  and  sy- 

forms  (epithelium  or  epidermis),  or  of  areo-  novial  membranes, 
lar  tissue  and  epithelium. 

4.  Tissues  which  retain  the  primitive  cellular    Adipose  tissue.  —  Cartilage. Gray 

structure  as  their  permanent  character.  nervous  matter. 

5.  Sclerous  or  hard  tissue.  Bone. — Teeth. 

6.  Compound  tissues. 

a.  Composed  of  tubes  of  homogeneous  mem-  Muscle.— Nerve, 
brane,  containing  a  peculiar  substance. 

b.  Composed  of  white   fibrous   tissues   and  Fibro-cartilage. 
cartilage.— M.  C.j 

616.  There  are  several  instances  in  which  Nucleated  Cells,  resembling  those 
of  the  primordial  fabric,  are  seen  even  in  the  adult  body.     The  most  striking 
examples  of  this  are  to  be  found  among  the  inferior  members  of  the  class  of 
Fishes.     Thus,  in  the  Myxinoid  family,  there  is  no  true  Vertebral  column, 
but  its  place  is  occupied  by  a  gelatinous  tube,  termed  the  chorda  dorsalis ; 
which  consists  entirely  of  nucleated  cellular  tissue,  and  which  is  precisely 
analogous  to  the  structure  occupying  the  same  situation  in  the  early  Embryo 
of  higher  animals  (§  760).     In  the  Short  Sun-fish,  a  corresponding  form  of 
tissue  forms  a  thick  covering  to  the  body,  replacing  the  true  skin.    And  in  the 
Lancelot  (a  little  fish  which  is  deficient  in  so  many  of  the  characters  of  the 
Vertebrated  division,  that  many  naturalists  have  doubted  its  right  to  a  place  in 
the  class),  a  considerable  portion  of  the  fabric  is  made  up  of  a  similar  paren- 
chyma.— We  shall  find,  however,  that  even  in  Man  a  considerable  part  of  the 
fabric  is  made  up  of  Cells  ;  and  that  these  perform  some  of  the  most  important 
offices  in  the  economy. 

617.  The  Pigment-cells,  which  give  colour  to  the  Skin,  and  of  which  the 
Pigmentum  Nigrum  of  the  eye  is  entirely  composed,  usually  exhibit  the  ori- 
ginal form  of  the  cell  with  little  alteration.     On  the  choroid  coat  of  the  eye 
they  are  seen  as  a  kind  of  pavement,  having  somewhat  of  a  polyhedral  shape, 
and  lying  in  a  very  regular  manner  with  some  intercellular  substance  interposed 
between  them.     In  the  Skin  of  Man,  they  are  scattered  through  the  ordinary 
epidermic  cells  ;  and  its  colour  is  determined  by  that  of  their  contents.    There 
is  no  distinct  coloured  layer,  as  was  formerly  supposed ;  but  the  cells  are  more 
closely  aggregated  in  some  parts  than  in  others.     This  is  as  much  the  case  in 
the  European,  however,  as  in  the  Negro ;  in  the  former,  they  are  concerned  in 
producing  the  spots  termed  freckles,  and  others  of  a  similar  kind.     In  some 
animals,  the  Pigment  cells  of  the  skin  frequently  undergo  a  change  of  form ; 
being  elongated  in  many  directions  into  hollow  fibres,  which,  meeting  other 
formations  of  the  same  kind,  produce  a  more  or  less  perfect  network  of  star- 
shaped  cells.     This  change  is  best  seen  in  the  skin  of  the  Batrachia,  where 
the  cells  are  frequently  isolated :  a  good  example  of  it  is  shown  in  Fig.  89  (p. 
360.)     The  black  colour  is  given  by  an  accumulation  within  the  cell,  of  a 


468 


OF  NUTRITION. 


number  of  rounded  granules,  which,  when  separately  viewed,  are  found  to  be 
transparent,  not  black  and  opaque  ;  these  granules  are  flat  oval  corpuscles, 
measuring  about  l-20,000th  of  an  inch  in  diameter,  and  about  a  quarter  as 
much  in  thickness  ;  they  exhibit  a  very  active  molecular  movement  when  set 
free  by  the  bursting  of  the  cell,  and  this  has  even  been  noticed  while  they  are 
enclosed.  The  chemical  nature  of  the  black  pigment  has  not  yet  been  made 
evident ;  it  has  been  shown,  however,  to  have  a  close  relation  to  that  of  the 
Cuttle-fish  ink  (which  derives  its  colour  from  pigment-cells  lining  the  ink-bag) ; 
and  to  contain  a  larger  proportion  of  Carbon  than  most  other  organic  sub- 
stances,— every  100  parts  containing  58<|  of  this  element.  The  nucleus  of 
the  pigment  cells  may  generally  be  traced  as  a  clear  spot. 

618.  The  Fat-cells,  of  which  Adipose  tissue  is  composed,  also  permanently 
exhibit  the  original  type  of  structure  in  its  simplest  form.  This  tissue  is  usually 
diffused  over  the  whole  body,  filling  up  interstices,  and  forming  a  kind  of  pad 
or  cushion  for  the  support  of  movable  parts.  Even  in  cases  of  great  ema- 
ciation, some  Fat  is  always  left ;  especially  at  the  base  of  the  heart,  around  the 
origin  of  the  large  vessels ;  in  the  orbit  of  the  eye  ;  in  the  neighbourhood  of 
the  kidney;  in  the  interior  of  the  bones  ;  and  within  the  spinal  canal,  between 
the  periosteum  and  the  dura  mater.  The  Fat  Cells  are  usually  spherical  or 
spheroidal ;  sometimes,  however,  when  closely  pressed  together  without  the 
intervention  of  any  intercellular  substance,  they  become  polyhedral.  The 
nucleus  is  not  always  to  be  distinguished ; — perhaps  in  consequence  of  its 
having  passed  to  the  interior  of  the  cell. 

[The  Fat-cell  is  composed  of  the  adipose  tissue,  a  closed  vesicle  formed  by  a  membrane 
of  extreme  tenuity,  and  the  material  which  it  contains,  ihefat.  The  membrane  is  per- 
fectly homogeneous  and  transparent,  about  the  2<j<J<yflth  of  an  inch  thick,  and  is  moistened 
by  a  watery  fluid,  for  which  it  has  a  greater  attraction  than  the  fat  it  contains.  Each 
vesicle  is  a  perfect  organ,  from  Tj^th  to  ^^th  of  an  inch  in  diameter,  with  capillaries 


Fig.  104. 


Fig.  105. 


Fat  vesicles,  assuming  the  poly- 
hedral form  from  pressure  against 
one  another.  The  capillary  vessels 
are  not  represented.  —  From  the 
omentum ;  magnified  about  300  dia- 
meters. 


Blood-Vessels  of  Fat ;  1,  minute  flattened  fat-lobule,  in  which 
the  vessels  only  are  represented;  3,  the  terminal  artery;  4,  the 
primitive  vein ;  5,  the  fat  vesicles  of  one  border  of  the  lobule, 
separately  represented,— magnified  100  diameters;  2,  plan  of  the 
arrangement  of  the  capillaries  on  the  exterior  of  the  vesicles,— 
more  highly  magnified. 


FORMATION  OF  THE  TISSUES— FAT.  469 

ramifying  on  its  exterior.  When  the  fat  cells  exist  in  any  number  their  arrangement  is 
usually  lobular,  with  an  investment  of  areolar  (cellular)  tissue,  which  favours  motion 
and  the  distribution  of  the  blood-vessels.  The  vessels  enter  the  interlobular  clefts,  ramify 
through  their  interior,  as  a  solid  capillary  net-work,  occupying  the  angles  formed  by  con- 
tiguous sides  of  the  vesicles,  and  anastomose  with  one  another  at  the  point  these  angles 
meet.— M.  C.] 

The  consistency  of  the  substance  contained  in  the  Fat-Vesicles  varies  in 
different  animals,  according  to  the  proportions  of  the  organic  elements  that 
enter  into  its  composition.  These  elements  are  known  under  the  names  of 
Stearine,  Margarine,  and  Oleine  ;  the  two  former,  which  are  solid  when  sepa- 
rate, being  dissolved  in  the  latter,  at  the  ordinary  temperature  of  the  body. 

[A  spontaneous  separation  of  these  proximate  principles 

mav  sometimes  be  detected  within  the  human  fat-vesicle.  [Fig.  106. 

The  stearine  collects  in  the  form  of  a  small  star  on  the 
inner  surface  of  the  membrane  (fig.  106,2,  2,2);  the  elaine 
occupying  the  remainder  of  the  vesicle,  except  where  there 
is  an  unusually  small  quantity  of  fat,  when  we  see  a  little 
aqueous  fluid  interposed  between  the  elaine  and  the  cell- 
membrane.  This  offers  the  best  condition  for  the  investi- 
gation of  the  membrane. — M.  C.] 

That  the  thick  oil  thus  formed  does  not  escape 
from  the  fat-cells  during  life,  may  be  attributed  to 

the  moistening  of  their  walls  by  the  aqueous  fluid  Fat  Vesicles  from  an  emaci- 
circulating  through  the  body.  In  all  fixed  oils,  ated  subject;  1,1,  the  ceii-mem- 
which  are  fluid  at  common  temperatures,  a  portion  bra"e;  *'  2'  2' the  solid  portion 
of  the  solid  constituents  of  fat  exists  :  these  may  be  ^  1LT?— 
separated  by  exposure  to  cold,  which  congeals  them,  with  it?  but  not  fiiling  ^  Ceii.] 
leaving  the  Oleine  fluid.  All  these  substances  are 

regarded  by  chemists  in  the  light  of  salts ;  being  compounds  of  acids,  the 
Stearic,  Margeric,  and  Oleic — with  a  common  base,  to  which,  from  its  sweetish 
taste,  the  name  of  Glycerine  has  been  given. 

Stearine  is  the  essential  constituent  of  nearly  all  solid  fats,  and  preponderates  in  pro- 
portion to  their  consistence.  It  exists  largely  in  mutton-suet;  from  this  it  may  be  obtained 
by  the  action  of  ether,  which  takes  up  all  the  oily  matter.  It  is  crystalline,  like  sperma- 
ceti; it  is  not  at  all  greasy  between  the  fingers,  and  melts  at  143°.  It  is  insoluble  in 
water,  and  in  cold  alcohol  and  ether;  but  it  dissolves  in  boiling  alcohol  or  ether,  crystal- 
lizing as  it  cools.  It  is  composed  of  2  proportionals  of  stearic  acid  to  1  of  glycerine, 
with  two  proportionals  of  water.  The  Stearic  acid  (which  is  the  substance  of  which  the 
stearine  candles  are  composed)  may  be  separated  by  causing  it  to  combine  with  a  stronger 
base,  such  as  lime  or  potash,  and  then  setting  it  free  from  this  by  a  stronger  acid. — Mar- 
garine exists  in  small  quantity,  along  with  Stearine,  with  most  fats;  but  it  is  the  princi- 
pal solid  constituent  of  Human  fat,  which  in  this  respect  resembles  olive  oil  rather  than 
the  other  animal  fats.  It  corresponds  with  Stearine  in  many  of  its  properties;  but  it  is 
much  more  soluble  in  alcohol  and  ether;  and  it  melts  at  118°.  Its  composition  is  analo- 
gous (except  in  the  presence  of  an  additional  atom  of  water)  to  that  of  stearine,  to  which 
indeed  it  bears  a  close  relation, — margaric  acid  being  procurable  from  stearic  acid,  by 
subjecting  it  to  a  dry  distillation. — Oleine  exists  in  small  quantity  in  the  various  solid 
fats;  but  it  constitutes  the  great  mass  of  the  liquid  fixed  oils.  The  tendency  of  these  to 
solidification  by  cold,  depends  upon  the  proportion  of  stearine  or  margarine  they  may 
contain;  for  oleine  itself  remains  fluid  at  the  zero  of  Fahrenheit's  thermometer.  It  is 
soluble  in  cold  ether,  from  which  it  can  only  be  separated  by  the  evaporation  of  the  latter. 
Its  composition  is  analogous  to  that  of  margarine;  for  it  consists  of  2  proportionals  of 
oleic  acid,  united  with  1  of  glycerine  and  two  of  water. —  Glycerine,  the  base  of  all  the 
fatty  acids,  may  be  obtained  from  any  fatty  matter,  by  saponifying  it  with  an  alkaline 
base,  by  which  this  compound  is  set  free.  It  cannot  be  obtained  in  a  solid  form,  but  may 
be  brought  to  the  consistence  of  a  thick  syrup.  It  dissolves  in  water  and  alcohol;  but  is 
insoluble  in  ether.  It  has  a  sweetish  taste,  whence  its  name  is  derived ;  and  it  is  remark- 
able for  its  solvent  powers,  which  are  scarcely  inferior  to  those  of  water.  It  is  regarded 
as  a  hydrated  oxyde  of  a  hypothetical  base,  Glyceryl ;  the  composition  of  which  is  stated 
by  Liebig  to  be  6  Carbon  united  with  7  Hydrogen.  Glycerin  is  composed  of  one  propor- 
40 


470  OF  NUTRITION. 

tional  of  this,  with  5  Oxygen  and  1  water. — The  following  table  represents  the  composi- 
tiun  of  the  fatty  acids,  and  of  the  compounds  just  mentioned. 

Stearic  Acid 68  Carbon,  66  Hydrogen,  5  Oxygen. 

viargaric  Acid       ....     34  Carbon,  33  Hydrogen,  3  Oxygen. 
Oleic  Acid 44  Carbon,  39  Hydrogen,  4  Oxygen. 

Stearin  e.  Margarine.  Oleine. 

1  atom  of  Glycerine 6  c,      7  H,     5  o     0  c,     7  H,    5  o     6  c,     7  H,    5  o 

2  atoms  of  Acid 136  c,  132  H,  10  o  68  r,  66  H,    6  o  88  c.  78  H,    80 

Water  (1  or  2  atoms)    ....  2  H,     2  o  1  H,    1  o  2  u,    2  o 

Total 142  c    141  H,  17  o   74  c,  74  H,  12  o   94  c,  87  H,  15  o 

619.  Besides  the  support,  combined  with  facility  of  movement,  which  Fat 
affords  to  the  moving  parts  of  the  body,  it  answers  the  important  purpose  of  as- 
sisting; in  the  retention  of  the  animal  temperature  by  its  non-conducting  power; 
and  the  still  more  important  object  of  serving  as  a  kind  of  reservoir  of  com- 
bustible matter  against  the  time  of  need  (§  730).     Herbivorous  animals,  whose 
food  is  scanty  during  the  winter,  usually  exhibit  a  strong  tendency  to  such  an 
accumulation  during  the  latter  part  of  the  summer,  when  their  food  is  most 
rich  and  abundant ;  and  the  store  thus  laid' up  is  consumed  during  the  winter. 
Fat  appears  to  be  deposited  only  when  there  is  an  excess  in  the  alimentary 
matter  introduced  into  the  body,  of  non-azotized  compounds  which  may  be 
converted  into  it  (§  433).     But  the  ingestion  of  a  large  quantity  of  these  in  the 
food,  is  by  no  means  sufficient  for  the  production  of  Fat ;  for  they  may  not  be 
absorbed  into  the  vessels ;  and,  if  absorbed,  there  may  be  a  want  of  power  to 
generate  Adipose  tissue, — so  that  they  would  accumulate  injuriously  in  the 
blood,  if  not  drawn  off  by  the  Liver  (§  664).     Hence  some  persons  never  be- 
come fat,  however  large  the  quantity  of  oily  matter  ingested  ;  and  it  is  in  such 
persons  that  the  tendency  to  disorder  of  the  Liver  from  over-work  is  most 
readily  manifested  ;  hence  they  are  obliged  to  abstain  from  the  use  of  fat- 
producing  articles  of  food. 

620.  We  have  next  to  speak  of  the  Epidermic  tissues,  which  were  long 
described  as  altogether  inorganic  in  their  character,  but  which  are  now  known 
to  have  the  same  origin  with  all  the  rest.     The  Epidermis  consists  of  a  series 
of  flattened  scale-like  cells,  which,  when  first  formed,  are  spheroidal,  but  which, 
gradually  dry  up,  their  nucleus  still  remaining  visible.     These  form  several 
layers,  of  which  the  deeper  can  be  seen  very  distinctly  to  possess  the  cellular 
character  ;  whilst  the  exterior  layers  are  scaly  ;  and  between  these,  all  stages 
of  transformation  can  be  traced.    The  outer  layers  are  continually  being  thrown 
off  by  desquamation ;  and  new  ones  are  as  constantly  being  formed  below, 
from  organizable  matter  exuded  by  the  basement  membrane.     What  has  been 
termed  the  rete  mucosum  is  simply  the  last  formed  portion  of  the  Cuticle : 
and  in  this  we  do  not  find  completely  formed  cells,  but  granular  nuclei,  in 
progress  of  development.     The  Epidermic  membrane,  which  is  formed  by 
this  aggregation  of  cells,  is  pierced  by  the  excretory  ducts  of  the  sebaceous  ancl 
sweat-glands,  and  also  by  the  shafts  of  the  hairs.     Its  layers  become  more 
numerous,  as  the  surface  is  rubbed ;  the  corium  being  thus  stimulated  to  an 
increased  exudation.     The  Chemical  constitution  of  this  tissue  is  of  peculiar 
interest,  in  relation  to  that  of  the  Horny  appendages  which  it  bears.     Recent 
analysis  has  shown  that  the  membranous  Epidermis  of  the  sole  of  the  foot,  and 
the  compact  Horny  matter  of  which  Nails,  Horn,  Wool,  and  Hair  are  com- 
posed, have  the  same  constitution  ;  the  formula  of  all  being  48  c,  30  H,  7  N, 
17  o  ;  this  bears  a  close  relation  to  Protein,  and  may  be  regarded  as  consisting 
of  one  proportional  of  Protein  with  1  atom  of  Ammonia,  and  3  of  Oxygen. 
The  Epidermis  covers  the  whole  exterior  of  the  body,  not  excepting  the  con- 
junctiva and  cornea ;  where,  however,  it  undergoes  a  modification  in  its  cha- 


FORMATION  OF  THE  TISSUES EPITHELIUM.  471 

racter. — The  Nails  may  be  considered  as  nothing  more  than  an  altered  form 
of  Epidermis.  When  near  their  origin,  they  are  found  to  consist  of  cells, 
which  gradually  dry  into  scales.  A  new  production  is  continually  taking 
place  in  the  groove  of  the  Skin  in  which  the  root  is  imbedded,  and  probably 
also  from  the  whole  subjacent  surface.  It  will  be  presently  seen,  that  hair 
also  originates  in  the  Epidermis  (§  623). 

(521.  The  internal  free  surfaces  are  also  covered  with  a  kind  of  cuticle,  to 
which  the  name  of  Epithelium  is  given.  The  existence  of  an  Epithelium, 
covering  the  Mucous  membrane  of  the  first  part  of  the  alimentary  canal,  has 
long  been  known ;  but  it  is  only  of  late  that  any  thing  analogous  to  it  has 
been  supposed  to  exist  elsewhere.  The  Epithelia  are  always  in  contact  with 
fluids,  and  remain  of  a  soft  and  pliant  nature ;  some  of  them  undergo  exfolia- 
tion in  a  less  degree  with  the  Cuticle  ;  being  less  exposed  to  external  influences, 
whilst  others  are  being  continually  thrown  off  and  renewed ;  in  all  instances, 
however,  when  the  surface  is  denuded,  they  are  restored  in  the  same  manner. 
The  forms  presented  by  the  Epithelial  cells  are  various.  The  two  chief, 
however,  are  founded  in  the  tessdaied  or  pavement-epithelium,  and  the  cylin- 
rfer-epithelium.  The  free  edges  of  the  cells  are  sometimes  fringed  with  cilia  ;* 
and  the  epithelium  is  then  said  to  be  ciliated. — The  Tesselated  Epithelium 
covers  the  serous  and  synovial  membranes,  the  lining  membrane  of  the  blood- 
vessels, and  the  mucous  membranes  (with  their  glandular  prolongations),  ex- 
cept where  the  cylinder-epithelium  exists.  The  cells  composing  it  are  usually 
polygonal,  and  their  number  of  layers  small ;  in  many  instances  there  is  but 
a  single  stratum.  A  very  good  example  of  it  will  be  shown  in  Fig.  152.  The 
tesselated  Epithelium  which  covers  the  delicate  pia  mater  that  lines  the  cere- 
bral cavities,  not  even  excepting  the  infundibulum  and  the  aqueduct  of  Sylvius, 
supports  an  abundance  of  very  active  cilia,  which  are  attached  along  the 
edges  of  its  cells. — The  cells  of  the  Cylinder-Epithelium  have  the  form  of  Jong 
cylinders,  or  rather  truncated  cones,  arranged  side  by  side,  having  one  extre- 
mity free,  and  the  other  seated  upon  the  subjacent  membrane  ;  frequently 
these  cylinders  seem  to  arise,  by  a  stalk-like  prolongation,  from  a  tesselated 
epithelium  beneath.  Sometimes  each  cylinder  is  formed  from  more  than  one 
cell ;  as  may  be  distinguished  by  the  number  of  nuclei  which  it  contains.  Vari- 
ous transitional  forms  may  be  detected  at  the  points  at  which  the  cylinder  and 
pavement-epithelia  pass  into  one  another ;  the  tesselated  scales  appearing  to 
rise  more  and  more  from  the  surface,  until  they  project  as  pedunculated  cells. 
The  cylinder-epithelium  is  found  in  the  intestinal  canal,  beyond  the  cardiac 
orifice  ;  in  the  larger  ducts  of  the  salivary  glands ;  in  the  ductus  communis 
choledochus  ;  in  the  prostate,  Cowper's  glands,  vesiculaB  seminales,  vas  defe- 
rens,  tubuli  seminiferi  and  urethra.  In  all  these  situations  it  is  continuous 
with  the  tesselate  epithelium ;  the  latter  lines  the  more  delicate  canals  of  the 
various  glands.  The  cylinders  are  often  fringed  with  cilia  at  their  extremi- 
ties ;  and  the  motions  of  these  are  towards  the  natural  outlets  of  the  cavities 
or  canals  they  cover.  A  Ciliated  Epithelium  is  found  lining  the  nasal  cavi- 
ties, the  frontal  sinuses,  maxillary  antra,  lachrymal  ducts  and  sac,  the  posterior 
surface  of  the  pendulous  velum  of  the  palate  and  fauces,  the  Eustachian  tube, 
the  larynx,  trachea,  and  bronchi,  to  the  finest  divisions  of  these  last  (where  it 
becomes  tesselate,  but  still  ciliated),  the  upper  portion  of  the  vagina,  the  uterus, 
and  the  Fallopian  tubes.  The  function  of  the  cilia  is  probably  to  propel  the 
viscid  secretions,  that  would  otherwise  accumulate  on  these  membranes,  to- 
wards the  exterior  orifices,  from  which  they  may  be  removed. 

*  Cilia  are  minute  hair-like  filaments,  which  are,  during  life,  and  for  some  time  after 
death,  in  a  state  of  continual  vibration.  See  Art.  Cilia  in  Cyclop,  of  Auat.  and  Phys. ; 
and  Princ.  of  Gen.  and  Comp.  Phys.,  §  146. 


472 


OF  NUTRITION. 


Fig.  101 


[Certain  surfaces,  which  are,  in  their  natural  and  healthy  state,  lubricated  by  fluid,  are 
covered  with  a  multitude  of  hair-like  processes,  of  extreme  delicacy  of  structure  and 
minuteness  of  size.  These  are  called  cilia,  from  ciliurn,  an  eyelash.  They  are  generally 
conical  in  shape,  being  attached  by  their  bases  to  the  epithelium  that  covers  the  surface 
on  which  they  play,  and  tapering  gradually  to  a  point;  or, as  Purkinje  and  Valentin  state, 
they  are  more  or  less  flattened  processes,  of  which  the  free  extremities  are  rounded ;  and 
this  latter  form  prevails  in  the  human  subject.  They  vary  in  length  from  the  1-lOOOth  to 
the  l-12,000th  of  an  inch.  They  are  disposed  in  rows,  and  are  adapted  in  their  arrange- 
ment to  the  shape  and  extent  of  the  surface  to  which  they  belong;  they  adhere  to  the 
edges,  or  to  a  portion  of  the  surface,  of  the  particles  of  the  epithelium,  preferring  the 
columnar  variety  of  them. 

During  life,  and  for  a  certain  period  after  death,  these  filaments  exhibit  a  remarkable 

movement,  of  a  fanning  or  a  lashing 
kind,  so  that  each  cilium  bends  rapidly 
in  one  direction,  and  returns  again  to 
the  quiescent  state.  The  motion,  when 
viewed  under  a  high  magnifying  power, 
is  singularly  beautiful,  presenting  an 
appearance  somewhat  resembling  that 
of  a  field  of  corn  agitated  by  a  steady 
breeze.  Any  minute  objects  coming  in 
contact  with  the  free  extremities  of  the 
cilia  are  hurried  rapidly  along  in  the 
direction  of  the  predominant  movement; 
one  or  more  blood  discs,  accidentally 
present,  will  sometimes  pass  rapidly 
across  the  field,  propelled  in  this  way, 
and  very  minute  particles  of  powdered 
charcoal  may  be  conveniently  used  to 
exhibit  this  phenomenon,  and  to  indicate 
the  direction  of  the  movement.  The 
action  of  the  cilia  produces  a  current  in 


Examples  of  Cilia;  1,  portion  of  a  bar  of  the  gill  of 
the  sea-mussel, Mytilus edulis, showing  cilia  attest  and 
in  motion ;  2,  ciliated  epithelium  particles  from  the  frog's 
mouth ;  3,  ciliated  epithelium  particles  from  inner  sur- 
face of  human  membrana  tympani;  4,  ditto,  ditto,  from 
the  human  bronchial  mucous  membrana;  5,  Leucophrys 
patula,  a  polygastric  infusory  animalcule ;  to  show  its 
surface  covered  with  cilia,  and  the  mouth  surrounded 
by  them. 


the  surrounding  fluid,  the  direction  of 
which  is  shown  by  the  course  which  the 
propelled  particles  take. 

An  easy  way  to  observe  this  pheno- 
menon is  to  detach  by  scraping  with  a 
knife  a  few  scales  of  epithelium  from 
the  back  of  the  throat  of  a  living  frog. 
These,  moistened  with  water  or  serum, 
will  continue  to  exhibit  the  movement 

of  their  adherent  cilia  for  a  very  considerable  time,  provided  the  piece  be  kept  duly 
moistened.  On  one  occasion  we  observed  a  piece  prepared  in  this  way  exhibit  motion 
for  seventeen  hours;  and  it  would  probably  have  continued  doing  so  for  a  longer  time, 
had  not  the  moisture  around  it  evaporated.  However,  Purkinje  and  Valentin  have 
observed  it  to  last  for  a  much  longer  time  than  this  in  connection  with  the  body  of  the 
animal.  In  the  turtle,  after  death  by  decapitation,  they  found  it  lasted,  in  the  mouth,  nine 
days;  in  the  trachea  and  the  lungs,  thirteen  days;  and,  in  the  oesophagus,  nineteen  days. 
In  frogs,  from  which  the  brain  had  been  removed,  it  lasted  from  four  to  five  days.  The 
longest  time  they  observed  it  to  continue  in  man  and  mammalia  was  two  days;  but  in 
general  it  did  not  last  nearly  so  long.  What  appears  to  be  immediately  necessary  to  the 
continuation  of  the  movement,  is  the  integrity  of  the  epithelial  cells  to  which  the  cilia 
adhere ;  for  as  soon  as  these  shrink  up  for  want  of  moisture,  or  become  physically  altered 
by  chemical  reagents  or  by  the  progress  of  putrefaction,  the  cilia  immediately  cease  to 
play. 

From  these  facts  we  learn  two  important  points  in  connection  with  this  phenomenon. 
The  first  is,  the  truly  molecular  character  of  the  movement.  Whatever  be  the  immediate 
cause  of  the  action  of  the  cilia,  it  is  evidently  intimately  connected  with  the  minute 
epithelial  particles  to  which  they  are  attached ;  for  cilia  never  exist  in  man  and  the 
higher  animals  without  epithelial  particles,  and  these  particles  have  no  organic  connec- 
tion with  the  subjacent  textures,  excepting  such  as  may  arise  from  simple  adhesion. 
And,  secondly,  we  perceive,  that  this  movement  is  independent  of  both  the  vascular  and 
the  nervous  systems,  for  it  will  continue  to  manifest  itself  for  many  hours  in  a  single 
particle  isolated  from  the  rest  of  the  system.  After  death  it  remains  longer  than  the  con- 
tractility of  muscle;  a  circumstance  which,  together  with  the  facts  just  mentioned,  indi- 
cates that  the  cilia  cannot  be  moved  by  little  muscles  inserted  into  their  bases,  as  some 


FORMATION  OF  THE  TISSUES EPITHELIUM.  473 

have  supposed.  And  experiment  also  shows  this  independence.  If  the  abdominal  aorta 
be  tied,  the  muscles  of  the  lower  extremities  will  be  paralyzed  in  consequence  of  their 
being  deprived  of  their  blood  ;  and  on  removing  the  ligature,  and  allowing  the  b'ood  to 
flow,  the  muscles  will  recover  themselves.  But  a  ciliated  surface  is  not  affected  at  all 
in  its  movements,  though  the  supply  of  blood  to  the  subjacent  tissues  be  completely  cut 
off.  Again,  hydrocyanic  acid,  opium,  strychnine,  belladonna,  substances  which  exert  a 
powerful  effect  on  the  nervous  system,  produce  no  influence  upon  ciliary  motion:  in  the 
bodies  of  animals  killed  by  these  poisons,  the  phenomenon  is  still  conspicuous;  and  even 
the  local  application  of  them  does  not  hinder  it,  provided  the  solutions  do  not  injure  the 
epithelial  texture.  Shocks  of  electricity  passed  through  the  ciliated  parts,  do  not  affect 
the  movement.  Lastly,  the  removal  of  the  brain  and  spinal  cord  in  Irogs,  by  which  all 
muscular  movements  are  destroyed,  does  not  stop  the  action  of  the  cilia.  This  striking 
fact  may  likewise  be  adduced  to  disprove  the  supposition,  that  these  movements  result 
from  the  action  of  minute  muscles;  for,  although  muscles  maybe  excited  to  contract 
without  nerves,  we  have  no  instances  in  the  higher  animals  in  which  they  habitually  act 
without  the  interference  of  the  nervous  system;  nor  is  it  likely  that  a  movement  existing 
over  so  extended  a  surface  as  that  by  the  cilia,  would,  if  effected  by  muscles,  be  inde- 
pendent of  nervous  influence. 

Alterations  of  temperature  affect  the  ciliary  motion,  owing,  doubtless,  to  the  physical 
change  they  induce  in  the  epithelial  particles.  In  warm-blooded  animals  it  ceases  on  a 
reduction  of  the  temperature  below  43°  F.  In  cold-blooded  animals,  however,  it  continues 
even  at  32°.  In  all,  a  very  high  temperature  effectually  puts  a  stop  to  it.  It  is  interest- 
ing to  notice,  that  all  observers  agree  in  stating,  that  blood  is  the  best  preservative  of  the 
ciliary  motion,  but  the  blood  of  Vertebrata  destroys  it  in  the  Invertebrata.  Bile  puts  a 
stop  to  it,  very  probably  by  reason  of  its  thick  and  viscid  nature,  arid  not  from  any  chemi- 
cal influence. 

This  phenomenon  exists  most  extensively  in  the  animal  kingdom.  It  has  been  found 
in  all  the  vertebrate  classes;  and  in  the  Invertebrata  likewise,  with  the  exception  of  the 
Crustacea,  arachnida,  and  insects.  It  is  the  agent  by  which  the  remarkable  rotation  of 
the  embryo  in  the  ova  of  Mollusca  is  effected;  and  it  occurs  on  the  surface  of  the  ova  of 
polypes  and  sponges.  The  bodies  of  some  of  the  Infusoria  are  covered  with  cilia,  which 
are  apparently  employed  by  them  as  organs  of  locomotion,  and  for  the  prehension  of  food 
(fig.  107,  2,  5). 

In  man,  the  ciliary  motion  has  been  ascertained  to  exist  on  several  surfaces: — 1.  On 
the  surface  of  the*  ventricles  of  the  brain  and  on  the  choroid  plexuses.  So  delicate  are 
the  cells  of  epithelium  here,  that  the  slightest  mechanical  injury  destroys  them;  it  is, 
therefore,  very  difficult  to  see  the  movement.  Valentin  states  that  its  duration  is  consi- 
derable in  these  parts,  so  that  it  may  be  seen  in  subjects  used  for  dissection.  2.  On  the 
mucous  membrane  of  the  nasal  cavities,  extending  along  the  roof  of  the  pharynx  to  its 
posterior  wall,  on  a  level  with  the  atlas,  on  the  upper  and  posterior  part  of  the  soft  palate, 
and  in  the  immediate  neighbourhood  of  the  Eustachian  tube,  extending  through  the  tube 
itself  to  the  cavity  of  the  tympanum.  3.  On  the  membrane  lining  the  sinuses  of  the 
frontal  bone,  the  sphenoid,  and  the  superior  maxillary.  4.  On  the  inner  surface  of  the 
lachrymal  sac  and  lachrymal  canal.  5.  On  the  membrane  of  the  larynx,  trachea,  and 
bronchial  tubes.  6.  On  the  lining  membrane  of  the  female  organs  of  generation.  It  does 
not  exist  in  the  vagina;  but  it  may  be  traced  from  the  lips  of  the  os  uteri,  through  its 
cavity,  and  through  the  Fallopian  tubes  to  their  nmbriated  margins. 

In  nearly  all  these  instances  there  appears  to  be  a  mechanical  use  for  the  ciliary  move- 
ment, namely,  to  promote  the  expulsion  of  the  fluid  secreted  by  the  surfaces  on  which  the 
cilia  exist.  Wherever  the  direction  of  the  motion  has  been  ascertained,  it  is  that  which 
would  be  favourable  to  such  a  purpose.  In  the  bronchial  tubes  and  trachea,  the  direction 
of  the  motion  is  towards  the  larynx,  so  that  the  cilia  may  be  regarded  as  agents  of  expec- 
toration. In  the  nose  of  the  rabbit,  Dr.  Sharpey  observed  the  impulse  to  be  directed  for- 
wards, and  in  the  maxillary  sinus  it  appeared  to  pass  towards  the  back  part  of  the  cavity, 
where  its  opening  is  situated.  In  the  Fallopian  tube,  the  direction  is  stated  by  Purkinje 
and  Valentin  to  be  from  the  fimbriated  extremity  towards  the  vagina.  It  seems  very 
probable  that  ciliary  motion  exists  in  the  kidney,  at  the  narrow  neck  of  each  uriniferous 
tube,  as  it  passes  off  from  the  capsule  of  the  Malpighian  body.  This  has  not  been  actu- 
ally observed  in  the  human  subject.  It  was  discovered,  and  has  been  frequently  seen  in 
the  frog.*  The  movement  is  here  directed  towards  the  uriniferous  tube,  and  it  doubtless 
is  destined  to  favour  the  flow  of  the  aqueous  portion  of  the  secretion  from  the  capsule  of 
the  tube. 

In  the  inferior  animals  the  cilia  seem  to  answer  a  similar  end  to  that  in  man.  'J  hey 
exist  extensively  on  respiratory  surfaces,  and  in  connection  with  the  generative  organs; 

*  Bowman,  Phil.  Trans.,  1842. 
40* 


474  OF  NUTRITION. 

and  also,  but  to  a  less  degree,  with  the  organs  of  digestion.  But  in  some  situations,  both 
in  man  and  in  the  inferior  creatures,  it  is  difficult  to  determine  what  functions  the  ciliary 
motion  can  perform.  Such  are,  in  man,  the  ventricles  of  the  brain  ;  and,  in  the  frog,  the 
closed  cavities  of  the  pericardium  and  peritoneum.  Here  there  are  no  excretory  orifices, 
towards  which  the  current  might  set. 

What  is  the  cause  of  ciliary  motion?  We  have  shown  it  to  be  independent  of  the 
blood  and  of  the  nerves,  arid  to  resist  those  depressing  causes  which  usually  put  a  stop 
to  the  action  of  contractile  tissue.  It  requires  for  its  continuance  three  conditions:  a 
perfect  epithelium  cell ;  moisture,  not  of  too  great  density ;  and  a  temperature  within  cer- 
tain limits.  From  Schwann's  observations  it  appears  that  cells  exhibit  a  power  of  endos- 
mose;  that  a  chemical  change  occurs  in  the  fluids  in  contact  with  them;  and  that  a 
movement  of  their  internal  granules  may  be  seen  under  certain  circumstances.  If 
ciliated  epithelium  cells  exert  an  attraction  of  endosmose  upon  the  surrounding  fluid, 
may  not  this  physical  phenomenon  afford  a  clue  to  determine  the  cause  of  the  movement  ] 

A  very  remarkable  movement  is  manifested  by  certain  particles  found  in  the  secretion 
of  the  testicle,  which  prevails  most  extensively  throughout  the  animal  series,  and  is  even 
found  among  plants.  From  the  regularity  of  these  movements  and  their  resemblance  to 
those  of  minute  animals,  a  place  has  been  assigned  by  naturalists  to  the  particles  in  ques- 
tion, in  their  zoological  classifications,  under  the  name  "  Cercarias  Seminis"  Spermatozoa, 
or  Spermatic  animalcules,  and  Ehrenberg  refers  them  to  the  Haustellate  Entozoa  (§  734). 
These  particles  consist  chiefly  of  a  long  filament  or  tail,  which  is  sometimes  swollen  at 
one  extremity,  to  form  the  body  of  the  supposed  animalcule.  The  motions  consist  in  a 
sculling  action  of  the  tail,  or  a  slight  lateral  vibration  of  it.  In  many  of  its  conditions  it 
closely  resembles  ciliary  motion;  and  its  duration  after  death,  or  after  the  separation  of 
the  fluid,  is  pretty  much  the  same  as  that  of  the  ciliary  movements.  The  particles  are 
extremely  minute,  even  measured  in  their  length;  but  especially  so  in  thickness.  They 
are,  therefore,  well  adapted  to  obey  those  impulses  which  we  have  shown  to  be  capable 
of  giving  rise  to  molecular  motions.* — M.  C.] 

622.  It  is  interesting  to  observe  that  the  Epidermoid  tissues  have  the  simplest 
structure  of  any  solid  parts  in  the  whole  animal  body ;  and  that  they  are  the 
most  readily  renewed.     There  appears  no  limit  to  their  power  of  reproduction  ; 
but,  when  once  formed,  they  undergo  no  transformation.     They  are  not  repro- 
duced from  each  other ;  and  their  origin  appears  to  be  in  germs  supplied  by  the 
basement  membranes,  through  which  the  plasma  transudes,  at  whose  expense 
they  are  developed.     The  duration  of  their  lives  seems  to  vary  greatly  in  dif- 
ferent parts.     The  Epidermic  cells,  being  exposed  on  one  side  to  the  air,  soon 
desiccate,  and  become  converted  into  flattened  scales  ;  but  by  the  adhesion  of 
these  to  each  other,  forming  the  outer  layers  of  the  cuticle,  they  are  not  rapidly 
abraded,  except  where  there  is  much  friction,  or  any  other  cause  producing  an 
unusual  desquamation.     The  Epithelium  covering  the  internal  Serous  surfaces, 
and  some  of  the  Mucous  surfaces,  appears  to  be  still  more  durable,  and  less 
frequently  needing  renewal.     But  on  most  of  the  Mucous  surfaces,  the  loss 
and  renewal  of  Epithelium  are  continually  taking  place.     It  will  be  shown 
hereafter  (§  651),  that  the  Epithelium-cells  are  the  real  agents  in  the  elabo- 
ration of  the  secretions  furnished  by  these  membranes  and  their  prolongations ; 
whether  they  consist  of  simple  mucus,  or  are  of  an  altogether  different  cha- 
racter;  and  the  production  and  casting  off  of  these  cells  will  take  place  with 
a  rapidity  proportional  to  the  activity  of  the  secreting  processes. 

623.  The  Hair  takes  its  origin  in  little  follicles  or  open  sacs,  formed  by  the 
inversion  of  the  Cutis,  and  lined  by  a  reflexion  of  the  Epidermis.     Each  of 
these  follicles  contains  what  is  designated  as  the  bulb  of  the  hair  ;  which  has 
generally  been  described  as  the  soft  newly-formed  part,  that  subsequently  con- 
solidates into  the  outer  portion ;  whilst  the  still  softer  interior  of  the  bulb, 
termed  the  pulp,  has  been  supposed  to  furnish  the  matter  of  the  interior. 
The  follicle  is  extremely  vascular ;  and  even  the  bulb  is  reddened  by  a  minute 
injection,  though  no  distinct  vessels  can  be  traced  into  it.     It  has,  until  recently, 
been  imagined  that  the  Hair,  like  the  other  extra-vascular  tissues,  is  a  mere 
product  of  secretion;  its  material  (horny  matter,  §  620)  being  elaborated  from 

[*  Todd  and  Bowman  on  the  Physiological  Anatomy  and  Physiology  of  Man,  p.  61.] 


FORMATION  OF  THE  TISSUES HAIR. 


475 


of  it ;  as  is  shown  by  the  results  of  recent  inquiries  into  its  structure.  Most 
Human  hairs  consist  of  two  distinct  substances  ;  an  external,  cortical,  hard  and 
fibrous  part ;  and  an  internal,  medullary,  granular  portion.  Although,  when 
Hairs  are  moderately  magnified,  they  look  like  empty  tubes,-— it  is  clearly 
proved,  by  making  fine  transverse  sections  of  them,  that  no  central  aperture 
exists ;  the  hollow  cylinder  of  cortical  substance  being  completely  filled  up 


[Fig.  1C8. 


[Fig.  109. 


A  Hair  from  an  adult  as  seen  under  the  nrero-  A  magnified  view  of  a  small  Hair  from  the 

scope ;  1.  1,  the  follicle  of  the  hair ;  2.  its  orifice  ;  face  of  a  man.  removed  with  its  follicle  and  seen 

:»,  the  base  of  the  follicle  ;  4,  pulp  of  the  hair:  5,  under  the  microscope ;  1, 1,  its  follicle ;  2,  root  of 

its  root;  6,  the  bulb  in  which  the  pulp  is  inserted;  the  hair;  3,  its  trunk;  4,  its  extremity ;  5, its  cor- 

7.  trunk  of  the  hair;  8  the  portion  which  projects  tical  or  external   substance;  6,  its  internal  or 

beyond  the  skin.]  medullary  substance.] 

the  surface  of  the  pulp.  This,  however,  proves  to  be  a  very  erroneous  account 
with  the  granular  medulla. — The  cortical  substance  of  the  hair  is  fibrous ;  the 
outlines  of  the  component  fibres  being  indicated  by  very  delicate  longitudinal 
striaB,  which  may  be  traced  in  it,  through  its  whole  thickness.  The  diameter 
of  these  fibres  is  stated  by  Henle  at  about  l-4000th  of  an  inch ;  but,  by  mace- 
ration in  hydrochloric  acid,  they  may  be  split,  according  to  Bidder,  into  fibrilla? 
of  no  more  than  l-27,000th  of  an  inch  in  diameter.  Besides  exhibiting  these 
longitudinal  striae,  the  surface  of  the  hair  presents  a  series  of  transverse  and 
oblique,  and  sometimes  apparently  spiral  wavy  lines,  arrange^  in  a  very  close 
series ;  these  have  been  shown  to  be  due  to  the  slightly-projecting  edges  of 
tiers  of  minute  scales,  like  those  of  the  epidermis,  but  much  smaller ;  which 
invest  the  whole  surface  of  the  hair,  forming  a  sheath  around  its  cortical  part. 
The  Medullary  portion  of  the  Hair  seems  composed  of  minute  globules,  like 
pigment-granules,  or  drops  of  oil  agglomerated  in  small  lumps,  and  enclosed 
in  a  membrane  which  lines  the  tube  of  cortical  substance ;  along  this  mem- 


476 


OF  NUTRITION. 


[Fig.  110. 


[Fig.  111. 


A  small  portion  of  the  Follicle  of  a  Ha:r  of  the 
Beard,  with  the  Arteries  supplying  it  —  very 
highly  m;ignified;  1,  its  follicle;  2,  its  pulp;  3, 
the  trunk  of  the  hair  without  the  follicle ;  4,  4,  two 
arteries  going  to  the  base  of  the  follicle;  5,5, 
their  distribution;  G.  6,  the  renticalated  tissue  of 
the  follicle.] 


The  Root  of  one  of  the  Hairs  of  the  Beard, 
with  its  Pulp  and  Follicle — cons:derably  magni- 
fied; 1,  a  small  portion  of  its  trunk;  2,  the  corti- 
cal substance ;  3,  the  medullary ;  4,  the  root  of 
the  hair;  5,  the  bifid  portion  of  the  root,  called  the 
bulb;  6,  its  excavated  base,  in  which  the  pulp, 
7,  is  inserted;  8,  a  small  artery;  9,  its  distribution 
to  the  pulp;  10,  the  membrane  of  the  follicle  of 
the  hair;  11,  its  base  placed  in  the  pulp  of  the 
hair;  12,  the  cuticle  or  epidernrs  of  the  follicle, 
which  joins  with  the  bulb  of  the  hair.] 

brane,  distinct  pigment-cells  may  often  be  seen.  In  several  Mammalia,  the 
medullary  substance  is  deficient  at  intervals ;  giving  to  the  hair  a  peculiar 
appearance,  often  very  characteristic  of  the  species. — A  better  notion  of  the 
relations  of  these  substances  may  be  obtained,  by  the  examination  of  the  quill 
of  the  Porcupine,  or  of  the  spine  of  the  Hedgehog,  which  are  nothing  else 
than  Hair  on  a  large  scale.  The  interior  of  these  is  composed  of  a  sort  of 
medulla,  which,  when  examined  with  the  Microscope,  is  found  to  consist  entirely 
of  distinct  cells,  resembling  those  of  the  pith  of  Plants  ;  whilst  the  exterior  is 
formed  by  a  cylinder  of  horny  fibres,  exactly  resembling  that  of  the  Human 
hair.— The  Chemical  constitution  of  Hair  has  been  already  noticed,  as  being 
the  same  as  that  of  Nails,  Horn,  &c. ;  that  of  the  colouring  matter,  however, 
is  not  precisely  known.  This  substance  is  bleached  by  Chlorine  ;  and  its  hue 
seems  in  part  to  be  influenced  by  the  presence  of  iron,  wrhich  is  found  in 
larger  proportion  in  dark  than  in  light  hair.  It  is  probably  nearly  related  to 
Haematosine. 

624.  It  is  quite  evident  that  the  active  Growth  of  the  Hair  can  only  take 
place  at  its  base,  where  alone  it  is  in  connection  with  the  vascular  system ;  but 
the  knowledge  of  its  organized  structure  enables  us  to  explain  many  pheno- 
mena which  were  previously  obscure.  Thus,  in  the  disease  termed  Plica  Po- 
lonica,  a  change  takes  place  in  the  Hair,  which  often  occurs  at  a  distance  from 
its  roots ;  this  change  consists  in  the  splitting  of  the  hair  into  fibres,  and  the 
exudation  from  it  of  a  glutinous  substance ;  and  these  two  causes  unite  in 
occasioning  that  peculiar  matting  of  the  hair,  which  has  given  origin  to  the 
name  of  the  disease.  It  is  said  that  bleeding  takes  place,  in  this  disease,  from 
the  stumps  of  hairs  which  are  cut  off  close  to  the  skin  ;  and  this  may  be  easily 
credited,  since  the  increased  activity  in  the  formative  power  of  the  cells  of  the 
hair  must  require  an  increase  in  their  supply  of  blood.  It  is  very  easy  to  un- 
derstand, from  the  analogy  of  the  Cellular  Plants  in  which  no  vessels  exist,  how 


FORMATION  OF  THE  TISSUES CARTILAGE.  477 

the  fluid  that  is  supplied  to  the  base  of  the  hair  may  find  its  way  upwards ; 

and  there  seems  reason  to  believe,  from  the  well-known  fact  of  sudden  change 
of  colour  in  the  Hair  under  the  influence  of  strong  mental  emotions,  that,  even 
in  its  healthy  state,  fluid  secreted  at  the  base  may  be  conveyed  to  its  point. — 
In  regard  to  the  Development  of  Hair,  no  very  satisfactory  account  can  yet  be 
given ;  as  there  are  great  differences  of  opinion  amongst  Microscopists  as  to 
the  precise  mode  in  which  it  is  effected.  The  pulp  unquestionably  consists  of 
an  aggregation  of  nucleated  cells  ;  and  these,  near  the  base  of  the  hair,  undergo 
a  change  of  form,  their  extremities  being  much  prolonged,  whilst  their  diame- 
ter diminishes.  They  now  form  connected  series,  which  adhere  to  each  other, 
and  constitute  what  are  known  as  the  roots  of  the  hair.  By  a  process  of  meta- 
morphosis, which  is  not  yet  properly  understood,  the  outer  cells  of  the  pulp 
become  converted  into  the  fibrous  structure  of  the  cortical  substance,  whilst 
the  inner  ones  form  the  medullary.  It  would  seem  as  if,  in  simple  hairs,  this 
last  does  not  acquire  its  full  development ;  for  it  presents  no  appearance  of  dis- 
tinct cells,  such  as  those  which  are  seen  in  the  spine  of  the  Porcupine  or 
Hedgehog ;  but  looks  like  the  compressed  contents  of  a  number  of  cells,  which 
have  themselves  disappeared. 

025.  In  several  of  the  Cartilages,  the  Cellular  structure  is  very  obvious, 
whilst  in  others  it  has  undergone  a  transition  to  the  Fibrous.  In  all,  however, 
the  early  stage  of  formation  appears  to  be  the  same.  The  structure  originates 
in  Cells,  analogous  to  those  of  which  the  rest  of  the  fabric  is  composed  ;  but 
between  these  cells  a  larger  quantity  than  usual  of  hyaline  or  intercellular 
substance  is  deposited ;  and  the  amount  of  this  substance  continues  increasing 
simultaneously  with  the  bulk  of  the  cells.  The  original  cells  are  pushed  far- 
ther and  farther  from  one  another;  but  new  cells  arise  between  them,  from 
cytoblasts  which  are  formed  in  the  hyaline  substance.  The  first  cells  frequently 
produce  two  or  more  young  cells  from  their  nuclei ;  and  thus  it  is  very  common 
to  meet  with  groups  of  such  cells,  which  are  known  under  the  name  of  carti- 
lage-corpuscles.— The  varieties  in  the  persistent  Cartilages  principally  depend 
upon  the  degree  of  organization  which  subsequently  takes  place  in  the  inter- 
cellular substance.  If  a  mass  of  Fibres,  analogous  to  those  of  the  fibrous 
membranes  (§  639),  should  originate  in  it,  the  Cartilage  presents  a  more  or  less 
fibrous  aspect ;  in  some  instances  the  Fibrous  structure  is  developed  so  much, 
at  the  expense  of  the  Cells,  that  the  latter  disappear  altogether,  and  the  whole 
structure  becomes  fibrous.  Sometimes  the  fibres  which  are  developed  are 
rather  analogous  to  those  of  the  Elastic  tissue  (§  639) ;  these  are  disposed 
around  the  cells,  forming  a  kind  of  network,  in  the  areolse  of  which  they  lie  ; 
and  this  kind  of  cartilage  may  be  termed  the  elastic.  The  Cartilages  which 
are  destined  to  become  Bone,  differ  in  structure  from  all  these,  but  have  the 
same  origin  ;  and  when  partial  ossific  deposits  take  place  in  old  age,  it  is  almost 
invariably  in  the  Cellular  cartilage  that  they  occur.  The  cartilaginous  septum 
narium,  the  cartilages  of  the  alse  and  point  of  the  nose,  the  semilunar  cartilage 
of  the  eyelids,  the  cartilages  of  the  larynx  (with  the  exception  of  the  epiglottis), 
the  cartilage  of  the  trachea  and  its  branches,  the  cartilages  of  the  ribs  (in  Man), 
and  the  ensiform  cartilage  of  the  sternum,  retain  for  the  most  part  their  primi- 
tive cellular  organization.  The  fibrous  structure  is  seen  in  all  those  Cartilages 
which  unite  the  bones  by  synchondrosis ;  this  is  the  case  in  the  vertebral 
column  and  pelvis,  the  cartilages  of  which  are  destitute  of  corpuscles,  except 
in  and  near  their  centres.  In  the  lower  Vertebrata,  however,  and  in  the  early 
condition  of  the  higher,  the  fibrous  structure  is  confined  to  the  exterior,  and 
the  whole  interior  is  occupied  by  the  ordinary  cartilaginous  corpuscles.  The 
reticular  structure  is  best  seen  in  the  epiglottis  and  in  the  concha  auris  :  in  the 
former  of  these,  scarcely  any  trace  of  Cartilage-Corpuscles  remains ;  in  the 


478  OF    NUTRITION. 

latter,  the  fibrous  network  disappears  by  degrees  towards  the  extremity  of  the 
concha,  and  the  structure  gradually  passes  into  the  cellular  form.* 

The  substance  that  gives  to  the  Cellular  Cartilages  their  peculiar  character,  has  re- 
ceived the  designation  of  Chondrin.  It  bears  much  resemblance  to  ordinary  Gelatin,  but 
requires  longer  boiling  in  water  for  its  solution;  the  solution  fixes  on  cooling,  like  that 
of  gelatin,  and  when  it  becomes  dry  by  evaporation  it  has  the  appearance  of  solid  glue. 
Chondrin  is  not  precipitated,  however,  by  tannic  acid;  on  the  other  hand,  it  gives  preci- 
pitates with  acetic  acid,  alum,  acetate  of  lead,  and  protosulphate  of  iron  which  do  not 
disturb  a  solution  of  Gelatin.  Its  chemical  constitution  chiefly  differs  from  that  of 
Gelatin  in  containing  less  nitrogen  and  more  hydrogen  ;  its  formula  (as  ascertained  by 
analysis  before  boiling)  is  48  c,40  H,6  if,  20  o;  and  it  may  thus  be  regarded  as  composed 
of  1  atom  of  protein,  with  2  additional  atoms  of  oxygen,  arid  4  proportionals  of  waier. — 
Chondrin  is  not  obtainable,  however,  from  any  of  the  Fibro-cartilages ;  these  yield  gelatin, 
on  boiling,  exactly  similar  to  that  of  the  tendons.  The  elastic  cartilages,  after  being 
boiled  for  several  days,  yield  a  small  quantity  of  an  extract,  which  does  not  form  a  jelly, 
but  which  has  the  other  chemical  properties  of  Chondrin.  The  cartilage  of  Bone,  before 
ossification,  yields  only  Chondrin ;  after  ossification,  however,  it  affords  only  Gelatin; 
and  it  is  curious  that  even  when  bony  deposits  take  place  in  the  permanent  cartilages, 
the  ossified  portion  contains  ordinary  Gelatin  in  the  place  of  Chondrin.  Many  of  the 
cartilages  naturally  contain  a  large  proportion  of  mineral  matter;  this  is  especially  the 
case  with  the  costal  cartilages,  fractures  in  which  are  generally  repaired  by  osseous 
substance.  The  ash  left  by  the  calcination  of  these  contains  a  large  proportion  of  the 
carbonate  and  sulphate  of  soda,  together  with  carbonate  of  lime  and  a  small  proportion 
of  phosphate :  as  age  advances,  the  phosphate  of  lime  predominates,  and  the  soluble 
compounds  diminish.  The  condition  of  the  skeletons  of  the  Cartilaginous  Fishes  ap- 
pears to  be  nearly  allied  to  this. 

626.  Like  the  tissues  already  described,  Cartilage  (at  least  in  its  simplest 
form)  is  nourished,  without  coming  into  direct  relation  with  the  Blood  through 
the  medium  of  blood-vessels.  From  the  inquiries  of  Mr.  Toynbee  it  appears 
that  the  cellular  Cartilages  are  never  penetrated  by  vessels  in  the  healthy 
state,  although  in  certain  diseased  conditions  they  become  distinctly  vascular. 
They  are,  however,  surrounded  by  Blood-vessels  ;  which  form  large  ampullae 
or  varicose  dilatations  at  their  edges  or  on  their  surfaces  (Fig.  112) :  and  from 
these  the  Cartilages  derive  their  nourishment  by  imbibition  (§  479),  in  exactly 
the  same  manner  as  the  frond  of  a  Sea-weed  (the  structure  of  which  is  alike 
cellular)  draws  into  itself  the  requisite  fluid  from  the  surrounding  medium. 
When,  however,  the  Cartilages  are  undergoing  Ossification,  large  vessels  are 
seen  in  them ;  and  these  vessels  remain  even  when  the  Bone  is  fully  formed. 
This  is  well  seen  in  the  long  bones,  towards  their  extremities.  At  an  early 
period  of  foetal  life,  there  is  no  distinction  between  the  cartilage  that  is  ultimate- 
ly to  become  the  Osseous  Epiphysis,  and  that  which  is  to  remain  as  Articular 
Cartilage;  both  are  alike  cellular;  and  the  vessels  that  supply  them  with 
nutrient  materials  penetrate  no  further  than  their  surfaces.  At  a  subsequent 
period,  however,  when  the  ossification  of  the  epiphysal  cartilage  is  about  to 

Fig.  112. 


Vessels  situated  between  the  articular  cartilage  and  attached  synovial  membrane.    (After  Toynbee.) 
*  See  Mr.  Toynbee's  Memoir  on  the  Non- Vascular  Tissues,  Phil.  Trans.,  1841. 


FORMATION  OF  THE  TISSUES CORNEA  AND  CRYSTALLINE.  47!) 

commence,  vessels  are  prolonged  into  it ;  and  a  distinct  line  of  demarkation  is 
seen  betwixt  the  vascular  portion,  which  is  to  be  converted  into  Bone,  and 
the  non-vascular  part,  which  is  to  remain  as  Cartilage.  At  this  period,  the 
Articular  Cartilage  is  nourished  by  a  plexus  of  vessels  spread  over  its  free 
surface,  beneath  its  synovial  membrane,  as  well  as  by  the  vessels  with  which 
it  comes  into  Contact  at  its  attached  extremity.  Towards  the  period  of  birth, 
however,  the  sub-synovial  vessels  gradually  recede  from  the  surface  of  the 
articular  cartilage  ;  and  at  adult  age  they  have  entirely  left  it,  though  they 
still  form  a  band  which  surrounds  its  margin.  At  the  same  time,  the  line  of 
demarkation  between  its  attached  surface  and  the  subjacent  bone  becomes  more 
distinct,  by  the  formation  of  a  thin  lamella  at  the  surface  of  the  latter;  which 
covers  the  subjacent  cancelli,  and  is  of  extremely  solid  texture,  not  containing 
any  perceptible  foramina  through  which  vessels  could  pass.  The  vessels  of 
the  cancelli,  however,  are  very  large ;  and  have  the  same  dilated  or  varicose 
character  with  those  which,  at  an  earlier  period,  cover  the  surface  of  the  car- 
tilage. It  appears  that  the  Articular  Cartilage  is  gradually  becoming  ossified 
through  the  whole  of  life  ;  in  old  age  it  is  sometimes  almost  completely  con- 
verted into  Bone.  From  Mr.  Toynbee's  researches  it  further  appears,  that 
the  Fibrous  cartilages  are  somewhat  vascular  ;  but  that  the  vessels  do  not  ex- 
tend to  the  cellular  portions,  where  such  exist.  No  vessels  can  be  traced 
(according  to  Mr.  T.)  into  the  substance  of  the  true  Cornea ;  which,  contrary 
to  the  statement  of  Muller,  is  a  cellular  rather  than  a  fibrous  cartilage.  The 
cells  are  not  so  numerous  as  are  those  of  the  articular  cartilages  ;  and  they  are 
surrounded  by  a  plexus  of  bright  fibres,  laxly  connected  together  so  as  to  re- 
semble areolar  tissue.  Two  sets  of  vessels,  a  superficial  and  a  deep-seated, 
surround  the  margin  of  the  cornea.  The  arteries  of  the  former  are  prolonged 
for  a  short  distance  upon  the  Conjunctival  membrane,  which  forms  the  outer 
lamina  of  the  cornea ;  but  they  terminate  in  veins  at  from  5  to  £  a  line  from 
its  margin.  The  deep-seated  vessels  belong  to  the  Cornea  proper ;  but  they 
do  not  enter  it,  the  arteries  terminating  in  veins  just  where  the  tissue  of  the 
Sclerotic  becomes  continuous  with  that  of  the  Cornea.  In  diseased  conditions 
of  the  Cornea  (as  of  the  articular  cartilages),  both  sets  of  vessels  extend  them- 
selves through  it ;  the  superficial  not  unfrequently  form  a  dark  band  of  con- 
siderable breadth  round  its  margin  ;  whilst  the  deep-seated  are  prolonged  into 
its  entire  substance.  Notwithstanding  the  absence  of  vessels  in  the  healthy 
condition  of  this  structure,  incised  wounds  commonly  heal  very  readily,  as  is 
well  seen  after  the  operation  of  extraction  of  Cataract ;  but  the  foregoing  de- 
tails make  evident  the  importance  of  not  carrying  the  incision  further  round 
than  is  necessary;  since  the  corneal  tissue  should  not  be  cut  off  from  the  sup- 
ply of  nourishment  afforded  by  the  vessels  in  its  immediate  proximity. 

627.  In  connection  with  the  cornea,  it  is  natural  to  allude  to  the  Crystalline 
lens  and  Vitreous  humour,  which  have  a  structure  essentially  the  same.  The 
structure  of  the  crystalline  lens  has  long  been  known  to  be  fibrous ;  and  Sir 
D.  Brewster  has  shown,  by  the  aid  of  polarized  light,  the  very  beautiful 
manner  in  which  the  fibres  are  arranged.*  They  are  united  into  laminae,  by 
means  of  numerous  teeth  or  sinuosities  at  their  edges,  which  lock  into  one 
another.  That  these  fibres  originate  in  cells,  has  been  clearly  ascertained ;  but 
the  nature  of  the  metamorphosis  has  been  differently  stated  by  two  eminent 
observers,  Schwann  and  Barry.  By  the  former,  the. fibres  are  considered  to  be 
prolonged  cells  :  whilst  the  latter  regards  them  as  rather  formed  upon  the  plan 
of  the  tubes  of  muscular  fibre  (§  642),  several  cells  coalescing  into  one  ;  in  this 
he  is  supported  by  Mr.  Toynbee,  who  states  that  he  has  frequently  seen  the 
fibres,  towards  the  margin  of  the  lens,  made  up  of  such  cells.  After  it  n  fully 

*  Philosophical  Transactions,  1833. 


480  OF  NUTRITION. 

formed,  however,  it  is  not  permeated  by  blood-vessels ;  these  being  confined 
to  the  capsule.  During  the  early  part  of  foetal  life,  and  in  inflammatory  con- 
ditions of  this  membrane,  both  the  anterior  and  posterior  portions  of  the  Capsule 
are  distinctly  vascular ;  but  at  a  later  period,  according  to  Mr.  Toynbee,  the 
posterior  half  only  of  the  capsule  has  vessels  distributed  over  its  surface  ;  and 
these  are  derived  from  the  Arteria  Centralis  Retinae.  From  optical  experi- 
ments which  have  been  suggested  to  him  by  this  circumstance,  he  infers  that 
"  objects  (radiating  lines  for  instance),  situated  on  the  anterior  surface  of  the 
crystalline  lens,  produce  an  indistinctness  in  the  image  which  is  formed  upon 
the  retina ;  whereas,  when  these  lines  exist  upon  the  posterior  surface  of  the 
lens,  the  image  is  clear,"  The  substance  of  the  Lens  contains  about  42  per 
cent,  of  animal  matter,  with  58  parts  of  water.  Nearly  the  whole  of  the  former 
may  be  dissolved  in  cold  water  by  trituration ;  the  solution  is  coagulated  by 
heat,  and  forms  a  granular  but  not  coherent  mass ;  alcohol  and  acids  produce 
the  same  effect.  Hence  it  appears  that  the  Lens  chiefly  consists  of  albumen 
in  its  soluble  form ;  and  this  may  be  supposed  to  be  contained  in  the  cavities 
of  the  cells,  as  it  is  in  those  of  the  vitreous  humour.  From  the  latest  analyses, 
it  appears  that  the  substance  of  the  lens  corresponds  most  with  that  modifi- 
cation of  albumen  which  forms  the  Globulin  of  the  blood  (§  573). — In  the 
Vitreous  humour  we  have  an  example  of  a  very  loose  form  of  cellular  tissue, 
strongly  resembling  that  which  constitutes  the  entire  structure  of  Acalephas 
(Jelly-fish).  That  the  Cells  composing  it  have  no  open  communication  with 
each  other,  is  evident  from  the  .fact  that,  when  the  general  enveloping  mem- 
brane is  punctured  in  several  places,  it  is  long  before  the  contained  fluid 
entirely  drains  away.  This  fluid  is  analogous  to  that  of  the  Aqueous  humour ; 
being  little  else  than  Water,  holding  a  small  quantity  of  Albumen  and  Saline 
water  in  solution.  From  Mr.  Toynbee's  inquiries,  it  would  appear,  that  the 
vessels  which  pass  through  the  Vitreous  humour  do  not  send  branches  into  its 
substance ;  but  that  it  is  nourished  by  the  vessels  which  are  minutely  dis- 
tributed upon  its  general  envelop.  The  Ciliary  processes  of  the  Choroid 
membrane  are  almost  entirely  composed  of  large,  plexiform  vessels,  which 
allow  a  great  quantity  of  blood  to  circulate  through  them  ;  and  these  have 
probably  an  important  share  in  the  nutrition  of  the  Vitreous  body. 

628.  In  all  the  tissues  hitherto  described,  the  structure  retains,  more  or  less 
completely,  its  original  Cellular  character  ;  and  it  is  nourished  by  fluid  supplied 
to  it,  not  by  vessels  permeating  its  own  substance,  but  by  those  of  the  nearest 
vascular  part,  with  which,  therefore,  its  surface  only  can  come  into  relation. 
In  some  of  these  tissues,  especially  the  Epidermic,  the  parts  once  formed 
would  seem  to  undergo  little  or  no  subsequent  vital  change,  but  gradually  lose 
their  connection  with  the  living  structure,  and  are  at  last  thrown  off  and  re- 
placed by  newly-formed  parts.  In  these,  a  constant  reproduction  is  taking 
place  ;  and  such  tissues,  when  accidentally  destroyed,  are  rapidly  regenerated. 
This  is  readily  understood,  when  their  very  close  proximity  with  an  extremely 
vascular  membrane  is  considered ;  the  exudation  from  it  speedily  takes  the 
form  of  a  layer  of  cells,  and  new  ones  are  produced  below,  until  the  whole 
thickness  of  the  Cuticle  or  Epithelium  is  renewed.  The  Epidermoid  tissues 
are  placed,  by  their  peculiar  functions,  in  the  very  circumstances  which  render 
such  a  regenerating  power  necessary :  in  Cartilage,  on  the  other  hand,  it  is 
not  required,  and  does  not  exist.  The  functions  of  Cartilage  are  purely 
mechanical ;  the  consolidation  of  its  texture  by  internal  deposit  renders  it  little 
disposed  to  change  by  spontaneous  decay  ;  and  it  is  protected  by  its  toughness 
and  elasticity  from  those  injuries  to  which  softer  or  more  brittle  tissues  are 
liable.  The^fe  very  circumstances,  however,  interfere  with  the  activity  of  its 
nutrition.  Cells  which  are  choked  up  with  interior  deposit  do  not  readily 
transmit  fluid :  it  is  doubtful  whether  any  interstitial  change  can  take  place  in 


FORMATION  OF  THE  TISSUES— BONE.  481 

the  interior  of  a  permanent  Cartilage  (except  when  it  has  become  vascular  by 
disease,  or  undergoes  ossification),  through  the  whole  of  life ;  and  there  seems 
ground  to  believe  that,  when  it  nas  been  injured  by  disease  or  accident,  the 
loss  of  substance  is  not  repaired  by  real  cartilaginous  tissue. — On  the  other 
hand,  the  softer  tissues  of  the  Eye  are  capable  of  complete  regeneration. 
Every  oculist  is  aware  that  a  great  loss  of  Vitreous  humour  may  take  place  with- 
out permanent  injury  ;  and  it  has  been  found  that  even  the  Crystalline  lens  may 
be  completely  regenerated,  after  it  has  been  entirely  removed  by  extraction. 

629.  Proceeding  now  to  •  the  Vascular  tissues,  in  which  the  processes  of 
interstitial  absorption  and  renewal  are  continually  taking  place,  we  commence 
with  Bone,  as  the  one  which  has  the  most  evident  relations  to  those  already 
described.  All  true  Bony  structure*  is  formed  upon  a  basis  of  Cartilage  ;  but 
upon  the  mode  of  transformation  of  one  tissue  into  the  other,  additional  infor- 
mation is  still  much  required.  We  shall  first  inquire  into  the  characteristic 
structure  of  Bone,  and  then  into  its  origin.  When  examined  with  the  naked 
eye,  it  is  seen  that  the  bone  possesses,  in  some  degree,  a  laminated  texture  ;  in 
the  long  bones,  the  external  and  internal  laminae  are  arranged  concentrically 
around  the  medullary  canal ;  and  in  the  flat  bones,  they  are  parallel  to  the 
surface.  Towards  the  extremities  of  the  long  bones,  and  between  the  external 
plates  of  the  flat  bones,  are  a  number  of  cancelli,  or  small  hollows  bounded  by 
very  thin  plates  of  bone  ;  these  communicate  with  the  medullary  canal  where 
it  exists  ;  having,  like  it,  an  extremely  vascular  lining  membrane  ;  and  their 
cavities  being  filled  with  a  peculiar  adipose  matter.  The  hard  substance  of 

Tig.  113. 


The  minute  structure  of  Bone,  drawn  with  the  microscope  fr«m  nature,  by  Bagg— magnified  300  diame- 
ters ;  1,  one  of  the  Haversian  canals  surrounded  by  its  concentric  lamellae ;  the  corpuscles  are  seen 
between  the  lamellae;  but  the  converging  tubuli  are  omitted;  2,  an  Haversian  canal  with  its  concentric 
lamellae,  Purkinjean  corpuscles  and  converging  tubuli ;  3,  the  area  of  one  of  the  canals;  4,  4,  direction  of 
the  lamellae  of  the  great  medullary  canal.  Between  the  lamellae,  at  the  upper  part  of  the  figure,  several 
very  long  corpuscles  with  their  tubuli  are  seen.  In  the  lower  part  of  the  figure,  the  outlines  of  three  other 
canals  are  given,  in  order  to  show  their  form  and  mode  of  arrangement  in  the  entire  bone.  (After  Wilson.) 

*  The  white  patches  formed  by  the  deposition  of  earthy  matter  in  the  dura  mater,  in 
the  coats  of  the  arteries,  and  in  similar  parts,  cannot  be  so  considered. — It  appears  from 
the  researches  of  Mr.  Smee  (Med.  Gaz.,  Nov.  1840),  that  the  true  bony  structure  is  to  be 
met  with  in  callus,  exostoses,  ossified  cartilages,  and  other  similar  products,  having  a 
near  relation  to  bone ;  but  not  in  the  calcareous  deposits  in  the  coats  of  arteries,  serous 
or  fibrous  membranes,  or  abnormal  growths  such  as  fibrous  tumours  of  the  uterus. 
41 


482 


OF  NUTRITION. 


the  bone  also  is  traversed  by  canals,  on  which  the  name  of  Haversian  has  been 
bestowed,  after  their  discoverer  ;  these  canals  run  for  the  most  part  in  the  direc- 
tion of  the  laminae  ;  but  they  have  many  transverse  communications,  both  with 
each  other  and  with  the  medullary  cavity,  so  that  they  form  a  complete  network, 
which  is  lined  by  a  continuation  of  the  highly-vascular  membrane  of  the 
latter.  When  a  thin  transverse  section  of  a  long  bone  is  made,  and  is  highly 
magnified,  .it  is  seen  that  the  bony  matter  of  the  greater  part  of  its  thickness  is 
arranged  in  concentric  circles  round  the  orifices  of  the  canals ;  these  circles  are 
marked  by  a  series  of  stellated  points  ;  and  when  the  latter  are  magnified  still 
more  highly,  it  is  seen  that  they  are  cavities  of  a  peculiar  form,  which  seems 
characteristic  of  Bone.  They  are  usually  oval  or  lenticular  in  form  ;  and  are 
so  placed  that  one  of  their  largest  surfaces  is  turned  from,  and  the  other  to- 
wards, the  Haversian  canal.  Their  long  diameter  is  commonly  from  l-2400th 
to  l-1600th  of  an  inch  ;  their  short  diameter  about  one-third,  and  their  thick- 
ness about  one-sixth  of  their  length.  From  all  parts  of  these  cavitiesf  but 
especially  from  their  two  largest  surfaces,  proceed  a  large  number  of  minute 
tubuli,  which  traverse  the  substance  of  the  bone,  and  communicate  irregularly 
with  one  another.  Their  direction,  however,  possesses  a  certain  degree  of 


[Fig.  114. 


[Fig.  115. 


Transverse  section  of  the  compact  tissue  Transverse  section  of  the  compact  tissue  of  a  Tibia 

of  a  long  Bone;  showing  1,  the  periosteal  from  an  aged  subject,  treated  with  acid;  showing  the 

layer;  2,  the  medullary  layer, and  the  inter-  appearance  of  lamellae  surrounding  the  Haversian  ca- 

mediate  Haversian  systems  of  lamellae,  each  nals.    Portions  of  several  systems  of  lamella;  are  seen, 

perforated  by  an  Haversian  canal.    Mag-  The  appearance  of  the  lacunae,  when  their  pores  are 

nified  about  15  diameters.]  filled  with  fluid,  is  also  seen,  as  well  as  the  radiation  from 

the  canals  which  then  remains.    From  Mr.  Tomes.] 

determinateness  ;  for  those  passing  off  from  the  inner  surface  converge  towards 
the  Haversian  canal ;  whilst  those  passing  off  from  the  surface  diverge  in  the 
contrary  direction,  so  as  to  meet  and  inosculate  with  those  proceeding  inwards 
from  the  cavities  of  the  next  annulus.  In  this  manner,  a  communication  is 
kept  up  between  the  Haversian  canal,  and  the  most  external  of  its  concentric 
lamellae  of  bone, — or  between  the  great  medullary  cavity,  and  the  most  distant 
of  the  lamellae  which  are  concentric  with  it.  It  is  not  to  be  imagined,  how- 
ever, that  blood  can  be  conveyed  by  these  tubuli,  they:  size  being  far  too  small ; 
the  diameter  of  each  canal,  at  its  largest  part,  is  estimated  at  from  l-14,000th 
to  1 -20,000th  of  an  inch,  whilst  that  of  the  smaller  branches  is  from  l-40,000th 
to  l-60,000th  of  an  inch.  It  may  be  surmised,  however,  that  they  may  convey 
matter  poured  forth  by  the  blood-vessels,  which  may  serve  for  the  nutrition  of 
the  bone-substance.  We  know  that,  in  young  animals,  this  substance  is  con^ 
tinually  undergoing  increase  and  renewal ;  and  even  in  adults  some  interstitial 


FORMATION  OF  THE  TISSUES BONE. 


483 


Haversian  canals,  seen  on  a  lon- 
gitudinal section  of  the  compact  tis- 
sue of  the  shaft  of  one  of  the  long 
bones;  1,  arterial  canal ;  2,  venous 
canal;  3,  dilatation  of  another  ve- 
nous canal.] 


change  appears  to  be  constantly  taking  place, —  [Fig.  116. 

perhaps  for  the  purpose  of  keeping   the    Bone- 
producing  apparatus  in  a  state  fit  for  use,  against 

the  time  when  its  actions  may  be  needed,  to  repair 

the  effects  of  injury  or  disease.     Although  a  large 

quantity  of  blood  is  sent  to  Bone,  the  vessels  do  not 

penetrate  its  minute  parts ;  being  confined  to  the 

Medullary  cavity,  and  to  the  Haversian  canals  and 

Cancelli  which  are  prolongations  of  it.     Hence,  as 

the  density  of  Bone  does  not  allow  fluid  to  transude 

its  substance  in  the  manner  of  Cartilage,  the  ne- 
cessity for  some  channel  of  nutritive  matter  is  easily 

to  be  understood.— It  may  be  desirable  to  mention 

that  the  cavities  and  tubuli  have  been  supposed, 

on  account  of  the  black  appearance  they  exhibit 

under  the  microscope,  to  be  filled  with  opaque 

matter ;  but  this  appearance  is  common  to  all  ca- 
vities excavated  in  a  highly-refracting  substance 

(being  shown  by  a  bubble  of  air  in  Water),  and 

ceases  when  a  very  thin  section  is  examined,  espe- 
cially if  it  have  been  placed  in  Canada  Balsam. 

In  the  bones  of  Mummies,  they  are  found  to  be 

filled  with  a  waxen  material ;  by  which  their  power 

of  imbibing  fluid  substances  is  clearly  proved.* — 

The  ultimate  substance  of  Bone   appears  to  be 

usually  granular ;  the  granules  are  stated  by  Mr. 

Tomest  to  be  often  very  distinctly  visible,  without  any  artificial  preparation, 

in  the  substance  of  the  delicate  spicula  of  the  cancelli,  when  viewed  with  a 
high  power ;  and  to  be  made  very  evident  by  prolonged  boiling  in  a  Papin's 
digester.  They  vary  in  size  from  l-6000th  to  l-14,000th  of  an  inch ;  their 
shape  is  oval  or  oblong,  often  angular ;  and  they  cohere  firmly  together,  pos- 
sibly by  the  medium  of  some  second  substance.  A  somewhat  fibrous  structure, 
however,  resembling  that  of  the  second  class  of  Cartilages,  sometimes  presents 
itself ;  and  this  is  especially  the  case  in  Cartilages  ossified  late  in  life,  as  those 
of  the  ribs,  larynx,  &c. 

630.  As  to  the  mode  in  which  Bone  is  produced  from  Cartilage,  great 
difference  of  opinion  has  prevailed :  and 
the  question  cannot  be  regarded  as  yet  by 
any  means  thoroughly  elucidated.  By 
some  it  has  been  maintained  that  the  cor- 
puscles or  cells  of  Cartilage  become  the 
stellate  cavities  of  bone ;  and  that  the 
intercellular  substance  of  the  one  remains 
in  the  other ;  although  consolidated  by 
the  deposit  of  mineral  matter.  A  careful 
examination  of  the  process  of  transforma- 
tion, however,  makes  it  appear  that,  in 
Cartilage  which  is  undergoing  ossifica- 
tion, the  cells  are  arranged  in  linear  series 
of  twenty  or  thirty ;  and  that  the  spaces 
occupied  by  these  ultimately  become  the 
cancelli  and  Haversian  canals.  In  the 
thin  lamellae  of  intercellular  substance,  by 


[Fig.  117. 


Scapula  of  a  Foetus  at  the  seventh  month; 
showing  the  progress  of  ossification.  Natural 
size.  The  light  parts  are  epiphyses  as  yet  car- 


tilaginous. — From  the  Museum  of  King's  Col- 
lege, London.] 


Smee,  loc.  tit. 


f  Todd  and  Bowman's  Physiological  Anatomy,  p.  108. 


484 


OF  NUTRITION. 


[Fig.  118. 


which  these  rows  of  cells  are  se- 
parated, ossific  matter  is  at  the 
same  time  deposited ;  and  when 
the  spaces  communicate  with  each 
other,  so  as  to  form  a  network 
receiving  blood-vessels,  this  pro- 
cess takes  place  with  greater  ra- 
pidity. It  is  then  observed  that 
few  of  the  original  cells  are  to  be 
seen  in  the  cavities ;  which  are 
chiefly  occupied  by  a  quantity  of 
new  substance  resembling  the 
formative  blastema,  from  which 
all  the  tissues  are  evolved.  The 
original  cells  appear  to  have  be- 
come flattened  against  the  walls 
of  the  cavity ;  and  to  have  coa- 
lesced into  the  osseous  lamellae, 
which  are  gradually  formed  con- 
centrically within  it.  In  these 
lamellae  are  included  the  nuclei 
of  the  cells ;  which  are  at  first 
granular,  but  which  subsequently 
remain  as  hollows  in  the  osseous 
deposit ;  and  from  these,  the  mi- 
nute tubuli  afterwards  shoot  out.* 

[The  nucleated  cells  of  temporary- 
cartilage  are  small,  and  pretty  uni- 
formly scattered  through  a  sparing, 
homogeneous  intercellular  substance. 
The  nuclei  are  granular,  and  large 
compared  with  the  cells,  which  are 
distinguished  from  the  surrounding 
substance  principally  by  their  trans- 
parency around  each  nucleus  (Fig. 
118,1,  1'.) 

In  the  vicinity  of  the  point  of  ossi- 
fication, (for  example,  in  one  of  the 
long  bones,)  a  singular  change  is  ob- 
served. The  cells  are  seen  to  be  gra- 
dually arranging  themselves  in  linear 
series,  which  run  down,  as  it  were, 
towards  the  ossifying  surface.  The 
appearance  they  present  on  a  vertical 
section  is  represented  in  Fig.  118.  At 
first  their  aggregation  is  irregular, 
and  the  series  small  (2,2');  but,  nearer 
to  the  surface  of  ossification,  they  form 
rows  of  twenty  or  thirty.  These  rows 
are  slightly  undulated,  and  are  separated  from  one  another  by  the  intercellular  substance. 
The  cells  composing  them  are  closely  applied  to  one  another,  and  compressed,  so  that 
even  their  nuclei  seem  in  many  instances  to  touch;  the  nuclei  themselves  are  also  flat- 
tened, and  expanded  laterally. 

The  lowest  rows  dip  into,  and  rest  in  deep  narrow  cups  of  bone,  formed  by  the  osseous 
transformation  of  the  intercellular  substance  between  the  rows.  These  cups  are  seen  by 
a  vertical  section  in  fig.  118,  3,  3'.  As  ossification  advances  between  the  rows,  these 

*  See  the  account  of  Mr.  Tome's  investigations,  contained  in  Todd  and  Bowman's 
Physiological  Anatomy,  pp.  117 — 122.  These  seem  to  correspond,  in  their  essential 
points,,  with  those  of  Gerber  (General  Anatomy,  p.  184). 


Vertical  section  of  Cartilage  near  the  surface  of  ossifi- 
cation; 1,  ordinary  appearance  of  the  temporary  cartilage; 
1',  portion  of  the  same  more  highly  magnified ;  2,  the  cells 
beginning  to  assume  the  linear  direction;  2',  portion  more 
magnified ;  opposite  3,  the  ossification  is  extending  in  the 
intercellular  spaces,  and  the  rows  of  cells  are  seen  resting 
in  the  cavities  so  formed,  the  nuclei  being  more  separated 
than  above ;  3',  portion  of  the  same  more  highly  magnified. 
—From  a  new-born  rabbit  which  had  been  preserved  in 
spirit.] 


FORMATION  OF  THE  TISSUES— BONE.  485 

cups  are  of  course  converted  into  closed  areoloe  of  bone,  the  walls  of  which  are  lamelli- 
form,  and  at  first  extremely  thin. 

Immediately  upon  the  ossifying  surface,  the  nuclei,  which  were  before  closely  com- 
pressed, separate  considerably  from  one  another  by  the  increase  of  material  within  the 
cells.  The  nuclei  likewise  often  enlarge  and  become  more  transparent;  a  condition 
first  pointed  out  to  us  by  Mr.  Tomes.  The  changes  now  enumerated  may  be  conve- 
niently considered  to  constitute  the  first  stage  of  the  process,  which  extends  only  to  the 
ossification  9f  the  intercellular  substance.  In  this  stage  there  are  no  blood-vessels 
directly  concerned. 

The  areolae  or  minute  cancelli,  when  first  formed,  contain  only  the  rows  of  cells  which 
they  have  enclosed.  It  is  remarkable,  that,  when  the  cartilage  is  torn  from  the  bone,  it 
usually  carries  with  it  one  or  two  layers  of  these  cancelli,  or  a  little  more  than  is  repre- 
sented in  Fig.  118.  If  the  specimen  be  examined  deeper  in  the  bone,  even  at  a  depth  of 
y'^th  or  £th  of  an  inch,  other  appearances  are  met  with.  The  lamellae  of  bone  enclosing 
the  cancelli  are  no  longer  simply  homogeneous  or  finely  granular  in  texture,  but  have 
acquired  more  the  aspect  of  perfect  bone.  They  are  also  thicker,  and  include  in  their 
substance  elongated  oval  spaces,  which,  excepting  that  they  are  of  a  roughly  granular 
nature,  exactly  resemble  the  lacunas  of  bone  already  described.  They  are  evidently  the 
nuclei  of  the  cells  of  the  temporary  cartilage.  They  are  scattered  at  pretty  uniform  dis- 
tances apart,  and  they  all  follow  the  direction  of  the  lamellae  to  which  they  belong.  The 
curvilinear  outline  of  their  now  ossified  cells  can  often  be  partially  discerned. 

Within  the  cancelli,  only  a  few  cells  can  be  detected,  these  cavities  being  chiefly  occu- 
pied by  a  quantity  of  new  substance,  consisting  of  granules,  and  resembling  a  formative 
blastema  or  basis,  like  that  out  of  which  all  the  tissues  are  evolved.  The  cells  that  are 
met  with  are  in  apposition  with  the  wall ;  and  sometimes  one  of  them  seems  half  ossified, 
and  its  nucleus  about  to  become  a  lacuna.  The  nuclei  of  these  cells  have  now  always 
the  same  direction  as  the  neighbouring  lacunas. 

It  hence  appears  that,  after  the  ossification  of  the  intercellular  substance,  the  rows  of 
cartilage-cells  arrange  themselves  on  the  inner  surface  of  the  newly-formed  cancelli,  and 
become  ossified,  with  the  exception  of  their  nuclei,  which  remain  granular,  and  subse- 
quently form  the  lacunae  of  bone  ;  and  that  a  new  substance,  or  blastema,  appears  within 
the  cancelli,  from  which,  probably,  vessels  are  developed,  and  the  future  steps  in  the 
growth  of  the  bone  proceed. 

The  cancelli  when  first  formed  are  closed  cavities.  At  a  subsequent  period  they  ap- 
pear to  communicate,  and  thus  to  form  the  cancelli  and  Haversian  canals  of  perfect 
bone;  a  complete  network  of  blood-vessels  becoming  developed  within  them  at  the  same 
time. 

The  subsequent  progress  of  ossification  seems  to  consist  essentially  of  a  slow  repeti- 
tion, on  the  entire  vascular  surface  of  the  bone,  of  that  process  which  has  been  now 
briefly  described.  It  is  probable  that  new  cartilage-cells  are  developed  on  that  surface, 
and  become  ossified  in  successive  layers,  their  nuclei  remaining  to  form  the  lacunas,  the 
uniform  dispersion  of  which  through  bone  is  thus  explained.  The  cause  of  the  lamina- 
tion of  bone,  parallel  to  its  vascular  surface,  is  also  thus  illustrated. 

The  first  appearance  of  pores  is  in  the  form  of  irregularities  in  the  margin  of  the  la- 
cunas. These  increase  with  the  consolidation  of  the  tissue,  and  are  converted  into  branch- 
ing tubules  which  communicate  with  those  adjacent.  These  pores  must  consequently 
be  formed  in  the  ossified  substance  of  the  cartilage-cells.  In  our  account  of  the  lacunas 
of  perfect  bone  it  was  mentioned  that,  for  the  most  part,  those  of  contiguous  Haversian 
systems  do  .not  communicate  across  the  narrow  interval  that  separates  the  Haversian 
rods ;  this  interval  having,  in  fact,  no  pores.  It  results  from  what  has  just  been  said  of 
the  mode  of  deposition  of  new  layers,  that  the  primary  osseous  net-work,  formed  in  the 
intercellular  substance  of  the  temporary  cartilage,  must  come  to  constitute  the  substance 
intervening  between  the  Haversian  rods,  the  non-porosity  of  which  is  thus  satisfactorily 
accounted  for,  as  well  as  the  facility  with  which  the  rods  themselves  may  be  made  to 
separate  from  one  another.  As  for  the  lacunae,  their  originally  granular  interior  seems 
to  be  gradually  removed,  so  that  they  become  vacuities  adapted  for  the  conveyance  of 
the  nutritious  fluids  through  the  compact  material*  of  the  perfect  bone.* — M.  C.] 

When  the  Calcareous  matter  of  Bone  has  been  dissolved  away  by  the  action  of  an 
acid,  the  Animal  substance  which  remains  is  almost  entirely  dissolved  by  a  short  boiling 
in  water;  yielding  to  it  a  large  quantity  of  Gelatin.  This,  indeed,  may  be  obtained,  by 
long  boiling  underpressure,  from  previously  unaltered  Bone;  and  the  calcareous  matter 
is  then  left  almost  pure.  The  lime  of  bones  is,  for  the  most  part,  in  the  state  of  Phos- 
phate, especially  among  the  higher  animals;  it  is  curious,  however,  that  in  callus  ami 
exostosis,  there  is  a  much  larger  proportion  of  Carbonate  of  lime  than  in  the  sound  bone  ; 

*  [Tomes  in  Todd  and  Bowman,  p.  117. 
41* 


486  OF  NUTRITION. 

in  which  respect  these  formations  correspond  with  the  bones  of  the  lower  animals  :  but 
in  caries,  the  quantity  of  the  carbonate  is  much  smaller  than  usual.  The  proportion  of 
the  earthy  constituents  of  bones,  to  their  organized  basis,  varies  much  in  different  parts 
of  the  skeleton,  and  at  different  ages.  Thus  when  the  scapula  contains  54  per  cent,  of 
bone-earth,  the  temporal  bone  contains  63|  per  cent.  According  to  Schreger,*  in  the 
bones  of  a  child,  the  earthy  matter  constitutes  one-half;  in  those  of  an  adult  it  amounts 
to  four-fifths,  and  in  those  of  an  old  person  to  seven-eighths  of  the  entire  mass  ;  this  is 
probably  too  high  an  estimate,  but  it  expresses  sufficiently  well  the  comparative  state  of 
the  bones  at  different  periods.f  The  following  are  the  results  of  the  most  recent  and 
careful  analyses  of  Bone,  by  Marchand  and  Lehmann :  those  of  the  former  were  made 
on  the  thigh-bones ;  and  those  of  the  latter  on  the  long  bones  of  the  arm  and  leg. 

MABCHAXD.  LEHMANN. 

I  Cartilage  insoluble  in  H.  cl."^ 

Organic  matter  < soluble                                              -  33-26  32-56 

f  Vessels  j 

Phosphate  of  lime                                                                           -  52-26  7  _,  fi. 

Fluateoflime      ....  -  1-00  5 

Carbonate  of  lime            ...                         .  io-21  9-41 

Phosphate  of  Magnesia  -                                                               -  1-05  1-07 

Soda        -                          -                                       ...  0-92  Ml 

Hydrochlorate  of  Soda    -                         -                                      -  0-25  0-38 

Oxides  of  iron  and  manganese  and  loss,                         -            -  1-05  -86 

100-00  100-00 

The  composition  of  the  Phosphate  of  Lime  in  bones  is  peculiar;  8  proportions  of  the 
base  being  united  with  3  of  the  acid.  According  to  Prof.  Graham,t  it  is  to  be  regarded 
as  a  compound  of  two  tribasic  phosphates:  namely,  2  Ca  O,  H  0,  P  O^  -f  2  (3  Ca  O,  P 
O5)  ;  with  the  addition  of  an  atom  of  water,  which  is  driven  off"  by  calcination.  It  appears 
to  be  united  with  the  animal  basis,  as  a  definite  chemical  compound.  The  presence  of 
Fluoride  of  Calcium  in  bones  has  been  denied ;  according  to  the  recent  inquiries  of  Dr. 
G.  0.  Rees§  and  M.  Gerardin,||  it  does  not  exist  in  recent  bones;  but  is  found  in  greater 
or  less  proportion,  in  those  which  have  become  fossilized, — having  probably  been  intro- 
duced by  infiltration  from  without.  If  this  be  true,  its  presence  may  be  regarded  as  a 
sign  that  the  bone  is  really  fossilized. 

631.  The  Growth  of  Bone  takes  place,  not  merely  by  the  addition  of  new 
matter  to  its  surface  and  extremities,  but  also  by  a  proper  interstitial  change, 
like  that  which  takes  place  in  the  softer  tissues.  In  this  respect,  its  nutrition 
differs  from  that  which  takes  place  in  the  skeletons  of  Invertebrated  animals ; 
for  these,  whether  external  or  internal,  grow  only  by  additions  to  their  surface. 
One  of  the  most  remarkable  changes  which  takes  place  during  the  growth  of 
long  Bones,  is  the  formation  of  the  central  medullary  canal.  In  early  life,  the 
internal  cancelli  are  small,  and  the  medullary  canal  does  not  exist ;  but  the 
cancelli  gradually  enlarge,  and  those  within  the  shaft  coalesce  with  each  other, 
until  a  continuous  tube  is  formed,  around  which  the  cancelli  are  very  large, 
open,  and  irregular.  During  this  process,  the  shaft  itself  undergoes  a  great 
increase  in  its  diameter, — the  bony  shell  being,  as  it  were,  pushed  outwards,  so 
as  to  form  a  larger  circle  than  previously ;  and  this  can  be  scarcely  due  to  any 
thing  else  than  interstitial  deposit.  But  the  increase  of  long  bones  in  length 
is  chiefly  due  to  the  progressive  addition  of  ossific  matter  at  their  extremities, 
by  the  transformation  of  the  Cartilage  which  covers  them.  And  their  increase 
in  diameter,  subsequently  to  the  formation  of  the  medullary  canal,  is  for  the 
most  part  effected  by  the  addition  ^f  new  layers,  with  new  systems  of  Haver- 
sian  canals  and  their  concentric  lamellae  and  radiating  cavities.— The  difference 
in  the  relations  of  the  Bony  substance  to  the  vascular  network,  at  different 

*  Hildebrandt's  Anatomy  by  Weber,  vol.  i.  p.  316. 

f  The  proportion,  however,  is  by  no  means  constant;  as  Dr.  Davy's  experiments  prove. 
See  his  Anatomical  and  Physiological  Researches. 

*  Elements  of  Chemistry,  [Am.  Ed.  p.  711.]  §  Guy's  Hospital  Reports,  vol.  v. 
1  Gazette  Medicale,  Oct.  15,  1842. 


FORMATION  OF  THE  TISSUES— BONE.  487 

ages, — accounting  for  the  variations  in  the  rapidity  of  its  nutrition  and  repara- 
tion,— is  well  displayed  by  the  effects  of  Madder.  When  animals  are  fed 
with  this  substance,  it  is  found  that  their  bones  become  tinged  with  it,  on 
account  of  the  affinity  of  the  colouring  principle  for  phosphate  of  lime.  In  a 
very  young  animal,  a  single  day  suffices  to  colour  the  entire  skeleton ; — for  in 
these  there  is  no  osseous  material  far  from  the  vascular  surface :— when  sec- 
tions are  made,  however,  of  the  bones  thus  tinged,  it  is  found  that  the  colour 
is  confined  to  the  immediate  neighbourhood  of  the  Haversian  canals,  each  of 
which  is  encircled  by  a  crimson  ring.  In  full-grown  animals,  the  bones  are 
very  slowly  tinged,  because  the  osseous  texture  is  much  more,  consolidated 
and  less  permeable  to  fluids  than  in  earlier  life;  and  because,  owing  to  the 
formation  of  new  lamellae,  the  outer  ones  are  pushed  to  a  greater  distance  from 
the  Haversian  canals. 

632.  The  Regeneration  of  Bone,  after  loss  of  its  substance  by  disease  or 
injury,  takes  place  more  completely  perhaps  than  that  of  any  other  tissue, 
except  the  Areolar  (§  638).  This  is  partly  due  to  its  high  degree  of  vascu- 
larity,  and  partly  to  the  simplicity  of  its  structure.  When  we  consider  the 
great  importance  of  the  mechanical  support  afforded  by  Bone,  in  every  func- 
tion of  the  -body,  and  the  necessity  for  an  entire  reparation  before  that  support 
can  be  obtained,  we  perceive  that  no  half-measures  (such  as  are  adopted  in 
the  repair  of  muscles,  ligaments,  &c.,)  would  here  suffice.  The  ordinary 
nutrition  of  Bone  takes  place  through  thie  vessels  of  the  Periosteum  and  those 
of  the  Medullary  membrane,  from  both  of  which  sets  the  branches  are  given 
off  that  traverse  the  Haversian  canals :  the  outer  layers,  however,  are  chiefly 
supplied  from  the  Periosteum,  and  the  inner  from  the  Medullary  membrane ; 
so  that,  when  the  external  membrane  is  destroyed,  the  outer  layers  die,  whilst 
the  inner  layers  suffer  no  interruption  of  their  supply  of  nutriment  received 
through  the  lining  membrane.  In  the  disease  termed  Necrosis,  it  is  seldom 
(if  ever)  that  the  whole  thickness  of  the  bone  loses  its  vitality;  either  the 
outer  or  the  inner  layers  suffer;  and  whichever  part  remains  alive,  it  becomes 
increased  in  thickness  by  Inflammation,  and  by  the  succeeding  processes. 
Plastic  lymph  is  thrown  out  in  layers ;  this  becomes  organized,  converted  into 
Cartilage,  and  finally  into  Bone.  When  a  bone  is  fractured,  the  same  kind 
of  process  takes  place.  Organizable  lymph  is  effused,  not  only  from  the  ves- 
sels of  the  bone  and  its  membranes,  but  from  those  of  the  surrounding  struc- 
tures ;  this  gradually  becomes  vascular,  and  in  time  assumes  a  cartilaginiform 
appearance,  although  its  structure  is  probably  not  exactly  the  same  with  that 
of  ordinary  cartilage.  Ossification  usually  commences  at  the  extremities  of 
the  fractured  bone ;  and,  if  these  be  near  each  other,  they  are  soon  united  by 
Callus.  If  they  be  distant,  however,  their  union  is  a  very  gradual  process. 
It  is  not  true  fas  maintained  by  some)  that  ossification  takes  place  only  in  the 
parts  where  the  new  substance  is  connected  with  old  bone.  Mr.  Gulliver* 
has  remarked  that,  when  the  broken  portions  of  bone  form  an  angle,  there  is 
quite  a  distinct  centre  of  ossification,  commencing  in  the  soft  parts  that  lie 
between  the  sides  of  the  angle.  This  new  bone,  being  a  provision  to  meet 
the  exigences  of  an  irregular  case,  is  termed  by  Mr.  G.  the  accidental  callus; 
it  forms  a  support  between  the  fragments,  in  a  situation  which  is  exactly  that 
of  the  greatest  mechanical  advantage.  Though  for  some  time  quite  uncon- 
nected with  the  old  bone,  it  soon  becomes  united  to  the  regular  callus.  A 
deposit  of  osseous  matter  also  takes  place  occasionally  on  the  interior  of  the 
Periosteum,  when  this  has  been  separated  from  the  bone  by  necrosis  of  the 
latter,  and  by  the  collection  of  fluid  between  them ;  whether  this  be  true  Bone, 
however,  has  not  been  ascertained.  It  is  quite  certain  that  in  this,  as  in  other 

*  Gerber's  Anatomy,  p.  13,  note,-  and  Edinb.  Med.  &  Surg.  Journal,  vol.  xlvi.,  p.  313. 


OF  NUTRITION. 


cases,  the  production  of  the  new  structure  takes  place  most  readily  in  the  parts 
that  are  in  apposition  with  the  old ;  but  we  are  not  warranted  in  saying  that 
the  presence  of  the  latter  is  essential.  The  different  membranous  structures 
belonging  to  the  Bone  contribute  to  its  regeneration ;  probably  in  proportion 
to  their  vascularity.  The  Bone  does  not  recover  its  perfect  structure  for  a 
long  period  after  the  Callus  has  become  firm  ;  the  latter  at  first  commonly  fills 
up  the  medullary  canal;  but  after  a  time,  cancelli  are  formed  in  it  by  intersti- 
tial absorption,  and  the  canal  becomes  again  continuous  by  their  coalescence, 
as  in  the  first  growth  of  the  Bone.* 

I  633.  The  Teeth  are  nearly  allied  to  Bone  in  structure  ;  and  in  some  of  the 
lower  Vertebrata,  there  is  no  separation  between  the  Bone  of  the  jaw,  and  the 
Teeth  projecting  from  it.  In  Man  and  the  higher  animals,  however,  there  is 
an  obvious  difference  both  in  their  structure  and  in  their  mode  of  develop- 
ment. These  subjects  have  lately  received  much  attention ;  and  the  practical 
importance  of  an  acquaintance  with  them  renders  it  desirable  that  they  should 
be  here  treated  somewhat  fully. — The  Teeth  of  Man,  and  of  most  of  the  higher 
animals,  are  composed  of  three  very  different  substances ;  Dentine  or  Ivory, 
Enamel,  and  Cementum  or  Crusta  Petrosa.  These  are  disposed  in  various 
methods,  according  to  the  purpose  Avhich  the  Tooth  is/ to  serve  :  in  Man,  the 
whole  of  the  crown  of  the  tooth  is  covered  with  Enamel ;  its  root  or  fang  is 
covered  with  Crusta  Petrosa ;  whilst  the  substance  or  body  of  the  tooth  is  com- 
posed of  Dentine.  In  the  molar  Teett  of  many  Herbivorous  animals,  however, 
the  Enamel  and  Cementum  form  vertical  plates,  which  alternate  with  plates  of 
Dentine,  and  present  their  edges  at  the  grinding  surface  of  the  tooth  ;  and  the 


[Fig.  119. 


[Fig.  120. 


A  view  of  an  Incisor  and  of  a  Molar  Tooth, 
given  by  a  longitudinal  section,  and  showing  that 
the  enamel  is  striated  and  that  the  stria?  are  all 
turned  to  the  centre ;  the  internal  structure  is  also 
seen;  1,  the  enamel;  2,  the  ivory;  3,  the  cavitas 

pui;.  * 


A  vertical  section  of  an  adult  Bicuspid,  cut  from 
without  inwards — magnified  4  times;  1, 1,  the  cor- 
tical substance  which  surrounds  the  root  up  to  the 
commencement  of  the  enamel ;  2,  2,  the  ivory  of 
the  tooth,  in  which  are  seen  the  greater  parallel 
curvatures,  as  wel]  as  the  position  of  the  main 
tubes ;  3,  apex  of  the  tooth,  where  the  tubes  are 
almost  perpendicular ;  4, 4,  the  enamel ;  5,  the  ca- 
vity of  the  pulp,  in  which  are  seen,  by  means  of 
the  glass,  the  openings  of  the  tubes  of  the  dental 
bone.] 

*  A  very  good  account  of  the  different  opinions  which  have  been  entertained  in  regard 
to  the  reparation  of  Bone,  and  of  the  facts  that  may  be  regarded  as  established,  is  given 
by  Mr.  Gulliver  in  the  Edinb.  Med.  and  Surg.  Journal,  vol.  xliv.  p.  42. 


FORMATION  OF  THE  TISSUES TEETH. 


489 


unequal  i.vear  of  these  substances,'— the  Enamel  being  the  hardest,  and  the 
Cementum  the  softest,— occasions  this  surface  to  be  always  kept  rough. 

634.  The  Enamel  is  composed  of  solid  prisms  or  fibres,  about  l-5600th  of 
an  inch  in  diameter,  arranged  side  by  side,  and  closely  adherent  to  each  other ; 


[Fig.  121. 


[Fig.  122. 


A  vertical  section  of  an  imperfectly  developed  Incisor, 
taken  from  the  follicle  in  which  it  was  enclosed;  this  sec- 
tion is  meant  to  show  the  position  of  the  enamel  fibres,  and 
also  that  a  part  of  the  appearances  which  are  seen  in  this 
substance  under  a  less  magnifying  power,  originate  in 
parallel  curvatures  of  the  fibres;  1, 1,  the  enamel ;  2, 2,  the 
dental  bone,  or  ivory ;  3,  3,  the  minute  indentations  and 
points  on  the  surface  of  the  ivory,  on  which  the  enamel 
fibres  rest;  4,  4,  brown  parallel  fibres;  5, parallel  flexions 
of  the  fibres  of  the  dental  bone  in  these  stripes.] 


A  portion  of  the  surface  of  the  Enamel 
on  which  the  hexagonal  terminations  of 
the  fibres  are  shown— highly  magnified; 
1,  2,  3,  are  more  strongly  marked  dark 
crooked  crevices,  running  between  the 
rows  of  the  hexagonal  fibres.] 


their  length  corresponds  with  the  thickness  of  the  layer  which  they  form ;  and 
the  two  surfaces  of  this  layer  present  the  ends  of  the  prisms,  which  are  usually 
more  or  less  regularly  hexagonal.  The  course  of  these  prisms  is  more  or  less 
wavy ;  but  their  curves  are  for  the  most  part  parallel  to  each  other.  In  the 


[Fig.  123. 


[Fig.  124. 


The  Fibres  of  the  Enamel  viewed  sideways 
under  a  magnifying  power  of  350  times ;  1, 1, 
the  enamel  fibres;  2,  2,  the  transverse  stripes 
upon  them.] 


A  small  portion  of  fig.  120  covered  with  turpentine 
varnish,  viewed  under  a  magnifying  power  of  350 
times;  1,  2,  3,  are  the  tubes  containing  a  powdery, 
lumpy  substance.  They  are  regular,  and  closely  un- 
dulating ;  but  the  branches  do  not  appear,  because  they 
are  penetrated  by  the  varnish.] 


perfect  state,  the  Enamel  contains  but  an  extremely  minute  quantity  of  animal 
matter;  but  if  a  young  tooth  be  examined,  it  is  found  that,  after  the  calcareous 
matter  of  the  tooth  has  been  dissolved  away  by  an  acid,  there  remains  a  set  of 


490 


OF  NUTRITION. 


distinct  prismatic  cells,  which  formed  (as  it  were)  the  moulds  in  which  the 
mineral  substance  was  deposited.*  According  to  Berzelius,  the  amount  of 
animal  matter  in  the  Enamel  is  less  than  2  parts  in  109  ;  whilst  the  phosphate 
of  lime  amounts  to  885,  the  carbonate  of  lime  to  8,  and  the  phosphate  of  mag- 
nesia to  !£.— • The  Dentine}  or  Ivery  consists  of  a  firm  substance,  in  which 


[Fig.  125. 


[Fig.  126. 


A  view  of  the  most  interior  portion  of  the  main 
tubes  of  the  dental  bone  in  an  incisor  of  a  child 
two  years  old,  close  to  their  commencement  in  the 
cavitas  pulpi,  in  order  to  show  their  first  division.] 


A  view  of  the  external  portion  of  the  tubes  of 
the  same  tooth,  exhibiting  their  more  minute  rami- 
fications, which,  for  the  most  part,  turn  towards 
the  crown.] 


mineral  matter  largely  predominates,  though  to  a  less  degree  than  in  the  ena- 
mel. It  is  traversed  by  a  vast  number  of  very  fine  cylindrical  branching  wavy 
tubuli,  which  commence  at  the  pulp-cavity  (on  whose  wall  their  openings  may 
be  seen),  and  radiate  towards  the  surface.  In  their  course  outwards,  the  tubuli 
occasionally  divide  dichotomously ;  and  they  frequently  give  off  minute 


[Fig.  127. 


[Fig.  128. 


A  view  of  a  small  portion  of  a  transverse  section  of 
the  crown  of  the  Tooth  seen  in  fig.  120,  viewed  under 
a  magnifying  power  of  350  times ;  1, 2. 3,  are  the  round 
openings  of  the  tubes,  with  parietes  of  a  peculiar 
substance ;  4,  5,  6,  are  the  tubes  cut  more  obliquely, 
in  consequence  of  their  more  external  position.] 


A  view  of  the  position  of  the  same  main  tubes, 
in  a  transverse  section  near  the  root  of  a  bicus- 
pid, magnified  5  diameters.  The  dark  patches 
in  this  figure  mark  the  places  in  which  the  bone 
was  especially  white  and  less  transparent  than 
in  the  clear  intermediate  tracts.] 


.   *  The  Author  has  discovered  a  structure  precisely  resembling  this,  in  the  shells  of 
many  Mollusca.    See  Annals  of  Natural  History,  December,  1843. 

j-  A  structure  exactly  resembling  Dentine  has  been  found  by  the  Author  in  the  shell  of 
the  Crab,  especially  at  the  tips  of  the  claws;  and  a  less  regular  structure  of  the  same 
kind  in  the  shells  of  many  Mollusca  (ioc.  cit.). 


FORMATION  OF  THE  TISSUES TEETH.  491 

branches,  which  again  send  off  smaller  ones.  In  some  animals,  these  tubuli 
may  be  traced  at  their  extremities  into  cells  exactly  resembling  the  bone-cavi- 
ties; and  here  the  Ivory  must  be  considered  as  having  undergone  a  transition 
into  the  substance  next  to  be  described.  The  diameter  of  the  tubuli  in  their 
largest  part  averages  about  1 -10,000th  of  an  inch  ;  their  smallest  branches  are 
immeasurably  fine.  It  is  impossible  that  they  can  receive  blood  ;  but  it  may 
be  surmised  that,  like  the  tubuli  of  bone,  they  absorb  matter  from  the  vascular 
lining  of  the  pulp-cavity,  which  aids  in  the  nutrition  of  the  tooth.  Although, 
when  once  fully  formed,  the  Tooth  undergoes  little  or  no  change,  there  is  evi- 
dence that  it  possesses  a  certain  power  of  repairing  the  effects  of  disease, — a 
new  layer  of  hard  matter  being  sometimes  thrown  out  on  a  surface  which  has 
been  laid  bare  by  Caries.  It  has  been  found,  too,  that  the  Dentine  is  sometimes 
tinged  by  colouring  matters  contained  in  the  blood.  This  is  most  evident, 
when  a  young  animal  is  fed  upon  madder,  during  the  period  of  the  formation 
of  the  tooth  ;  but  even  in  an  adult,  some  tinge  will  result  from  a  prolonged  use 
of  this  substance  ;  and  it  has  been  noticed  that  the  teeth  of  persons  who  have 
long  suffered  from  Jaundice  sometimes  acquire  a  tinge  of  bile.  Some  uncer- 
tainty exists  in  regard  to  the  organization  of  the  animal  matter  of  Dentine. — 
Appearances  have  been  seen  by  Mr.  Owen,  especially  in  the  tooth  of  the  Du- 
gong,  which  appear  distinctly  to  indicate,  that  the  cellular  structure  of  the  pulp 
may  be  to  a  certain  degree  persistent  in  the  Dentine ;  and  he  regards  the 
tubuli  as  formed  from  the  nuclei  of  these  cells,  as  are  the  stellate  cavities  of 
bone.  On  the  other  hand,  it  is  stated  by  Henle  that,  in  the  cartilaginous  basis 
of  Dentine,  a  distinctly  fibrous  structure  prevails ;  each  of  the  tubuli  being 
surrounded  with  a  fasciculus  of  flat  pale  granular  fibres.  The  Cartilaginous 
basis  obtained  by  the  action  of  acid  resembles  that  of  Bone  in  its  composition, 
but  only  forms  about  28  parts  in  100 ;  the  phosphate  of  lime  constitutes  about 
64  5  parts,  carbonate  of  lime  5£  parts ;  phosphate  of  magnesia  and  soda,  and 
chloride  of  sodium,  2|  parts. — The  Crusta  Petrosa  or  Cementum  has  the 
characteristic  structure  of  true  Bone ;  and  does  not  seem  to  differ  from  it  in 
any  essential  particular. — Besides  these  three  substances,  a  fourth  has  been 
described  by  Mr.  Nasmyth,  as  occurring  normally  in  many  of  the  lower  ani- 
mals, and  as  occasionally  presenting  itself  in  Man.  This  is  formed  by  the 
consolidation  of  the  central  part  of  the  pulp,  which  usually  remains  uncal- 
cified,  occupying  the  centre  of  the  tooth :  it  "  partakes  much  of  the  fibrous 
character  of  the  ivory,  being  composed  of  irregularly  radiating  filaments, 
blended  with  small  calcigerous  cells,  in  which  the  ossified  vessels  are  seen  to 
ramify ;"  and  may  be  considered,  therefore,  as  intermediate  between  true  Ivory 
and  Bone.  By  Mr.  Nasmyth,  the  occurrence  of  this  substance  in  the  Human 
Tooth  was  regarded  as  the  result  of  diseased  action ;  but  it  has  been  pointed 
out  by  Mr.  Lintott,*  that  it  constantly  occurs  after  the  age  of  twenty,  and  in- 
creases with  advancing  years. 

635.  The  Development  of  the  Teeth  presents  many  points  of  great  interest ; 
and  will  therefore  be  described  in  some  detail.  The  following  account  of  the 
early  formation  of  the  teeth  in  the  Human  foetus,  is  derived  from  the  researches 
of  Mr.  Goodsir.t 

a.  At  the  sixth  week  of  Foetal  life,  a  deep  narrow  groove  may  be  perceived,  in  the 
upper  jaw  of  the  Human  embryo,  between  the  lip  and  the  rudimentary  palate;  this  is 
speedily  divided  into  two  by  a  ridge,  which  afterwards  becomes  the  external  alveolar 
process;  and  it  is  in  the  inner  groove  that  the  germs  of  the  teeth  subsequently  appear. 
Hence  this  may  be  termed  the  primitive  dental  groove.  At  about  the  seventh  week,  an 
ovoidal  papilla,  consisting  of  a  granular  substance,  makes  its  appearance  on  the  floor  of 
the  groove,  near  its  posterior  termination;  this  papilla  is  the  germ  of  the  Anterior  supe- 

*  Lancet,  June  24,  1843. 

f  Edinb.  Med.  and  Surg.  Journal,  vol.  li. 


492 


OF  NUTRITION. 


Fig.  129. 


Upper  Jaw  of  human  embryo  at  sixth 
week;  showing  6,  the  primitive  dental 
groove,  behind  a,  the  lip.  After  Goodsir. 


rior  Milk  Molar  tooth.  About  the  eighth  week,  a 
similar  papilla,  which  is  the  germ  of  the  Canine 
tooth,  arises  in  front  of  this ;  and  during  the  ninth 
week  the  germs  of  the  Incisors  make  their  appear- 
ance under  the  same  form.  Daring  the  tenth  week, 
processes  from  the  sides  of  the  dental  groove,  parti- 
cularly the  external  one,  approach  each  other,  and 
finally  meet  before  and  behind  the  papilla  of  the 
anterior  Molar;  so  as  to  enclose  it  in  a  follicle, 
through  the  mouth  of  which  it  may  be  seen.  By  a 
similar  process,  the  other  teeth  are  gradually  en- 
closed in  corresponding  follicles.  The  germ  of  the 
Posterior  milk  Molar  also  appears  during  the  tenth 
week,  as  a  small  papilla.  By  the  thirteenth  week, 
the  follicle  of  the  Posterior  Molar  is  completed;  and  the  several  papillae  undergo  a  gra- 
dual change  of  form.  Instead  of  remaining,  as  hitherto,  simple,  rounded,  blunt  masses 
of  granular  matter,  each  of  them  assumes  a  particular  shape;  the  Incisors  acquire  in 
some  degree  the  form  of  the  future  teeth;  the  Canines  become  simple  cones;  and  the 
Molars  become  cones  flattened  transversely,  somewhat  similar  to  carnivorous  molars. 
During  this  period,  the  papillae  grow  faster  than  the  follicles ;  so  that  the  former  protrude 
from  the  mouth  of  the  latter.  At  this  time,  the  mouths  of  the  follicles  undergo  a  change, 
consisting  in  the  development  of  their  edges,  so  as  to  form  Opercula;  which  correspond 
in  some  measure  with  the  shape  of  the  crowns  of  the  future  teeth.  There  are  two  of 
these  opercula  in  the  Incisive  follicles,  three  for  the  Canines,  and  four  or  five  for  the 
Molars.  At  the  fourteenth  week,  the  inner  lip  of  the  dental  groove  has  increased  so 
much  as  to  meet  and  apply  itself  in  a  valvular  manner  to  the  outer  lip  or  ridge,  which 
has  been  also  increasing.  The  follicles  at  this  time  grow  faster  than  the  papillae,  so  that 
the  latter  recede  into  the  former.  The  primitive  dental  groove  then  contains  ten  papillae, 
enclosed  in  as  many  follicles;  and  thus  all  necessary  provision  is  made  for  the  produc- 
tion of  the  first  set  of  teeth.  (This  series  of  changes  is  represented  in  Fig.  130,  a — g.) 
The  groove  is  now  situated,  however,  on  a  higher  level  than  at  first;  and  it  has  under- 
gone such  a  change  by  the  closure  of  its  edges,  as  to  entitle  it  to  the  distinctive  appella- 
tion of  secondary  dental  groove.  It  is  in  this  secondary  groove  that  those  structures  origi- 
nate which  are  destined  for  the  development  of  the  Second  or  Permanent  set  of  Teeth, — 
of  those  at  least  which  replace  the  Milk  Teeth.  This  is  accomplished  in  the  following 
manner. 

Fig.  130. 


Diagrams  illustrative  of  the  formation  of  a  temporary,  and  its  corresponding  permanent  Tooth,  from  a 
mucous  membrane.  After  Goodsir. 

b.  At  about  the  fourteenth  or  fifteenth  week,  a  little  crescentic  depression  may  be  ob- 
served immediately  behind  the  inner  Opercula  of  each  of  the  Milk-tooth  follicles.  This 
depression  gradually  becomes  deeper,  and  constitutes  what  may  be  termed  a  cavity  of 


FORMATION  OF  THE  TISSUES TEETH.  493 

reserve,-  adapted  to  furnish  delicate  mucous  membrane  for  the  future  formation  of  the 
sacs  and  pulps  of  the  ten  anterior  Permanent  teeth.  These  cavities  of  reserve  are  gradu- 
ally separated  from  the  secondary  dental  groove,  by  the  adhesion  of  their  edges ;  and  they 
thus  become  minute  compressed  sacs,  situated  between  the  surface  of  the  gum  and  the 
milk-sacs.  They  gradually  recede,  however,  from  the  surface  of  the  gum,  so  as  to  be 
posterior  instead  of  inferior  to  the  milk  sacs;  and  at  last  they  imbed  themselves  in  the 
submucous  cellular  tissue,  which  has  all  along  constituted  the  external  layer  of  the  milk- 
sacs.  The  implantation  of  the  Permanent  tooth-sacs  in  the  walls  of  the  Temporary  folli- 
cles, gives  to  the  former  the  appearance  of  being  produced  by  a  gemmiparous  process 
from  the  latter.  This  series  of  changes  is  represented  in  Fig.  130  ,«•— n. 

c.  We  now  return  to  the  Milk-teeth,  the  papillae  of  which,  from  the  time  that  their  fol- 
licles close,  become  gradually  moulded  into  their  peculiarly  Human  shape.    The  Molar 
pulps  begin  to  be  perforated  by  three  canals,  which,  proceeding  from  the  surface  towards 
the  centre,  gradually  divide  their  primary  bases  into  three  secondary  bases;  and  these 
become  developed  into  the  fangs  of  the  future  teeth.     Whilst  this  is  going  on,  the  sacs 
grow  more  rapidly  than  the  papillae,  so  that  there  is  an  intervening  space,  which  is  filled 
with  a  gelatinous  granular  substance;  this  closely  applies  itself  to  the  surface  of  the 
papilla,  but  does  not  adhere  to  it.     The  branch  of  the  dental  artery  which  proceeds  to 
each  sac,  ramifies  minutely  in  its  proper  membrane,  but  does  not  send  the  smallest  twig 
into  the  granular  substance.     At  this  period,  the  tubercles  and  apices  of  the  papillae  or 
pulps  become  converted  into  real  dentine  or  tooth-substance,  in  the  manner  hereafter 
stated  (§  633);  and  the  granular  matter  is  absorbed  as  fast  as  this  appears;  so  that, 
when  the  process  of  conversion  has  reached  the  base  of  the  pulp,  the  interior  of  the 
dental  sac  is  left  in  the  villous  and  vascular  condition  of  a  true  Mucous  membrane, 
having  upon  it  a  very  thin  layer  of  the  granular  substance,  which  may  be  considered  as 
a  sort  of  Epithelium;  and  it  is  by  the  deposition  of  calcareous  matter  in  the  long  pris- 
matic cells  of  this,  that  the  enamel  is  formed. 

d.  Whilst  these  changes  are  going  on,  other  important  preparations  are  being  made 
for  the  Permanent  set.     The  general  adhesion  of  the  edges  of  the  Primitive  Dental 
Groove,  (§  a)  does  not  invade  the  portion  which  is  situated  behind  the  Posterior  Milk 
follicle;  this  retains  its  original  appearance  for  a  fortnight  or  three  weeks  longer,  and 
affords  a  nidus  for  the  development  of  the  papilla  and  follicle  of  the  Anterior  Permanent 
Molar  tooth,  which  is  developed  in  all  respects  on  the  same  plan  with  the  milk  teeth. 
After  its  follicle  has  closed,  the  edges  of  the  dental  groove  meet  over  its  mouth;  but  as 
the  walls- of  the  groove  do  not  adhere,  a  considerable  cavity  is  left  between  the  sac  of  the 
tooth  and  the  surface  of  the  gum.    The  cavity  is  a  reserve  of  delicate  mucous  membrane, 
to  afford  materials  for  the  formation  of  the  Second  Permanent  Molar,  and  of  the  Third 
Permanent  Molar,  or  Wisdom-tooth.    The  process  just  described  is  represented  in  Fig. 
131,  a — c.    It  will  be  convenient  here  to  continue  the  account  of  the  development  of 
these  teeth,  although  it  takes  place  at  a  much  later  period.    Towards  the  end  of 'foetal 
life,  the  increase  of  the  bulk  of  the  Milk-tooth  sacs  takes  place  so  much  more  rapidly 
than  the  growth  of  the  jaw,  that  the  sac  of  the  Anterior  Permanent  Molar  is  forced 


00 


HXXJ 


Digrams  illustrative  of  the  formation  of  three  permanent  Molar  Teeth,  from  the  non-adherent  portion  of 
the  dental  groove.    (After  Goodsir.) 

42 


494  OF  NUTRITION. 

backwards  and  upwards,  into  the  maxillary  tuberosity;  and  thus  it  not  only  draws  the 
surface  of  the  gum  in  the  same  direction,  but  lengthens  out  the  great  cavity  of  reserve 
(Fig.  131  d).  During  the  few  months  which  succeed  birth,  however,  the  jaw  is  greatly- 
lengthened;  and  when  the  infant  is  eight  or  nine  months  old,  the  Anterior  Permanent 
Molar  resumes  its  former  position  in  the  posterior  part  of  the  dental  arch:  and  the  great 
cavity  of  reserve  returns  to  its  original  size  and  situation  (c).  This  cavity,  however, 
soon  begins  to  bulge  out  at  its  posterior  side,  and  projects  itself,  as  a  sac,  into  the  max- 
illary tuberosity  (/);  a  papilla  or  pulp  appears  in  its  fundus;  and  a  process  of  con- 
traction separates  it  from  the  remainder  of  the  cavity  of  reserve.  Thus  the  formation 
of  the  Second  Permanent  Molar  from  the  first,  takes  place  on  precisely  the  same  plan 
with  the  formation  of  the  Permanent  Bicuspids  from  the  Temporary  Molars.  The  new 
sac  at  first  occupies  the  maxillary  tuberosity  (g) ;  but  the  lengthening  of  the  jaw  gradually 
allows  it  to  fall  downwards  and  forwards,  into  the  same  line,  and  on  a  level,  with  the  rest 
(A).  Before  it  leaves  the  tuberosity  altogether,  the  posterior  extremity  of  the  remainder 
of  the  cavity  of  reserve  sends  backwards  and  upwards  its  last  offset— the  sac  and  pulp 
of  the  Wisdom-tooth  (t);  this  speedily  occupies  the  tuberosity  after  the  second  molar  has 
left  it  (j) ;  and  ultimately,  when  the  jaw  lengthens  for  the  last  time,  at  the  age  of  nine- 
teen or  twenty,  it  takes  its  place  at  theposterior  extremity  of  the  range  of  the  adult  teeth  (k). 
Thus,  the  Wisdom-teeth  are  the  second  products  of  the  posterior  y  great  cavities  of 
reserve ;  and  the  final  effects  of  development  in  the  secondary  dental  groove.  In  the 
Elephant,  in  which  there  is  a  continual  new  production  of  molar  teeth  at  the  back  of 
the  jaw,  it  is  probable  that  from  each  sac  a  cavity  of  reserve  is  formed,  which  produces 
the  succeeding  tooth;  and  thus  the  only  essential  difference  between  its  dentition  and 
that  of  Man,  consists  in  the  degree  of  continuance  of  this  gemmiparous  process ;  which 
ceases  in  Man  after  being  twice  performed,  but  is  repeated  in  the  Elephant  until  nearly 
the  close  of  its  life. 

e.  We  have  thus  sketched  the  history  of  the  Development  of  the  Teeth,  up  to  the  time 
when  they  prepare  to  make  their  way  through  the  gum.  The  first  stage  of  this  deve- 
lopment may  be  termed  the  papillary ,-  and  the  second,  the  follicular.  The  latter  termi- 
nates when  the  papillae  are  completely  hidden  by  the  closure  of  the  mouths  of  the  folli- 
cles, and  of  the  groove  itself.  The  succeeding  stage,  which  has  long  been  known  as  the 
saccular,is  the  one  during  which  the  whole  formation  of  the  Tooth-substance,  and  of  the 
Enamel,  takes  place.  It  is  during  this  period,  also,  that  the  ossification  of  the  jaw  is 
taking  place;  and  that  the  bony  sockets  are  formed  for  the  teeth,  by  the  consolidation  of 
the  anterior  and  posterior  ridges  bounding  the  alveolar  groove  (in  which  the  dental  groove 
was  originally  imbedded),  and  of  the  interfollicular  septa,  which  are  produced  by  the 
meeting  of  transverse  projections  from  these  ridges. — The  history  of  development  in  the 
Lower  Jaw  is  very  nearly  the  same;  the  chief  difference  being  in  the  origin  and  situation 
of  the  primitive  dental  groove. 

/.  We  have  now  only  to  consider  the  fourth  or  eruptive  stage, — that  in  which  the  Teeth 
make  their  way  through  the  gum.  This  process  chiefly  results  from  the  lengthening  of 
the  fang,  by  the  addition  of  a  new  bony  matter;  and  the  crown  of  the  tooth  is  thus 
made  to  press  against  the  closed  mouth  of  the  sac  (Fig.  130,  m).  This  at  last  gives  way, 
so  that  the  sac  assumes  its  previous  condition  of  an  open  follicle.  When  the  edge  of 
the  tooth  has  once  made  its  way  through  the  gum,  it  advances  more  rapidly  than  can 
well  be  accounted  for,  by  the  usual  rate  of  lengthening  of  its  fang;  and  this  appears  to 
be  due  to  the  separation  of  the  bottom  of  the  sac  from  the  fundus  of  the  alveolus ;  so 
that  the  whole  tooth-apparatus  is  carried  nearer  to  the  surface,  leaving  a  space  at  the 
bottom  of  the  alveolar  cavity,  in  which  the  further  lengthening  of  the  root  can  take 
place  (n).  The  open  portion  of  the  sac  remains  as  the  narrow  portion  of  the  gum, 
which  forms  a  vascular  border  and  groove  round  the  neck  of  the  perfected  tooth  (o).  The 
deeper  portion  of  the  sac  adheres  to  the  fang  of  the  tooth,  and  is  converted  by  ossifi- 
cation into  the  Cementum  or  Crusta  Petrosa  (§  634).  What  is  commonly  denominated 
the  Periosteum  of  the  Tooth,  really  belongs  as  much  to  the  Alveolus.  It  is  connected 
with  the  tooth  by  the  submucous  cellular  tissue,  which  originally  intervened  between  the 
tooth-sac  and  the  walls  of  the  osseous  cavity.  It  appears  from  Mr.  Nasmyth's  researches, 
that  the  inner  layer  of  the  portion  of  the  capsule,  which  covered  the  crown  of  the  tooth, 
remains  adherent  to  it ;  forming  a  thin  coating  of  Crusta  Petrosa  (most  of  which  is, 
however,  soon  worn  off)  over  the  Enamel. — During  the  period  that  the  Milk-teeth  have 
been  advancing,  along  with  their  sockets,  to  their  perfect  state  and  ultimate  position,  the 
Permanent  sacs  have  been  receding  in  an  opposite  direction,  and  have  with  their  bony 
crypts  been  enlarging;  and  at  last  they  occupy  a  position  almost  exactly  below  the 
former  (n  and  o).  They  still  retain  a  communication  with  the  gum,  however;  the 
channel  by  which  they  descended  not  having  completely  closed  up,  and  the  neck  of  the 
sac  being  elongated  into  a  cord  which  passes  through  this.  The  channels  may  after- 


FORMATION  OF  THE  TISSUES TEETH.  495 

wards  serve  as  the  itinera  dentium,  and  the  cords  as  gubernacula ;  but  it  is  uncertain 
whether  they  really  afford  any  assistance  in  directing  the  future  rise  of  the  tooth  to  the 
surface;  the  successive  stages  of  which  are  represented  in  Fig.  130,  p — t.  The  sacs  of 
the  permanent  teeth  derive  their  first  vessels  from  the  gums,  ultimately  they  receive  their 
proper  dental  vessels  from  the  Milk-sacs;  and,  as  they  separate  from  the  latter  into  their 
own  cells,  the  newly-formed  vessels,  conjoining  into  common  trunks,  also  retire  into  per- 
manent dental  canals,  and  gradually  become  the  most  direct  channels  for  the  blood  trans- 
mitted through  the  jaw. 

g.  The  following  interesting  generalizations  respecting  the  development  of  the  teeth, 
result  from  Mr.  Goodsir's  researches.  1.  The  Milk-leeih  are  formed  on  both  sides  of 
either  jaw  in  three  divisions, — a  Molar,  a  Canine,  and  an  Incisive;  in  each  of  which, 
dentition  proceeds  in  an  independent  manner.  2.  The  dentition  of  the  whole  arch  pro- 
ceeds from  behind  forwards;  the  Molar  division  commencing  before  the  Canine, and  the 
Canine  before  the  Incisive.  3.  The  dentition  of  each  of  the  divisions  proceeds  in  a  con- 
trary direction,  the  Anterior  Molar  appearing  before  the  Posterior,  the  Central  Incisor 
before  the  Lateral.  4.  Two  of  the  subordinate  phenomena  of  nutrition  also  obey  this 
inverse  law;— the  follicles  closing  by  commencing  at  the  medium  line  and  proceeding 
backwards;  and  the  dental  groove  disappearing  in  the  same  direction.  5.  Dentition 
commences  in  the  Upper  Jaw,  and  continues  in  advance  during  the  most  important  period 
of  its  progress.  The  development  of  the  Superior  Incisors,  however,  is  retarded  by  a 
peculiar  cause;  so  that  the  Inferior  Incisors  have  the  priority  in  the  time  of  their  com- 
pletion and  appearance.  6.  The  germs  of  the  Permanent  teeth,  with  the  exception  of  that 
of  the  Anterior  MoLtr,  appear  in  a  direction  from  the  median  line  backwards.  7.  The 
Milk-teeth  originate,  or  are  developed,  from  mucous  membrane.  8.  The  Permanent 
teeth,  also  originating  from  mucous  membrane,  are  of  independent  origin,  and  have  no 
connection  with  the  milk-teeth.  9.  A  Tooth-pulp  and  its  sac  must  be  referred  to  the 
same  class  of  organs  as  the  combined  Papilla  and  Follicle  from  which  a  hair  or  feather 
is  developed. 

h.  The  following  is  the  usual  order  and  period  of  appearance,  of  the  several  pairs  of 
Milk-teeth.  The  Four  Central  Incisors  first  present  themselves,  usually  about  the  seventh 
month  after  birth,  but  frequently  much  earlier  or  later:  those  of  the  Lower  Jaw  appear 
first.  The  Lateral  Incisors  next  show  themselves,  those  of  the  Lower  Jaw  coming 
through  before  those  of  the  upper;  they  usually  make  their  appearance  between  the 
seventh  and  tenth  months.  After  a  short  interval,  the  Anterior  Molars  present  themselves, 
— generally  soon  after  the  commencement  of  the  Second  Year,-  and  these  are  followed  by 
the  Canines,  which  usually  protrude  themselves  between  the  fourteenth  and  twentieth 
months.  The  Posterior  Molars  are  the  last,  and  the  most  uncertain  in  regard  to  their 
time  of  appearance ;  this  varying  from  the  eighteenth  to  the  thirty-sixth  month.  In  regard 
to  all  except  the  front  teeth,  there  is  no  settled  rule  as  to  the  priority  of  appearance  of 
those  in  the  Upper  or  Under  jaw;  sometimes  one  precedes,  and  sometimes  the  other;  but 
in  general  it  may  be  stated,  that,  whenever  one  makes  its  appearance,  the  other  cannot 
be  far  off.  The  same  holds  good  in  regard  to  the  two  sides,  in  which  development  does 
not  always  proceed  exactly  part  passu. — The  period  of  Dentition  is  one  of  considerable 
risk  to  the  Infant's  life.  The  pressure  upon  the  nerves  of  the  gum,  which  necessarily 
precedes  the  opening  of  the  sac  and  the  eruption  of  the  tooth,  is  a  fruitful  source  of  irri- 
tation; producing  disorder  of  the  whole  system,  especially  of  the  Digestive  organs,  and 
not  unfrequently  giving  origin  to  fatal  Convulsive  affections.  These  last  have  been  par- 
ticularly studied  by  Dr.  M.  Hall,  who  recommends  the  free  use  of  the  gum-lancet,  as  a 
most  important  means  of  prevention  and  cure.  Even  where  dentition  proceeds  quite 
naturally  and  is  not  itself  a  cause  of  diseased  action,  it  induces  an  irritable  state  of  the 
whole  constitution,  which  aggravates  the  effects  of  other  morbific  causes.  It  is,  there- 
fore, of  the  greatest  consequence  that  the  infant  should  be  withdrawn,  during  this  period, 
from  all  injurious  influences;  and  that  no  irregularity  of  diet,  or  deficiency  of  fresh  air 
and  exercise,  should  operate  to  its  disadvantage. 

i.  After  the  lapse  of  a  few  years,  the  further  elongation  of  the  jaw  permits  the  appear- 
ance of  the  First  True  Molar;  which,  as  already  remarked,  is  really  a  Milk-tooth,  so' far 
as  its  formation  is  concerned.  This  commonly  presents  itself  about  the  middle  or  end 
of  the  Seventh  year;  sometimes  preceding,  and  sometimes  following,  the  exchange  of  the 
Central  Incisors,  which  takes  place  about  the  same  time.  When  the  Permanent  Teeth 
have  so  much  enlarged  that  they  can  no  longer  be  contained  within  their  own  alveoli, 
they  press  upon  the  anterior  parietes  of  those  cavities,  and  cause  their  absorption ;  so 
that  each  tooth  is  allowed  to  come  forwards,  in  some  degree,  into  the  lower  part  of  the 
socket  of  the  corresponding  Temporary  tooth.  The  root  of  the  temporary  tooth  now 
begins  to  be  absorbed,  generally  at  the  part  nearest  its  successor;  and  this  absorption 
proceeds  as  the  new  tooth  advances,  until  the  root  of  the  Milk-tooth  is  completely 


496  OF  NUTRITION. 

removed;  when  its  crown  falls  off,  leaving  room  for  the  permanent  tooth  to  supply  its 
place  (Fig.  130, p — /).  This  absorption  is  usually  regarded  as  due  to  the  pressure  of  the 
Permanent  tooth, but  this  does  not  appear  to  be  the  case;  for  it  is  mentioned  by  Mr. Bell, 
that  it  is  not  an  uncommon  occurrence  for  the  root  of  the  temporary  tooth  to  be  wholly 
absorbed,  and  for  the  crown  to  fall  out  spontaneously,  long  before  the  succeeding  tooth 
has  approached  the  vacant  space.  The  same  has  been  remarked  by  Mr.  Bell,  of  the 
cavity  in  the  jaw  which  is  formed  for  the  reception  of  the  sac  of  the  Permanent  tooth,  at 
the  time  that  it  buds  off  from  that  of  the  milk-tooth; — the  excavation  being  often  seen  to 
commence  before  the  new  sac  is  formed.  Hence,  although  the  two  processes,  growth 
and  absorption,  are  usually  cotemporaneous  in  each  instance,  they  are  by  no  means 
dependent  on  each  other.  Still  it  would  seem  that  the  existence,  if  not  the  pressure,  of 
the  new  Tooth  is  necessary  to  determine  the  absorption  of  the  old;  for  cases  are  not 
unfrequent,  in  which  the  Temporary  teeth  retain  their  situation  in  the  mouth,  with  con- 
siderable firmness,  until  adult  age, — the  corresponding  Permanent  ones  not  having  been 
formed. 

k.  In  the  successive  replacement  of  the  Milk-teeth  by  the  Permanent  set,  a  very  regular 
order  is  usually  followed.  The  Middle  Incisors  are  first  shed  and  renewed,  and  then  the 
Lateral  Incisors.  The  Anterior  Milk  Molars  next  follow;  and  these  are  replaced  by  the 
Anterior  Bicuspid  teeth.  About  a  year  afterwards,  the  Posterior  Milk  Molars  are  shed, 
and  replaced  in  like  manner,  by  Bicuspid  teeth.  The  Canines  are  the  last  of  the  Milk- 
teeth  to  be  exchanged;  the  development  of  the  new  ones  not  taking  place  until  the  12th 
year.  In  the  succeeding  year,  the  Second  pair  of  True  Molars  appears;  the  third  pair, 
or  denies  sapientise,are  seldom  developed  until  three  or  four  years  subsequently,  and  often 
much  longer.  It  has  been  recently  proposed*  (and,  from  the  evidence  adduced  in  its 
favour,  the  proposition  would  seem  entitled  to  considerable  attention)  to  adopt  the  suc- 
cessive stages  in  the  Second  Dentition,  as  standards  for  estimating  the  physical  capabili- 
ties of  Children,  especially  in  regard  to  those  two  periods  which  the  Factory  Laws  render 
it  of  the  greatest  importance  to  determine, — namely,  the  ages  of  nine  and  thirteen  years. 
Previously  to  the  former,  a  Child  is  not  permitted  to  work  at  all ;  and  up  to  the  latter,  it 
may  be  only  employed  during  9  hours  a  day.  The  necessities  or  the  cupidity  of  Parents 
is  continually  inducing  them  to  misrepresent  the  ages  of  their  children;  and  it  has  been 
found  desirable,  therefore,  to  seek  for  some  test  by  which  the  capability  of  the  Child  may 
be  determined,  without  a  knowledge  of  its  age.  A  standard  of  Height  has  been  adopted 
by  the  Legislature  for  this  purpose;  but  upon  grounds  which,  Physiologically  considered, 
are  very  erroneous ;  since,  as  is  well  known,  the  tallest  children  are  frequently  the  weak- 
liest. According  to  Mr.  Saunders,  the  degree  of  advance  of  the  Second  Dentition  may 
be  regarded  as  a  much  more  correct  standard  of  the  degree  of  general  development  of  the 
organic  frame,  and  of  its  physical  powers;  and  it  appears  from  his  inquiries,  that  it  may 
be  relied  on  as  a  guide  to  the  real  age,  in  a  large  proportion  of  cases;  whilst  no  serious 
or  injurious  mistake  can  ever  arise  from  its  use.  It  may  happen  that  local  or  constitu- 
tional causes  may  have  slightly  retarded  the  development  of  the  Teeth;  in  which  case 
the  age  of  the  individual  would  rather  be  under-estimated,  and  no  harm  could  ensue:  on 
the  other  hand,  instances  of  premature  development  of  the  Teeth  very  rarely,  if  ever, 
occur:  so  that  there  is  no  danger  of  imputing  to  a  Child  a  capability  for  exertion  which 
he  does  not  possess,  as  the  test  of  height  is  continually  doing.  Moreover,  if  such  an 
advance  in  Dentition  should  occur,  it  might  probably  be  regarded  as  indicative  of  a  cor- 
responding advance  in  the  development  of  the  whole  organism;  so  that  the  real  capa- 
bility would  be  such  as  the  teeth  represent  it. 

/.  The  following  is  Mr.  Saunders's  statement  of  the  Ages,  at  which  the  permanent  teeth 
respectively  appear.  The  first  True  Molars  usually  make  their  appearance  towards  the 
end  of  the  7th  year.  Occasionally  one  of  them  protrudes  from  the  gum  at  6,  or  more  fre- 
quently at  6£  years  of  age;  but  the  evolution  of  the  whole  of  them  may  be  regarded  as 
an  almost  infallible  sign  of  the  Child's  being  7  years  old.  In  other  instances,  however, 
where  the  tooth  on  one  side  of  the  mouth  is  freely  developed,  it  is  fair  to  reckon  the  two 
as  having  emerged  from  their  capsule;  since  the  development  of  the  other  must  be  con- 
sidered as  retarded.  This  rule  only  holds  good,  however,  in  regard  to  teeth  in  the  same 
row;  for  the  development  of  the  teeth  in  either  jaw  must  not  be  inferred  from  that  of  the 
corresponding  teeth  in  the  other.  With  this  understanding,  the  results  of  the  application 
of  the  following  table  will  probably  be  very  near  the  truth. 

Central  Incisors  developed  at  .     .     8  years 

Lateral  Incisors 9     — 

First  Bicuspid 10    — 

*  "The  Teeth  a  Test  of  Age,  considered  with  reference  to  the  Factory  Children."  By 
Edwin  Saunders. 


FORMATION  OF  THE  TISSUES TEETH.  497 

Second  Bicuspid 11  years 

Cuspidati 12  to  12£ 

Second  Molars 12^  to  14 

The  following  are  the  results  of  the  application  of  this  test,  in  a  large  number  of  cases 
examined  by  Mr.  Saunders.  Of  708  Children  of  nine  years  old,  530  would  have  been 
pronounced  by  it  to  be  near  the  completion  of  their  ninth  year;  having  the  central,  and 
either  three  or  four  lateral,  incisors  fully  developed.  Out  of  the  remaining  178,  it  would 
have  indicated  that  126  were  8£  years  old,  as  they  presented  one  or  two  of  the  Lateral 
Incisors;  and  the  52  others  would  have  been  pronounced  8  years  old,  all  having  three  or 
four  of  the  Central  Incisors.  So  that  the  extreme  deviation  is  only  12  monlhs;  and  this 
in  the  inconsiderable  proportion  (when  compared  with  the  results  obtained  by  other 
means)  of  52  in  708,  or  7£  per  cent.  Again,  out  of  338  children  of  13  years  of  age,  294 
might  have  been  pronounced  with  confidence  to  be  of  that  age,  having  the  Cuspidati, 
Bicuspid,  and  Second  Molars,  either  entirely  developed,  or  with  only  the  deficiency  of 
one  or  two  of  either  class.  -  Of  the  44  others,  36  would  have  been  considered  as  in  their 
13th  year,  having  one  of  the  Posterior  Molars  developed;  and  8  as  near  the  completion 
of  the  12th,  having  two  of  the  Cuspidati,  and  one  or  two  of  the  Second  Bicuspid.  In  all 
these  instances,  the  error  is  on  the  favourable  side, — that  is,  on  the  side  on  which  it  is 
calculated  to  prevent  injury  to  the  objects  of  the  inquiry;  in  no  instance  did  this  test 
cause  a  Child  to  be  estimated  as  older  or  more  fit  for  labour  than  it  really  was. 

m.  The  value  of  this  test,  as  compared  with  that  of  Height,  is  manifested  by  a  striking 
example  adduced  by  Mr.  Saunders.  The  height  of  one  lad,  J.  J.,  aged  8  years  and  4 
months,  was  4  feet  and  £  of  an  inch ;  that  of  another  boy,  aged  8  years  and  7  months,  was 
only  3  feet  7|  inches.  According  to  the  standard  of  height  adopted  by  the  Factory  Com- 
missioners (namely  3  feet  10  inches),  the  taller  lad  would  have  been  judged  fit  for  labour, 
whilst  the  shorter  would  have  been  rejected.  The  Dentition  of  the  latter,  however,  was 
further  advanced  than  that  of  the  former:  for  he  had  two  of  the  Lateral  Incisors,  whilst 
the  former  had  only  the  Central ;  and  the  determination  of  their  relative  physical  powers, 
which  would  have  been  thus  formed,  would  have  been  in  complete  accordance  with  the 
truth.  The  Elder  boy,  though  shorter  than  the  other  by  5£  inches,  possessed  a  much 
greater  degree  both  of  corporeal  and  mental  energy,  and  his  pulse  was  strong  and  regu- 
lar; whilst  that  of  the  younger  lad,  who  was  evidently  growing  too  fast,  was  small  and 
frequent. — An  instance  even  more  striking  has  come  under  the  Author's  own  observation. 

636.  The  development  of  the  Human  Tooth  can  only  be  rightly  understood, 
when  it  is  compared  with  the  same  process  in  the  inferior  animals.  Thus  in 
certain  Fishes,  as  the  Shark,  the  tooth  is  completed,  without  the  formation  of 
the  matrix  ever  having  proceeded  beyond  the  first  or  papillary  stage ;  and  re- 
mains attached  to  the  mucous  membrane  oniy  of  the  mouth.  In  many  other 
Fishes  and  in  Serpents,  the  follicular  and  saccular  stages  are  completed ;  but 
the  enamel-organ  is  not  developed.  It  is  evident,  then,  that  the  papillary  pulp 
alone  is  concerned  in  the  formation  of  the  real  tooth  substance.  From  the 
description  of  Purkinje  and  Ra^chkow,  it  appears  that  the  parenchyma  of  the 
papilla  is  composed  of  minute  spherical  cells,  the  free  surface  of  which  is 
covered  by  a  peculiarly  dense,  structureless,  pellucid  membrane  (basement 
membrane  ?)  and  it  is  within  this  that  the  formation  of  the  Dentine  commences. 
Blood-vessels  soon  penetrate  the  granular  pulp,  form  several  anastomoses  in 
their  course  through  its  substance,  and  terminate  in  a  rich  and  delicate  network 
of  capillaries,  on  that  part  of  the  surface  of  the  pulp  where  the  Dentine  has 
begun  to  be  formed.  The  cellules  of  the  pulp  immediately  beneath  the  pre- 
formative  membrane,  have  a  more  elongated  form  than  the  rest,  and  are  placed 
either  vertically  or  at  an  acute  angle  with  the  membrane.  This  appears  to  be 
a  stage  of  transition  towards  the  structure,  which  is  afterwards  characteristic 
of  the  Dentine  ;  but  the  actual  nature  of  the  transformation  has  not  yet  been 
clearly  demonstrated.  As  the  outer  layer  of  cells  becomes  calcified,  those  of 
the  layer  beneath  elongate  themselves,  and  arrange  themselves  regularly  in 
preparation  for  the  same  change ;  and  so  on,  until  the  greater  part  of  the  pulp 
is  ossified.  Hence,  when  young  animals  are  fed  on  madder,  their  teeth  are 
marked  by  a  number  of  concentric  rings  of  colouring  matter. — As  already  men- 
tioned (§  635,  c),  the  Enamel  is  formed  by  the  calcification  of  the  prismatic  cells, 

42* 


498 


OF  NUTRITION. 


which  cover  the  interior  of  the  opercula  of  the  dental  sac,  like  an  Epithelium. 
These  opercula  attain  a  much  greater  development  in  the  Molar  teeth  of  Herbi- 
vorous animals ;  where  they  dip  down  into  the  midst  of  the  pulp,  and  give 
origin  to  the  vertical  plates  of  Enamel  already  mentioned  (§  633).  It  has  been 
remarked  by  Mr.  Lintott,  that  the  line  along  which  the  opercula  meet,  on  the 
crown  of  the  Human  molar  teeth, — that  is  to  say,  the  groove  which  separates 
their  tubercles,— is  by  far  the  most  frequent  seat  of  incipient  decay ;  probably 
from  its  tissue  having  been  at  the  first  least  perfectly  formed. — The  Cementum 
is  formed  by  the  transformation  of  the  inner  layer  of  the  dental  sac  itself;  or 
by  matter  effused  from  it  as  from  the  periosteum  of  Bone.  In  the  Human 
tooth,  it  is  formed  as  a  thin  layer  over  the  crown,  as  well  as  around  the  fang ; 
but  the  former  soon  wears  away.  In  the  teeth  of  Herbivorous  animals,  its 
vertical  plates  are  formed  from  the  Opercula ;  which,  as  just  mentioned,  dip 
down  into  the  dental  pulp.  The  amount  of  this  deposit  around  the  fangs  may 
be  very  much  increased  by  an  inflammatory  state  of  the  capsular  membrane  ; 
and  thus  are  produced  those  exostoses  which  are  often  very  troublesome  ap- 
pendages to  the  Teeth. 

637.  A  very  large  proportion  of  the  body,  in  the  higher  Animals,  is  com- 
posed of  a  tissue,  to  which  the  name  of  Cellular  is  ordinarily  given  ;  this  term, 
however,  is  so  much  more  applicable  to  those  structures  which  are  composed 
of  a  congeries  of  distinct  Cells,  and  the  use  of  it  for  both  purposes  is  likely  to 
engender  so  much  confusion,  that  it  is  to  be  wished  that  its  application  to  this 


[Fig,  132. 


[Fig.  133. 


The  two  elements  of  Areolar  tissue,  in  their  natural  rela- 
tions to  one  another;  l,the  white  fibrous  element,  with  cell- 
nuclei,  9,  sparingly  visible  in  it ;  2,  the  yellow  fibrous  ele- 
ment, showing  the  branching  or  anastomosing  character  of 
its  fibrillae;  3.  fibrilke  of  the  yellow  element,  far  finer  than 
the  rest,  but  having  a  similar  curly  character ;  8,  nucleolated 
cell-nuclei,  often  seen  apparently  loose.— From  the  areolar 
tissue  under  the  pectoral  muscle,  magnified  320  diameters.] 


Development  of  the  Areolar  tissue. 
(white  fibrous  element);  4,  nucleated 
cells,  of  a  rounded  form;  5.  G,  7,  the 
same,  elongated  in  different  degrees,  and 
branching.  At  7,  the  elongated  extremi- 
ties have  joined  others,  and  are  already 
assuming  a  distinctly  fibrous  character. 
(After  Sehwami.)] 


FORMATION  OF  THE  TISSUES AREOLAR  TISSUE.  499 

purpose  should  be  altogether  discontinued.  The  tissue  in  question,  now  gene- 
rally designated  the  Areolar,  is  found,  when  examined  under  the  Microscope, 
to  consist  of  a  network  of  minute  fibres  and  bands,  interwoven  in  every  direc- 
tion, so  as  to  leave  innumerable  interstices,  which  communicate  with  each 
other.  According  to  Messrs.  Todd  and  Bowman,  the  two  kinds  of  Fibrous 
tissue  which  elsewhere  exist  separately, — the  white,  and  the  yellow,— may 
be  detected  in  Areolar  tissue.  The  White  presents  itself  in  the  form  of  in- 
elastic bands,  the  largest  l-500th  of  an  inch  in  breadth,  somewhat  wavy  in 
their  direction,  and  marked  longitudinally  by  numerous  streaks  ;  these  streaks 
are  rather  the  indications  of  a  longitudinal  creasing  than  a  true  separation 
into  component  fibres;  for  it  is  impossible  by  any  art  to  tear  up  the  band  into 
filaments  of  a  determinate  size,  although  it  manifests  a  decided  tendency  to 
tear  lengthways.  These  bands  vary  considerably  in  size ;  the  smallest  re- 
quiring a  good  instrument  to  render  them  visible.  The  Yellow  fibrous 
element  exists  in  the  form  of  long,  single,  elastic,  branched  filaments,  with 
a  dark  decided  border,  and  disposed  to  curl  when  not  put  on  the  stretch. 
These  interlace  with  the  others,  but  appear  to  have  no  continuity  of  substance 
with  them.  They  are  for  the  most  part  between  1 -5000th  and  l-10,000th  of 
an  inch  in  thickness ;  but  they  are  often  met  with  both  larger  and  smaller. 
The  effect  of  Acetic  acid  upon  these  two  elements  is  very  different ;  the 
white  immediately  swells  up,  and  becomes  transparent ;  whilst  the  yellow 
remains  unchanged.  This  agent  frequently  brings  into  view  certain  oval 
corpuscles,  which  lie  in  the  midst  of  the  bands  and  threads,  and  which  some- 
times appear  to  have  delicate  prolongations  among  them.  These  are  usually 
supposed  to  be  the  persistent  nuclei  of  the  cells  from  which  the  tissue  was 
developed.  According  to  Henle,  the  fasciculi  or  bands  are  occasionally  con- 
stricted by  one  or  more  dark  filaments,  which  wind  spirally  round  them,  or 
encircle  them  with  distinct  rings  ;  these  are  termed  by  him  nucleus-filaments, 
from  his  idea  of  their  origin  (§  613).—- The  interstices  of  Areolar  tissue  are. 
filled  during  life  with  a  fluid,  which  resembles  very  dilute  Serum  of  the  blood ; 
it  consists  chiefly  of  water,  but  contains  a  sensible  quantity  of  common  salt 
and  albumen,  and  (when  concentrated)  a  trace  of  alkali  sufficient  to  affect  test- 
paper.— The  great  use  of  this  Tissue  appears  to  be,  to  connect  together  organs 
and  parts  of  organs  which  require  a  certain  degree  of  motion  upon  one  another; 
and  to  envelop,  fix,  and  protect,  the  blood-vessels,  nerves,  and  lymphatics, 
with  which  these  organs  are  to  be  supplied.  It  can  scarcely  be  said  to  enjoy 
any  vital  powers,  and  is  connected  solely  with  physical  actions  (§  611).  It  is 
extensible  in  all  directions,  and  very  elastic,  in  virtue  of  the  physical  arrange- 
ment of  its  elements  ;  and  it  posesses  no  contractility  beyond  that  of  the  vessels 
which  are  distributed  through  it.  It  cannot  be  said  to  be  endowed  with  sen- 
sibility ;  for  the  nerves  which  it  contains  seem  to  be  merely  en  route  to  other 
organs,  and  not  to  be  distributed  to  its  own  elements.  And  its  asserted  powers 
of  absorption  and  secretion  appertain  rather  to  the  walls  of  the  capillary  blood- 
vessels than  to  the  threads  and  bands  of  which  it  is  composed. — Areolar  tissue 
yields  Gelatin  by  boiling ;  but  this  is  derived  from  the  White  fibrous  element 
only ;  the  yellow  not  being  affected  by  the  process. 

638.  The  White  Fibrous  tissue  exists  alone  in  Ligaments,  Tendons,  Fibrous 
Membranes,  Aponeuroses,  &c. ;  where  it  presents  the  same  characters  as  those 
just  described, — except  that  the  bands  are  less  wavy,  and  frequently  quite 
straight,  so  that  it  is  inextensible.  It  receives  very  few  blood-vessels,  and  still 
fewer  nerves ;  indeed  it  would  seem  that,  in  many  structures  (as  tendons),  it 
is  totally  insensible.  It  seems  entirely  destitute  of  any  vital  property;  and 
its  chemical  nature  is  such,  that  it  needs  very  little  interstitial  change  to  main- 
tain its  normal  composition.  If  dried,  it  has  not  the  least  tendency  to  putrefy ; 
and  when  moist,  it  resists  the  putrefactive  process  more  strongly  than  any  of 


500  OF  NUTRITION. 

the  softer  textures.  The  peculiar  and  important  property  of  this  tissue  is  its 
capability  of  resisting  extension ;  and  we  find  it  in  situations  where  a  firm 
resistance  is  to  be  made  to  traction.  If  the  traction  be  applicable  in  one  direc- 
tion only,  as  in  Tendons  and  most  Ligaments,  we  find  the  bundles  of  fibres  or 
bands  arranged  side  by  side;  but  if  it  may  be  exerted  in  various  directions, 
the  fasciculi  cross  one  another,  as  in  Fibrous  Membranes.  The  reparation  of 
this  tissue  is  effected  by  the  interposition  of  a  new  substance,  every  way 
similar  to  the  original,  except  that  it  wants  its  peculiar  glistening  aspect,  and 
is  more  bulky  and  transparent. — The  Yellow  Fibrous  tissue  exists  separately 
in  the  middle  coat  of  the  Arteries,  the  Chordse  Vocales,  the  Ligamentum 
Nuchae  (of  quadrupeds),  and  the  Ligamenta  subflava;  and  it  enters  largely 
into  the  composition  of  some  other  parts.  It  differs  remarkably  from  the 
white,  in  the  possession  of  a  high  degree  of  elasticity ;  so  that  the  tissues 
which  are  composed  of  it  alone  are  among  the  most  elastic  of  all  known  sub- 
stances. There  is  less  tendency  to  spontaneous  decay  in  this  tissue  than  in 
any  othe*f  .of  the  softer  parts  of  the  fabric.  It  undergoes  scarcely  any  change 
by  long  boiling ;  a  very  small  quantity  only  of  Gelatin  being  yielded  by  it, 
which  is  perhaps  derived  from  the  Areolar  tissue  that  penetrates  it.  It  is  un- 
affected by  the  weaker  acids,  and  undergoes  no  solution  in  the  gastric  fluid ; 
and  it  preserves  its  elasticity  for  an  almost  unlimited  period.  It  requires  but 
little  renovation,  therefore,  in  the  living  body  ;  and  is  but  very  sparingly  sup- 
plied with  blood-vessels.  According  to  Scherer,  the  yellow  fiibrous  tissue 
from  the  middle  coat  of  the  Arteries  consists  of  48  C,38  H,  6  N,  16  O;  which 
may  be  regarded  as  1  Protein  +  2  Water.  When  burned,  it  leaves  1*7  per 
cent,  of  ashes. 

639.  These  elements  are  variously  combined  in  several  other  tissues.    Thus 
they  enter,  as  already  mentioned  (§  625),  into  the  composition  of  the  Fibro-Car- 
tilages.     And  they  form  a  large  proportion  of  the  tissues  known  as  Serous 
Membrane,  Mucous  Membrane,  and  Skin. — Serous  and  Synovial  Membranes 
belong,  both  structurally  and  chemically,  to  the  same  category  with  Areolar 
tissue.     When  examined  with  the  Microscope,  their  free  surface  is  found  to 
be  covered  with  a  single  layer  of  pavement-epithelium,  which  lies  on  a  con- 
tinuous sheet  of  basement-membrane.    Beneath  this  last  is  a  layer  of  condensed 
Areolar  tissue,  which  constitutes  the  chief  thickness  of  the  membrane,  and 
confers  upon  it  its  strength  and  elasticity ;  this  gradually  passes  into  that  laxer 
variety,  by  which  the  membrane  is  attached  to  the  parts  it  lines,  and  which  is 
commonly  known  as  the  sub-serous  tissue.     The  yellow  fibrous  element  enters 
largely  into  the  composition  of  the  membrane  itself;  and  its  filaments  interlace 
into  a  beautiful  network,  which  confers  upon  it  equal  elasticity  in  every  direc- 
tion.    The  membrane  is  traversed  by  blood-vessels,  nerves,  and  lymphatics,  in 
varying  proportions.     The  Serous  and  Synovial  membranes  form,  as  is  well 
known,  closed  sacs,  which  contain  a  greater  or  less  proportion  of  fluid.     The 
liquid  secreted  from  the  Serous  membranes  contains  as  much  as  7  or  8  per  cent, 
of  albumen  and  salts ;  and  it  is  distinctly  alkaline,  from  the  presence  of  car- 
bonate or  albuminate  of  soda.     The  Liquor  Amnii  and  the  fluid  of  Hydatids 
are  of  the  same  composition.     The  fluid  contained  in  the  Synovial  capsules, 
and  in  the  Bursse  Mucosae,  may  be  considered  as  serum  with  from  6  to  10  per 
cent,  of  additional  albumen ;  it  shows  an  alkaline  reaction.     The  fluid  of  Dropsy 
(at  least  in  some  forms  of  this  disease)  contains  in  addition  urea,  and  cholesterin 
suspended  in  fine  plates ;  also  (according  to  Dr.  Kane)  stearine  and  elaine. 

640.  The  general  term  Mucous  Membrane  may  be  applied  to  that  great 
system  of  membranous  expansions,  which  forms  the  external  tegument,  or 
Skin, — the  lining  of  the  internal  cavities  whose  walls  are  continuous  with  it, 
or  Mucous  Membrane  proper, — and  the  prolongations  of  this  into  the  secreting 
organs,  forming  the  tubes  and  follicles  of  the  Glands.     These  all  consist,  as 


FORMATION  OF  THE  TISSUES MUCOUS  MEMBRANES.  501 

Mr.  Bowman  has  justly  remarked,*  "  of  certain  elements  which  the  Anatomist 
may  detect  and  discriminate  ;  some  of  them  being  essential,  others  appended 
or  superadded  :  and  the  broad  characteristic  distinctions  between  these  struc- 
tures, appreciable  to  ordinary  sense, — as  well  as  the  innumerable  gradations 
by  which  they  everywhere  blend  insensibly  with  one  another, — are  solely  due 
to  various  degrees  and  kinds  of  modification  wrought  in  the  form,  quantity, 
and  properties  of  these  respective  elementary  parts." — The  Mucous  Mem- 
brane may  be  said,  like  the  Serous,  to  consist  of  three  chief  parts, — the  epithe- 
lium or  epidermis  covering  its  free  surface, — the  subjacent  basement-membrane, 
—and  the  areolar  tissue,  with  its  vessels,  nerves,  &c.,  which  forms  the  thick- 
ness of  the  membrane,  and  connects  it  to  the  adjacent  parts.  Of  the  Epithelium 
and  Epidermis,  a  general  description  has  been  already  given  (§§  621,  622). — 
The  cells  of  which  they  are  composed,  have  very  different  offiOs  in  the  dif- 
ferent situations  ;  on  the  Skin,  they  serve  only  for  protection ;  on  the  proper 
Mucous  Membranes,  they  secrete  a  protective  Mucus ;  and  in  the  Glandular 
tubuli  and  follicles  they  elaborate  the  peculiar  secretions  of  the  respective 
organs.  The  Basement- Membrane  may  be  frequently  demonstrated  with  very 
little  trouble,  in  the  tubuli  of  the  glands,  especially  the  kidney;  which  are  but 
very  slightly  adherent,  by  their  external  surface,  to  the  surrounding  tissue.*— 
Its  existence  on  the  Skin,  and  on  many  parts  of  the  proper  Mucous  Membrane, 
has  not  yet  been  fully  proved ;  but  there  can  be  no  reasonable  doubt  of  its 
continuity  in  these  situations. — These  two  elements  may  be  regarded  as  the 
essential  constituents  of  Mucous  Membrane ;  which  is  thus  found  to  be,  strictly 
speaking,  extra-vascular.  Its  difference  from  Serous  Membrane  must  be  con- 
sidered, therefore,  as  depending  rather  upon  its  arrangement,  and  upon  the 
peculiar  secretion  of  its  epithelium-cells,  than  upon  any  decided  anatomical 
character.  All  the  Mucous  Membranes  are  exposed  to  the  contact  of  irritating 
substances,  or  of  air  ;  and  the  secretion  which  they  form  seems  to  have  for  its 
special  object,  to  protect  them  from  these  sources  of  injury.  The  constant 
elaboration  of  it  requires  a  continual  renewal  of  its  Epithelium-cells ;  and 
hence,  whilst  those  of  Serous  Membranes  seem  to  have  considerable  perma- 
nence, those  of  Mucous  Membranes  are  being  continually  thrown  off  and 
reformed.  Where  this  secretion  is  required  in  great  abundance,  we  find  that 
the  surface  of  the  membrane  is  greatly  extended,  by  being  involuted  into  folli- 
cles, which  are  more  or  less  closely  set  together ;  these  follicles  are  lined  by  a 
layer  of  epithelium-cells,  continuous  with  that  of  the  free  surface ;  and  their 
secretion  is  destined  for  the  same  purpose.  In  some  parts  of  the  intestinal 
tube,  the  follicles  are  very  long,  and  are  closely  set  together  (§  704,  Fig.  170). 
641.  The  tissues  appended  to  these  elements,  and  less  essential  to  the  cha- 
racter of  Mucous  Membrane,  are  Capillary  Blood-vessels,  Absorbents,  Nerves, 
and  areolar  tissue.  The  former  are  almost  everywhere  abundant;  in  the 
Skin  they  seem  chiefly  destined  to  supply  the  nervous  papillae,  and  thus 
minister  to  its  acute  sensibility  (§  117) ;  whilst  in  the  Mucous  Membrane  of  the 
Alimentary  canal,  they  seem  more  concerned  in  the  functions  of  Absorption 
(§  463)  and  Secretion ;  and  in  the  Glandular  organs,  they  supply  the  mate- 
rials for  the  last-named  process.  The  Absorbents  are  most  abundant,  as 
Lymphatics,  in  the  Skin ;  and,  as  Lacteals,  in  the  Mucous  Membrane  of  the 
first  part  of  the  Intestinal  canal ;  but  the  Lymphatics  are  also  largely  distri- 
buted through  some  of  the  Glandular  organs.  The  Skin  is  the  only  part  of 
this  system,  which  is  largely  supplied  with  Nerves ;  except  the  Conjuctival 
Membrane,  and  the  Mucous  Membrane  of  the  Nose  :  hence  the  sensibility  of 
this  structure  is  usually  low,  although  its  importance  in  the  organic  functions 
is  so  great.  The  Areolar  tissue  of  Mucous  Membranes  usually  makes  up  the 
greatest  part  of  their  thickness ;  and  is  so  distinct  from  the  subjacent  layers,  as 

*  Cyclopaedia  of  Analomy  and  Physiology,  vol.  iii.  p.  485. 


502  OF  NUTRITION. 

to  be  readily  separable  from  them.  It  differs  not,  however,  in  any  important 
particular,  from  the  same  tissue  elsewhere  ;  and  the  white  and  yellow  fibrous 
elements  may  be  detected  in  it  in  varying  proportions,  in  different  parts, — the 
latter  being  especially  abundant  in  the  Skin  and  the  Lungs,  which  owe  to  it 
their  peculiar  elasticity.  Hence  the  Mucous  Membranes  for  the  most  part 
yield  Gelatin,  on  being  boiled.  There  is  some  reason  to  believe,  that  the  Skin 
also  contains  non-striated  muscular  fibres  scattered  through  it. — The  regene- 
ration of  all  the  forms  of  Mucous  Membrane,  after  loss  of  substance  by  disease 
or  injury,  is  very  complete,  and  takes  place  with  considerable  rapidity. 

642.  The  structure  of  the  Muscular  tissue  has  been  already  described  in 
detail  (Chap,  v.) ;  and  it  only  remains  here  to  add,  in  regard  to  its  origin  and 
development,  that  there  seems  reason  to  believe  that  the  primitive  fibres  are 
at  first  formed  by  the  junction  of  cells  of  a  cylindrical  shape ;  the  cavities  of 
which  coalesce,  so  as  to  become  a  continuous  tube, — the  Sarcolemma ;  whilst 
from  their  contents,  the  fibrillse  are  ultimately  generated.     Their  nuclei  may 
be  brought  into  view  in  the  fully-formed  fibre  (§  374) ;  but  are  seen  with  least 
difficulty  in  the  non-striated  fibres,  which  seem  like  striated   fibres  whose 
development  has  been  arrested. — If  the  view  which  has  been  given  (§  77) 
respecting  the  continual  death  and  decay  of  the  Muscular  tissue,  consequent 
upon  the  demand  for  its  vital  activity,  should  be  correct,  its  growth  must  be 
rapid,  even  in  the  adult ;  and,  as  the  difference  in  the  diameter  of  the  fibres 
at  various  ages  is  very  small,  there  must  be  a  continual  production  of  new 
tissue,  and  not  a  mere  expansion  of  the  old.    Notwithstanding  this,  it  is  doubtful 
whether  Muscular  tissue  is  ever  regenerated.     Wounds  of  muscles  are  united 
by  Areolar  tissue,  which  gradually  become  condensed,  but  its  fibres  do  not 
possess  any  degree  of  contractility. 

The  solid  matter  of  Muscle  consists  of  little  else  than  Fibrin;  as  will  be  seen  from  the 
following  analysis  by  Berzelius.  It  should  be  added,  however,  that  it  is  impossible  to 
separate  completely  the  vessels,  nerves,  areolar  tissue  and  blood,  from  the  muscular  fibre 
itself;  and  that  the  analysis  cannot,  therefore,  be  regarded  as  perfectly  accurate  in  regard 
lo  the  composition  of  the  essential  constituent. 

Fibrin 15-80 

Areolar  substance       --....  1-90 

Albumen  and  Heematosine          ....  2-20 

Alcoholic  extract  and  lactates     -        -        -        -  1-80 

Osmazome  (?)  and  watery  extractive          -        -  1-05 

Phosphate  of  lime  with  albumen         -        -        -  -08 

Water  and  loss 77-17 

100.00 

Thus  something  less  than  23  per  cent,  of  solid  matter  exists  in  ordinary  meat;  and  in 
100  parts  of  this  solid  matter  there  are  about  7£  parts  of  fixed  salts. 

643.  The  structure  of  the  Nervous  System,  also,  has  been  sufficiently  dwelt 
on  in  the  former  part  of  Volume  (§§  110 — 112).     The  production  of  its  tubes 
and  their  contents  from  cells,  appears  to  take  place  on  the  same  plan  as  that 
of  the  tubular  fibres  of  Muscle.     From  the  large  amount  of  Blood  with  which 
the  Nervous  System  is  supplied,  and  from  the  tendency  of  its  substance  to 
undergo  rapid  decomposition,  it  may  be  inferred  that  the  Nutritive  operations 
are  performed  in  this  tissue  with  great  activity ;  and  this  appears  to  be  espe- 
cially the  case  at  the  central  and  peripheral  terminations,  where  the  Blood- 
Vessels  are  most  intimately  connected  with  it.     Reason  has  been  given  (§  77) 
for  the  belief,  that  this  tissue,  like  the  muscular,  is  continually  undergoing 
waste  and  renewal ;  with  a  rapidity  proportional  to  the  demand  for  its  func- 
tional activity.     This  change  may  be  inferred  to  take  place  rather  in  the  gray 
substance  than  in  the  white;  the  functions  of  the  former  being  an  active 
generating  character,  whilst  those  of  the  latter  are  more  passive.     Appearances 


FORMATION  OF  THE  TISSUES MUCOUS  MEMBRANES.  503 

have  been  observed  by  Henle,  in  the  gray  matter  of  the  brain,  which  have  led 
him  to  the  belief,  that  the  ganglionic  globules  or  nucleated  cells  are  being 
continually  developed  on  the  exterior,  and  advance  progressively  towards  the 
deeper  layers,  where  they  replace  those  which  have  become  disintegrated, 
and  in  their  turn  undergo  the  same  change. — The  regeneration  of  Nervous 
tissue  is  performed  more  completely  than  that  of  any  other  that  is  so  highly 
organized.  The  degree  to  which  it  takes  place  has  been  a  question  among 
Physiologists  ;  but  many  facts,  well  known  to  Surgeons,  prove  that  it  must  be 
complete.  For  it  will  scarcely  be  denied  that  the  complete  recovery  of  the 
functions  of  a  Nervous  trunk  or  fibre  indicates  that  the  continuity  of  its  com- 
ponent tubes  has  been  restored ;  since  all  we  know  of  the  transmission  of 
Nervous  influence  leads  to  the  belief  that  such  complete  continuity  is  requisite. 
In  the  various  operations  which  are  practised  for  the  restoration  of  lost  parts, 
a  portion  of  tissue  removed  from  one  spot,  is  grafted,  as  it  were,  upon  another ; 
its  original  attachments  are  more  or  less  completely  severed, — frequently  en- 
tirely destroyed,— and  new  ones  are  formed.  Now  in  such  a  part,  as  long  as 
its  original  connections  exist,  and  new  ones  are  not  completely  formed,  the 
sensation  is  referred  to  the  spot  from  which  it  was  taken ;  but  after  an  interval, 
during  which  it  frequently  loses  all  sensibility,  its  power  of  feeling  is  restored, 
and  the  sensations  received  through  it  are  referred  to  the  right  spot.  A  more 
familiar  case  is  the  regeneration  of  Skin,  containing  sensory  nerves,  which 
takes  place  in  the  well-managed  healing  of  wounds  involving  loss  of  substance 
(§  599).  A  more  striking  example  of  regeneration  of  Nervous  tissue,  how- 
ever, is  to  be  found  in  those  cases  (of  which  there  are  now  several  on  record), 
in  which  portions  of  the  extremities  that  have  been  completely  severed  by 
accident,  have  been  made  to  adhere  to  the  stump,  and  have,  in  time,  com- 
pletely recovered  their  natural  connection  with  the  circulating,  nervous,  and 
other  systems.  The  rapid  production  of  Nervous  substance  in  particular 
cases,  is  evidenced  by  Dr.  R.  Lee's*  recent  investigations  on  the  nerves  of 
the  pregnant  Uterus.  Not  only  Nerves,  but  Ganglia  of  considerable  size,  that 
seem  to  have  no  existence  under  other  circumstances,  are  then  apparent. 

The  Chemical  composition  of  the  Brain  has  occupied  much  attention;  and  the  fol- 
lowing is  an  outline  of  the  most  recent  account  of  it,  that  of  M.  Fremy.f  In  100  parts 
of  Cerebral  matter,  there  exist  80  of  water,  7  parts  of  albumen  (or  rather  fibrin),  and  5 
parts  of  fatty  matter.!  This  statement  agrees  with  that  of  many  previous  analysts;  and 
it  is  chiefly  with  the  fatty  matter  that  the  attention  of  Chemists  has  been  occupied.  This 
is  stated  by  M.  Fremy  to  contain,  besides  the  ordinary  fatty  substances,  two  peculiar 
Acids,  termed  the  Cerebric  and  Oleophosphoric. — Cerebric  acid,  when  purified,  is  white, 
and  presents  itself  in  crystalline  grains.  It  contains  a  small  proportion  of  Phosphorus; 
and  differs  from  the  ordinary  fatty  matter  in  being  partly  composed  of  Nitrogen.  It  is 
composed  of  66-7  per  cent,  of  carbon,  10-6  of  hydrogen,  2-3  of  nitrogen,  19-5  of  oxygen, 
and  0-9  of  phosphorus ;  and  thus,  comparing  it  with  the  ordinary  fatty  acids,  contains 
more  than  twice  their  proportion  of  oxygen. — Oleophosphoric  acid  is  separated  from  the 
former  by  its  solubility  in  ether;  it  is  of  a  viscid  consistence;  but,  when  boiled  for  a  long 
time  in  water  or  alcohol,  it  gradually  loses  its  viscidity,  and  resolves  itself  into  a  fluid 
oil,  which  is  pure  oleine,  while  phosphoric  acid  remains  in  the  liquor.  The  proportion 
of  Phosphorus  which  this  acid  contains  is  about  2  per  cent.— Cholesterine  (§  662)  has 
also  been  extracted  from  the  brain  by  M.  Fremy,  in  considerable  quantity. — On  the  whole, 
the  proportion  of  Phosphorus  in  the  brain  appears  to  be  about  1  per  cent.;  a  small 
quantity  of  Sulphur  is  also  present.  The  proportion  of  Fixed  Salts  is  small,  being  not 
above  3£  parts  in  100  of  dry  Cerebral  matter;  which  is  less  than  half  the  proportion 
that  exists  in  Muscle. 


*  Proceedings  of  the  Royal  Society,  June  17, 1841 ;  and  Phil.  Trans.  1841,  Part  ii. 

•j-  Graham's  Chemistry  [Am.  ed.,  p.  713].  It  is  there  stated  that  the  analytic  method  of 
M.  Couerbe  was  very  defective. 

$  According  to  Lassaigne,  the  chemical  composition  of  the  Cortical  and  Medullary 
substance  is  essentially  different;  the  former  containing  much  more  water  than  the  latter, 
and  little  colourless  fat,  but  nearly  4  per  cent,  of  red  fat,  which  does  not  exist  in  the  other. 


504  OF  NUTRITION. 

644.  From  the  foregoing  details  the  obvious  inference  results,— that  each 
part  of  the  organism  has  an  individual  Life  of  its  own,  whilst  contributing  to 
uphold  the  general  Life  of  the  entire  being.     This  Life,  or  state  of  Vital  Action, 
depends  upon  the  due  performance  of  the  functions  of  all  the  subordinate 
parts,  which  are  closely  connected  together.     The  lowest  classes  of  organized 
beings  are  made  up  of  repetitions  of  the  same  elements ;  and  each  part,  there- 
fore, can  perform  its  functions  in  great  degree  independently  of  the  rest.     But, 
in  ascending  the  scale,  we  find  that  the  lives  of  the  individual  parts  become 
gradually  merged  (so  to  speak)  in  the  general  life  of  the  structure ;  for  these 
parts  gradually  become  more  and  more  different  in  function,  and  therefore 
more  and  more  dependent  on  each  other  for  their  means  of  support ;  so  that 
the  activity  of  all  is  necessary  for  the  maintenance  of  any  one.     Hence  the 
interruption  of  the  function  of  any  important  organ  is  followed  by  the  Death 
of  the  whole  structure  ;  because  it  interferes  with  the  elaboration,  circulation, 
or  purification  of  that  nutritious  fluid  which  supplies  the  pabulum  for  the 
growth  and  reproduction  of  the  individual  parts.     But  their  lives  may  be  pro- 
longed for  a  greater  or  less  duration,  after  the  suspension  of  the  regular  series 
of  their  combined  actions  ;  hence  it  is,  that  molecular  Death  is  not  always  an 
immediate  sequence  of  somatic  Death.*      But  if  the  function  of  the  part 
have  no  immediate  relation  to  the  indispensable  actions  just  adverted  to,  it  may 
cease  without  affecting  them ;  so  that  Molecular  death  may  take  place,  to  a  con- 
siderable extent,  without  Somatic  death  necessarily  resulting. 

645.  The  doctrine  of  Development  from  Cells  has  another  important  bearing 
on  the  Philosophy  of  Physiology.     It  gives  us  a  clearer  idea  of  the  nature  of 
the  continual  processes  of  decay  and  renewal,  which  take  place  in  the  Animal 
body.     Every  Cell  has,  to  a  certain  degree,  an  individual  life  of  its  own. 
This  individuality  is  much  more  decided  in  the  lower  forms  of  organized  being, 
where  each  cell  can  maintain  an  independent  existence,  than  it  is  in  the  higher, 
in  whose  fabric  a  large  number  having  different  functions  are  united  into  one 
structure,  the  combined  activity  of  the  whole  of  which  is  necessary  to  the  life 
of  any  one.     But,  even  in  the  highest,  it  is  evident  that  each  cell  will  possess 
a  certain  duration  of  its  own ;  and  that,  from  its  first  period  of  development, 
all  the  changes  which  it  undergoes  are  governed  by  laws  peculiar  to  it.     In  the 
various  parts  of  the  Vegetable,  as  in  those  of  the  Animal,  we  find  a  great  dif- 
ference in  the  duration  of  the  existence  of  the  cells  composing  them.     These 
differences  may  be  reduced  to  five  heads. 

I.  Cells  may  be  generated,  which  have  a  very  transient  existence,  and  which 
disappear  again,  without  reproducing  themselves,  or  undergoing  any  trans- 
formation.    This  may  be  seen  in  the  Vegetable  ovule,  and  in  the  Germinal 
Vesical  of  the  Animal  Ovum ;  as  well  as  in  many  other  parts.     Thus  we  have 
absorbent  Cells  (§  461),  secreting  Cells  (§  651),  and  probably  Assimilating 
or  Fibrin-elaborating  Cells  (§  578) ;   all  of  which  originate  in  pre-existing 
germs,  attain  their  full  development  (in  the  course  of  which  they  perform  their 
allotted  function),  and  then  disappear  by  rupture  or  liquefaction.     In  such  in- 
stances it  is  obvious  that,  from  their  first  origin,  the  cells  are  subject  to  a  law 
of  limited  duration,  and  that  their  death  and  decay  are  as  much  the  result  of 
their  inherent  constitution,  as  are  those  of  each  entire  Animal  or  Vegetable  or- 
ganism. 

II.  The  contrary  extreme  to  this  may  be  found  in  those  Cells  of  which  the 
function,  instead  of  being  transient,  is  to  be  indefinitely  prolonged ;  such  are 
those  of  which  the  organs  of  mechanical  support  are  usually  formed.     Here 
the  cell,  instead  of  changing  its  form,  or  of  giving  origin  to  new  cells  within 
itself,  becomes  the  subject  of  an  internal  deposit  of  hard  matter,  which  lines 

*  Cyclop,  of  Anat.  and  Phys.,  vol.  i.  Art.  Death. 


FORMATION  OF  THE  TISSUES— GENERAL  CONCLUSIONS.  505 

its  walls,  and  cuts  it  off,  more  or  less  completely,  from  the  general  course  of 
Vital  Action.  When  this  is  the  case,  and  the  hard  matter  is  not  itself  liable  to 
decomposition,  the  duration  of  the  cell-walls,  which  are  protected  by  their  pe- 
culiar aggregation  from  exposure  to  decomposing  agents,  may  undergo  little  or 
no  change  for  an  almost  indefinite  period.  Thus  the  heart-wood  of  Plants,  the 
Bones  of  Animals,  and  still  more  their  Hair,  Hoofs,  Horns,  &c.,  may  remain 
unaltered  through  a  long  series  of  years.  Of  some  of  these  parts  it  can  scarcely 
be  said  that  they  are  less  alive,  when  removed  from  the  organism  to  which 
they  belonged,  than  when  included  in  it.  In  the  heart-wood  of  a  Plant,  for 
example,  no  vital  change  takes  place  from  the  time  that  the  woody  tubes  and 
cells  are  once  consolidated  by  internal  deposition ;  it  may  decay  whilst  still 
forming  part  of  the  stem,  without  interfering  with  the  nutritive  operations  of 
the  tree  ;  and  if  we  could  possibly  remove  it  entirely,  without  doing  injury  by 
the  operation  to  the  rest  of  the  structure,  its  absence  would  be  productive  of 
no  other  evil  consequences  than  those  which  would  necessarily  result  from  the 
withdrawal  of  the  mechanical  support  afforded  by  it.  The  same  may  be  said 
of  the  Epidermic  Appendages  of  Animals,  and  of  the  External  Skeletons  of 
many  Invertebrata ;  which  remain  equally  unchanged  from  the  time  of  their 
first  formation. — Now  as  long  as  these  structures  hold  together,  it  is  evident 
that  the  organized  part  of  them  must  have  undergone  little  change  from  the 
condition  in  which  it  existed  in  the  living  fabric ;  and  that  their  death  takes 
place,  in  reality,  only  when  the  structures  decay, — this  decay  being,  in  fact, 
the  consequence  of  it.  The  law  of  existence  of  such  cells,  therefore,  is  that 
of  indefinitely  prolonged  duration ;  this  law  must  have  been  impressed  upon 
them  from  their  origin  ;  and  the  power  by  which  their  walls  secrete  and  de- 
posit the  consolidating  materials,  appears  to  be  the  chief  means  of  keeping  it 
in  operation. 

III.  In  all  the  higher  forms  of  Animal  structure,  the  Cells  originally  com- 
posing it  are  only  the  means  of  generating  tissues  of  other  kinds,  in  which  the 
Cellular  character  is  less  obvious.     Thus  the  Muscular  and  Nervous  tissues 
have  their  origin  in  cells,  which  at  first  appear  in  no  respect  different  from 
others,  but  which  subsequently  undergo  a  peculiar  metamorphosis,  and  them- 
selves no  longer  exist  as  such.     Upon  all  these  primordial  cells,  therefore,  a 
law  of  transformation  is  impressed,  from  the  time  of  their  first  production.    In 
their  original  aspect,  they  cannot  be  distinguished  from  the  cells  which  are  not 
destined  to  undergo  any  such  metamorphosis  ;  but,  just  as  the  first  cell  of  the 
embryo,  from  which  man  is  produced,  must  have  some  real  though  not  appa- 
rent difference  from  that  in  which  the  Polype  originates,  so  must  the  cell  which 
is  afterwards  developed  into  Muscular  Fibre  be  inherently  different  from  that 
which  is  subsequently  converted  into  Nervous  Tissue. 

IV.  The  tissues  thus  formed  by  the  transforming  processes  to  which  certain 
Cells  are  subject,  are  evidently  governed  by  the  same  laws  of  Nutrition  as 
those  which  regulate  ordinary  Cell-growth ;  these  are  modified  in  their  action, 
however,  by  the  conditions  in  which  they  are  placed,  in  regard  to  the  activity 
of  the  function  which  the  Tissue  is  called  upon  to  perform.     In  all  instances, 
however,  these  Tissues  have  a  definite  period  of  existence.— They  are  gene- 
rated, they  grow  from  the  alimentary  materials  with  which  they  are  supplied, 
they  arrive  at  maturity,  they  decline,  they  die,  and  they  decay  ;  just  as  do  the 
isolated  vesicles  constituting  the  humblest  forms  of  vegetation.    For  all  of  them 
there  is  an  appointed  duration  of  life,  just  as  there  is  for  the  entire  Man. — Now 
on  this  view,  we  can  explain  many  physiological  phenomena,  which  cannot 
otherwise  be  very  satisfactorily  accounted  for.     It  is  owing  to  the  continual 
death  and  decay  of  its  component  cells,  that  the  process  of  decomposition  goes 
on  with  such  constancy  and  uniformity  in  the  living  body ;  whilst,  on  the  other 
hand,  it  is  by  the  continual  reproduction  of  new  cells,  in  the  place  of  those 

43 


506  OF  NUTRITION. 

which  have  disappeared,  that  the  normal  organization  is  maintained.  The 
limited  duration  of  the  life  of  the  cells  composing  the  various  tissues  is  further 
made  evident  by  the  rapid  disappearance  of  the  normal  organization,  and  by 
the  loss  of  the  functional  power  of  those  tissues,  when  the  deficiency  of  the 
required  stimuli  prevents  the  development  of  the  new  cells,  by  which  alone 
their  character  can  be  maintained.  Of  the  change  of  structure  and  loss  of 
power  which  result  from  disuse  and  consequent  want  of  nutrition,  in  Muscu- 
lar and  Nervous  Tissues,  instances  have  already  been  given  (§§  221  and  382). 
The  ordinary  processes  of  Decomposition  and  Interstitial  Absorption  are  pro- 
bably less  rapid  than  usual  under  such  circumstances  ;  so  that  the  length  of 
time  required  for  the  disappearance  of  the  characteristic  structure,  and  the 
consequent  loss  of  functional  power,  affords  us  some  idea  of  the  limit  to  the 
duration  of  the  life  of  the  tissue.  It  may  be  stated,  then,  as  a  general  propo- 
sition, that  the  interstitial  change  which  the  whole  structure  of  the  body  is,  in 
its  normal  or  physiological  condition,  continually  undergoing,  is  due  to  the 
regularly  occurring  death  and  reproduction  of  its  component  cells,  of  which 
every  one  has  its  own  limit  of  duration.  We  uniformly  find  that  those  Tis- 
sues in  which  the  most  active  vital  changes  are  going  on  (such  as  the  Nervous 
and  Muscular),  are  those  in  which  the  duration  of  the  individual  component 
portions  is  the  least ;  as  is  shown  by  the  rapidity  of  the  changes  of  removal 
and  reposition,  which  are  continually  taking  place  in  them.  The  converse 
holds  good  also.  Further  it  may  be  remarked, — and  this  is  a  matter  of  much 
practical  importance,—- that  any  thing  which  increases  the  functional  activity 
of  any  particular  tissue,  thus  causing  it  to  live  faster,  diminishes  the  duration 
of  its  life  ;  as  is  shown  in  the  increased  demand  for  nourishment,  which  is  set 
up  as  a  consequence  of  the  continued  exercise  of  the  Muscular  or  Nervous 
system,  and  which,  being  far  greater  than  can  be  required  for  such  increase  of 
their  amount  as  results  from  that  exercise,  necessarily  indicates  that  a  corre- 
sponding removal  of  effete  matter,  resulting  from  the  death  of  the  cells,  has 
taken  place. 

V.  There  is  yet  another  phase  under  which  Cellular  life  presents  itself  as 
a  natural  condition  in  the  lower  organisms,  and  in  the  early  condition  of  the 
higher ;  but  which  constitutes  a  morbid  state  in  the  adult  condition  of  the 
latter.  This  is  when  cells  reproduce  themselves  with  extreme  rapidity, — 
neither  the  primary  nor  secondary  cells  undergoing  any  further  transformation, 
— and  the  duration  of  each  individual  being  limited  by  the  development  of  its 
progeny  within  it,  causing  its  own  distension  and  final  rupture  or  disappear- 
ance. The  growth  of  the  lower  Fungi  offers  a  striking  example  of  this  in  the 
Vegetable  kingdom ;  and  the  early  processes  of  development  in  the  Ovum  of 
the  highest  Animals,  exhibit  the  same  character.  Every  cell,  as  it  is  gene- 
rated, proceeds  at  once  to  the  work  of  multiplication,  for  which  it  seems 
specially  destined ;  and  thus  it  is  subject  from  the  first  to  the  ]aw  of  Repro- 
duction. It  is  this  which  distinguishes  the  Fungoid  diseases ;  which  derive 
the  character  designated  by  the  Surgeon  as  malignancy  simply  from  their 
tendency  to  propagation,  and  his  want  of  power  to  control  it.  It  seems  pro- 
bable that  many  other  changes  of  structure  are  due  to  a  corresponding  cause. 

646.  The  duration  of  the  existence  of  the  individual  Cells  in  corresponding 
parts,  is  further  subject  to  variation,  in  accordance  with  the  period  of  life  of 
the  entire  organism.  Thus  all  the  tissues,  even  those  most  consolidated,  are 
undergoing  continual  changes  in  the  young  animal,  in  which  the  processes  of 
decay  and  renewal  go  on  much  faster  than  in  the  adult ;  and  in  the  adult  than 
in  the  aged  person.  Even  the  cells  of  the  Bony  structure,  which  in  the  adult 
are  almost  permanent,  and  in  the  aged  person  are  subject  to  extremely  little 
change,  are  liable  in  the  infant  to  an  early  decomposition  ;  their  places  being 
filled  up  by  others,  of  which  the  form  adapts  itself  to  the  growth  of  the  struc- 


OF  SECRETION  IN  GENERAL.  507 

ture.  This  may  be  partly  accounted  for  by  the  imperfect  degree  in  which,  so 
long  as  the  entire  organism  is  undergoing  rapid  increase,  the  normal  structure 
is  developed  in  any  one  portion  of  it;  for  the  degree  of  consolidation  bcin^- 
less,  the  tendency  to  decay  will  naturally  be  greater.  But  this  explanation  is 
not  in  itself  sufficient ;  and  we  must  be  content  for  the  present  to  regard  it  as 
a  general  law  (which  may  ultimately  prove  to  be  but  a  result  of  some  more 
general  principle),  that  the  duration  of  the  existence  of  individual  cells  in- 
creases, cseteris  paribus,  with  the  advance  of  life.  At  the  same  time,  their 
functional  activity  diminishes.  They  may  be  said  to  live  more  slowly.  The 
dull  perceptions,  and  slow  and  feeble  movements  of  the  aged  man,  form  a 
striking  contrast  with  the  acute  sensibility,  and  the  rapid  and  vigorous  mus- 
cular actions  of  the  child  ;  and  the  same  change  may  be  noticed  in  the  organic 
functions.  Hence  it  may  be  stated  as  a  general  law,  that  the  vital  activity  of 
the  Cells  (and  of  the  tissues  produced  by  their  transformation)  diminishes  in 
proportion  to  the  prolongation  of  life ;  and  this  law  exactly  corresponds  with 
what  has  just  been  observed  as  to  the  comparison  of  the  tissues  of  different 
kinds,  which  are  present  in  the  same  body. 


CHAPTER    XII. 

OF    SECRETION. 

I.  Of  Secretion  in  General. 

647.  THE  literal  meaning  of  the  term  Secretion  is  separation  ;  and  this  is 
nearly  its  true  acceptation  in  Physiology.  We  have  seen  that  the  Nutritive 
materials,  which  are  received  into  the  living  body,  are  combined  in  a  certain 
proportion  in  the  circulating  fluid ;  and  that  they  are  carried  in  its  current  to 
every  part  of  the  structure.  A  part  of  the  elements  of  the  Blood, — probably 
the  Fibrin  and  mineral  matter  exclusively, — are  being  continually  separated 
from  it,  and  introduced  into  the  solid  textures,  of  which  they  become  consti- 
tuents ;  forming,  as  it  were,  the  organized  framework,  in  the  interstices  of 
which  various  other  matters  (also  separated  from  the  blood)  are  deposited  in 
an  inorganic  condition.  This  separation,  the  object  of  which  is  to  build  up  a 
living  fabric,  has  been  already  considered  under  the  head  of  Nutrition ;  but  it 
may  be  here  remarked,  that  the  deposition  of  Calcareous  matter  in  the  Bones 
and  Teeth,  of  Chondrin  and  Gelatin  in  the  Bones  and  Cartilages,  and  of  Horny 
matter  in  the  cells  of  the  Epithelium  and  its  appendages  (Hair,  Nails,  Hoofs, 
&c.),  is  accomplished  by  a  process  analogous  in  all  respects  to  that  concerned 
in  the  separation  of  those  other  products  which  are  ordinarily  considered  as 
Secretions.  The  same  may  be  said  of  the  Serous  fluid,  which  distends  the 
interspaces  of  areolar  tissue,  the  Oily  matter  contained  in  the  Fat-cells,  the 
Albuminous  fluid  of  the  Humours  of  the  Eye,  and  other  analogous  constituents 
of  the  living  fabric.  But  we  have  chiefly  to  consider  under  the  present  head, 
the  nature  and  origin  of  these  products,  which  are  continually  being  cast  forth 
from  the  living  body ;  the  amount  of  which  is  usually,  in  the  adult  animal, 
equal  to  that  of  the  solids  and  fluids  ingested,  after  allowance  has  been  made 


508  OF  SECRETION. 

for  the  portion  rejected,  in  the  form  of  faoces,  as  indigestible.  The  experi- 
ments of  Dr.  Dalton*  on  his  own  person,  giVe  the  following  as  the  proportional 
quantities  discharged  through  the  principal  channels  of  excretion.  The  mean 
quantity  of  solid  and  fluid  Aliment  taken  into  the  system  daily  (during  14  days 
in  spring^)  being  91  oz.,  or  about  5f  Ibs.,  the  average  amount  of  Faeces  (in- 
cluding me  solid  matter  of  the  bile)  was  5  oz. ;  the  average  amount  of  Urine 
was  48i  oz.  daily ;  and,  as  the  total  weight  of  the  body  remained  the  same, 
the  quantity  of  fluid  and  solid  matter  excreted  by  the  Skin  and  the  Lungs 
must  have  been  37£  oz.  At  other  periods  of  the  year,  a  variation  was  ob- 
served ;  especially  in  the  relative  amount  of  fluid  passing  off  by  the  Urine, 
and  by  Cutaneous  exhalation. 

648.  It  can  scarcely  be  questioned,  that  the  chief  source  of  the  Excretions 
is  to  be  found  in  the  continued  Decomposition  of  the  various  tissues  of  the 
body,  which  has  been  several  times  alluded  to  (§§  84  and  645) ;  and  it  is 
probable,  from  considerations  heretofore  adduced,  that  they  are  derived, not  so. 
much  from  the  fluid  returned  into  the  blood  by  the  Lymphatics  (as  formerly 
supposed),  as  from  the  blood  itself  (§  469).  It  has  been  pointed  out  by  Lie- 
big,  that  there  is  a  remarkable  correspondence  between  the  elements  of  the 
Blood  and  those  of  the  Bile  and  Urine  taken  together;  so  that  the  Tissues, 
which  are  all  formed  from  the  nutritious  fluid,  may  be  regarded  as  resolving 
themselves,  by  their  ultimate  decomposition,  into  these  two  excretions.  More- 
over, the  Blood,  during  its  circulation,  gives  up  one  portion  of  its  constituents 
in  one  part  of  the  body — another  at  a  different  situation, — and  so  on.  Thus, 
the  elaboration  of  Gelatin,  which  is  deposited  so  largely  in  the  solid  tissues, 
must  occasion  a  considerable  alteration  in  the  blood:  since,  in  its  production 
from  Albumen,  a  certain  residuum  must  be  left  (§  615).  This  residuum  is 
probably  another  important  source  of  the  products  of  Excretion.  The  same 
may  be  remarked  in  regard  to.  the  Nutrition  of  the  Nervous  System  (§  643). 
In  several  other  instances,  peculiarities  of  action  in  different  parts  will  deprive 
the  Blood  that  passes  through  them  of  its  due  proportion  of  certain  of  its  con- 
stituents ;  these  are  partly  restored  by  its  admixture  in  the  Heart,  with  the 
Blood  that  has  returned  from  other  parts  ;  but  still  a  general  alteration  in  the 
character  of  the  Blood  is  the  result  of  its  Circulation ;  and  for  this  alteration, 
it  is  the  province  of  the  Excretory  function  to  compensate.  A  striking  illus- 
tration may  be  found  in  the  change  of  the  colour  and  of  the  proportional 
amount  of  free  Oxygen  and  Carbonic  Acid,  which  takes  place  in  the  Systemic 
capillaries,  and  which  is  reversed  in  the  passage  of  the  Blood  through  the 
Lungs  (§  520). — Moreover,  it  appears  that  two,  at  least,  of  the  Excreting 
organs  have  for  their  function  to  prevent  the  accumulation  in  the  Blood,  of 
matters  which  have  been  taken  in  as  food,  but  for  which  there  is  no  demand 
in  the  economy.  Thus  the  Liver  appears  to  be  the  peculiar  channel  for  the 
elimination  of  superfluous  non-azotized  matter  (§  664) ;  and  the  Kidney  of 
these  azotized  compounds,  which  cannot  be  worked  up  (so  to  speak)  into 
tissue  (§  679).  Particular  sources  for  the  respective  contents  of  other  Excre- 
tions will  be  pointed  out  when  they  are  considered  in  detail. 

649.  A  distinction  has  already  been  drawn  (§  95)  between  the  proper  Ex- 
cretions, the  retention  of  which  in  the  Blood  would  be  positively  injurious, 
and  those  Secretions  which  are  destined  for  particular  purposes  within  the 
system,  and  the  cessation  of  which  has  no  immediate  influence  on  any  but 
the  function  to  which  they  are  destined.  This  distinction  is  one  of  great 
importance,  especially  when  it  is  considered  with  reference  to  the  Chemical 
Elements  that  are  found  in  the  two  classes  of  fluids  respectively.  The  solid 
matter  dissolved  in  those  of  the  latter  class,  is  little  else  than  a  portion  of  the 

*  Edinburgh  New  Philosophical  Journal,  1832,  1833. 


OF  SECRETION  IN  GENERAL.  509 

constituents  of  the  Blood,  either  pure,  or  but  slightly  altered ;  thus,  in  the 
Lachrymal  fluid,  the  Saliva,  the  Pancreatic  juice,  the  Serous  fluid  of  areolar 
tissue  and  of  serous  and  synovial  membranes,  we  'find  little  else  than  Albu- 
minous and  Saline  matter,  derived  at  once  from  the  blood.  The  Casein, 
which  is  the  most  characteristic  ingredient  of  milk  (§  680),  is  but  a  slightly 
altered  form  of  Albumen  ;  and  some  curious  evidence  has  recently  been  ob- 
tained, that  this  alteration  commences  in  the.  Blood,  and  goes  on  during 
pregnancy  as  a  preparation  for  lactation-.*  On  the  other  hand,  the  character- 
istic ingredients  of  the  Excretions  are  very  different  in  character  from  the 
normal  elements  of  the  Blood.  They  are  all  of  them  completely  unorgani- 
zable ;  and  they  possess,  for  the  most  part,  a  simple  atomic  constitution.  Some 
of  them,  also,  have  a  tendency  to  assume  a  crystalline  form,  which  is  consi- 
dered by  Dr.  Prout  to  indicate  their  unfitness  to  enter  into  the  composition  of 
organized  tissues.  With  regard  to  some  of  the  chief  of  these,  there  is  sufficient 
evidence  of  their  existence,  in  small  quantity,  in  the  circulating  Blood;  but  it 
is  also  clear,  that  they  exist  there  as  products  of  decomposition,  and  that  they 
are  destined  to  be  separated  from  it  as  speedily  as  possible.  If  their  separa- 
tion be  prevented,  they  accumulate,  and  communicate  to  the  circulating  fluid 
a  positively  deleterious  character.  .Of  this,  we  have  already  seen  a  striking- 
example  in  the  case  of  Asphyxia  (§  546) ;  and  the  history  of  the  other  two 
principal  Excretions, — the  Bile  and  Urine, — will  furnish  evidence  to  the  same 
effect.  As  a  general  fact,  then,  it  may  be  stated  that  the  materials  of  the  Se- 
cretions pre-exist  in  the  Blood,  in  a  state  nearly  resembling  that  in  which  they 
are  thrown  off  by  the  secreting  organs  ;  but  that  the  materials  of  those  secre- 
tions, which  are  only  destined  to  perform  some  particular  function  in  the 
economy,  are  derived  from  the  substances  which  are  appropriated  to  its  gene- 
ral purposes  ;  whilst  those  of  the  excretions  are  the  result  of  the  changes  that 
have  taken  place  in  the  system,  and  cannot  be  retained  in  it  without  injury. 
650.  Of  the  reason  why  certain  compounds  forming  part  of  the  circulating 
Blood,  are  separated  from  it  by  one  organ,  and  others  by  a  different  one,  no- 
thing whatever  is  known ;  arid  there  is  nothing  in  the  evident  structure  of 
Glands  that  can  afford  any  clue  to  the  attainment  of  such  knowledge.  When 
their  ultimate  structure  is  considered,  it  is  found  to  be  neither  more  nor  less 
than  a  vascular  membrane,  covered  with  epithelium-cells,  and  made  up  into 
various  forms  for  convenience  of  packing.  Of  such  a  membrane,  in  its  most 
expanded  state,  that  which  composes  the  walls  of  the  Serous  cavities,  or  of  the 
Synovial  capsules,  affords  a  good  example  ;  and  the  fluid  which  these  cavities 
contain  is  secreted  by  it.  Of  Mucous  membrane,  the  structure  is  in  some  in- 
stances almost  equally  simple  ;  but  in  general  the  secreting  surface  is  extended 
by  the  inversion  of  the  membrane  into  a  large  number  of  little  open  sacs  or  folli- 
cles, which  are  copiously  supplied  with  blood-vessels,  and  are  equally  con- 
cerned with  the  external  superficies,  in  the  elaboration  of  the  protective  secre- 
tion that  covers  these  membranes.  In  the  most  complex  form  of  gland,  we 
find  nothing  but  a  very  obvious  modification  of  this  structure.  Either  the 
sacs  are  prolonged  into  coeca  or  blind  tubes,  as  is  the  case  in  the  Human 
Kidney  or  Testis ;  or  they  are  very  greatly 'multiplied,  and  are  clustered 
together  (just  like  currants  upon  a  stalk)  upon  efferent  ducts  common  to 
several  of  them,  as  is  seen  in  the  Parotid.  Now,  that  the  particular  modi- 
fication of  structure,  which  the  Gland  may  present,  has  no  essential  connection 
with  the  character  of  the  Secretion  it  is  destined  to  form,  is  evident  from  this 
circumstance, — that  almost  every  gland  may  be  found  under  a  variety  of  forms, 
in  different  parts  of  the  Animal  series.  The  Secreting  system,  like  every 

*See  Dr.  G.  Bird,  in  Guy's  Hospital  Reports,  vol.  v. 
43* 


510  OF  SECRETION. 

other,  is  far  simpler  in  the  lower  classes  of  Animals  than  in  the  higher ;  the 
number  of  effete  compounds,  to  be  excreted  from  the  circulating  fluid,  is  much 
smaller  ;  and  the  variety  of  purposes  for  which  special  secretions  are  required 
is  much  less.  Hence,  for  almost  every  Gland,  there  is  a  part  of  the  Animal  scale 
below  which  it  does  not  exist ;  and  when  it  makes  its  first  appearance,  it  almost 
invariably  presents  a  character  nearly  as  simple  as  that  of  the  least  complex 
glandular  structures  in  the  higher  animals.  Thus  the  Pancreas  in  fishes,  the 
Mammary  Gland  in  the  Ornithorhyncus,  the  Salivary  glands  in  the  Echinoder- 
mata,  and  the  Urinary  organs  of  Insects,  are  nothing  more  than  follicles  more  or 
less  extended,  and  having  separate  orifices.  Again,  in  Insects,  we  find  that  all 
the  glands, — the  Liver  and  Salivary  glands,  as  well  as  the  Kidneys  and  Testes, 
— have  the  form  of  prolonged  tubes  ;  whilst  in  Mollusca,  all  the  secreting  or- 
gans, the  Urinary  and  Genital,  as  well  as  the  Biliary  and  Salivary, — consist  of 
multiplied  vesicles  connected  with  a  ramifying  duct.  Moreover,  it  is  a  well- 
ascertained  fact  that  even  in  the  highest  organisms,  the  functions  of  Glandular 
structures  (especially  of  those  concerned  in  Excretion),  are  to  a  certain  degree 
vicarious  with  each  other;  so  that,  when  the  secretion  from  one  of  them  is 
checked,  the  system  makes  an  effort  to  throw  off,  by  another  channel,  the 
injurious  products  that  would  otherwise  accumulate  in  the  Blood.  What  is 
the  nature  of  the  change  in  any  secreting  organ,  that  causes  it  thus  to  take 
on  a  new  function,  is  a  question  upon  which  we  can  at  present  only  speculate  ; 
we  have  no  more  certain  knowledge  of  it  than  we  have  of  the  cause  which 
occasions  their  normal  actions. 

651.  It  has  been  recently  proved,  beyond  all  reasonable  doubt,  that  in  all 
secreting  organs,  the  Cells  which  cover  the  membranous  surfaces,  and  line 
the  follicles  and  tubes,  constitute  the  really  operative  part.  The  simplest 
condition  of  a  Secreting  Cell,  in  the  Animal  body,vis  that  in  which  it  exists  in 
Adipose  tissue  ;  every  cell  of  which  possesses  the  power  of  secreting  or  sepa- 
rating Fatty  matter  from  the  Blood.  In  this  case,  the  secreted  product  re- 
mains stored  up  in  the  cavity  of  the  cell,  as  it  usually  does  in  the  Cellular 
tissue  of  Plants  ; — not  being  poured  forth,  as  it  generally  is  elsewhere,  by  the 
subsequent  bursting  or  liquefaction  of  the  cell.  But  when  the  Secreting  Cells 
are  disposed  on  the  surface  of  a  membrane,  instead  of  being  aggregated  in  a 
mass,  it  is  obvious  that,  if  they  burst  or  dissolve  away,  their  contents  will  be 
poured  into  the  cavity  bounded  by  that  membrane  ;  and  this  is  the  case  in  the 
ordinary  Secreting  processes.  Thus  the  mucus,  which  covers  the  surface  of 
the  mucous  membranes,  and  which  is  being  continually  renewed,  is  the  pro- 
duct of  the  elaboration  performed  by  the  Epithelium-cells,  which  cover  their 
free  surfaces,  and  line  their  follicles.*  These  cells  are  being  continually  cast 
off,  and  replaced  by  a  fresh  growth,  which  has  its  origin  in  germs  supplied  by 
the  subjacent  membrane  ;  and  it  is  in  the  act  of  Cell-growtlTthat  the  Secreting 
process  is  accomplished.  For  just  as  the  cells,  at  the  extremities  of  the  Intes 
tinal  Villi,  select,  from  the  contents  of  the  alimentary  tube,  the  nutritious  por- 
tion which  is  to  be  introduced  into  the  absorbent  vessels, — so  do  the  cells  of 
the  secreting  Tubuli  or  Follicles  select  from  the  Blood  those  effete  particles 
which  it  is  their  peculiar  province  to  assimilate,  and  then  discharge  them  into 
the  canals  by  which  they  will  be  carried  out  of  the  system.!  Hence,  as  Mr. 
Goodsir  justly  remarks,  "  there  are  not,  as  has  been  hitherto  supposed,  two 
vital  processes  going  on  at  the  same  time,  viz.,  growth  and  secretion;  but  only 
one,  viz.,  growth.  The  only  difference  between  this  kind  of  growth,  and  that 

*  In  the  same  manner,  the  solid  matter  of  the  Urine  is  separated  from  the  Blood,  by 
the  Epithelium-cells  lining  the  Tubuli  Uriniferi. 

j-  We  shall  hereafter  meet  with  an  instance  (§  658)  in  which,  from  the  position  of  the 
cells  secreting  it,  Adipose  matter  is  discharged  from  the  body  as  an  Excretion. 


THE  LIVER SECRETION  OF  BILE.  511 

which  occurs  in  other  organs  is,  that  a  portion  of  the  product  is,  from  the 
anatomical  condition  of  the  part,  thrown  out  of  the  system."  The  Secreting 
Cells  of  different  organs  have  the  power  of  elaborating  a  great  variety  of  pro- 
ducts ;  and' no  more  essential  differences  can  be  discovered  in  their  character, 
than  in  the  structure  of  the  glands  into  whose  composition  they  enter.  We 
are  entirely  ignorant,  therefore,  of  the  reason  why  one  set  of  cells  should 
secrete  Bile,  another  Urea,  another  a  colouring  substance,  and  so  on ;  but  we 
are  as  ignorant  of  the  reason  why,  in  the  parti-coloured  petal  of  a  Flower,  the 
cells  of  one  portion  should  secrete  a  red  substance,  whilst  those  in  immediate 
contact  with  it  form  a  yellow  or  blue  colouring  matter ;  and  we  know  as  little 
of  the  cause  which  occasions  one  set  of  the  Cells  of  the  Embryo  to  be  con- 
verted into  Muscular  tissue,  another  into  Cartilage,  and  so  on. — Although, 
therefore,  there  is  a  limit  to  our  knowledge,  beyond  which  it  does  not  at  pre- 
sent seem  probable  that  we  shall  ever  pass,  it  is  an  important  step  in  the 
Science  of  Physiology  to  have  attained  the  general  principle,— that  in  Animals, 
as  in  Plants,  the  act  of  Secretion  is  effected  by  the  process  of  Cell-growth. 

652.  It  is  important  to'  bear  in  mind  that  an  essential  difference  exists 
between  the  vital  power  concerned  in  the  true  Secreting  process,  and  the 
physical  property  which  occasions  fluid  Exhalation  or  Transudation.     This 
difference  is  precisely  the  same  as  that  which  exists  between  the  vital  act  of 
Selective  Absorption,  and  the  physical  operation  of  Endosmose  or  Imbibition. 
By  Imbibition  and  Transudation,  certain  fluids  may  pass  through  organic 
membranes,  in  the  dead  as  well  as  in  the  living  body ;  and  this  passage 
depends  merely  upon  the  physical  condition  of  the  parts,  in  regard  to  the 
amount  and  the  nature  of  the  fluid  it  contains,  and  the  permeability  of  its  tis- 
sues.    Not  only  does  water  thus  transude,  but  various  substances  that  are 
held  in  complete  solution  in  it,  especially  albumen  and  saline  matter :  it  is  in 
this  manner  that  the  Blood  absorbs  fluids  from  the  digestive  cavity  (§  463), 
and  pours  out  the  serous  fluid,  which  occupies  the  interspaces  of  the  areolar 
tissue  and  the  serous  cavities.     The  transudation  of  the  watery  portion  of  the 
blood  is  much  increased  by  any  impediment  to  its  flow  through  the  vessels, — 
as  in  Congestion  and  Inflammation ;  and  also  by  any  causes  that  produce  a 
diminished  resistance  in  their  walls.— -We  shall  hereafter  see,  in  examining 
the  Physiology  of  the  Urinary  secretion,  a  very  striking  example  of  the  con- 
trast between  physical  Transudation  and  vital  Secretion  (§  668). 

II.   The  Liver.— Secretion  of  Sile. 

653.  The  Liver  is  probably  more  universally  found,  throughout  the  Animal 
scale,  than  any  other  gland.     Its  form  varies  so  greatly,  however,  in  different 
tribes,  that,  without  a  knowledge  of  its  essential  structure,  we  should  be  dis- 
posed to  question  whether  any  identity  of  character  exists  amongst  the  several 
organs,  which  we  include  under  this  designation. — In  the  higher  Polypes,  for 
example,  we  find  it  to  consist  of  a  number  of  distinct  follicles,  lodged  within 
the  walls  of  the  stomach,  and  pouring  their  secretion  into  its  cavity  by  as 
many  separate  orifices  ;  and  it  is  more  by  the  peculiar  character  of  their  secre- 
tion than  by  any  other  distinction,  that  these  follicles  are  recognized  as  Hepa- 
tic.—In  the  lower  Articulata,  a  very  similar  confirmation  is  met  with ;  but  in 
the  higher  classes  of  this  series,  such  as  Insects,  the  follicles  are  prolonged 
into  tubes  of  considerable  extent.     It  is  very  curious  to  observe,  in  animals  of 
such  complex  structure,  that  a  few  long  tubes,  closed  at  one  end,  and  opening 
at  the  other  into  the  alimentary  canal,  are  all  which  they  have  to  represent  a 
Liver;   but  the  wonder  is  readily  accounted  for,  by  keeping  in  view  the 
extremely  active  Respiration  of  these  beings,  which  renders  unnecessary  any 
other  complex  apparatus  for  elaborating  carbon  from  the  system.— -On  the  other 


512 


OF  SECRETION. 


hand,  among  the  Mollusca,  the  Liver  attains  a  much  greater  development. 
Instead  of  the  follicles  being  prolonged  into*  tubes  (which  is  the  usual  form  of 
the  glandular  system  in  Insects),  they  are  very  much  increased  in  number, 
and  arranged  on  the  sides  of  canals  or  efferent  ducts,  which  either  separately 
pour  their  fluid  into  the  intestine,  or  partially  unite  with  each  other  before 
doing  so.  The  Liver  thus  acquires  a  tabulated  character,^each  lobe  consisting 
of  a  duct  with  its  branching  follicles ;  and  the  whole  organ  forms  a  considera- 
ble proportion  of  the  mass  of  the  viscera,  and  is  evidently  of  great  importance 
in  the  economy  of  the  animal. — It  is  interesting  to  compare  this  complex  struc- 
ture with  the  very  simple  condition  presented  by  the  Liver  in  Insects ;  and, 
when  we  keep  in  view  the  relative  amount  of  Respiration  in  the  two  groups 
of  animals,  we  are  at  once  struck  with  the  fact,  that  the  development  of  the 
Liver  bears  an  inverse  proportion  to  the  opportunity  afforded  by  the  Respira- 
tory organs  for  the  aeration  of  the  blood;  it  being  peculiarly  extended,  when 
these,  either  from  their  small  size,  or  from  their  employment  in  an  aquatic 
medium,  cannot  perform  their  function  with  great  activity.  This  conclusion 
is  confirmed  in  an  interesting  manner  by  the  fact,  that  the  Crustacea,  which 
have  the  general  organization  of  Insects,  but  which  inhabit  the  water  and 
breathe  by  gills  instead  of  by  a  complex  system  of  air-tubes,  possess  a  Liver 
corresponding  in  form  and  in  degree  of  development  with  that  of  the  Mollusca. 
654.  In  the  Vertebrated  Sub-kingdom,  we  may  trace  the  operation  of  the 
same  principle ;  but  the  internal  structure  of  the  Liver,  in  the  adult  condition 
at  least,  is  less  easily  demonstrated  than  it  is  in  the  lower  classes  ;  owing  to  its 
increased  complexity  of  structure,  and  the  closer  union  between  its  different 
parts.  In  Fishes  and  Reptiles,  the  Liver  is  of  considerable  size,  and  seems  to 
perform  a  very  important  part  in  the  decarbonization  of  the  blood :  its  form  is 
adapted  to  that  of  the  cavity  in  which  it  is  lodged,  sometimes  one  lobe  only  being 
developed.  In  Birds,  on  the  other  hand,  whose  respiration  is  so  much  more 

[Fig.  134. 


The  inferior  or  concave  surface  of  the  Liver,  showing  its  subdivisions  into  lobes ;  1,  centre  of  the  right 
lobe;  2,  centre  of  the  left  lobe ;  3,  its  anterior,  inferior  or  thin  margin ;  4,  its  posterior,  thick  or  diaphragmatic 
portion;  5,  the  right  extremity ;  6,  the  left  extremity ;  7,  the  notch  in  the  anterior  margin ;  8,  the  umbilical 
or  longitudinal  fissure;  9,  the  round  ligament  or  remains  of  the  umbilical  vein;  10,  the  portion  of  the  sus- 
pensory ligament  in  connection  with  the  round  ligament;  11,  pons  hepatis,  or  band  of  liver  across  the  um- 
bilical fissure ;  12,  posterior  end  of  longitudinal  fissure ;  13, 14,  attachment  of  the  obliterated  ductus  venosus 
to  the  ascending  vena  cava;  15,  transverse  fissure;  16.  section  of  the  hepatic  duct;  17,  hepatic  artery;  18,  its 
branches;  19,  vena  portarum ;  20,  its  sinus,  or  division  into  right  and  left  branches;  21,  fibrous  remains  of 
the  duclus  venosus;  22,  gall  bladder;  23,  its  neck;  24,  lobulus  quartus;  25,  lobulus  spigelii;  20.  lobulus 
caudatus ;  27,  inferior  vena  cava;  28,  curvature  of  liver  to  fit  the  ascending  colon  ;  29,  depression  to  fit  the 
right  kidney;  30,  upper  portion  of  its  right  concave  surface  over  the  renal  capsule;  31,  portion  of  liver 
uncovered  by  the  peritoneum ;  32,  inferior  edge  of  the  coronary  ligament  in  the  liver ;  33,  depression  made 
by  the  vertebral  column.] 


THE  LIVER SECRETION  OF  BILE. 


513 


active,  it  is  much  smaller,  but  is  placed  on  the  median  line,  in  conformity  with 
the  general  symmetry  of  their  internal  as  well  as  external  organs  (§  51).  In 
Mammalia,  also,  it  is  comparatively  small ;  but,  though  reduced  in  proportional 
size,  it  is  at  the  same  time  much  more  compact  and  firm  than  in  the  lower  Ver- 
tebrata.  The  Liver  of  Man  is  much  less  developed  than  that  of  many  other 
Mammalia ;  and  presents,  as  rudimentary  indications,  certain  organs  which 
are  elsewhere  fully  developed.  The  whole  mass,  which  we  are  accustomed  to 
describe  as  consisting  of  a  right  and  left  lobe,  does  in  reality  form  but  one  (there 
being  no  real  division  between 

its  two  portions),  which  must  [Fig.  135 

be  regarded  as  the  Central 
lobe  ;  the  Lobulus  Spigelii  is 
the  rudiment  of  a  second  or 
light  lobe,  and  the  Lobulus 
Caudatus  is  a  Lobule  developed 
from  it.  In  the  Carnivori  and 
Rodentia,  which  present  the 
most  complex  form  of  Liver 
that  we  meet  with  among 
Mammalia,  there  are  five  dis- 
tinct parts  ; — a  central  or  prin- 
cipal lobe,  corresponding  with 
the  principal  part  of.  the  liver 
of  Man ;  a  right  lateral  lobe, 
with  a  lobular  appendage,  cor- 
responding to  the  Lobulus 
Spigelii  and  Lobulus  Cauda- 
tus ;  and  a  similar  lobe  and 
lobule  on  the  left  side. — The 
Gall-bladder  is  an  appendage 
to  the  Liver,  of  which  we  find 
no  traces  in  the  Invertebrata. 
It  may  be  regarded  as  simply 
a  dilatation  of  the  efferent  duct, 
more  or  less  prolonged  from  it, 
adapted  to  store  up  the  hepatic 
secretion  against  the  time  when 
it  may  be  required.  In  Fishes 
it  frequently,  but  by  no  means 
constantly,  presents  itself;  in 
Reptiles,  on  the  other  hand,it 
invariably  exists.  In  Birds  it 
is  occasionally  absent,  even  in 
species  closely  allied  to  others 
that  possess  it,  and  without  any 
marked  difference  in  the  food, 
habits,  &c.,  of  the  two.  In 
Mammalia,  again,  it  is  frequent- 
ly absent,  especially  among 
herbivorous  animals ;  some- 
times, on  the  other  hand,  two 
are  present,  a  second  or  ac- 
cessary gall-bladder  being  formed  upon  the  Ductus  communis  choledochus, 
which  elsewhere  not  unfrequently  presents  a  dilatation  in  the  same  situa- 


Shows  the  three  coats  of  the  Gall-Bladder  separated  from 
each  other;  1,  the  external  or  peritoneal  coat;  2,  the  cellular 
coat  with  its  vessels  injected;  3,  the  mucous  coat  covered 
with  wrinkles ;  4,  4,  valves  formed  by  this  coat  in  the  neck  of 
the  gall-bladder  j  5,  5,  orifices  of  the  mucous  follicles  at  this 
point] 

[Fig.  136. 


A  view  of  the  Gall-Bladder  distended  with  air,  and  with 
its  vessels  injected;  1,  cystic  artery;  2,  the  branches  of  it 
which  supply  the  peritoneal  coat  of  the  liver;  3,  the  branch  of 
the x hepatic  artery  which  goes  to  the  gall-bladder;  4,  the 
lymphatics  of  the  gall-bladder.] 


514  OF  SECRETION. 

tion.*  In  the  Human  species  the  gall-bladder  is  rarely  absent,  except  in  cases  of 
malformation  depending  upon  general  arrest  of  development,  in  which  several 
organs  are  involved.  The  Excretory  Ducts  of  the  Liver  and  Gall-bladder  have 
three  coats, — an  internal  or  mucous,  a  middle  or  fibrous,  and  an  external  or 
areolar.  The  internal  coat  is  continuous  with  the  Mucous  membrane  of  the 
Intestinal  tube,  into  which  it  opens ;  and  the  whole  glandular  structure  may 
indeed  be  considered  as  a  complex  prolongation  of  this,  copiously  supplied 
with  blood-vessels,  and  packed  into  the  smallest  possible  compass.  The  mid- 
dle or  fibrous  coat  bears  a  considerable  resemblance  in  aspect  to  that  of  the 
Arteries  ;  in  its  properties,  however,  it  is  still  more  nearly  allied  to  true  muscle, 
being  capable  of  exhibiting  contraction  on  the  application  of  stimuli  to  the  gan- 
glionic  nerves  supplying  it  (§  200) ;  and  in  some  instances  of  obstruction,  it  has 
presented  an  appearance  very  closely  resembling  that  of  the  muscular  coat  of 
the  alimentary  canal.t  Dr.  Davy  has  pointed  out  that  the  mucous  coat  of  the 
Ductus  communis  is  disposed  in  valve-like  folds,  in  such  a  manner  as  to  pre- 
vent the  reflux  of  the  bile,  or  of  the  contents  of  the  intestine. 

655.  The  Liver  may  be  regarded  as  essentially  consisting  of  the  ramifica- 
tions of  the  Hepatic  Duct,  in  close  rela- 

[Fig.  137.  tion  with  those  of  the  Portal  Vein  and 

Hepatic  Artery,  that  serve  to  convey 
blood  to  the  minutest  parts  of  this  organ, 
and  with  those  of  the  Hepatic  Vein, 
which  return  it  to  the  heart,  after  it  has 
been  subservient  to  the  Nutrition  of  the 
structure  and  to  the  -elaboration  of  the 
Secretion.  Besides  these,  the  Liver  con- 

1  Nucleated  cells  composing  the  parenchyma  ^  Lymphatics  and  Nerveg  the  ]atter 
of  the  gland ;  2,  lobules  of  human  liver  with  ,  .  Ja  r,  . 

ramifications  of  the  hepatic  vein.]  are  chiefly  derived  from  the  Sympathetic 

system,  and  are  distributed  on  the  walls 

of  the  vessels  and  ducts.  These  various  portions  of  the  structure  are  con- 
nected together  by  a  fibrous  tissue,  to  which  the  name  of  Glisson's  Capsule 
has  been  given.  For  our  present  knowledge  of  their  ultimate  arrangement, 
we  are  almost  entirely  indebted  to  Mr.  Kiernan,^  whose  account  of  them  will 
be  here  followed. 

a.  When  the  Liver  is  closely  examined  with  the  naked  eye,  it  is  seen  to  be  made  up  of 
a  great  number  of  small  granular  bodies,  about  the  size  of  a  millet  seed,  of  an  irregular 
form,  and  presenting  a  number  of  rounded  projecting  processes  upon  their  surface. — 
These  are  commonly  termed  lobules,  although  by  some  Anatomists  they  are  spoken  of  as 
acini.  When  divided  longitudinally,  they  have  a  somewhat  foliated  appearance,  arising 
from  the  distribution  of  the  Hepatic  Vein ;  which,  passing  into  the  centre  of  each  division, 
is  termed  the  m/ra-lobular  vein.  The  exterior  of  each  Lobule  is  covered  by  a  process  of 
the  capsule  of  Glisson;  and  its  substance  is  composed  of  the  minute  ramifications  of  the 
before-mentioned  vessels,  arranged  in  the  manner  presently  to  be  described;  the  spaces 
between  which  are  filled  up  with  a  parenchyma,  composed  of  nucleated  cells,  as  shown 
in  Fig.  138,  1.  The  structure  of  each  lobule,  then,  gives  us  the  essential  characters  of  the 
whole  gland. 

.*».  The  Lobules,  when  transversely  divided,  are  usually  found  to  present  somewhat  of 
a  pentagonal  or  a  hexagonal  shape;  the  angles  being  generally  somewhat  rounded,  so  as 
to  form  a  series  of  passages,  or  m/er-lobular  spaces  ;  "in  these  He  the  branches  of  the  Vena 
Portland  of  the  Hepatic  Artery  and  Duct,  from  which  are  derived  the  plexuses  that  com- 
pose the  lobules.  Each  Lobule,  when  examined  with  the  microscope,  is  found  to  be  ap- 
parently composed  of  numerous  minute  bodies,  of  a  yellowish  colour  and  of  various 
forms,  connected  together  by  vessels;  to  these  the  name  of  acini  was  given  by  Malpighi; 


*  In  the  first  Giraffe  dissected  by  Mr.  Owen,  no  gall-bladder  was  found;  in  the  second 
there  were  two. 

f  In  the  Horse  and  Dog  this  coat  is  clearly  muscular. 
t  Philosophical  Transactions,  1833. 


THE  LIVER SECRETION  OF  BILE. 

Fig.  138. 


515 


Fig.  139. 


Connection  of  the  Lobules  of  the  Liver  with  the  Hepatic  Vein; 
1.  trunk  of  the  vein;  2,  2,  2,  lobules  depending  from  its  branches 
like  leaves  on  a  tree,  the  centre  of  each  being  occupied  by  a 
venous  twig— the  intralobular  vein.  (After  Kiernan.) 


Glandular  Cells  of  Liver;  o,  nu- 
cleus; fc,  nucleolus  (?)  c,  adipose 
particles. 


and  to  these,  if  they  deserve  a  name,  it  ought  to  be  restricted.  They  will  be  presently 
shown,  however,  lo  be  nothing  else  than  the  irregular  islets,  left  between  the  meshes  of 
the  plexus  formed  by  the  ultimate  ramifications  of  the  Portal  Vein.  The  Vena  Portae,  it 
will  be  recollected,  is  formed  by  the  con- 


Fig.  140. 


vergence  of  the  veins,  which  return  the 
blood  from  the  chylopoietic  viscera;  and 
there  is  reason  to  believe  that  it  also  re- 
ceives the  blood,  which  is  conveyed  to  the 
Liver  for  the  purposes  of  Nutrition  by  the 
Hepatic  Artery.  As  it  is  an  afferent,  not 
an  efferent  vessel,  it  has  a  strong  claim 
to  the  character  of  an  Artery;  even  al- 
though it  conveys  Venous  blood.  Like 
an  artery,  it  gradually  subdivides  into 
smaller  and  yet  smaller  branches;  and  at 
last  forms  a  plexus  of  vessels,  which  lie 
in  the  inter-lobular  spaces,  and  spread 
with  the  freest  inosculation  throughout 
the  entire  Liver.  To  these  vessels  the 
name  of  trzter-lobular  Veins  is  given  by 
Mr.  Kiernan.  They  ramify  in  the  capsules 
of  the  lobules,covering  with  their  ramifica- 
tions the  whole  external  surface  of  these ; 
and  then  enter  their  substance.  When 
they  enter  the  Lobules,  they  are  termed 
lobular  veins;  and  the  plexus  formed  by 
their  convergence,  from  the  circumfe- 
rence of  each  lobule  towards  its  centre 
(where  their  ultimate  ramifications  ter- 
minate in  those  of  the  intra-lobular  or  he- 
patic vein),  is  designated  as  the  Lobular 
Venous  plexus. — In  the  islets  of  this  plexus 
the  acini  of  (Malpighi)  the  ramifications  of  the  hepatic  duct  are  distributed,  in  the  man- 
ner next  to  be  described. 

c.  The  Hepatic  Duct  forms,  by  its  subdivision  and  ramification,  an  Interlobular  plexus 
of  a  very  similar  character;  but  the  anastomosis  between  the  branches  going  to  the  dif- 
ferent lobules  is  less  intimate  than  that  of  the  interlobular  veins,  and  cannot  be  directly 
demonstrated;  although  Mr.  Kiernan  thinks  that  his  experiments  leave  but  little  doubt  of 
its  existence, — a  communication  (which  cannot  be  seen  to  be  established  by  any  nearer 
channel)  being  proved  to  exist  between  the  right  and  left  primary  subdivisions  of  the 
duct.  The  Interlobular  Ducts  ramify  upon  the  capsular  surface  of  the  lobules,  with  the 
branches  of  the  Portal  Vein  and  Hepatic  Artery;  they  then  enter  its  substance,  and  sub- 
divide into  minute  branches,  which  anastomose  with  each  other,  and  form  a  reticulated 
plexus,  termed  by  Mr.  K.  the  Lobular  Biliary  plexus.  This  plexus  constitutes  the  princi- 
pal part  of  the  substance  of  the  lobule ;  and  when  seen  through  the  meshes  of  the  Portal 
plexus,  gives  rise  to  the  appearance  of  coecal  terminations  of  ducts.  rnu~  "u: — *~  '"" 


Horizontal  section  of  three  superficial  Lobules, 
showing  the  two  principal  systems  of  blood-vessels ; 
1, 1,  inZro-lobular  veins,  proceeding  from  the  hepatic 
veins;  2,  2,  inter-lobular  plexus,  formed  by  branches 
of  the  portal  veins.  (After  Kiernan.) 


The  ultimate  ter- 


516 


OF  SECRETION. 


Horizontal  section  of  two  superficial  Lobules,  showing 
the  interlobular  plexus  of  biliary  ducts;  1, 1,  intralobular 
veins;  2,  2,  trunks  of  biliary  ducts,  proceeding  from  the 
plexus  which  traverses  the  lobules ;  3,  interlobular  tissue ; 
4,  parenchyma  of  the  lobules.  (After  Kiernan.) 


initiations  of  these  ducts  have  not,  however,  been  traced  in  the  adult  Liver  of  any  of  the 
higher  animals,  although  they  are  sufficiently  evident  in  the  embryonic  condition.  From 
the  analogy  of  other  organs,  there  would  seem  good  reason  to  believe,  that  the  ultimate 

ramifications  of  the  hepatic  ducts  an- 

Fig  141.  astomose    freely  together,  and    that 

they  form  a  net-work,  in  which  their 
terminations  are  lost,  as  it  were,  with- 
out forming  true  caeca.*  This  view  of 
the  matter  finds  confirmation  in  the 
curious  fact  pointed  out  by  Mr.  Kier- 
nan, that,  in  the  left  lateral  ligament, 
the  essential  parts  of  a  lobe  are  found 
in  the  simplest  form  and  arrangement. 
From  the  edge  of  the  liver  next  to  the 
ligament,  numerous  Ducts  emerge, 
which  ramify  between  the  two  layers 
of  peritoneum  of  which  the  ligament 
is  composed.  They  are  accompanied 
by  branches  of  the  Portal  and  Hepatic 
Veins,  and  of  the  Hepatic  Artery; 
which  also  ramify  in  this  ligament, 
especially  around'  the  parietes  of  the 
ducts.  These  ducts,  of  which  some 
are  occasionally  of  considerable  size, 
divide,  subdivide,  and  anastomose 
with  each  other;  and  the  meshes 

formed  by  the  network  of  larger  or  excreting  Ducts,  are  occupied  by  minute  plexuses 
of  their  ultimate  ramifications  or  secreting  Ducts. 

d.  The  Hepatic  Artery  sends  branches  to  every  part  of  the  Liver,  supplying  the  walls 
of  the  Portal  and  Hepatic  Veins,  and  of  the  Hepatic  Ducts,  as  well  as  Glisson's  capsule. 
The  principal  distribution  of  its  branches,  however,  is  to  the  Lobules,  which  they  reach 
in  the  same  manner  with  the  Portal  vessels  and  Biliary  Ducts,  by  spreading  themselves 
through  the  interlobular  spaces.    There  they  ramify  upon  the  interlobular  ducts,  and 
upon  the  capsular  surface  of  the  lobules,  which  they  then  penetrate;  their  minuteness 
prevents  their  distribution  within  the  lobules  from  being  clearly  demonstrable;  but,  as 
they  enter  along  with  the  biliary  ducts,  there  can  be  little  doubt  that,  here  as  elsewhere, 
they  are  principally  distributed  upon  the  walls  of  these.    As  to  the  ultimate  termination 
of  the  capillaries  of  the  Hepatic  Artery, — whether  they  enter  the  Portal  plexus  or  the 
Hepatic  Vein, — there  is  a  difference  of  opinion  amongst  anatomists;   the  former  view 
being  upheld  by  Kiernan,  the  latter  by  Mullen    The  question  is  a  very  interesting  one 
in  a  physiological  point  of  view;   since  if  the  former  account  be  the  true  one,  the  Blood 
which  is  brought  to  the  Liver  by  the  Hepatic  Artery  becomes  subservient  to  the  secretion 
of  Bile,  only  by  passing  into  the  Portal  plexus;  whilst,  if  the  latter  be  the  correct  state- 
ment, either  the  arterial  Blood  is  not  at  all  subservient  to  the  formation  of  Bile,  or  the 
secretion  can  be  elaborated  from  the  arterial  capillaries.     The  experiments  of  Mr.  Kier- 
nan have  satisfactorily  proved,  that  the  Intra-lobular  or  Hepatic  Veins  cannot  be  filled 
by  injection  from  the  Hepatic  Artery,  though  they  may  be  readily  filled  from  the  Portal 
plexus;  whilst,  on  the  other  hand,  there  is  reason  to  believe  that  a  very  fine  injection 
into  the  Hepatic  arteries  will  find  its  way  into  the  Portal  plexus.f    It  is  certain  that  all 
the  branches  of  the  Hepatic  artery,  of  which  the  termination  can  be  ascertained,  end  in 
the  Vena  portae;   a  free  capillary  communication  existing  between  their  two  systems  of 
branches,  on  the  walls  of  the  larger  blood-vessels  and  ducts.     According  to  Muller,  there 
is  an  ultimate  plexus  of  capillary  vessels,  with  which  all  the  three  systems  freely  com- 
municate ;  but  for  this  idea  there  is  no  adequate  foundation  ;  and  it  is  inconsistent  with 
the  fact  just  stated,  that  injection  into  the  Hepatic  Artery  does  not  return  by  the  Hepatic 
vein.     And  the  views  of  Mr.  Kiernan  have  lately  received  important  confirmation  from 
the  researches  of  Mr.  Bowman  on  the  circulation  in  the  Kidney  (§  667,  6). 

e.  It  now  only  remains  to  describe  the  Hepatic  Veins,  the  branches  of  which  occupy 
the  interior  of  the  Lobules,  and  are  termed  intra-lobular  veins  (1,  1,  Fig^s.  140  and  141). 
On  making  a  transverse  section  of  a  Lobule,  it  is  seen  that  the  central  vessel  is  formed 
by  the  convergence  of  from  four  to  six  or  eight  minute  venules,  which  arise  from  the 
processes  upon  the  surface  of  the  lobule.    In  the  superficial  lobules  (by  which  term  are 

*  See  Wilson  in  Cyclopaedia  of  Anatomy  and  Physiology,  vol.  iii.,  p.  170. 
-[This  is  stated  to  have  been  the  case  in  the  injections  of  Lieberkuhn,  although  Mr. 
Kiernan  has  not  succeeded  in  effecting  it. 


THE  LIVER SECRETION  OF  BILE.  517 

designated  those  lobules  which  lie  upon  the  exterior  of  the  glandular  substance,  not  only 
upon  the  surface  cf  the  Liver,  but  also  against  the  walls  of  the  larger  vessels,ducts,&c.,) 
the  Intralobular  Veins  commence  directly  from  their  surface;  and  the  minute  venules  of 
which  each  is  composed  may  be  seen  in  an  ordinary  injection,  converging  from  the 
circumference  towards  the  centre,  as  in  the  transverse  section  of  other  lobules*  The 
Intralobular  Veins  terminate  in  the  larger  trunks,  which  pass  along  the  bases  of  the 
lobules,  collecting  from  them  their  venous  blood;  these  are  called  by  Mr.  Kiernan  sub- 
lobular  veins.  The  main  trunk  of  the  Hepatic  Vein  terminates  in  the  ascending  Vena 
Cava. 

/.  In  regard  to  the  mode  in  which  the  nucleated  Cells,  that  are  the  real  agents  in  the 
Secreting  process,  are  arranged  in  the  Liver  of  Man  and  the  higher  animals,  there  is 
much  uncertainty;  owing  especially  to  our  want  of  acquaintance  with  the  mode  in  which 
the  Hepatic  Ducts  terminate.  They  would  seem  to  form  the  greatest  part  of  the  paren- 
chyma, which  fills  up  the  interstices  between  the  reticulations  of  the  Blood-vessels  and 
Ducts ;  but  it  is  obvious,  from  their  functional  operation,  that  they  must  have  a  more 
close  relation  to  the  latter  than  to  the  former.  Their  diameter  is  usually  from  l-15UOth  to 
l-2000th  of  an  inch;  and  they  are  consequently  easily  recognized,  whenever  a  portion  of 
the  substance  of  the  Liver  is  torn  up  and  examined  with  the  higher  powers  of  the  Micro- 
scope. Their  shape  is  usually  spheroidal.  They  have  a  distinct  biliary  tinge ;  and 
contain  a  granular  amorphous  matter,  with  a  few  small  adipose  globules.  (Fig.  139.) 

g.  In  regard  to  the  Embryonic  Development  of  the  Human  Liver,  a  considerable  part 
of  our  information  must  necessarily  be  derived  from  the  study  of  that  of  other  animals  ; 
and  this  not  so  much  from  Mammalia  as  from  Birds;  since  the  development  of  this 
organ  commences  so  early  in  the  former,  its  phases  are  so  rapidly  hurried  through,  and 
its  evolution  is  so  soon  completed,  that  the  process  cannot  be  continuously  watched. — In 
the  Chick,  the  rudiments  of  the  Liver  are  found  at  the  commencement  of  the  third  day  of 
incubation,  in  the  form  of  two  coscal  pouches,  which  are  prolonged  from  the  Intestinal 
tube;  these  carry  before  them  a  fold  of  the  vascular  layer,  from  which  the  blood-vessels 
subsequently  originate;  and  they  soon  begin  to  ramify  in  this,  sending  off  branches,  of 
which  the  coscal  extremities  are  still  evident.  At  the  end  of  the  fourth  day,  the  tubuli 
and  their  ramifications  have  attained  a  considerable  size;  and  they  approach  each  other 
and  coalesce  at  the  base,  entering  the  intestine  by  an  orifice  common  to  the  two.  In  this 
process,  it  is  easy  to  recognize  the  analogy  to  the  succession  of  forms  which  we  en- 
counter in  ascending  the  animal  scale.  The  size  and  density  of  the  organ  are  gradually 
increased;  but  it  is  not  until  several  days  afterwards  that  the  gall-bladder  is  developed. 
In  the  Human  Embryo,  the  formation  of  the  Liver  begins  at  about  the  third  week  of  intra- 
uterine  existence;  the  organ  is  from  the  first  of  very  large  size,  when  compared  with 
that  of  the  body ;  and  between  the  third  and  the  fifth  week,  it  is  one-half  the  weight  of 
the  entire  embryo.  It  is  at  that  period  divided  into  several  lobes.  By  the  third  lunar 
month,  the  liver  extends  nearly  to  the  pelvis,  and  almost  fills  the  abdomen ;  the  right 
side  now  begins  to  gain  upon  the  left :  the  gall-bladder  begins  to  appear  at  this  time. 
The  subsequent  changes  chiefly  consist  in  the  consolidation  of  the  viscus,  and  the 
diminution  of  its  proportional  size.  Up  to  the  period  of  birth,  however,  the  bulk  of  the 
Liver,  relatively  to  that  of  the  entire  body,  is  much  greater  than  in  the  adult;  the  pro- 
portion being  as  1  to  18  or  20  in  the  new-born  child,  whilst  it  is  about  1  to  36  in  the 
adult:  and  the  difference  between  the  right  and  left  sides  is  still  inconsiderable.  During 
the  first  year  of  extra-uterine  life,  however,  a  great  change  takes  place ;  the  right  lobe 
increases  a  little  or  remains  stationary,  whilst  the  left  lobe  undergoes  an  absolute  dimi- 
nution, being  reduced  nearly  one-half;  and  as,  during  the  same  period,  the  bulk  of  the 
rest  of  the  body  has  been  rapidly  increasing,  the  proportion  is  much  more  reduced  during 
that  period  than  in  any  subsequent  one  of  the  same  length.  According  to  Meckel,  the 
liver  of  the  newly-born  infant  weighs  one-fourth  heavier  than  that  of  a  child  of  eight  or 
ten  months  old;  and  as  the  weight  of  the  whole  body  is  more  than  doubted,  during  the 
same  time,  it  is  obvious  that  the  change  in  the  proportion  of  the  two  must  be  principally 
effected  at  this  epoch. 

656.  The  knowledge  of  the  distribution  of  the  Biliary  ducts,  and  of  the  two 
chief  systems  of  Blood-vessels,  in  the  Lobules  of  the  Liver,  has  enabled  Mr. 
Kiernan  to  give  a  most  satisfactory  explanation  of  appearances,  by  which 
Pathological  anatomists  had  been  previously  much  perplexed.  When  the 
Liver  is  in  a  state  of  Anaemia  (which  rarely  happens  as  a  natural  condition, 
although  it  may  be  induced  by  bleeding  an  animal  to  death,)  the  whole  sub- 
stance of  the  lobules  is  pale,  as  represented  in  Fig.  142.  In  general,  however, 
the  Liver  is  more  or  less  congested  at  the  moment  of  death ;  and  this  congestion 
44 


518 


OF  SECRETION 


Fig.  142. 


Fig.  143. 


-N3 


1.  Angular  lobules  in  a  state  of  anaemia,  as  they 
appear  on  the  external  surface  of  the  liver ;  2,  in- 
terlobular  spaces;  3,  interlobular fissures ;  4,  intra- 
lobular  veins,  occupying  the  centres  of  the  lobules ; 
5,  smaller  veins,  terminating  in  the  central  veins. 


1,  1,  Rounded  lobules  in  first  stage  of  hepatic 
venous  congestion,  as  they  appear  on  the  surface 
of  the  liver;  2,  2,  interlobular  spaces  and  fissures. 


may  manifest  itself  in  several  ways.  The  whole  substance  may  be  congested ; 
in  which  case  the  lobules  present  a  nearly  uniform  dark  colour  throughout 
their  substance,  their  centres  being  usually  more  deeply-coloured  than  the 
margins.  An  appearance  more  frequently  offered  after  death,  however,  is 
that  represented  at  Fig.  143,  and  termed  by  Mr.  Kiernan  the  first  stage  of 
Hepatic  Venous  congestion.  In  this,  the  isolated  centres  of  the  Lobules  alone 
present  the  colour  of  sanguineous  congestion  ;  and  the  surrounding  substance 
varies  from  a  yellowish-white,  yellow,  or  greenish  colour,  according  to  the 
quantity  and  quality  of  the  Bile  which  it  contains.  This  accumulation  of  the 
blood  in  the  Hepatic  Veins,  and  the  emptiness  of  the  Portal  plexus,  seem  due 
to  the  continuance  of  capillary  action  after  the  general  circulation  has  ceased ; 
a  circumstance  to  which  we  find  an  exact  parallel,  in  the  emptiness  of  the 
systemic  arteries,  and  the  fulness  of  the  veins,  after  most  kinds  of  death.  In 
the  second  stage  of  Hepatic  Venous  congestion,  the  accumulation  of  blood  is 
found  not  only  in  the  Intralobular  Veins,  but  even  in  parts  of  the  Portal  or 
Lobular  Venous  plexus.  The  parts  which  are  freest  from  it  are  those  sur- 
rounding the  interlobular  spaces ;  so  that  the  non-congested  substance  here 
appears  in  the  form  of  circular  or  irregular  patches,  in  the  midst  of  which  the 
spaces  and  fissures  are  seen  (Fig.  144).*  Although  the  Portal  as  well  as  the 
Hepatic  venous  system  is  thus  involved  in  this  form  of  congestion,  yet,  as  the 
obstruction  evidently  originates  in  the  latter,  the  term  given  by  Mr.  Kiernan 
is  still  applicable  ;  and  it  is  important  to  distinguish  this  appearance  from  that 
next  to  be  described.  The  Second  stage  of  Hepatic  venous  congestion  very 
commonly  attends  disease  of  the  heart,  and  other  disorders  in  which  there  is 
an  impediment  to  the  venous  circulation;  and  in  combination  with  accumula- 
tion in  the  biliary  ducts,  it  gives  rise  to  those  various  appearances  which  are 
known  under  the  name  of  dram-drinkers'  or  nutmeg  liver.  The  other  form  of 
partial  congestion  arises  from  an  accumulation  of  blood  in  the  Portal  veins, 
with  a  reverse  condition  of  the  Hepatic  or  intralobular  veins ;  in  this  con- 
dition, which  Mr.  K.  designates  as  portal  venous  congestion,  the  marginal 
portions  of  the  lobules  are  of  deeper  colour  than  usual,  and  form  a  continuous 

*  This  very  common  aspect  of  the  Liver,  which  presents  numerous  modifications,  has 
been  a  source  of  great  perplexity  to  those  who  have  studied  the  minute  anatomy  of  this 
organ,  and  has  even  led  Anatomists  of  the  highest  eminence  into  serious  errors.  See 
Cyclop,  of  Anat.  and  Physiol.,  vol.  iii.  pp.  185,  186. 


THE  LIVER SECRETION  OF  BILE. 


519 


Fig.  145. 


A,  Lobules  in  the  second  stage  of  hepatic  venous  A,  Lobules  as  they  appear  on  the  surface  in  a 

congestion;  B  and  c,  interlobular  spaces;  D,  con-  state  of  portal  venous  congestion;  B,  interlobular 

gested  intralobular  veins ;  i,  congested  patches,  ex-  spaces  and  fissures;  c,  intralobular  hepatic  veins, 

tending  to  the  circumference  of  the  lobules ;  F,  non-  containing  no  blood;  D,the  central  portions  in  a 

congested  portions  of  lobules.  state  of  anaemia;  E,  the  marginal  portions  in  a 

congested  state. 

network,  the  isolated  spaces  between  which  are  occupied  by  the  non-congested 
portions  (Fig.  145).  This  is  a  very  rare  occurrence;  having  been  seen  by 
Mr.  K.  in  children  only. — These  differences  fully  explain  the  diversity  of 
the  statements  of  different  anatomists  as  to  the  relative  positions  of  the  so- 
called  red  and  yellow  substances  ;  for  it  now  appears,  that  the  red  substance 
is  the  congested  portion  of  the  lobules,  which  may  be  either  interior  or  exte- 
rior, or  irregularly  disposed ;  whilst  the  yellow  is  the  non-congested  part,  in 
which  the  Biliary  plexus  shows  itself  more  or  less  distinctly. 

657.  Another  very  interesting  form  of  Pathological  change  in  the  aspect  of 
the  Liver,  which  the  knowledge  of  the  structure  of  the  Lobules  enables  us  to 
comprehend,  is  that  to  which  the  name  of  Cirrhosis  has  been  given.     This 
has  been  erroneously  attributed  to  the  presence  of  a  new  deposit,  analogous  to 
that  of  Tubercular  matter ;  but  it  is  really  due  to  Atrophy  and  partial  Conges- 
tion in  the  Liver  itself.     It  is  described  by  Laennec  as  usually  presenting  itself 
in  small  masses,  varying  in  size  from  a  cherry-stone  to  a  millet-seed,  and  scat- 
tered through  the  substance  of  the  Liver.    When  these  are  minute,  and  closely 
set,  they  impart  what  appears  at  first  to  be  a  uniform  brownish-yellow  tint  to 
the  divided  surface  of  the  Liver;  but  when  the  tissue  is  more  attentively  ex- 
amined, their  separation  becomes  evident.     These  small  masses  are  not  distinct 
lobules  in  a  variable  state  of  hypertrophy  (as  supposed  by  Cruveilhier) ;  but 
small  uncongested  patches,  composed  of  parts  of  several  adjoining  lobules,  and 
having  one  or  more  interlobular  spaces  for  a  centre ;  and  the  biliary  plexuses 
of  these,  being  filled  with  bile,  give  them  their  yellow  colour.     On  the  other 
hand,  there  is  an  atrophy,  more  or  less  complete,  of  the  portions  of  the  sub- 
stance of  the  liver  intervening  between  them ;  so  that  the  bulk  of  the  whole 
organ  is  much  diminished,  very  commonly  to  one-half,  and  sometimes  to  one- 
third  of  its  original  size. 

658.  The  application  of  the  Microscope  to  the  Hepatic  Cells,  in  various 
states  of  disease,  has  afforded  many  facts  of  great  interest.     The  fatty  liver, 
which  is  often  found  in  the  bodies  of  persons  who  have  died  from  diseases  ob- 
structing the  pulmonary  circulation,  has  been  shown  by  Mr.  Bowman*  to  depend 

*  Medical  Gazette,  Jan.,  1842. 


520  OF  SECRETION. 

upon  the  presence  of  a  large  quantity  of  fatty  matter  in  the  interior  of  the 
cells ;  which  frequently  appear  as  if  gorged  with  it.     This  would  seem  to  be 
occasioned  by  the  want  of  elimination  of  the  fatty  matter  through  the  respira- 
tory process ;  and  the  consequent  accumulation  of  it 
Fig.  146.  in  the  Blood,  by  which  the  burden  of  separating  it  is 

thrown  upon  the  Liver. — Dr.  Williams*  mentions  that, 
in  a  case  of  obstruction  of  the  ductus  choledochus  by 
malignant  disease,— -which  occasioned  complete  inter- 
ruption to  the  passage  of  bile,  and  consequent  jaun- 
dice,— scarcely  an  entire  nucleated  cell  could  be  dis- 
covered by  attentive  examination  of  a  large  part  of  the 

Hepatic  Cells  gorged  with  •»<     ••  •  •,  .  r    c  •    i          r 

fat;  «,  atrophied  nucleus;  6,     organ.     Nothing  more  than  minute  free  particles  of 

adipose  globules.  iat>  and  free  floating  amorphous  granular  matter,  could 

be  detected.     He  further  states  that,  in  a  case  of  fever, 

the  hepatic  cells  were  found  to  be  almost  entirely  destitute  of  fat  particles ; 
and  that  in  what  is  known  as  "granular  liver,"  the  granules  (which  have 
much  the  appearance  of  tubercles)  consist  of  cells,  which  strongly  resemble  the 
ordinary  cells  of  the  Parenchyma  of  the  Liver  in  every  respect,  except  that 
they  are  almost  or  completely  destitute  of  yellow  contents. — In  two  cases  of 
jaundice  examined  by  Mr.  Gulliver,  the  hepatic  cells  were  gorged  with  biliary 
matter  ;  some  of  them  to  such  an  extent  that  they  had  become  nearly  opaque. 
Perhaps  if  this  condition  had  continued,  these  cells  would  have  been  all  rup- 
tured, and  the  state  of  the  organ  would  have  resembled  that  described  by  Dr. 
Williams. 

659.  Previously  to  birth,  the  Liver  is  the  only  decarbonizing  organ  in  the 
system,  the  Lungs  being  at  that  time  inert ;  but  as  soon  as  the  latter  come  into 
play,  they  separate  from  the  Venous  blood  a  large  proportion  of  the  carbon 
with  which  it  is  charged,  and  less  blood  is  transmitted  to  the  Liver  for  this 
purpose.     The  diminution  in  the  quantity  of  the  Blood  circulating  through  this 
organ  is  extremely  rapid ;  and  it  is  usually  very  evident  within  a  short  time 
after  birth,  in  the  comparative  paleness  of  the  substance  of  the  gland.     It  has 
been  proposed  to  give  this  fact  a  practical  bearing,  in  those  judicial  inquiries 
which  are  directed  to  the  determination  of  the  question,  whether  or  not  an 
Infant  has  respired  after  birth ;  it  having  been  conceived  that  the  diversion  of 
the  current  of  the  Blood  from  the  Liver  to  the  Lungs,  consequent  upon  the 
first  inspiration,  would  be  sufficient  to  make  a  certain  difference  in  their  rela- 
tive weights,  if  that  inspiration  had  taken  place.     More  careful  and  extended 
observations,  however,  have  satisfactorily  proved  that,  although  an  increase  in 
the  weight  of  the  Lungs,  and  a  diminution  of  that  of  the  Liver,  are  generally 
found  to  exist  after  respiration  has  been  fully  established,  they  are  not  by  any 
means  constantly  produced  when  the  inspirations  have  been  feeble,  as  they 
frequently  are  for  some  hours  or  days  after  birth ;  whilst,  on  the  other  hand, 
it  is  not  uncommon  to  meet,  in  infants  that  have  not  breathed,  with  Lungs  as 
heavy,  and  Livers  as  light,  as  in  the  average  of  those  which  have  respired.! 

660.  We  have  now  to  consider  the  conditions  under  which  the  secretion  of 
Bile  takes  place ;  and  one  of  the  most  important  of  these  is  the  character  of 
the  Blood  with  which  the  organ  is  supplied.     We  have  seen  that  there  is  ana- 
tomical reason  for  the  belief,  that  the  blood  supplied  by  the  Hepatic  Artery  is 
not  directly  concerned  in  the  Secretion ;  but  that  it  first  serves  for  the  Nutri- 
tion of  the  organ,  and  then  passing  into  the  Portal  system  (in  the  same  manner 
as  does  the  blood  of  the  mesenteric  and  other  arteries),  forms  a  part  of  the  mass 
of  Venous  Blood,  from  which  the  secreting  cells  elaborate  their  product.    This 

*  Guy's  Hospital  Reports,  1843. 

•j-  See  Dr.  Guy,  in  Edmb.  Med.  and  Surg.  Journal,  vols.  Ivi.  and  Ivii. 


SECRETION  OF  BILE.  521 

view  is  borne  out  by  the  results  of  Experiment,  and  of  Pathological  observa- 
tion. Thus,  if  the  Vena  Portae  be  tied,  the  secretion  of  bile  still  continues, 
though  in  diminished  quantity ;  and  several  cases  are  on  record,  in  which, 
through  a  malformation,  the  Vena  Portre  terminated  in  the  Vena  Cava  without 
ramifying  through  the  liver,  and  in  which  secretion  of  Bile  took  place, — evi- 
dently from  the  blood  of  the  Hepatic  Artery,  which  had  become  venous  by 
circulating  through  the  substance  of  the  Liver ;  and  this  blood  appears*  to 
have  passed  into  the  ramifications  of  the  Umbilical  Vein,  which  formed  a  plexus 
in  the  lobules,  exactly  resembling  the  ordinary  portal  plexus.  It  must  be  re- 
membered, however,  that  in  all  these  instances,  the  arterial  Blood  will  become 
abnormally  charged  with  the  elements  of  Bile ;  since  the  blood  of  the  chylo- 
poietic  viscera,  from  which  it  ought  to  have  been  separated,  returns  to  the 
heart  without  undergoing  any  such  purification :  and  the  secretion  of  Bile 
from  the  blood  supplied  by  the  Hepatic  Artery  under  such  circumstances 
cannot,  therefore,  be  considered  as  proving  that  the  arterial  blood  is  ordinarily 
concerned  in  the  secretion  to  the  same  degree. 

661.  That  the  proximate  elements  of  the  Bile  accumulate  in  the  Blood, 
when  from  any  cause  the  secretion  is  suspended,  is  a  fact  now  well  ascertained  ; 
and  this  satisfactorily  accounts  for  the  disturbance  of  the  other  functions,  espe- 
cially those  of  the  Nervous  system,  which  then  ensues.     When   the  sup- 
pression is  complete,  the  patient  suddenly  becomes  jaundiced,  the  powers  of 
that  system  are  speedily  lowered  (almost  as  by  a  narcotic  poison),  and  death 
rapidly  supervenes.!     When  the  secretion  is  diminished,  but  not  suspended, 
the  same  symptoms  present  themselves  in  a  less  aggravated  form.     It  is  pro- 
bable that  much  of  the  disorder  in  the  functions  of  the  Brain,  which  so  con- 
stantly accompanies  deranged  action  of  the  Digestive  system,  is  due  to  the 
less  severe  operation  of  the  same  causjj, — the  partial  retention  within  the  Blood 
of  certain  constituents  of  the  Bile,  which  should  have  eliminated  from  the  cir- 
culating ijjfcd.     In  such  a  condition,  we  derive  great  benefit  from  the  use  of 
mercuri$  medicines ;  which,  by  stimulating  the  Liver  to  increased  action,  cause 
the  removal  of  the  morbific  agent  from  the  blood.     Deficient  secretion  of  the 
Liver  may  be  recognized  as  the  cause  of  this  and  of  other  diseases,  by  the 
paleness  of  the  alvine  evacuations,  the  diffused  yellowness  of  the  surface  of 
the  body,  the  yellowish-brown  fur  upon  the  tongue  and  the  congestion  of  the 
portal  system ;  this  last  results  from  the  same  cause  as  that  which  stagnates 
the  blood  in  the  Lungs  when  there  is  deficient  Respiration  (§  548),  and  fre- 
quently occasions  Ascites,  and  other  disorders  of  the  contents  of  the  abdomen. 
An  abnormal  accumulation  of  the  elements  of  the  Bile  in  the  Blood,  is  habitual 
in  some  persons;  and  it  produces  a  degree  of  indisposition  to  bodily  or  mental 
exertion,  which  it  is  difficult  to  counteract.     It  may  often  be  recognized  by  the 
accumulation  of  dark  mucus  having  distinctly  the  taste  of  bile,  on  the  surface 
of  the  tongue,  especially  during  the  night ;  this  secretion  being  apparently 
eliminated  by  the  mucous  membrane  of  the  tongue,  when  the  function  of  the 
liver  is  not  duly  performed. 

662.  Much  discussion  has  taken  place  among  Chemists,  in  regard  to  the 
proximate  principles  of  the  Biliary  secretion ;  a  large  number  of  analyses 
having  been  made,  amongst  the  results  of  which  there  is  a  great  want  of  con- 
formity.     The   discrepancies  principally  arise  from  this  source,— that  the 
secretion  is  acted  on  with  great  facility  by  chemical  reagents ;  so  that  many 
of  the  component  parts  which  have  been  enumerated  are  not  true  educts  ;  but 
are  products  of  the  operations,  to  which  the  fluid  has  been  subjected.     The 
proportion  of  solid  matter  is  usually  from  9  to  12  per  cent. ;  and  nearly  the 

*  This,  at  least,  was  found  to  be  the  case,  in  the  only  instance  in  which  the  liver  was 
examined  with  sufficient  care. 

f  See  Dr.  Alison  in  Edinb.  Med.  and  Surg.  Journal,  vol.  xliv.,  p.  287. 

44* 


522  OF  SECRETION. 

whole  of  this  consists  of  a  substance  peculiar  to  Bile,  in  which  the  oleaginous 
character  certainly  predominates.  This  substance  contains  a  large  proportion 
of  Carbon  and  Hydrogen,  with  very  little  Azote.  We  are  probably  to  distin- 
guish it  in  two  very  different  compounds. — The  first  of  these  is  termed  Choles- 
terine;  it  is  a  white  crystallizable  fatty  matter,  somewhat  resembling  Sper- 
maceti, free  from  taste  and  odour,  not  soluble  in  water,  but  dissolving  freely  in 
alcohol,  from  which  it  is  deposited  on  cooling  in  pearly  scales.  It  is  almost 
entirely  composed  of  Carbon  and  Hydrogen  ;  its  constitution  being  36  Carbon, 
32  Hydrogen,  1  Oxygen.  This  may  be  pretty  certainly  considered  as  a  real 
proximate  element  of  the  Bile ;  since  it  frequently  separates  itself,  when  present 
in  superabundant  quantity, — forming  Biliary  Concretions,  which  are  some- 
times composed  of  this  alone,  but  more  commonly  contain  a  small  portion  of 
resinous  and  colouring  matter.  Moreover,  it  may  be  obtained  by  a  chemical 
process  of  no  great  complexity,  from  the  Serum  of  the  Blood ;  and  it  is  not 
unfrequently  deposited  as  a  result  of  diseased  action  in  other  parts  of  the  body, 
especially  in  the  fluids  of  local  Dropsies,  as  hydrocele,  ovarian  dropsy,  &c. — 
The  other  substance,  now  termed  Bilin  (formerly  Picromel),  is  that  to  which 
the  peculiar  taste  of  the  Bile,  which  is  at  the  same  time  bitter  and  sweet,  is 
due.  According  to  the  account  most  recently  given  of  this  compound,  by 
Berzelius,  it  is  a  translucent,  colourless,  inodorous  mass,  without  crystalliza- 
tion ;  it  is  very  soluble  in  water  and  alcohol,  but  insoluble  in  ether ;  it  contains 
nitrogen  ;  and  is  decomposed  by  heat,  with  the  formation  of  ammoniacal  pro- 
ducts. Bilin  is  a  readily  alterable  substance  ;  it  is  decomposed  by  acids  into 
five  different  substances,  namely,  Ammonia,  Taurin,  Fellinic  and  Cholinic 
acids,  and  Dyslysin ;  and  it  appears  that  this  decomposition  may  take  place  in 
the  bile  of  the  living  body.  The  last  of  these  products  appears  to  be  that 
which  has  been  spoken  of  by  some  chemists  as  the  Resin  of  the  Bile.* — The 
colouring  matter  of  the  bile  is  now  termed  Biliverdin.  It  contains  no  azote  ; 
and  that  of  the  Ox  appears  to  be  identical  with  the  Chlorophyll  of  plants. 
When  exposed  to  the  air,  it  becomes  of  a  deep  green,  absorbing  oxygen ;  and 
the  same  change  is  produced  by  nitric  acid, — the  liquor  soon  passing,  how- 
ever, to  a  red  hue.  This  frequently  takes  place  within  the  body,  in  cases  of 
Jaundice  ;  but  more  especially  in  the  urine.  Though  the  colouring  matter  is 
usually  present  but  in  small  quantity  during  health,  it  sometimes  accumulates 
in  disease,  so  as  to  produce  solid  masses,  which  include  little  else.t 

663.  The  amount  of  the  secretion  of  Bile  appears  to  bear  some  proportion 
to  that  of  the  Food  digested.  That  its  formation  is  continually  going  on  to  a 
certain  degree,  appears  unquestionable ;  but  that  its  quantity  is  greatly  in- 
creased during  the  solution  of  food  in  the  stomach,  appears  also  to  be  well 
established.  Whether  the  stimulus  to  the  increased  secretion  at  that  period 
is  occasioned  by  an  increased  flow  of  Blood,  or  is  propagated  through  the 
Nervous  System,  there  is  no  evidence  ;  the  analogy  of  the  Salivary,  Lachry- 

*  By  Demar5ay  it  is  considered  that  the  organic  matter  of  Bile  is  to  be  regarded  as  a 
Soap,  formed  by  the  union  of  an  acid  with  soda.  Of  this  acid,  which  he  has  named  the 
Choleic,  the  following  is  the  composition  according  to  Liebig;— C.  76,  H.  66,  N.  2,  0.  22. 
Dr.  Kemp,  whose  analyses  are  the  most  recent,  agrees  with  Demargay  in  regarding  the 
organic  matter  of  Bile  as  an  electro-negative  body  in  combination  with  soda;  but  he  holds 
that  this  is  neither  the  choleic  acid  of  Demarcay  (since  it  is  not  precipitated  from  the  soda, 
as  that  acid  is,  by  acetic  acid),  nor  the  bilin  of  Berzelius  (not  being  precipitated  from  the 
soda  by  carbonic  acid).  He  has  therefore  termed  it  Bilic  acid.  It  has  a  peculiar  bitter, 
sweet  taste ;  and  in  mass  resembles  a  fine  resin.  Dr.  Kemp  has  further  pointed  out,  that 
there  is  a  much  greater  difference  than  is  usually  imagined  between  the  bile  in  the 
hepatic  ducts,  and  that  of  the  gall-bladder;  the  former,  in  the  Ox,  being  destitute  of  the 
bitter  taste  of  the  latter,  and  having  a  different  smell. 

f  A  full  account  of  the  latest  researches  of  Berzelius  on  this  subject  will  be  found  in 
Graham's  Chemistry,  [Am.  ed.,  p.  704.] 


SECRETION  OF  BILE.  533 

mal,  and  other  secretions  would  indicate  the  latter.  In  those  animals  which 
are  most  constantly  ingesting  food,  we  find  no  Gall-bladder ;  for  in  them,  the 
Bile  may  be  poured  into  the  Intestine  as  fast  as  it  is  formed.  In  those  which 
only  take  food  occasionally,  on  the  other  hand,  and  which  are  provided  with  a 
Gall-bladder,  the  Bile,  when  not  required  in  the  Intestine,  flows  back  into  that 
reservoir.  This  reflux  would  appear  due  to  the  valve-like  termination  of  the 
Ductus  Choledochus  in  the  walls  of  the  Intestine  ;  by  which  a  certain  resist- 
ance is  offered  to  the  entrance  of  the  fluid,  unless  it  be  propelled  by  some 
decided  force.  The  flow  of  Bile  into  the  Intestinal  tube,  when  its  action  is 
needed  there,  is  commonly  imputed  to  the  pressure  of  the  distended  Duodenum 
against  the  Gall-bladder ;  it  may  be  doubted,  however,  whether  the  contractile 
power  of  the  Duct  itself  does  not  afford  important  aid  in  the  process  ;  and  it  is 
easy  to  understand,  from  the  known  influence  of  the  Sympathetic  system  of 
nerves  upon  it  (§  654),  that  peristaltic  movements  may  be  excited  at  the  time 
when  they  are  needed.  It  is  an  interesting  fact,  proving  how  completely  the 
passage  of  Bile  into  the  Intestine  is  dependent  upon  the  presence  of  aliment 
in  the  latter,  that  the  Gall-bladder  is  almost  invariably  found  turgid  in  persons 
who  have  died  of  starvation ;  the  secretion  formed  at  the  ordinary  slow  rate 
having  gradually  accumulated  for  want  of  demand.  This  fact  is  important  in 
juridical  inquiries. 

664.  Of  the  operation  of  the  Bile  in  the  Digestive  process,  enough  has 
already  been  said  (§  446).      No  certain  information  has  yet  been  obtained, 
whether  any  of  the  elements  of  the  Bile  itself  are  absorbed  in  the  form  of 
Chyle ;  or  whether  the  Bile  acts  simply  as  a  precipitant,  and  is  altogether 
cast  out  of  the  system,  with  the  useless  portion  of  the  chyme.     There  can  be 
no  question,  however,  that  by  far  the  largest  part  of  the  secretion  is  destined 
to  be  entirely  thrown  off;  and  it  would  seem,  from  the  character  of  its  proxi- 
mate elements,  as  if  it  were  intended  to  remove  from  the  Blood  its  superfluous 
Hydro-Carbon, — whether  this  have  been  absorbed  as  such  from  the  aliment, 
or  have  been  taken  up  by  the  Blood  as  effete  matter,  during  the  course  of  the 
circulation.     If  more  non-azotized  food  be  taken  into  the  system  than  can 
be  got  rid  of  by  the  Respiratory  process,  and  if  there  is  not  a  sufficiently  rapid 
production  of  Adipose  tissue  to  admit  of  its  being  deposited  as  Fat,  it  would 
accumulate  in  the  Blood,  unless  separated  by  the  Liver.     If  too  much  work 
be  thrown  upon  this  organ,  its  function  becomes  disordered,  from  its  inability 
to  separate  from  the  Blood  all  that  it  should  draw  off:  the  injurious  substances 
accumulate  in  the   Blood,  therefore,  producing  various  symptoms  that  are 
known  under  the  general  term  of  bilious.    This  is  particularly  liable  to  happen 
in  warm  climates,  in  consequence  of  the  diminished  excretion  through  the 
Lungs, — occasioned  by  the  warmth  of  the  surrounding  air,  and  the  small 
quantity  of  exercise  usually  taken.     To  remove  these  symptoms,  medicines 
are  required,  which  shall  stimulate  the  Liver  to  increased  action.     The  con- 
stant use  of  such,  however,  has  a  very  pernicious  effect  upon  the  constitution ; 
and  careful  attention  to  the  regulation  of  the  diet,— especially  the  avoidance 
of  a  superfluity  of  oily  or  farinaceous  matter, — together  with  the  employment 
of  an  increased  amount  of  exercise,  will  probably  answer  the  same  end  in  a 
much  better  manner.     Besides  the  source  of  Biliary  matter  already  pointed 
out,  in  the  decomposition  of  the  Fibrinous  tissues  (§  648),  it  seems  probable 
that  there  is  another  very  important  one  in  the  continual  waste  of  Nervous 
matter,  which  nearly  approaches  bile  in  composition  (§  643) ;  especially  if,  as 
asserted  by  Fremy,  the  peculiar  acids  of  the  Brain  may  be  detected  in  the 
Liver.     In  cases  of  slow  Asphyxia,  the  amount  of  the  Biliary  secretion  is 
much  increased. 

665.  It  would  not  seem  improbable,  that  the  Liver  acts  towards  the  absorbed 
matters  which  enter  the  blood  by  the  Mesenteric  Veins,  the  same  part  which 


524  OF  SECRETION. 

the  Lungs  perform  for  those  which  are  introduced  through  the  Lymphatic 
system ;  namely,  the  affording  an  opportunity  for  the  excretion  of  superfluous 
or  injurious  substances  contained  in  the  absorbed  fluid,  before  it  enters  the 
general  current  of  the  Circulation.  There  is  every  reason  to  believe  that  the 
conversion  of  Chyle  into  Blood  is  a  slow  process,  requiring  the  prolonged 
influence  of  the  latter  fluid  upon  the  former;  during  this  influence  many 
chemical  changes  take  place,  which  are  almost  certain  to  be  attended  with  an 
extrication  of  Carbon  and  Hydrogen,  these  being  the  ingredients  of  which  the 
Chyle  contains  most,  when  compared  with  Blood ;  and  for  the  extrication  of 
these,  the  Lungs  and  Liver  afford  ready  means.  Hence  we  see  why  the 
Lacteal  system  should  terminate  in  a  Venous  trunk  near  the  Heart,  so  that  the 
fluid  discharged  by  it  will  proceed  at  once  to  the  Lungs ;  and  why  the  Liver, 
wherever  it  has  a  distinct  circulation,  should  receive  the  blood  from  the  walls 
of  the  Intestines.*  This  view  derives  interesting  confirmation  from  the  ex- 
periments of  Cruveilhier,  on  the  artificial  production  of  purulent  deposits  by 
injection  of  Mercury  into  the  veins.  He  found  that  when  the  mercury  was 
introduced  into  any  part  of  the  general  Venous  system,  abscesses  in  the  Lungs 
were  induced ;  each  inclosing  a  globule,  the  irritation  occasioned  by  which 
was  the  cause  of  the  purulent  deposit.  When  the  mercury  was  introduced 
into  one  of  the  Intestinal  veins,  on  the  other  hand,  similar  purulent  deposits 
occurred  in  the  Liver.  It  is  well  known  that  abscesses  in  the  Lungs  and 
Liver  are  very  common  in  sequelae  of  wounds  of  the  head,  and  of  surgical 
operations,  especially  those  involving  bones  ;  and  there  seems  good  reason  to 
believe  that  in  such  cases  Pus  (or  some  of  its  elements,  which  may  act  the 
part  of  a.  ferment  in  exciting  suppuration  elsewhere),  is  actually  carried  along 
with  the  current  of  blood  into  the  Lungs  and  Liver ;  and  that,  like  the  glo- 
bules of  mercury,  not  being  susceptible  of  elimination  by  these  two  great 
emunctories,  it  acts  as  a  disturbing  cause,  and  occasions  disease  of  their  tissue. 
The  fact  that  a  considerable  amount  of  Copper  may  be  detected  in  the  sub- 
stance of  the  Liver,  after  the  prolonged  introduction  of  its  salts  into  the  system, 
seems  to  add  weight  to  this  view  of  its  function.  It  is  yet  to  be  ascertained, 
however,  why  some  substances  should  be  arrested  in  this  organ,  whilst  others 
are  allowed  to  pass. 

III.   The  Kidneys. — Secretion  of  Urine. 

666.  The  Kidneys  cannot  be  regarded  as  inferior  in  importance  to  the 
Liver,  when  considered  merely  as  excreting  organs  ;  but  their  functions  only 
consist  in  separating  from  the  blood  certain  effete  substances,  which  are  to  be 
thrown  off  from  it ;  and  has  no  direct  connection  with  any  of  the  nutritive 
operations  concerned  in  the  introduction  of  aliment  into  the  system.  Organs 
destined  to  the  elaboration  of  a  Urinary  secretion  may  be  traced  very  low 
down  in  the  Animal  scale.  Among  many  of  the  Mollusca  we  find  a  small  sac, 
filled  with  a  semi-fluid  secretion  which  has  been  shown  to  contain  uric  acid, 
opening  into  the  intestine  near  its  anal  orifice.  In  Insects,  we  often  meet  with 
prolonged  tubes,  resembling  the  biliary  vessels  in  form,  but  terminating  in  a 
lower  part  of  the  intestinal  tube ;  in  some  species  these  are  dilated  near  their 
extremity  into  a  receptacle  for  their  secretion,  or  a  urinary  bladder.  Through- 
out the  Vertebrated  classes,  they  exist  in  a  still  more  evident  form.  They  are 
uniformly  composed  of  a  congeries  of  prolonged  tubes,  subdividing  and  rami- 
fying more  or  less ;  which  spring  from  the  ureter  or  efferent  duct,  and  termi- 

*  Among  the  Mollusca,  the  chyle  is  absorbed  by  the  mesenteric  veins,  there  being  no 
separate  lacteal  system.  These  veins,  instead  of -returning  to  the  heart  through  the  liver, 
terminate  in  the  branchial  vessels;  and  the  process  of  depuration  is  effected  by  the  gills. 
Their  liver  is  supplied  only  by  the  hepatic  artery. 


THE  KIDNEYS SECRETION  OF  URINE. 


525 


[Fig.  147. 


Fig.  148. 


A  view  of  the  Right  Kidney  with  its  Renal  Capsule; 
1,  anterior  face  of  the  kidney  ;  2,  external  or  convex 
edge ;  3,  its  internal  edge ;  4,  hilum  renale ;  5,  inferior 
extremity  of  the  kidney;  6,  pelvis  of  the  ureter;  7, 
ureter;  8,  9,  superior  and  inferior  branches  of  the 
emulgent  artery ;  10, 11, 12,  the  three  branches  of  the 
emulgent  vein;  13,  anterior  face  of  the  renal  capsule; 
14,  its  superior  edge ;  15,  its  external  edge;  16,  its  in- 
ternal extremity;  17,  the  fissure  on  the  anterior  face 
of  the  capsule.] 

[Fig.  149. 


A  section  of  the  Kidney,  surmounted  by  the 
Supra-Renal  Cupsule;  1,  the  supra-renal  cap- 
sule; 2,  the  vascular  portion;  3,  3,  its  tubular 
portion,  consisting  of  cones ;  4,  4,  two  of  the 
calices,  receiving  the  apex  of  their  correspond- 
ing cones;  5,  5,  5,  the  three  infundibula;  6,  the 
pelvis ;  7,  the  ureter. 


A  view  of  half  a  Kidney  divided  vertically  from  its  convex 
to  its  concave  edge;  one  of  its  extremities  is  perfect;  1, 1, 
the  lobes  which  form  the  kidney ;  2, 2,  the  lines  of  separation 
of  these  lobes ;  3,  the  cortical  substance ;  4,  5,  the  pyramids 
of  Malpighi;  6,  the  hilum  renale  split  up  and  cleared  of  its 
vessels ;  7,  7,  points  to  the  tubes  of  Bellini ;  8,  one  of  the 
papillae;  9, 10,  two  other  papillae,  uncut,  but  deprived  of  the 
calices  that  surrounded  them;  11,  OTIC  of  the  foveolae  in  the 
papilla;  12, 12,  the  vascular  circle  surrounding  the  papilla?; 
13,  circumference  of  the  tubular  portion;  14,  external  surface 
of  the  kidney ;  15,  the  portion  of  its  external  surface  on  a 
line  with  its  fissure.] 


Represents  the  half  of  a  Kidney  divided 
vertically,  and  with  its  arteries  injected  ! 
the  matter  has  also  passed  into  the  ex- 
cretory ducts ;  1, 2,  branches  of  the  emul- 
gent artery ;  3,  3,  hilum  renale ;  4,  4,  cor- 
tical substance,  as  essentially  formed  by. 
the  capillary  terminations  of  the  vessels 
of  the  kidney ;  5,  medullary  or  tubular 
portion.] 


526  OF  SECRETION. 

nate  either  in  blind  extremities,  or  in  a  plexus  formed  by  their  inosculation. 
There  are  considerable  variations  in  the  arrangement  of  these  tubes,  however, 
in  different  tribes  of  animals.  In  Fishes,  the  Kidneys  very  commonly  extend 
the  whole  length  of  the  abdomen ;  and  they  consist  of  tufts  of  uniform-sized 
tubules,  which  shoot  out  transversely  at  intervals  from  the  long  ureter.  These 
tubes  frequently  divide  into  pairs,  but  without  any  great  alteration  in  their 
diameter.  They  appear  to  terminate  in  coscal  extremities,  without  any  inos- 
culation ;  the  number  of  bifurcations,  and  the  degree  of  convolution,  vary 
greatly  in  different  species.  The  uriniferous  tubes  are  connected  together  by 
a  very  loose  areolar  web.  The  structure  of  the  gland  in  Reptiles  appears  to 
be  essentially  the  same  ;  its  form,  however,  varies  considerably  in  the  different 
tribes,  being  greatly  prolonged  in  the  Serpents,  and  abbreviated  in  the  Tor- 
toises. In  the  Crocodile,  the  distinction  between  the  cortical  and  medullary 
portion  begins  to  show  itself;  the  tubes  being  nearly  straight  where  they  issue 
from  the  ureter,  and  being  convoluted  near  the  surface  only  of  the  lobes.  The 
Corpora  Malpighiana  (§  667),  however,  where  they  exist  in  this  class,  are 
scattered  through  the  whole  substance ;  not  being  confined,  as  in  higher 
animals,  to  the  cortical  portion.— In  Birds,  the  Urinary  tubes,  forming  the 
several  clusters,  are  more  closely  united  together ;  they  frequently  ramify  to 
a  considerable  degree. — In  the  Mammalia,  as  in  Man,  there  is  an  evident  dis- 
tinction between  the  straight  and  the  convoluted  portions  of  the  system  of 
tubes ;  the  former  character  is  seen  in  the  medullary  substance ;  the  latter  is 
the  cortical.  In  nearly  all  below  the  Mammalia,  the  kidneys  present  exter- 
nally a  lobulated  aspect ;  resulting  from  the  want  of  union  between  the  dif- 
ferent bundles  of  tubes,  which  arise  from  separate  parts  of  the  ureter.  In  the 
kidney  of  the  Mammalia,  however,  the  ureter  dilates  into  a  capacious  recep- 
tacle, towards  which  the  several  bundles  of  uriniferous  tubes  converge,  so  that 
they  open  into  it  in  close  proximity  with  each  other;  and  the  lobules  formed 
by  these  bundles  are  so  closely  brought  together,  that  no  appearance  of  a 
division  presents  itself,  until  a  section  of  the  gland  is  made.  Among  some 
Mammalia,  however,  the  lower  form  is  still  retained ;  and  it  is  presented  in 
the  Human  species  also,  at  an  early  period  of  its  foetal  development. 

667.  The  following  is  an  account  of  the  structure  of  the  Kidney,  according 
to  the  most  recent  investigations. 

a.  The  distinction  between  the  cortical  and  medullary  parts  of  the  Kidney  essentially 
consists  in  this, — that  the  former  is  by  far  the  most  vascular,  and  the  plexus  formed  by 
the  tubuli  uriniferi  seems  to  come  into  the  closest  relation  with  that  of  the  sanguiferous 
capillaries,  so  that  it  is  probably  the  seat  of  the  greater  part  of  the  process  of  secretion ; 
whilst  the  latter  is  principally  composed  of  tubes,  passing  in  a  straight  line  from  the 
former  towards  their  point  of  entrance  into  the  ureter.    In  this  respect  there  is  a  consider- 
able analogy  of  structure  and  comparative  function,  between  the  two  parts  of  the  kidney 
and  the  two  parts  of  the  brain.    The  adjoined  figure  represents  the  appearances  presented 
by  a  portion  of  an  injected  kidney,  as  seen  by  the  naked  eye,  and  under  a  low  magnifying 
power.     The  tubuli  uriniferi,  in  passing  outwards  from  the  calices,  increase  in  number 
by  divarication,  to  a  considerable  extent,  as  shown  in  Fig.  148;  but  their  diameter  re- 
mains the  same.     When  they  arrive  in  the  cortical  substance,  their  previously  straight 
direction  is  departed  from,  and  they  become  much  convoluted.     The  closeness  of  the 
texture  formed  by  their  interlacement  with  the  blood-vessels,  renders  it  difficult  to  obtain 
a  clear  view  of  their  mode  of  termination.    They  seem  to  inosculate  with  each  other, 
forming  a  plexus,  with  a  free  extremity  here  and  there  (Fig.  154)  ;  each  of  which  (ac- 
cording to  Mr.  Bowman)  is  connected,  in  the  manner  to  be  presently  described,  with  one 
of  the  Corpora  Malpighiana.    The  number  of  these  free  extremities,  however,  does  not 
appear  to  be  nearly  equal  to  that  of  the  uriniferous  tubes  themselves. 

b.  Scattered  through  the  plexus  formed  by  the  blood-vessels  and  uriniferous  tubes,  a 
number  of  little  dark  points  may  be  seen  with  the  naked  eye,  to  which  the  designation  of 
Corpora  Malpighiana  has  been  given,  after  the  name  of  their  discoverer.    Each  one  of 
these,  when  examined  with  a  high  magnifying  power,  is  found  to  consist  of  a  mass  of 
minute  blood-vessels  (Fig.  154,g);  somewhat  resembling  those  convoluted  masses  of  Ab- 


SECRETION  OF  URINE 
[Fig.  151. 


527 


A  section  of  one  of  the  Pyramids  of  Malpighi,  and  of  its  corresponding  cortical  substance,  as  seen  under 
the  microscope ;  1,  portion  of  the  surface  of  the  kidney ;  2,  from  this  figure  up  to  1,  is  the  cortical  substance  of 
the  kidney ;  3,  from  2  to  this  number  is  the  tubular  portion ;  4,  the  foveola;  5, 6,  arteries  and  veins  ramifying 
through  the  kidney;  7,  arteries  to  the  acina  of  the  kidney ;  8,  capillary  extremities  of  veins  anastomosing 
with  corresponding  arterioles;  9,  tortuous  extremities  of  the  arteries  directed  into  the  interior  of  the  gland  ; 
10,  bases  of  the  cones  of  the  cortical  and  pyramidal  substance  of  the  kidney;  from  10  to  4  is  a  collection 
of  these  cones;  11,  the  envelop  of  the  cortieal  layer;  12,  prolongations  of  the  tubular  portion;  13.  tortuous 
tubes,  or  those  of  Ferrien;  14,  straight  tubes,  or  those  of  Bellini;  15,  vessels  which  wind  between  them: 
1C,  course  of  the  uriniferous  tubes  in  the  tubular  portion;  17,  the  matter  between  these  tubes;  16,  bifurcation 
of  <he  straight  tubes;  19,  sections  of  these  tubes;  20,  their  orifices.] 

sorbents,  termed  Lymphatic  Glands.  According  to  the  recent  inquiries  of  Mr.  Bowman,* 
each  one  of  these  is  included  in  the  extremity  of  one  of  the  tubuli  uriniferi,  which  swells 
into  a  flask-like  dilatation  to  receive  it  (Fig.  155,  c').  The  Epithelium  which  elsewhere 
lines  the  tube  (whose  usual  character  is  shown  in  Fig.  153)  is  altered  in  appearance,  where 

*  Philosophical  Transactions,  1842. 


528 


OF  SECRETION. 


Fig.  152. 


Fig.  153. 


Portion  of  the  Kidney  of  a  new-born  infant;  A,  natural  Supposed  coecal  extremity  of  one  of  the 

size ;  1, 1,  corpora  Malpighiana,  as  dispersed  points  in  the  tubuli  uriniferi,  from  the  kidney  of  an 

cortical  substance;  2,  2,  papilla;  B,  a  smaller  part  magni-  adult;  showing  its  tesselated  epithelium — 

fied;  1, 1,  corpora  Malpighiana;  2,  2,  tubuli  uriniferi  (After  magnified 250 diameters.  (After  Wagner.) 
Wagner.) 

the  tube  is  continuous  with  this  capsular  dilatation  (Fig.  155,6');  being  there  more  trans- 
parent, and  furnished  with  cilia  (as  shown  at  6"),  which  in  the  Frog  may  be  seen,  for 
many  hours  after  death,  in  very  active  motion,  directing  a  current  down  the  tube.  Fur- 
ther within  the  capsule,  the  Epithelium  is  excessively  delicate,  and  even  in  many  cases 
absent. — The  Renal  Artery,  on  entering  the  Kidney,  divides  itself  into  minute  twigs, 
which  are  the  afferent  vessels  of  the  Malpighian  tufts  (Fig.  156).  After  it  has  pierced  the 
capsule,  the  twig  dilates ;  and  suddenly  divides  and  subdivides  itself  into  several  minute 
branches,  terminating  in  convoluted  capillaries,  which  are  collected  in  the  form  of  a  ball; 
and  from  the  interior  of  the  ball,  the  solitary  efferent  vessel  arises,  which  passes  out  of 
the  capsule  by  the  side  of  the  single  afferent  vessel.  This  ball  lies  loose  and  bare  in  the 
capsule,  being  attached  to  it  only  by  its  afferent  and  efferent  vessels  (Fig.  156,  m);  and 
every  vessel  composing  it  is  bare  and  uncovered, — an  arrangement  of  which  the  economy 
presents  no  other  example.  The  efferent  vessels,  on  leaving  the  Malpighian  bodies,  sepa- 
rately enter  the  plexus  of  capillaries  surrounding  the  tubuli  uriniferi,  and  supply  that 
plexus  with  blood ;  from  this  plexus  the  renal  vein  arises.— In  Mr.  Bowman's  opinion,  all 
the  free  extremities  of  the  tubuli  uriniferi  thus  include  Corpora  Malpighiana;  and  the  ap- 
pearance of  coecal  terminations,  such  as  those  represented  in  Fig.  153,  and  at  a  and  c  Fig. 
154,  he  regards  as  an  optical  illusion,  caused  by  a  change  in  the  direction  of  the  tubuli, 
which  occasions  them  to  dip  away  suddenly  from  the  observer. 

c.  The  Embryological  Development  of  the  Urinary  organs  in  Vertebrated  animals  is  a 
subject  of  peculiar  interest,  owing  to  the  correspondence  which  may  be  traced  between 
the  transitory  forms  they  present  in  the  higher  classes,  and  their  permanent  condition  in 
the  lower.  In  this  respect  there  is  an  evident  analogy  with  the  Respiratory  system ;  and 
it  may  be  remarked  that  the  analogy  does  not  cease  here.  Both  the  Urinary  and  the  Pul- 
monary organs  are  destined  to  excrete  the  products  of  decomposition,  united  in  their  sim- 
plest forms  of  combination ;— carbon  and  oxygen  being  thrown  off  from  the  lungs  or  gills, 
in  the  form  of  carbonic  acid  ; — and  carbon  and  nitrogen  from  the  kidneys,  in  the  form  of 
cyanogen,  which  unites  with  oxygen  to  produce  cyanic  acid,  and  this  combines  with  am- 
monia (a  compound  of  nitrogen  and  hydrogen)  to  form  urea,  the  characteristic  element  of 
the  urinary  secretion.  Both  organs,  moreover,  have  the  important  function  of  getting  rid 
of  the  superfluous  fluid  of  the  body.  Again,  it  is  an  interesting  fact  that,  in  the  Holo- 
thuria  and  other  animals  of  its  type,  the  Respiration  is  performed  by  the  introduction  of 
water  through  a  system  of  branching  tubes,  that  extend  from  the  cloaca  into  the  interior 
of  the  body;  this  system  of  tubes,  considered  in  regard  to  its  structure  and  position,  is 
evidently  analogous  to  the  Urinary  apparatus  of  higher  animals. — The  first  appearance 
of  any  thing  resembling  a  Urinary  apparatus  in  the  Chick,  is  seen  on  the  second  half  of 
the  third  day.  The  form  at  that  time  presented  by  it  is  that  of  a  long  canal,  extending  on 
each  side  of  the  Spinal  Column  from  the  region  of  the  heart  towards  the  Allantois ;  and 
the  sides  of  this  present  a  series  of  elevations  and  depressions,  indicative  of  the  com- 
mencing development  of  coeca.  On  the  fourth  day,  the  Corpora  Wolffiana,  as  they  are 
then  termed,  are  distinctly  recognized,  as  composed  of  a  series  of  coecal  appendages, 
which  are  attached  along  the  whole  course  of  the  first-mentioned  canal,  opening  into  its 
outer  side.  On  the  fifth  day  these  appendages  are  convoluted,  and  the  body  which  they 
form  acquires  increased  breadth  and  thickness.  They  evidently  then  possess  a  secreting 
function ;  and  the  fluid  which  they  separate  is  poured  by  the  long  straight  canal  into  the 


SECRETION  OF  URINE. 

Fig.  154. 


529 


A  small  portion  of  the  Kidney,  magnified  about  60  times;  1,  supposed  coecal  extremity  of  a  tubulus 
uriniferus;  3,3,  recurrent  loops  of  tubuli;  5,5,  bifurcations  of  tubuli;  4,  5,  6,  tubuli  converging  towards 
the  papilla ;  7,  7,  7,  Corpora  Malpighiana,  seen  to  consist  of  plexuses  of  blood-vessels,  connected  with  a 
capillary  net-work;  8,  arterial  trunk.  (After  Wagner.) 

cloaca.  Between  their  component  shut  sacs,  numbers  of  small  points  appear,  which 
consist  of  little  clusters  of  con  voluted  vessels,exactly  analogous  to  the  Corpora  Malpighiana 
of  the  kidney. — The  Corpora  Wolffiana,  however,  have  only  a  temporary  existence  in  the 
higher  Vertebrata;  although  it  seems  that,  in  Fishes,  they  constitute  the  permanent  kid- 
45 


530 


OF  SECRETION. 


Fig.  155. 


Fig.  156. 


Uriniferous  Tube,  Malpighian  Tuft  and  Capsule, 
from  Kidney  of  Frog;  a,  cavity  of  the  tube;  b, 
epithelium  of  the  tube;  6',  ciliated  epithelium  of 
the  neck  of  the  capsule;  b",  detached  epithelium 
scale ;  c,  basement  membrane  of  tube ;  e' ,  basement 
membrane  of  capsule.  Magnified  about  320  dia- 
meters. (After  Bowman.) 


Distribution  of  the  Renal  vessels,  from  Kidney 
of  Horse ;  a,  branch  of  renal  artery ;  a/",  afferent 
vessel ;  m,  m,  Malpighian  tufts;  tf,  rf,  efferent  ves- 
sels; p,  vascular  plexus  surrounding  the  tubes; 
st,  straight  tube;  ct,  convoluted  tube.  Magnified 
about  30  diameters.  (After  Bowman.) 


ney.*     The  development  of 
day.    They  are  seen  on  the 


157. 


Corpora  Wolffiana,  with  kidney 
and  testes,  from  embryo  of  Bird  ; 
1,  kidney;  2,  2,  ureters;  3,  corpus 
Wolffianum ;  4,  its  excretory  duct ; 
5,  5,  testicles;  at  the  summit  are 
seen  the  supra-renal  capsules. — 
(After  Miiller.) 


the  true  Kidneys  commences  in  the  Chick  about  the  fifth 
sixth,  as  lobulated  grayish  masses,  which  sprout  from  the 
outer  edges  of  the  Wolffian  bodies ;  and  they  gradually 
increase,  the  temporary  organs  diminishing  in  the  same 
proportion.  The  sexual  organs,  as  will  be  hereafter  ex- 
plained (§  699),  also  originate  in  the  Wolffian  bodies  ;  and 
at  the  end  of  foetal  life,  the  only  vestige  of  the  latter  is  to 
be  found  as  a  shrunk  rudiment  situated  near  the  testes  of 
the  male. — The  progress  of  development  in  the  Human 
embryo  seems  closely  conformable  to  the  foregoing  ac- 
count. The  Wolffian  bodies  begin  to  appear  towards  the 
end  of  the  first  month;  and  it  is  in  the  course  of  the  sev- 
enth week,  that  the  true  Kidneys  first  present  themselves. 
From  the  beginning  of  the  third  month,  the  diminution  in 
the  size  of  the  Wolffian  bodies  goes  on  part  passu  with  the 
increase  of  the  Kidneys:  and  at  the  time  of  birth,  scarcely 
any  traces  of  them  can  be  found.  At  the  end  of  the  third 
month,  the  kidneys  consist  of  seven  or  eight  lobes,  the  fu- 
ture pyramids;  their  excretory  ducts"  still  terminate  in  the 
same  canal  which  receives  those  of  the  Wolffian  bodies 
and  of  the  sexual  organs  ;  and  this  opens,  with  the  rectum, 
into  a  sort  of  cloaca,  or  sinus  urogenitalis,  analogous  to 
that  which  is  permanent  in  the  oviparous  Vertebrata.  The 
Kidneys  are  at  this  time  covered  by  the  Supra-Renal  Cap- 
sules, which  are  very  large  ;  about  the  sixth  month,  how- 
ever, these  have  decreased,  whilst  the  kidneys  have  in- 
creased, so  that  their  proportional  weight  is  as  1  to  2£.  At 
birth,  the  weight  of  the  Kidneys  is  about  three  times  that 
of  the  Supra-Renal  Capsules;  and  they  bear  to  the  whole 
body  the  proportion  of  1  to  80:  in  the  adult,  however,  they 


See  Principles  of  General  and  Comparative  Physiology,  §659. 


SECRETION  OF  URINE.  531 

are  no  more  than  1  to  240.  The  Corpora  Wolffiana  are,  when  at  their  greatest  deve- 
lopment, the  most  vascular  parts  of  the  body  next  to  the  liver;  four  or  five  branches 
from  the  aorta  are  distributed  to  each,  and  two  veins  are  returned  from  each  to  the  vena 
cava.  The  upper  veins  and  their  corresponding  arteries  are  converted  into  the  Renal  or 
emulgent  vessels,  and  the  lower  into  Spermatic  vessels.  The  lobulated  appearance  of 
the  kidney  gradually  disappears;  partly  in  consequence  of  the  condensation  of  the  areo- 
lar  tissue,  which  connects  the  different  parts;  and  partly  through  the  development  of  ad- 
ditional tubuli  in  the  interstices.  The  Urinary  Bladder  is  formed  quite  independently  of 
the  secreting  apparatus,  being  a  part  of  the  allantois,  which  is  first  developed  as  a  large 
ccecum  or  diverticulum  from  the  lower  extremity  of  the  alimentary  canal  (Chap.  xiv.). 
The  part  of  the  tube  below  this  forms  the  Cloaca,  or  common  termination  of  the  intesti- 
nal and  vesical  apparatus.  The  sides  of  this  cloaca,  however,  gradually  approach  one 
another,  so  as  to  form  a  transverse  partition,  which  separates  the  Rectum  from  the  Genito- 
urinary canal;  and  the  Urethra  of  the  female  is  afterwards  separated  from  the  Vagina 
by  a  similar  process. 

668.  The  researches  of  Mr.  Bowman  on  the  structure  of  the  Malpighian 
bodies,  and  on  the  vascular  apparatus  of  the  Kidney,  have  thrown  great  light 
upon  the  mode  in  which  the  Urinary  secretion  is  elaborated.  One  of  the 
most  remarkable  circumstances  attending  this  excretion,  in  the  Mammalia 
particularly,  is  the  large  but  variable  quantity  of  water,  which  is  thus  got  rid 
of, — the  amount  of  which  bears  no  constant  proportion  to  that  of  the  solid  mat- 
ter dissolved  in  it.  The  Kidneys,  in  fact,  seern  to  form  a  kind  of  regulating 
valve,  by  which  the  quantity  of  water  in  the  system  is  kept  to  its  proper 
amount.  The  Exhalation  from  the  Skin,  which  is  the  other  principal  means 
of  removing  the  superfluous  liquid  from  the  blood,  is  liable  to  great  variations, 
from  the  temperature  of  the  air  around  (§  731) :  hence,  if  there  were  not  some 
other  means  of  adjusting  the  quantity  of  fluid  in  the  Blood-vessels,  it  would  be 
liable  to  continual  and  very  injurious  variation.  This  important  function  is 
performed  by  the  Kidneys ;  which  allow  such  a  quantity  of  water  to  pass  into 
the  urinary  tubes  as  may  keep  the  pressure  within  the  vessels  nearly  at  a 
uniform  standard.  The  quantity  of  water  which  is  passed  off  by  the  Kidneys, 
therefore,  will  depend  in  part  upon  that  exhaled  by  the  Skin ;  being  greatest 
when  this  is  least,  and  vice  versa:  but  the  quantity  of  solid  matter  to  be  con- 
veyed away  in  the  secretion  has  little  to  do  with  this ;  being  dependent  upon 
the  amount  of  waste  in  the  system,  and  upon  the  quantity  of  surplus  azotized 
aliment  which  has  to  be  discharged  through  this  channel. — The  Kidney  con- 
tains two  very  distinct  provisions  for  these  purposes.  The  cells  lining  the 
Tubuli  Uriniferi  are  probably  here,  as  elsewhere,  the  instruments  by  which 
the  solid  matter  of  the  secretion  is  elaborated  ;  whilst  it  can  scarcely  be 
doubted  that  the  office  of  the  Corpora  Malpighiana  is  to  allow  the  transudation 
of  the  superfluous  fluid  through  the  thin- walled  and  naked  capillaries  of  which 
they  are  composed.  "It  would,  indeed,"  Mr.  Bowman  remarks,  "be  difficult 
to  conceive  a  disposition  of  parts  more  calculated  to  favour  the  escape  of  water 
from  the  blood  than  that  of  the  Malpighian  body.  A  large  artery  breaks  up 
in  a  very  direct  manner  into  a  number  of  minute  branches ;  each  of  which 
suddenly  opens  into  an  assemblage  of  vessels  of  far  greater  aggregate  capacity 
than  itself,  and  from  which  there  is  but  one  narrow  exit.  Hence  must  arise 
a  very  abrupt  retardation  in  the  velocity  of  the  current  of  blood.  The  vessels 
in  which  this  delay  occurs  are  uncovered  by  any  structure.  They  lie  bare  in 
a  cell,  from  which  there  is  but  one  outlet,  the  orifice  of  the  tube.  This  orifice 
is  encircled  by  cilia,  in  active  motion,  directing  a  current  towards  the  tube.— 
These  exquisite  organs  must  not  only  serve  to  carry  forward  the  fluid  which 
is  already  in  the  cell,  and  in  which  the  vascular  tuft  is  bathed ;  but  must  tend 
to  remove  pressure  from  the  free  surface  of  the  vessels,  and  so  to  encourage 
the  escape  of  their  more  fluid  contents." 

669.  There  is  a  striking  analogy  between  the  mode  in  which  the  Tubuli 
Uriniferi  are  supplied  with  blood  for  the  purpose  of  elaborating  their  secre- 


532  OF  SECRETION. 

tion,  and  the  plan  on  which  the  Hepatic  circulation  is  carried  on.  The 
secretion  of  the  Liver  is  formed  from  blood  conveyed  to  it  by  one  large  vessel, 
the  Vena  Portae,  which  has  collected  it  from  the  Venous  capillaries  of  the 
chylopoietic  viscera,  and  which  subdivides  again  to  distribute  it  through  the 
liver.  The  secretion  of  the  Kidney,  in  like  manner,  is  elaborated  from  blood 
which  has  already  passed  through  one  set  of  capillary  vessels,— 'those  of  the 
Malpighian  tufts ;  this  blood  is  collected  and  conveyed  to  the  proper  secreting 
surface,  not  by  one  large  trunk  (which  would  have  been  a  very  inconvenient 
arrangement),  but  by  a  multitude  of  small  ones, — the  efferent  vessels  of  the 
Matpighian  bodies,  which  may  be  regarded  as  collectively  representing  the 
Vena  Portae,  since  4hey  convey  the  blood  from  the  systemic  to  the  secreting 
capillaries.  Hence  The  Kidney  may  be  said  to  have  a  portal  system  within 
itself. — This  ingenious  view  of  Mr.  Bowman's  finds  support  from  the  fact  that 
in  Reptiles  (in  which,  as  in  Fishes,  the  Portal  trunk  receives  the  blood  from 
the  whole  posterior  part  of  the  body,  and  supplies  the  Kidneys  as  well  as  the 
Liver),  the  efferent  vessels  of  the  Malpighian  bodies — which  receive  .their 
blood,  as  elsewhere,  from  the  Renal  Artery — unite  with  the  branches  of  the 
Portal  vein,  to  form  the  secreting  plexus  around  the  Tubuli  Uriniferi.  Here, 
therefore,  the  blood  of  the  secreting  gle-xus  has  a  double  source ;  the  vessels 
which  supply  it  receiving  their  blood  irr  part  from  the  capillaries  of  the  organ 
itself,  and  in  part  from  those  of  viscera  external  to  it ;  just  as,  in  the  Liver,  the 
secreting  plexus  is  supplied  in  part  bijl  the  blood  conveyed  from  the  chylo- 
poietic viscera  through  the  Vena  Portae,  and  in  part  by  the  nutritive  capillaries 
of  the  organ  itself,  which  receive  their  blood  from  the  Hepatic  Artery. 

670.  The  nature  and  purpose  of  the  Urinary  secretion,  and  the  alterations 
which  it  is  liable  to  undergo  in  various  conditions  of  the  system,  are  much 
better  understood  than  are  those  of  the  Bile;  this  is  owing,  in  great  part,  to 
the  circumstance  that  it  may  be  readily  collected  in  a  state  of  purity ;  and 
that  its  ingredients  are  of  such  a^^ure,  as  to  be  easily  and  definitely  sepa- 
rated from  each  other  by  simplecllRfcic'al  means.  There  can  be  no  doubt  that 
the  chief  purpose  of  this  excretidn  is  to  remove  from  the  system  the  effete 
azotized  matters,  which  the  bloo^  takes  up  in  the  course  of  the  circulation,  or 
which  may  have  been  produced  by  changes  occurring  in  itself.  This  is  evi- 
dent from  the  large  proportion  of  Nitrogen  which  is  contained  in  the  solid 
matter  dissolved  in  it ;  and  from  the  crystalline  form  presented  by  this  solid 
matter  when  separated— a  form  which  indicates  that  its  state  of  combination 
is  such  as  to  prevent  it  from  conducing  to  the  nutrition  of  the  system.  The 
injurious  effects  of  the  retention  in  the  blood  of  the%omponents  of  the  Urinary 
secretion  are  fully  demonstrated  by  the  results  of  its  cessation  ;  whether  this 
be  made  to  take  place  experimentally  (as  by  tying  the  renal  artery),  or  be  the 
consequence  of  a  disordered  condition  of  the  kidney.  Symptoms  of  great  dis- 
order of  the  nervous  centres,  analogous  to  those  produced  by  many  narcotic 
poisons,  soon  exhibit  themselves ;  and  the  patient  dies  comatose,  if  the  secre- 
tion be  not  restored.  In  such  cases,  Urea  (the  characteristic  ingredient  of  the 
urine)  is  found  to  have  accumulated  in  the  Blood ;  and  it  may  even  be  delected 
by  the  smell,  in  the  fluid  effused  into  the  Ventricles  of  the  Brain.  The 
conclusion  which  may  be  drawn  from  this  circumstance,  regarding  the  pre- 
existence  in  the  Blood  of  the  components  of  the  secretion,  is  strengthened  by 
the  fact  that,  even  in  the  healthy  state,  Urea  may  be  detected  in  the  blood ; 
it  only  exists  there  normally,  however,  in  very  small  quantity ;  but  when 
there  is  any  impediment  to  its  excretion,  it  goes  on  accumulating,  and  produces 
consequences  more  or  less  serious  in  proportion  to  its  amount.  It  is  not  im- 
probable that,  as  in  the  case  of  the  retention  of  Bile  in  the  Blood  (§  661), 
many  of  the  minor  as  well  as  of  the  severer  forms  of  sympathetic  disturbance, 
connected  with  disordered  secretion  from  the  Kidney,  are  due  to  the  directly 


SECRETION  OF  URINE.  533 

poisonous  operation  of  the  elements  of  the  Urine,  upon  the  several  organs 
whose  function  is  disturbed ;  and  that  many  complaints,  in  which  no  such 
agency  has  been  until  recently  suspected, — especially  Convulsive  disorders 
arising  from  a  disordered  action  of  the  Nervous  centres,— are  due  to  the  in- 
sufficient elimination  of  Urea  from  the  Blood. 

671.  In  order  to  form  a  correct  opinion  of  the  state  of  the  Urinary  secretion 
in  morbid  conditions  of  the  system,  it  is  desirable  to  be  acquainted  with  every 
leading  particular  regarding  its  healthy  characters.  The  average  quantity, 
during  24  hours,  has  been  variously  estimated :  it  differs,  of  course,  with  the 
amount  of  fluid  ingested,  and  it  is  influenced  also  by  the  external  temperature, 
— a  much  smaller  amount  of  the  superfluous  fluid  of  the  body  being  set  free 
from  the  skin  in  winter  than  in  summer,  and  a  larger  proportion  being  carried 
off  by  the  kidneys.  Probably  we  shall  be  pretty  near  the  truth,  in  estimating 
the  amount  at  about  30  oz.  in  summer,  to  40  oz.  in  winter,  for  a  person  who 
does  not  drink  more  than  the  simple  wants  of  nature  require. — The  Specific 
Gravity  comes  to  be  a  very  important  character,  in  various  morbid  conditions 
of  the  urine  :  and  it  is  therefore  desirable  to  estimate  it  correctly.  This  also 
is,  of  course,  liable  to  the  same  causes  of  variation ;  since,  when  the  same 
amount  of  solid  matter  is  dissolved  in  a  larger  or  smaller  quantity  of  water,  the 
specific  gravity  will  be  proportionably  lower  or  higher.  From  long  and  repeat- 
ed attention  to  this  subject,  Dr.  Prout  is  satisfied  that  the  standard  Specific 
Gravity  of  the  Urine  of  a  healthy  person  in  the  prime  of  life,  during  the  whole 
year  in  this  country,  is  something  less  than  1020,  ranging  from  about  1015  in 
the  winter  to  1025  in  the  summer. — The  urine  of  Man  in  health  usually  ex- 
hibits an  acid  reaction ;  this  depends,  however,  upon  certain  conditions  fur- 
nished by  the  aliment ;  and  may  be  altered  (as  will  presently  appear)  by  a 
change  in  the  ingesta. — The  following  Analysis  of  Healthy  Urine  by  Berze- 
lius,  is  regarded  by  Dr.  Prout  as  correctly  representing  its  components.  We 
shall  presently  find,  however,  that  it  is  dissented  from  by  Liebig,  as  to  several 
important  particulars. 

'a.  Water 933-00 

b.  Urea 30-10 

c.  Lithic  acid   ........  I'OO 

j  C  Free  lactic  acid,  lactate  of  ammonia,  and?  17-14 

fl  £  'C        '    ^      animal  matters  not  separable  from  them    5 

e.   Mucus  of  the  bladder 0-32 

'       C  Sulphate  of  soda 3-16 

/'    ? potash 3-71 

Phosphate  of  soda 2-94 

1-65 


03 
|J 

o^i 


ammona 


7      \  Muriate  of  soda          ...... 

*"    £ ammonia  ......  1-50 

C  Earthy  phosphates,  with  trace  of  fluate  of  lime     .  1-00 

'•     )silexy  -03 


1000-00 

672.  The  most  important  of  all  these  ingredients  is  evidently  that  which, 
from  its  being  the  principal  cause  of  the  characteristic  properties  of  the  urine, 
is  termed  Urea.  This  may  be  readily  separated  from  Urine,  in  the  form  of 
transparent  colourless  crystals ;  which  have  a  faint  and  peculiar,  but  not 
urinous  odour  ;  and,  as  already  mentioned,  it  is  distinctly  traceable  in  the 
Blood,  where  it  rapidly  accumulates,  if  its  continual  elimination  be  in  any  way 
interfered  with.  It  is  very  soluble  in  water,  and  combines  with  acids  without 
neutralizing  them :  in  the  Human  urine  it  is  believed  by  Dr.  Prout  to  exist 

45* 


534  OF  SECRETION. 

in  the  state  of  a  Lactate ;  whilst  in  the  urine  of  Herbivorous  animals  it  is 
combined  with  Hippuric  acid.  In  its  chemical  composition,  it  is  identical 
with  cyanate  of  ammonia ;  and  its  composition  is  2  Carbon,  4  Hydrogen,  2 
Nitrogen,  and  2  Oxygen, — a  formula  much  more  simple  than  that  of  almost 
any  other  organic  substance.  The  amount  of  Urea  excreted  in  twenty-four 
hours  has  been  made  the  subject  of  examination  by  Lecanu  ;*  and  the  following 
are  its  results,  as  deduced  from  a  series  of  120  analyses. 

Minimum.  Mean.  Maximum. 

By  men 357-51  grs.  433-13  grs.  510-36  grs. 

£y  women         ....         153-25  295-15  437-06 

By  old  men  (84  to  86  years)       .  61-08  125-22  295-15 

By  children  of  eight  years  .          161-78  207-99  254-20 

By  children  of  four  years   .         .  57-28  59-55  81-83 

It  is  very  interesting  to  perceive,  in  this  table,  how  large  an  amount  of  Urea 
is  excreted  by  children ;  and  how  small  a  quantity,  in  proportion  to  their  bulk, 
by  old  men.  This  corresponds  precisely  with  the  rapidity  of  interstitial  change 
at  different  periods  of  life.  (See  §  646).  Moreover,  as  this  continual  disinte- 
gration is  very  much  accelerated  by  increased  vital  activity  of  the  Tissues,  the 
amount  of  Urea  undergoes  a  like  augmentation  ;  so  that — other  circumstances 
being  equal — the  amount  of  Urea  excreted  may  fairly  serve  as  a  measure  of 
the  waste  of  the  tissues,  and  consequently  of  the  degree  in  which  they  have 
been  exercised.  This  will  be  especially  the  case  in  regard  to  the  Muscular 
Tissue ;  which  constitutes  so  large  a  part  of  the  fabric.  In  some  experiments 
recently  made  on  the  influence  of  various  causes  upon  the  constitution  of 
Urine,  Dr.  Lehmann  found  that,  by  the  substitution  of  violent  for  moderate 
exercise,  the  quantity  of  Urea  was  raised  from  32£  to  45|  parts.  If  such  in- 
creased waste  be  not  compensated  by  increased  nutrition,  a  diminution  in  the 
bulk  of  the  body  is  the  necessary  consequence. 

673.  The  next  important  ingredient,  Uric  or  Lithic  Acid,  exists  much  more 
largely  in  the  Urine  of  the  lower  Vertebrata  than  in  that  of  Mammalia ;  thus 
the  nearly  solid  urinary  excretion  of  Serpents,  and  the  semi-fluid  urine  of 
Birds,  is  almost  entirely  composed  of  this  acid,  in  combination  with  Am- 
monia. Its  presence  has  not  yet  been  detected  in  healthy  blood ;  but  when 
its  elimination  is  checked,  we  are  assured  of  its  accumulation  in  the 
circulating  fluid,  by  its  deposition,  in  combination  with  Soda,  in  the  neigh- 
bourhood of  the  joints, — forming  Gouty  concretions,  or  Chalk-stones.  Pure 
Lithic  acid  crystallizes  in  fine  scales  of  a  brilliant  white  colour,  and  silky 
lustre  ;  it  is  tasteless  and  inodorous,  and  is  so  sparingly  soluble  in  water,  that 
at  least  10,000  times  its  own  weight  is  required  to  dissolve  it.  As  it  exists  in 
a  state  of  perfect  solution  in  healthy  Urine,  it  must  be  in  combination  with 
some  base  ;  and  that  this  is  the  case,  is  at  once  proved  by  the  fact,  that  it  is 
precipitated  immediately  on  the  addition  of  a  small  quantity  of  any  acid,  even 
the  Carbonic.  It  is  generally  believed  that  the  base  is  Ammonia;  but  it  has 
recently  been  affirmed  by  Liebig,t  that  the  Uric  Acid  (with  the  Hippuric)  is 
held  in  solution  by  the  Phosphate  of  Soda, — which,  from  being  Dibasic  or 
alkaline,  is  rendered  acid,  by  yielding  up  a  part  of  its  soda  to  these  organic 
acids,  which  are  thereby  rendered  soluble.  It  is  in  this  manner  that  he  partly 
explains  the  usually  acid  reaction  of  healthy  urine ;  the  other  causes  of  which 
will  be  presently  noticed. — If  there  be  an  undue  proportion  of  Lithic  acid  in 
the  urine,  it  will  be  precipitated  on  cooling ;  because  it  is  less  soluble  in  a 
cold  than  in  a  warm  solution  of  phosphate  of  soda;  and  the  same  result  will 

*  Journal  de  Pharmacie,  torn.  xxv. 
f  Lancet,  June  8,  1844. 


SECRETION  OF  URINE.  535 

happen,  if  there  be  a  predominance  of  other  acids  in  the  urine,  which  will 
seize  upon  its  base,  as  soon  as  its  own  affinity  for  it  is  diminished  by  the 
lowering  of  its  temperature.  By  Dr.  Prout  it  is  believed  that  Lactic  acid, 
existing  in  the  Blood  or  in  the  Urine  in  excess,  is  an  ordinary  source  of  this 
deposit ;  but  the  presence  of  this  acid  is  altogether  denied  by  Liebig  (§  670). 
The  composition  of  Lithic  Acid  is  as  follows : — 10  Carbon,  4  Hydrogen,  4 
Nitrogen,  6  Oxygen.  The  amount  of  it  usually  excreted  in  the  Urine  of  Man 
is  but  very  small ;  it  is  occasionally,  however,  considerably  increased  ;  but  the 
circumstances  under  which  this  increase  takes  place  have  not  yet  been  exactly 
determined. 

674.  Uric  acid  is  replaced  in  the  Herbivorous  animals  by  the  Hippuric ; 
the  composition  and  properties  of  which  are  very  different  from  those  presented 
by  that  substance.     When  pure,  it  forms  long  transparent  four-sided  prisms  ; 
it  is  soluble  in  400  parts  of  cold  water,  and  dissolves  readily  at  a  boiling  heat ; 
and  it  has  a  strong  acid  reaction,  and  bitterish  taste.     Its  formula  is  18  Carbon, 
8  Hydrogen,  1  Nitrogen,  and  5  Oxygen,  with  1  equiv.  of  Water.     It  has  very 
curious  relations  with  Benzoic  acid ;  which  it  yields,  together  with  Benzoate 
of  Ammonia,  when  acted  upon  by  a  high  temperature,  or  during  the  putrefac- 
tion of  the  urine  of  which  it  forms  a  part.     According  to  Liebig,  the  Hippuric 
acid  in  the  urine  of  the  Horse  and  Ox  is  replaced  by  Benzoic  acid,  when  the 
animal  is  subjected  to  hard  labour. — It  appears,  from  his  recent  experiments,* 
that  we  are  to  regard  Hippuric  acid  as  a  normal  element  of  Human  urine  ;  for 
he  has  detected  Benzoic  acid  among  the  products  of  its  putrefaction ;  and  as 
we  know  that  the  latter  does  not  exist  in  the  Urine  of  Man,  and  as  there  is  no 
other  substance  at  the  expense  of  which  it  can  be  formed  during  the  putre- 
factive process,  we  can  scarcely  hesitate  to  admit  that  such  must  be  the  case. 
It  is  a  very  curious  fact,  that  the  introduction  of  Benzoic  acid  into  the  system 
causes  a  large  increase  in  the  amount  of  Hippuric  acid  in  the  Urine  ;  and  if  this 
be  formed  at  the  expense  of  the  elements,  which  would  otherwise  have  pro- 
duced Uric  acid,  an  easy  method  is  pointed  out  for  the  elimination  of  the  latter 
substance  from  the  blood,  when  it  has  accumulated  there, — the  salts  of  Hippuric 
acid  being  so  much  more  soluble  than  those  of  the  Uric.     According  to  Keller,! 
whose  experiments  were  made  upon  himself,  both  Urea  and  Uric  acid  existed 
in  normal  quantity  in  his  urine  ;  whilst  a  large  quantity  of  Hippuric  acid  was 
being  excreted  ;  whilst  Mr.  Alexander  Ure  states,J  that  he  has  succeeded,  by 
the  administration  of  Benzoic  acid,  in  preventing  the  deposition  of  Gouty  con- 
cretions, and  even  in  removing  them  when  they  had  been  formed. 

675.  Many  remarkable  changes  are  effected  in  Lithic  acid,  by  the  operation 
of  other  chemical  agents ;  and  these  changes  are  very  important,  in  their  bear- 
ing on  Pathological  conditions  of  the  Urine.     When  Uric  acid  is  subjected  to 
the  action  of  Oxygen,  it  is  first  resolved  into  Urea  and  a  compound  termed 
Jilloxan.     Now  this  Alloxan,  when  acted  on  by  a  new  supply  of  Oxygen,  is 
resolved  into  Urea  and  Oxalic  acid ;  or,  with  a  still  further  amount  of  Oxygen, 
into  Urea  and  Carbonic  Acid : — a  fact,  which  has  a  very  important  bearing 
on  the  production  of  Calculi  composed  of  Uric  and  Oxalic  acids,  and  which 
explains  the  remarkable  alterations  which  are  often  observed  in  the  layers  of 
these  concretions.     It  is  affirmed  by  Liebig,  that  the  calculi  which  are  com- 
posed of  Urate  of  Ammonia,  or  of  Oxalate  of  Lime,  occur  in  persons,  in  whom, 
from  want  of  exercise,  or  from  other  causes,  the  quantity  of  Oxygen  intro- 
duced into  the  system  is  beneath  what  it  ought  to  be.     When  patients  suffer- 
ing under  Uric  acid  Calculi  take  more  exercise,  the  Urates  are  replaced  by 
Oxalates,  in  consequence  of  the  larger  amount  of  Oxygen  introduced  into  the 

*  Loc.  cit.  t  Liebig's  Animal  Chemistry,  [Am.  ed.  p.  325.] 

*  Medico-Chirurgical  Transactions,  vol.  xxiv. 


536  OF  SECRETION. 

system ;  and  if  the  oxygenatipn  could  be  carried  still  further,  the  latter  would 
cease  to  be  deposited,  their  elements  passing  off  in  the  form  of  Urea  and  Car- 
bonic acid.  These  views  are  borne  out  by  the  results  of  Lehmann's  experi- 
ments upon  himself;  for  he  found  that  the  violent  exercise,  which  raised  the 
proportion  of  Urea  in  the  urine  by  more  than  one-third  (§  672),  brought  down 
the  amount  of  Uric  acid  from  1'18  to  -642,  or  nearly  one-half.— Another 
change  is  that  which  gives  rise  to  the  peculiar  compound  termed  Allantoin; 
which  naturally  exists  in  the  fluid  of  the  Allantois  of  the  foetal  calf.  This 
may  be  formed  artificially  by  boiling  Uric  acid  with  peroxide  of  lead ;  from 
which  process  there  result  an  Oxalate  of  the  protoxide  of  lead,  Urea,  and 
Allantoin ;  the  composition  of  which  last  substance  is  very  different  from  that 
of  urea  or  uric  acid,  being  8  Carbon,  5  Hydrogen,  4  Nitrogen,  and  5  Oxygen. 
By  the  operation  of  Nitric  acid  upon  Uric  acid,  several  new  products  are 
generated,  some  of  which  are  of  much  practical  interest.  To  one  of  these  the 
name  of  Murexid  has  been  given,  on  account  of  its  reddish  purple  colour 
(resembling  that  of  the  Tyrian  die  which  was  obtained  from  a  species  of 
Murex) ;  this  is  a  crystalline  substance,  sparingly  soluble  in  cold  water,  but 
copiously  soluble  in  warm,  imparting  to  it  its  vivid  colour.  By  Dr.  Prout  it 
was  long  since  described  as  consisting  of  a  peculiar  acid,  the  Purpuric,  in 
combination  with  Ammonia;  this  view  of  its  composition  is  not  generally 
received  by  German  Chemists  ;  but  it  has  lately  been  supported  by  Fritzche, 
who  has  shown  the  real  existence  of  the  acid,  by  obtaining  Purpurates  of  other 
bases.  This  substance  is  one  source  of  the  colours  of  the  pink  and  lateritious 
sediments,  which  so  often  present  themselves  in  the  Urine:  these  hues  partly 
depend,  however,  on  the  influence  of  nitric  acid  upon  the  peculiar  Colouring 
principles  of  the  urine,  the  nature  of  which  principles  is  not  yet  fully  under- 
stood. 

676.  Although  the  proportion  of  Lactic  acid  in  healthy  urine  cannot  be 
exactly  specified,  it  has  been  hitherto  regarded  as  considerable.     This  sub- 
stance, may  be  referred  to  the  class  of  Saccharine  principles ;  being  obtainable 
from  them  (as  from  milk,  beet-root,  &c.)  by  fermentation.    Its  existence  in  the 
Blood  cannot  be  clearly  demonstrated;  although  there  is  reason  to  believe 
that  it  is  present  in  that  fluid,  in  combination  with  alkaline  bases.     Its  exist- 
ence in  the  Urine,  however,  appears  from  the  recent  experiments  of  Liebig  to 
be  at  least  doubtful;  in  fact,  he  asserts  that  it  cannot  be  present  there.     Yet 
it  may  be  questioned  whether  this  is  not  too  dogmatic  an  assumption ;  for  its 
presence  in  the  Blood  can  scarcely  be  regarded  as  unlikely,  when  we  consider 
the  large  amount  of  Saccharine  matters  taken  into  the  circulation,  and  the 
facility  with  which  these  matters  are  converted  into  Lactic  acid  under  the' 
influence  of  a  ferment ;  and  if  it  be  present  in  the  Blood,  it  will  be  likely  to 
find  its  way  into  the  Urine.     It  is  not  easily  distinguished,  when  in  combina- 
tion, from  certain  other  Organic  acids ;  which  renders  the  determination  of  the 
question  of  its  presence  or  absence  a  matter  of  some  difficulty.     The  idea  of 
Dr.  Prout,  that  the  precipitation  of  Lithic  acid  in  the  Urine  is  often  to  be 
attributed  to  the  presence  of  an  undue  amount  of  free  Lactic  Acid,  certainly 
corresponds  well  with  the  fact,  that  such  deposits  are  frequent  results  of  slight 
disorders  of  the  digestive  process,  which  occasion  mal-assimilation  of  the  Sac- 
charine principles. 

677.  It  has  been  shown  (§671),  that  the  Urine  contains  a  considerable 
amount  of  Saline  matter ;  the  excretion  of  which  from  the  system  appears  to 
be  one  of  the  principal  offices  of  the  Kidney.    Various  saline  compounds,  and 
the  bases  of  others,  are  being  continually  introduced  with  the  food  (§  434) ; 
and  these,  after  performing  their  part  in  the  organism,  must  be  eliminated 
from  the  circulating  fluid,  in  order  to  prevent  injurious  accumulation.     Of 
these  we  shall  now  examine  the  chief  sources. — The  mode  in  which  the 


SECRETION  OF  URTNE.  537 

Muriates  find  their  way  into  the  Urine  is  easily  understood.  Of  the  Common 
Salt  ingested,  a  considerable  part  is  decomposed  into  Muriatic  Acid  and  Soda; 
the  former  being  found  uncombined  in  the  Gastric  juice ;  and  the  latter  in  the 
Bile.  By  the  mixture  of  the  Bile  with  the  Chyme,  a  re-union  of  these  two 
constituents  takes  place ;  and  Salt  is  again  formed,  which  is  received  into  the 
Circulation,  that  it  may  be  eliminated — its  part  in  the  economy  having  been 
now  performed— by  the  Kidney. — The  quantity  of  the  Sulphates  present  in 
the  Urine  appears  to  have  no  relation  with  that  of  the  amount  of  Sulphuric 
acid  ingested;  for  it  much  surpasses  what  could  be  thus  accounted  for, — being 
often  considerable  when  no  Sulphate  whatever  can  be  detected  in  the  food. 
But  most  of  the  azotized  compounds  employed  as  food  have  Sulphur  in  com- 
bination with  them ;  and  there  can  be  no  doubt,  that  this  undergoes  oxidation 
within  the  system  and  thus  generates  Sulphuric  acid,  which  unites  with  any 
free  or  weakly-combined  bases  it  may  meet  with,  to  form  the  Sulphates 
present  in  the  Urine. — The  Phosphates  are  probably  derived  in  part  from  the 
Phosphates  taken  in  with  the  food,  and  in  part  from  the  free  Phosphorus, 
which  its  elements  contain.  Of  the  latter,  great  use  is  made,  in  the  produc- 
tion of  Nervous  matter  (§  643) :  the  continual  waste  of  which  must  set  it  free 
again.  When  thus  set  free,  there  is  obviously  no  channel  for  its  elimination, 
save  by  its  conversion  into  Phosphoric  acid,  and  its  union  with  an  alkaline 
base.*  That  this  is  really  the  case,  would  appear  from  the  fact  noticed  by 
Dr.  Prout,  and  confirmed  by  many  others, — that  mental  or  bodily  labour, 
which  involves  much  waste  of  the  Nervous  System,  is  followed  by  an  increase 
in  the  quantity  of  the  Phosphates  in  the  Urine.  This  increase  cannot  pro- 
ceed from  the  waste  of  the  Muscular  system ;  for  this  would  set  free  Phosphate 
of  Lime,  which  passes  off  by  the  faeces. 

678.  The  alkaline  or  acid  reaction  of  the  Urine,  therefore,  will  not  only 
depend  upon  the  quantity  of  alkaline  Phosphates  converted  into  acid  Phos- 
phates by  the  Uric  and  Hippuric  acids  (§  673) ;  but  also  upon  the  amount  of 
the  bases  in  the  ingesta,  compared  with  that  of  the  permanent  Acids  intro- 
duced into  the  system  or  generated  within  it.  The  Urine  of  animals  which 
live  chiefly  or  entirely  upon  Vegetable  food,  is  almost  invariably  alkaline; 
because  this  food  contains  a  large  quantity  of  alkaline  bases,  in  combination 
with  Citric,  Tartaric,  Oxalic,  and  other  acids,  which  are  decomposed  within 
the  system ;  and  the  amount  of  Sulphuric  and  Phosphoric  acids  produced  is 
not  sufficient  to  neutralize  them.  On  the  other  hand,  the  food  of  Carnivorous 
animals  contains  no  free  or  weakly  combined  basis ;  and  as  its  Sulphur  and 
Phosphorus,  when  oxidized  in  the  system,  produce  a  considerable  quantity  of 
free  acids,  which  share  the  bases  with  the  Muriatic  acid  already  there,  the 
Urine  must  necessarily  have  an  acid  reaction.  The  character  of  the  Urine  of 
Man,  in  this  respect,  is  considered  by  Liebig  to  depend  entirely  upon  that  of 
the  food  ingested. t 

*  This  circumstance  has  been  entirely  overlooked  by  Liebig,  in  his  late  discussion 
(loc.  czV.)  of  the  Constitution  of  the  Urine ;  the  Phosphates  being  regarded  by  him  as  hav- 
ing their  sole  origin  in  the  Phosphates  of  the  ingesta. 

•j-  Proceeding  upon  his  assumption  (borne  out  certainly  by  the  results  of  his  own  ex- 
periments, but  not  to  be  received  until  these  experiments  have  been  repeated  in  a  greater 
variety  of  modes)  that  no  Lactic  acid  is  ever  present  in  the  Urine,  he  remarks :— "The 
acid,  neutral,  or  alkaline  reaction  of  Urine  of  healthy  individuals  does  not  depend  on  any 
difference  in  the  processes  of  digestion,  respiration,  or  secretion,  in  the  various  classes 
of  animals,  but  upon  the  constitution  of  the  aliments,  and  upon  the  alkaline  bases  which 
enter  the  organism  through  the  medium  of  these  aliments.  If  the  amount  of  these  bases 
is  sufficiently  large  to  neutralize  the  acids  formed  in  the  organism,  or  supplied  by  the 
aliments,  the  urine  is  neutral ;  whilst  it  manifests  an  alkaline  reaction,  when  the  amount 
of  alkaline  bases  thus  supplied  to  the  organism  is  more  than  sufficient  to  neutralize  the 
acids;  but  in  all  these  cases,  the  urine  accords  with  the  nature  of  the  aliments  taken." 
The  varying  amount  of  Uric  Acid,— which,  on  Prof.  Liebig's  own  showing,  is  very  much 


538  OF  SECRETIOX. 

679.  The  amount  of  Azotized  matter  in  the  Urine,  also,  is  greatly  influenced 
by  the  nature  of  the  food  ingested,  whilst  the  constitution  of  the  animal  frame 
remains  nearly  the  same  ;  hence  it  appears  that  a  large  portion  of  it  must  be 
derived  from  the  unassimilated  materials,  which  have  been  taken  into  the 
blood,  and  which,  being  superfluous,  are  injurious.     It  is  well  known  that  the 
ingestion  of  an  over  supply  of  azotized  matter  does  not  occasion  an  increased 
production  of  the  fibrinous  or  gelatinous  tissues  ;  and  it  may  be  hence  inferred 
that,  as  there  is  no  means  by  which  the  superfluous  amount  can  be  stored  up 
in  the  system  (in  the  mode  that  non-azotized  matter  is  stored  up  as  Fat),  it 
must  be  continually  eliminated  from  the  Blood.     And  there  can  be  no  doubt 
that  the  Kidneys  are  the  principal  channel  by  which  this  is  effected  ;  the 
amount  of  azote  thrown  off  in  a  given  time,  in  the  various  compounds  which 
they  excrete,  being  equal  to  10-1  Iths  of  the  whole  quantity  ingested.     The 
following  are  the  results  of  the  most  satisfactory  inquiries  that  have  yet  been 
made  in  regard  to  the  influence  of  various  kinds  of  Aliment  upon  the  amount 
of  the  solid  matters  in  the  Urine.     These  experiments  were  performed  by  Dr. 
Lehmann,  of  Leipsig,  upon  himself.     In  the  first  series,  Dr.  L.  adopted  an 
ordinary  mixed  diet ;  but  he  took  no  more  solid  or  liquid  aliment  than  was 
needed  to  appease  hunger  or  thirst,  and  abstained  from  fermented  drinks. 
Every  two  hours  he  took  exercise  in  the  open  air,  but  he  avoided  immoderate 
exertion  of  every  kind.     The  average  result  of  the  examination  of  the  Urine 
passed  under  these  circumstances,  for  fifteen  days,  is  given  in  the  first  line  of 
the  subsequent  Table. — In  a  second  series  of  experiments,  Dr.  L.  lived  for 
twelve  days  on  an  exclusively  Animal  diet ;  and  for  the  last  six  of  these,  it 
consisted  solely  of  eggs.     He  took  32  eggs  daily;  which  contained  189*7 
grammes  of  dry  albumen,  and  157-48  of  fatty  matters;    or  about   228-75 
grammes  of  carbon,  and  30-16  of  azote.     The  amount  of  Urea  is- shown,  in 
the  second  line  of  the  Table,  to  have  undergone  a  very  large  increase  ;  and  it 
contained  more  than  five-sixths  of  the- whole  azote  ingested. — In  a.  third  series 
of  experiments,  Dr.  L.  lived  for  twelve  days  on  a  Vegetable  diet ;  and  its  effect 
upon  the  solid  matter  of  the  Urine  is  shown  in  the  third  line  of  the  Table. — 
For  two  days  he  took  no  azotized  food  of  any  kind ;  and  the  azotized  matter 
of  the  Urine  must  therefore  have  been  solely  the  result  of  the  disintegration  of 
the  tissues.     It  is  seen  to  undergo  a  very  marked  diminution,  under  this  regi- 
men ;  as  is  shown  in  the  fourth  line  of  the  Table. 

Solid  Matters.        Urea.  Uric  Acid.    Lactic  Acid    Extractive 

and  Lactates.    Matters. 

I.  Mixed  diet.     .     67-82        32-498  1-183          2-257  10-480 

II.  Animal  diet      .     87-44         53-198  1-478  2-167  5-145 

III.  Vegetable  diet  .     59-24         22-481  1-021  2-669  16-499 

IV.  Non-azotized  diet  41-68         15-408          0-735          5-276  11-854 

680.  The  following  inferences  are  drawn  by  Dr.  Lehmann,  from  these  ex- 
periments : — 1.  Animal  articles  of  diet  augment  the  solid  matters  of  the  Urine. 
Vegetable  substances,  and  still  more  such  as  are  deprived  of  azote,  on  the  con- 
trary, diminish  it. — 2.  Although  Azote  be  a  product  of  decomposition  of  the 
organism,  yet  its  proportions  in  the  urine  depend  also  on  the  food,  for  we  find 
a  richly-azotized  diet  augment  considerably  the  quantity  of  Urea.    In  the  above 
experiments,  the  proportion  of  the  Urea  to  the  other  solid  matters  was  as  100 
to  116  in  a  mixed  diet;  as  100  to  63  in  an  animal  diet;  as  100  to  156  in  a 
vegetable  diet;  and  as  100  to  170  in  a  non-azotized  diet. — 3.  The  quantity  of 
Uric  Acid  depends  less  on  the  nature  of  the  diet  than  on  other  circumstances ; 
the  differences  observed  in  it  being  too  slight  to  warrant  us  in  ascribing  them 

influenced  by  the  respiration, — is  altogether  left  out  of  consideration  in  this  sweeping 
generalization. 


SECRETION  OF  URINE.  539 

to  the  former  cause. — 4.  The  combinations  of  Proteine,  and  consequently  the 
azote  of  the  food,  are  absorbed  in  the  intestinal  canal ;  and  what  is  not  em- 
ployed in  the  formation  of  the  tissues,  is  thrown  off  by  the  Kidneys  in  the  form 
of  Urea  or  Uric  acid, — these  organs  being  the  chief,  if  not  the  sole,  channel 
through  which  the  system  frees  itself  of  its  excess  of  azote. — 5.  The  urine 
contains  quantities  of  Sulphates  and  Phosphates  proportional  to  the  azotized 
matters  which  have  been  absorbed  ;  and  the  proportion  of  these  salts  is  sensi- 
bly increased  under  the  use  of  a  large  amount  of  those. — 6.  In  the  same  cir- 
cumstances, the  Extractive  matters  diminish,  while  their  quantity  is  increased 
by  the  use  of  vegetable  diet,— -a  fact  which  proves  the  influence  of  vegetable 
aliment  over  the  production  of  these  matters  in  the  urine.— -7.  Under  an  animal 
diet,  the  quantity  of  Lactic  acid  diminishes ;  but  the  greater  part  of  this  acid 
is  free.  It  is  the  reverse  under  a  vegetable  diet;  there  is  more  lactic  acid,  but 
it  is  united  to  bases.  The  largest  production  of  lactic  acid  is  under  a  non- 
azotized  diet ;  and  most  of  it  is  then  combined  with  ammonia.  Therefore  the 
lactic  acid  eliminated  with  the  urine,  is  in  great  part  the  product  of  non- 
azotized  substances  not  entirely  assimilated  ;  but  it  results  also  in  part  from  the 
decomposition  of  the  azotized  substances  entering  into  the  composition  of  the 
body  and  the  food.— 8.  The  Kidneys  not  only  separate  certain  constituent  parts 
of  the  organs,  which  have  become  inadequate  for  the  maintenance  of  life,  but 
they  also  expel  the  superfluous  nutritive  matters  that  may  have  been  absorbed."* 
It  seems  right  to  remark,  with  regard  to  these  inferences,  that  all  the  statements 
concerning  the  amount  of  Lactic  acid  and  the  Lactates  must  be  received  with 
hesitation,  in  consequence  of  the  statements  of  Liebig  already  referred  to. — 
The  most  unequivocal  facts  determined  by  Dr.  Lehmann's  inquiries,  are  those 
which  relate  to  the  influence  of  Diet  on  the  amount  of  Urea  excreted.  The 
experiments  upon  a  purely  non-azotized  diet  were  not  continued  long  enough 
for  a  satisfactory  result  to  be  obtained ;  but  it  is  evident  that,  so  long  as  the  in- 
gesta  contain  no  azote,  the  whole  of  that  element  in  the  Urine  must  be  attributed 
to  the  disintegration  or  waste  of  the  Tissues,  and  may  be  fairly  taken  as  a 
measure  of  its  amount. 

681.  The  fact  of  the  pre-existence  of  the  chief  constituents  of  Urine  in  the 
Blood,  is  important  as  explaining  the  facility  with  which  the  secreting  function 
appears  to  be  transferred  to  other  membranes,  in  some  of  the  cases  in  which 
the  Kidney  does  not  perform  its  function.     Doubtless  there  has  been  much 
error  on  this  subject,  arising  out  of  deceptions  practised  by  impostors;  but  a 
sufficient  number  of  indubitably  genuine  cases  are  on  record,  to  put  it  beyond 
doubt  that  such  transferences  have  taken  place,  urinous  fluid  being  secreted 
from  the  stomach,  mammae,  umbilicus,  nose,  &c.t — On  the  other  hand,  the 
Kidney  may  serve  as  the  channel  for  the  elimination  of  substances,  which  are 
usually  drawn  off  by  other  organs.     Thus,  when  the  secreting  action  of  the 
Liver  has  been  gradually  impaired  by  structural  disease,  the  Kidneys  appear 
to  have  performed  their  function,  in  separating  some  (at  least)  of  the  elements 
of  Bile.     And  a  case  has  recently  been  mentioned,  in  which  the  urine  of  a  par- 
turient female,  who  did  not  suckle  her  infant,  was  found  to  contain  a  conside- 
rable amount  of  Butyric  acid,  during  several  days.     The  elimination  of  Kies- 
tene  by  the  Kidney  during  pregnancy  will  be  presently  noticed  (§  690J. 

682.  The  facility  with  which  substances  taken  into  the  current  of  the  Cir- 
culation pass  into  the  Urinary  secretion,  varies  extremely ;  and  no  general  law 
can  be  stated  in  regard  to  it.     It  appears  from  Woehler's  elaborate  researches 
on  this  subject,  that  the  salts  which  are  most  readily  excreted  are  those  which 
excite  the  action  of  the  kidneys.:}:     The  rapidity  with  which  absorption  and 

*  L'Experiqrice,  Dec.  7,  1843;  andEdinb.  Monthly  Journal,  March,  1844. 

j-  For  a  scientific  explanation  of  this  fact,  see  Princ.  of  Gen.  and  Comp.  Phys.,  §  539. 

*  See  Muiler's  Physiology,  p.  589. 


540  OF  SECRETION. 

\ 

elimination  take  place  is  often  extremely  remarkable ;  Prussiate  of  Potash 
having  been  detected  in  the  urine  within  two  minutes  after  it  had  been  intro- 
duced into  the  stomach.  The  variations  in  this  respect  would  appear  to  depend 
chiefly  on  the  degree  of  concentration  of  the  saline  solution,  which  will  affect 
the  rapidity  of  its  absorption,  according  to  the  laws  of  Endosmose  ; — its  recep- 
tion into  the  blood  being  more  rapid,  in  proportion  as  its  density  is  lower  in 
comparison  with  that  of  the  circulating  fluid.  Pure  water,  or  water  containing 
but  a  small  admixture  of  saline  matter,  is  readily  absorbed  into  the  blood-ves- 
sels of  the  Intestinal  villi ;  but  it  is  as  readily  drawn  off  through  the  Kidneys 
(by  the  agency,  as  it  would  seem,  of  the  Malpighian  bodies,  §  668) ;  and  con- 
sequently a  large  amount  may  be  ingested  in  a  short  time.  But  if  the  water 
contain  an  amount  of  saline  matter  equal  to  that  of  the  Serum,  no  absorption 
of  it  takes  place ;  it  remains  in  the  intestinal  tube,  and  it  is  voided  by  the 
rectum.  Further,  if  the  quantity  of  saline  matter  in  the  solution  be  greater 
than  that  of  the  Serum,  not  only  will  no  absorption  take  place,  but  there  will 
be  an  endosmose  of  the  water  of  the  blood  towards  the  solution ;  so  that  a  large 
quantity  of  fluid  is  discharged  by  the  Intestinal  canal.  This  simple  explana- 
tion, first  offered  by  Liebig,*  accounts  well  for  the  diuretic  effect  of  most  weak 
saline  solutions,  and  the  purgative  qualities  of  stronger  ones. — For  the  transit 
of  the  peculiar  principles  of  Vegetables,  however,  it  appears  that  from  one  to 
two  hours  is  usually  required.  The  effect  of  Oil  of  Turpentine,  and  probably 
of  other  volatile  agents,  is  produced  much  more  rapidly;  the  characteristic 
odour  of  violets  being  perceptible  in  the  Urine  passed  but  a  few  minutes  after 
the  vapour  of  the  oil  had  been  received  into  the  lungs. 

IV.  Mammary  Glands. — Secretion  of  Milk. 

683.  We  now  come  to  those  Glands,  whose  action  is  rather  to  elaborate  from 
the  Blood  certain  products,  which  are  destined  for  special  uses  in  the  economy 
than  to  eliminate  matters,  whose  retention  in  the  circulating  current  would  be 
injurious.  Pre-eminent  amongst  these  in  size  and  importance,  at  least  during 
their  period  of  activity,  are  the  Mammary  Glands ;  which  are  found  only  in 
the  animals  of  the  Class  Mammalia,  and  which  present  themselves  in  an  almost 
rudimentary  state  in  some  of  the  non-placental  subdivisions  of  the  class  (§  55). 

a.  The  structure  of  the  Human  Mammary  Gland,  which  has  been  recently  investigated 
fully  by  Sir  A.  Cooper,  is  very  simple,  and  easily  described.  It  consists  of  a  series  of 
ducts  passing  inwards  from  their  termination  in  the  nipple,  and  then  ramifying  like  the 
roots  of  a  tree,  their  ultimate  subdivisions  terminating  in  minute  follicles.  The  mamillary 
tubes  are  usually  about  ten  or  twelve  in  number;  they  are  straight  ducts,  of  somewhat 
variable  size ;  and  their  orifices,  which  are  situated  in  the  centre  of  the  nipple,  and  are 
usually  concealed  by  the  overlapping  of  its  sides,  are  narrower  than  the  tubes  them- 
selves. At  the  base  of  the  nipple,  these  tubes  dilate  into  reservoirs,  which  extend  beneath 
the  areola  and  to  some  distance  into  the  gland,  when  the  breast  is  in  a  state  of  lactation. 
These  are  much  larger  in  many  of  the  lower  Mammalia  than  they  are  in  the  Human 
female;  their  use  is  to  suppjy  the  immediate  wants  of  the  child  when  it  is  first  applied 
to  the  breast,  so  that  it  shall  not  be  disappointed,  but  shall  be  induced  to  proceed  with 
sucking  until  the  draught  be  occasioned  (§  426).  From  each  of  these  reservoirs  com- 
mence five  or  six  main  branches  of  the  lactiferous  tubes,  each  of  which  speedily  sub- 
divides into  smaller  ones;  and  these  again  divaricate,  until  their  size  is  very  much 
reduced,  and  their  extent  greatly  increased.  The  proportional  size  of  the  trunk  and  of 
its  branches  appears  to  follow  the  same  law  which  governs  that  of  the  blood-vessels. 
The  breast  is  not  formed  into  regular  lobes  by  the  ramifications  of  the  ducts ;  because 
they  ramify  between,  and  intermix  with  each  other  so  as  to  destroy  the  simplicity  and 
uniformity  of  their  divisions.  It  is  very  rarely,  however,  that  they  inosculate.  The 
mammary  ducts  are  composed  of  a  fibrous  coat  lined  by  a  mucous  membrane;  the  latter 
is  highly  vascular,  and  forms  a  secretion  of  its  own,  which  sometimes  collects  in  con- 
siderable quantity  when  the  milk  ceases  to  be  produced. 

*  Chemistry  applied  to  Agriculture  and  Physiology,  Part  ii. 


MAMMARY  GLANDS— SECRETION  OF  MILK. 


541 


[Fig.  159.  ] 


The  Mammary  Gland  after  the  removal  of  the 
skin,  as  taken  from  the  subject  three  days  after 
delivery;  1,  the  surface  of  the  chest j  2,  subcuta- 
neous fat ;  3,  the  skin  covering  the  gland  ;  4,  cir- 
cumference of  the  gland ;  5,  its  lobules  separated 
by  fat;  6,  the  lactiferous  ducts  converging  to  unite 
in  the  nipple;  7,  the  nipple  slightly  raised  and 
showing  the  openings  of  the  tubes  at  its  extremity.] 


A  vertical  section  of  the  Mammary  Gland, 
showing  its  thickness  and  the  origins  of  the  lacti- 
ferous ducts ;  1,  2,  3,  its  pectoral  surface ;  4,  section 
of  the  skin  on  the  surface  of  the  gland  ;  5,  the  thin 
skin  covering  the  nipple  ;  6,  the  lobules  and  lobes 
composing  the  gland ;  7,  the  lactiferous  tubes  com- 
ing from  the  lobules ;  8,  the  same  tubes  collected 
in  the  nipple.] 


Fig.  160. 


Distribution  of  the  milk-ducts  in  the  mamma  of  the  human  female,  during  lactation;  the  ducts  injected 
with  wax.    (After  Sir  A.  Cooper.) 

46 


542  OF  SECRETION. 

b.  The  gland  itself  is  composed  of  the  union  of  a  number  of  glandules,  which  are  con- 
nected by  means  of  the  fibrous  or  fascial  tissue  of  the  gland ;  it  is  between  these,  that 
the  mammary  tubes  may  be  observed  to  ramify;  and  from  them  their  branches  spring. 
When  the  glandules  are  filled  with  injection,  and  for  a  long  time  macerated  in  water  and 
unraveled,  they  are  found  to  be  disposed  in  lobuli;  and  when  a  branch  of  a  mammary 
tube  is  separated,  with  the  glandules  attached,  the  part  appears  like  a  bunch  of  fruit 
hanging  by  its  stalk.    When  the  lactiferous  tube  proceeding  from  a  glandule  is  minutely 
injected,  the  latter  will  be  found  to  be  composed  of  numerous  follicles,  in  which  the  ulti- 
mate ramifications  of  the  former  terminate,  or  rather  originate.    Their  size,  in  full  lacta- 
tion, is  that  of  a  hole  pricked  in  paper  by  the  point  of  a  very  fine  pin  ;  so  that  the  follicles 
are,  when  distended  with  quicksilver  or  milk,  just  visible  to  the  naked  eye.     At  other 

times,  however,  the  follicles  do  not  admit  of  being  injected, 
Fig.  161.  though  the  lactiferous  tubes  may  have  been  completely 

filled.    They  are  lined  by  a  continuation  of  the  same  mem- 
brane, with  that  which  lines  the  ducts ;  and  this  possesses 
a  high  vascularity.    The  arteries  which  supply  the  glan- 
dules with  blood,  become  very  large  during  lactation ;  and 
their  divisions  spread  themselves  minutely  on  the  follicles. 
From  the  blood  which  they  convey,  the  milk  is  secreted 
and  poured  into  the  follicles,  whence  it  flows  into  the  ducts. 
From  the  researches  of  Mr.  Goodsir  it  appears,  that,  in 
common  with  other  glandular  structures,  the  inner  surface 
Termination  of  portion  of  milk-     of  the  milk-follicles  is  covered  with  a  layer  of  epithelium- 
duct  in  follicles ;  from  a  mercurial     cells ;  which,  being  seen  to  contain  milk-globules,  may  be 
injection,  by  Sir  A.  Cooper;  en-     without  doubt  regarded  as  the  real  agents  in  the  secreting 
larged  4  times.  process.     Absorbent  vessels  are  seen  to  arise   in  large 

numbers  in  the  neighbourhood  of  the  follicles;  their  func- 
tion appears  to  be,  to  absorb  the  more  watery  part  of  the  milk  contained  in  the  follicles 
and  tubes,  so  as  to  render  it  more  nutrient  than  it  is  as  first  secreted;  and  also  to  relieve 
the  distension  which  would  occur  during  the  absence  of  the  child,  from  the  continuance 
of  the  secreting  process. 

c.  The  Mammary  gland  may  be  detected  at  an  early  period  of  foetal  existence ;  being 
easily  distinguishable  from  the  surrounding  parts,  by  the  redness  of  its  colour  and  its 
high  vascularity,  especially  when  the  whole  is  injected.    At  this  period,  it  presents  no 
difference  in  the  male  and  female;  and  it  is  not  until  near  the  period  of  puberty,  that  any 
striking  change  manifests  itself, — the  gland  continuing  to  grow,  in  each  sex,  in  propor- 
tion to  the  body  at  large.    About  the  age  of  thirteen,  however,  the  enlargement  of  the 
gland  commences  in  the  Female;  and  by  sixteen  years,  it  is  greatly  evolved,  and  some 
of  the  lactiferous  tubes  can  be  injected.    At  about  the  age  of  twenty,  the  gland  attains  its 
full  size  previous  to  lactation;  but  the  milk-follicles  cannot  even  then  be  injected  from 
the  tubes.    During  pregnancy,  the  mammse  receive  a  greatly-increased  quantity  of  blood. 
This  determination  often  commences  very  early,  and  produces  a  feeling  of  tenderness 
and  distension,  which  is  a  valuable  sign  (where  it  exists  in  connection  with  others)  of 
the  commencement  of  gestation.     The  Areola  at  this  time  becomes  darker  in  its  colour, 
and  thicker  in  substance,  and  ,more  extended;  its  papillae  become  more  developed,  and 
the  secretion  from  its  follicles  increased.*     The  vascularity  of  the  gland  continues  to 
increase  during  pregnancy;  and  at  the  time  of  parturition,  its  lobulated  character  can  be 

Distinctly  felt.  The  vesicles  are  not,  however,  developed  sufficiently  for  injection,  until 
lactation  has  commenced.  After  the  cessation  of  the  catamenia  from  age,  so  that  preg- 
nancy is  no  longer  possible,  the  lactiferous  ducts  continue  open,  but  the  milk-follicles  are 
incapable  of  receiving  injection.  The  substance  of  the  glandules  gradually  disappears, 
so  that  in  old  age  only  portions  of  the  ducts  remain,  which  are  usually  loaded  with 
mucus;  but  the  place  of  the  glandules  is  commonly  filled  up  by  adipose  tissue,  so  that 
the  form  of  the  Breast  is  preserved.  Sir  A.  Cooper  notices  a  curious  change,  which  he 
states  to  be  almost  invariable  with  age,— namely,  the  ossification  of  the  arteries  of  the 
breast,  the  large  trunks  as  well  as  the  branches ;  so  that  their  calibre  is  greatly  dimi- 
nished, or  even  obliterated. 

d.  The  Mammary  gland  of  the  Male  is  a  sort  of  miniature  picture  of  that  of  the  female. 
It  varies  extremely  in  its  magnitude,  being  in  some  persons  of  the  size  of  a  large  pea; 

*  This  change  is  greatly  relied  on  by  many  Obstetricians,  as  an  unequivocal  Sign  of 
Pregnancy.  It  is  probably  one  of  the  best  single  signs,  to  which  the  medical  man  can 
have  recourse,  in  the  early  months  ;  but  it  must  not  be  implicitly  relied  on.  The  change 
of  colour  varies  in  degree  in  different  individuals ;  and  all  the  alterations  referred  to  may 
take  place,  when  the  uterus  is  distended  by  hydatids,  fibrinous  concretions,  &c.,  as 
occurred  in  a  well-marked  case  within  the  Author's  own  experience. 


MAMMARY  GLAND— SECRETION  OF  MILK.  543 

whilst  in  others  it  is  an  inch,  or  even  two  inches,  in  diameter.  In  its  structure  it  corre- 
sponds exactly  with  that  of  the  female,  but  is  altogether  on  a  smaller  scale.  It  is  com- 
posed of  lobules  containing  follicles,  from  which  ducts  arise;  and  these  follicles  and 
ducts  are  not  too  minute  to  be  injected,  although  with  difficulty.  The  evolution  of  the 
gland  goes  on  part  passu  with  that  of  the  body,  not  undergoing  an  increase  at  any  par- 
ticular period;  it  is  sometimes  of  considerable  size  in  old  age.  A  fluid,  which  is  proba- 
bly mucus,  may  be  pressed  from  the  nipple  in  many  persons;  and  this  in  the  dead  body, 
with  even  more  facility  than  in  the  living.  That  the  essential  character  of  the  gland  is 
the  same  in  the  male  as  in  the  female,  is  shown  by  the  instances,  of  which  there  are  now 
several  on  record,  in  which  infants  have  been  suckled  by  men.*  Corresponding  facts 
are  also  recorded  of  the  male  of  several  of  the  lower  animals. 

684.  The  secretion  of  Milk  consists  of  Water,  holding  in  solution  Sugar, 
various  Saline  ingredients,  and  a  peculiar  albuminous  substance  termed  Casein; 
and  having  Oleaginous  globules  suspended  in  it.  These  globules  appear  to 
be  surrounded  by  a  thin  pellicle  (probably  originating  simply  in  the  contact  of 
oil  with  albuminous  matter,  which  is  known  to  give  rise  to  a  membranous 
film),  that  keeps  them  asunder,  so  long  as  the  milk  remains  at  rest.  The  con- 
stitution of  this  fluid  is  made  evident  by  the  ordinary  processes,  to  which  it  is 
subjected  in  domestic  economy.  If  it  be  allowed  to  stand  for  some  time, 
exposed  to  the  air,  a  large  part  of  the  oleaginous  globules  come  to  the  surface, 
being  of  less  specific  gravity  than  the  fluid  through  which  they  are  diffused. 
At  the  same  time,  there  is  reason  to  believe  that  they  undergo  a  change, 
which  will  be  presently  described.  The  cream  thus  formed  does  not,  how- 
ever, consist  of  oily  particles  alone ;  but  includes  a  considerable  amount  of 
casein,  with  the  sugar  and  salts  df  the  milk.  These  are  further  separated  by 
the  continued  agitation  of  the  cream ;  which,  by  rupturing  the  envelops  of 
the  oil-globules,  separates  it  into  butter,  formed  by  their  aggregation,  and  but- 
termilk, containing  the  casein,  sugar,  &c.  A  considerable  quantity  of  casein, 
however,  is  entangled  with  the  oleaginous  matter ;  and  this  has  a  tendency  to 
decompose,  so  as  to  render  the  butter  rancid.  It  may  be  separated  by  melting 
the  butter  at  the  temperature  of  180° ;  when  the  casein  will  fall  to  the  bottom, 
leaving  the  butter  pure,  and  much  less  liable  to  change.— -The  milk,  after  the 
cream  has  been  removed,  still  contains  the  greatest  part  of  its  casein  and  sugar. 
If  it  be  kept  long  enough,  spontaneous  change  takes  place  in  its  composition ; 
the  sugar  is  converted  into  |actic  acid,  and  this  coagulates  the  casein,  precipi- 
tating it  in  small  flakes.  The  same  precipitation  may  be  accomplished  at  any 
time,  by  the  addition  of  an  acid ;  all  the  acids,  however,  which  act  upon  albu- 
men, do  not  precipitate  casein,  as  will  presently  be  pointed  out  in  detail ;  the 
most  effectual  is  that  contained  in  the  dried  stomach  of  a  calf,  known  as  rennet. 
This  exerts  so  powerful  an  influence  over  it,  that,  according  to  the  experiments 
of  Berzelius,  a  piece  of  the  membrane  coagulated  the  casein  of  1800  times  its 
weight  of  milk,  with  the  loss  of  only  l-17th  part  of  its  own  weight :  so  that 
the  active  principle,  dissolved  from  the  rennet,  must  have  coagulated  the 
casein  of  about  30,000  times  its  weight  of  milk.  The  whey  left  after  the  curd 

*  See  the  case  described  by  the  Bishop  of  Cork,  in  the  Philosophical  Transactions, 
vol.  xli.  p.  813:  one  mentioned  by  Captain  Franklin  (Narrative  of  a  Journey  to  the 
Polar  Sea,  p.  157) ;  and  one  which  fell  under  the  notice  of  the  celebrated  traveler  Hum- 
boldt  (Personal  Narrative,  vol.  iii.  p.  58).  The  following  is  given  by  Dr.  Dunglison 
(Physiology,  vol.  ii.  p.  437).  "  Professor  Hall,  of  the  University  of  Maryland,  exhibited 
to  his  Obstetrical  class,  in  the  year  1837,  a  coloured  man,  fifty-five  years  of  age,  who  had 
large,  soft,  well-formed  mammse,  rather  more  conical  than  those  of  the  female,  and  pro- 
jecting fully  seven  inches  from  the  chest;  with  perfect  and  large  nipples.  The  glandu- 
lar structure  seemed  to  the  touch  to  be  exactly  like  that  of  the  female.  This  man  had 
officiated  as  wet-nurse,  for  several  years,  in  the  family  of  his  mistress ;  and  he  repre- 
sented that  the  secretion  of  milk  was  induced  by  applying  the  children  entrusted  to  his 
care,  to  the  breasts,  during  the  night.  When  the  milk  was  no  longer  required,  great 
difficulty  was  experienced  in  arresting  the  secretion.  His  genital  organs  were  fully 
developed." 


544  OF  SECRETION. 

has  been  separated,  contains  a  large  proportion  of  the  saccharine  and  saline 
matter,  entering  into  the  original  composition  of  the  milk.  This  may  be  readily 
separated  by  evaporation.* 

685.  When  Milk  is  examined  with  the  microscope,  it  is  seen  to  contain  a 
large  number  of  particles  of  irregular  size  and  form,  suspended  in  a  somewhat 
turbid  fluid ;  these  particles  (according  to  the  measurement  of  Donnet)  vary 
in  size  from  about  the  l-12,700th  to  the  l-3040th  of  an  inch ;  and  they  are 
termed  milk-globules.  They  are  not  affected  by  the  mere  contact  of  ether  or 
alkalies  ;  but  if  these  reagents  are  shaken  with  them,  an  immediate  solution  is 
the  result.  The  same  effect  happens,  if  they  are  first  treated  with  acetic 
acid.  Hence  it  is  evident,  that  the  globules  consist  of  oily  matter,  enclosed  in 
an  envelop  of  some  kind :  and  an  extremely  delicate  pellicle  may,  in  fact,  be 
distinguished  after  the  removal  of  the  oily  matter  by  ether ;  or  after  the  glo- 
bules have  been  ruptured,  and  their  contents  pressed  out,  by  rubbing  a  drop 
of  milk  between  two  plates  of  glass.  No  proof  of  the  organization  of  this  pel- 
licle has,  however,  been  detected ;  and  it  can  scarcely  be  regarded  in  the  light 
of  a  true  cell. — Besides  these  milk-globules,  other  globules  of  much  smaller 
size  are  seen  in  milk  ;  and  these  present  the  peculiar  movement  which  is  ex- 
hibited by  molecules  in  general.  Most  of  them  seem  to  consist  of  oily  matter, 
not  enclosed  in  an  envelop  ;  as  they  are  at  once  dissolved  when  the  fluid  is 
treated  with  ether :  but,  according  to  the  statements  of  Donne,  it  would  seem 
that  a  portion  of  them  are  composed  of  casein,  suspended,  not  dissolved,  in  the 
fluid.  It  may  be  reasonably  doubted,  however,  whether  these  were  not  in  a 
state  of  change ;  whether  from  their  own  ^decomposition,  or  from  incipient 
coagulation ;  either  of  which  might  have  taken  place  during  the  processes  of 
filtration,  &c.,  that  were  required  to  determine  their  nature.  Besides  the 
foregoing  particles,  there  are  found  in  the  Colostrum,  or  milk  first  secreted 
after  delivery,  large  yellow  granulated  corpuscles,  which  are  described  by 
Donne  as  composed  of  a  multitude  of  small  grains  aggregated  together,  and 
frequently  including  a  true  globule  of  milk  in  their  centre  :  these  are  for  the 
most  part  soluble  in  ether  ;  but  traces  of  some  adhesive  matter,  probably  mucus, 
holding  together  the  particles,  are  then  seen.  Lamellae  of  epithelium  are  also 
found  in  the  milk. — All  the  larger  globules  may  be  removed  by  repeated 
filtration;  and  the  fluid  is  then  nearly  transparent.  This,  in  fact,  is  the 
simplest  way  of  separating  the  oleaginous  from  the  other  constituents  of  the 
milk ;  as  little  casein  then  adheres  to  the  former.  That,  the  transparent  fluid 
which  has  passed  through  the  filter  contains  nearly  the  whole  amount  of  the 
casein  of  the  milk,  appears  a  sufficient  proof  that  this  is,  for  the  most  part, 
truly  dissolved  in  the  fluid.  We  shall  now  consider  the  chemical  characters 
of  each  of  the  foregoing  ingredients. 

686.  The  Oleaginous  matter  of  milk  principally  consists,  like  fatty  matter 
in  general,  of  the  two  substances,  elaine  and  stearine  ;  which  are  converted  in 
the  process  of  saponification  into  the  elaic,  stearic,  and  margaric  acids :  but  it 
also  contains  another  substance  peculiar  to  it,  which  yields  in  saponification 
three  volatile  acids,  of  strong  animal  odour,  to  which  Chevreul  has  given  the 
names  of  butyric,  caproic,  and  capric  acids  ;  whilst  the  fatty  substance  itself, 
to  which  the  peculiar  smell  and  taste  of  butter  are  due,  is  designated  as 
butyrine.  The  peculiar  acids  are  not  only  formed  when  the  butyrine  is  treated 
with  alkalies ;  but  are  produced  by  the  ordinary  decomposition  of  this  prin- 
ciple, which  is  favoured  by  time  and  moderate  warmth. — The  Casein,  or 
cheesy  matter  of  milk,  which  is  obtained  with  some  slight  admixture  of  fatty 
matter  in  the  production  of  cheese  from  skimmed  milk,  is  chiefly  distinguished 

*  A  considerable  quantity  is  thus  obtained  for  household  purposes  in  Switzerland. 
f  Cours  de  Microscopic,  Douzieme  Le9on. 


MAMMARY  GLAND-— SECRETION  OF  MILK.  545 

from  Albumen,  by  the  peculiar  readiness  with  which  it  is  precipitated  by^ 
feeble  organic  acids,  such  as  the  lactic  and  acetic  ;  and  by  its  non-coagulability 
by  heat  alone.  The  Casein  of  Human  milk,  however,  is  much  less  precipi- 
table  by  acids  than  is  that  of  the  Cow ;  very  commonly  resisting  the  action  of 
the  mineral  acids,  and  even  that  of  the  acetic ;  but  being  always  coagulated 
by  rennet,  though  the  curd  is  long  in  collecting.  It  is  remarked  by  Dr.  G.  O. 
Rees,*  that  the  casein  of  human  milk  thus  bears  somewhat  the  same  relation 
to  that  of  the  cow,  that  the  albumen  of  chyle  bears  to  that  of  the  blood.' — The 
Sugar  of  milk,  which  may  be  obtained  by  evaporating  whey  to  the  consistence 
of  a  syrup  and  then  setting  it  aside  to  crystallize,  contains  a  large  proportion 
(12  per  cent.)  of  water,  so  that  it  may  be  considered  as  really  a  hydrate  of 
sugar ;  it  is  nearly  identical  in  its  composition  with  starch,  and  may,  like  it,  be 
converted  into  true  sugar  by  the  action  of  sulphuric  acid ;  and  when  in  contact 
with  a.  ferment,  or  decomposing  azotized  compound,  it  is  extremely  prone  to  be 
converted  into  lactic  acid,  by  appropriating  to  itself  the  elements  of  water.  It  is, 
in  fact,  through  this  process,  that  the  coagulation  of  the  casein  is  effected,  by 
means  of  rennet ;  for  as  soon  as  a  very  minute  quantity  of  lactic  acid  is  gene- 
rated, it  withdraws  from  the  casein  the  free  alkali  which  kept  it  in  solution, 
and  the  casein  is  consequently  precipitated.  The  same  effect  will  be  produced 
by  incipient  decomposition  of  the  casein  itself;  \vhich  will  soon  occasion  lactic 
acid  to  be  generated  from  the  sugar,  in  sufficient  quantity  to  give  to  the  milk 
a  distinctly  acid  reaction. — The  Saline  matter  contained  in  milk,  appears  to  be 
nearly  identical  with  that  of  the  blood ;  with  a  larger  proportion  of  the  phos- 
phates of  lime  and  magnesia,  which  amount  to  2  or  %%,  parts  in  1000.  These 
phosphates  are  held  in  solution  chiefly  by  the  Casein ;  which  seems  to  have 
a  power  of  combining  with  them,  even  greater  than  that  of  Albumen  :  the 
presence  of  a  minute  proportion  of  free  alkali,  also,  assists  their  solution.  A 
small  portion  of  iron  in  the  state  of  phosphate,  together  with  the  chlorides  of 
potassium  and  sodium,  may  also  be  detected  in  milk.t 

687.  It  is  very  interesting  to  observe  that  Milk  thus  contains  the  three 
classes  of  principles  which  are  required  for  human  food, — the  albuminous, 
oleaginous,  and  saccharine :  and  is  the  only  secreted  fluid,  in  wrhich  these 
all  exist  in  any  considerable  amount.     It  is,  therefore,  the  food  most  perfectly 
adapted  for  the  young  animal;  and   is  the  only  single  article  supplied  by 
nature,  in  which  such  a  combination  exists.     Our  artificial  combinations  will 
be  suitable  to  replace  it,  just  in  proportion  as  they  imitate  its  character ;  but 
in  none  of  them  can  we  advantageously  dispense  with  milk,  under  some  form 
or  other.     It  should  be  remembered  that  the  saline  ingredients  of  Milk,  espe- 
cially the  phosphates  of  lime,  magnesia,  and  iron,  have  a  very  important  func- 
tion in  the  nutrition  of  the  infant, — affording  the  material  for  the  consolidation 
of  its  bones,  and  for  the  production  of  its  red  blood-corpuscles  ;  and  any  fluid 
substituted  for  milk,  which  does  not  contain  these,  is  deficient  in  essential  con- 
stituents.    It  is  very  justly  remarked  by  Dr.  Rees,  that,  of  all  the  secreted 
fluids,  Milk  is  most  nearly  allied  in  its  composition  to  Blood. 

688.  The  proportion  of  the  different  ingredients  in  the  Milk  of  different  ani- 
mals, is  subject  to  considerable  variation :  and  this  fact  is  of  much  practical 
importance  in  guiding  our  selection,  when  good  Human  milk  cannot  be  con- 
veniently obtained  for  the  nourishment  of  an  infant 4     The  first  point  to  be 

*  Art.  MILK,  in  the  Cyclopaedia  of  Anatomy  and  Physiology, 
f  Haidlen  in  Annalen  der  Chemie  und  Pharmacie,  xlv.  p.  263. 

*  It  appears,  from  the  recent  inquiries  of  Dr.  Playfair,  that  the  proportion  of  two,  at 
least,  of  the  principal  ingredients  of  the  Milk,  is  liable  to  great  variation  with  the  circum- 
stances of  the  animal.  That  of  the  butter  depends  in  part  upon  the  quantity  of  oily  matter 
in  the  food;  and  in  part  upon  the  amount  of  exercise  which  the  animal  takes,  and  the 
warmth  of  the  atmosphere  in  which  it  is  kept.    Exercise  and  cold,  by  increasing  the 

46* 


546  OF  SECRETION. 

inquired  into,  is  the  quantity  of  solid  matter  contained  in  each  kind  ;  this  may 
be  determined  either  by  evaporation,  or  by*  the  specific  gravity  of  the  fluid. 
The  Specific  Gravity  of  Human  milk  is  stated  by  Dr.  Rees  to  vary  between 
1030  and  1035  ;  others,  however,  have  estimated  it  much  lower.  That  of  the 
Cow  appears  to  be  usually  about  1027;  that  of  the  cream  being  1024,  and  that 
of  the  skimmed  milk  about  1035.  The  variation  will  in  part  depend  (as  in 
the  case  of  the  urine),  upon  the  quantity  of  fluid  ingested,  and  in  part,  it  is 
probable,  upon  the  manner  in  which  the  milk  is  drawn  ;  for  it  is  well  known 
to  milkers,  that  the  last  milk  they  obtain  is  much  richer  than  that  with  which 
the  udder  is  distended  at  the  commencement.  The  quantity  of  solid  matter, 
obtainable  from  Human  and  from  Cow's  Milk  by  evaporation,  seems,  like  the 
specific  gravities  of  the  fluids,  to  be  nearly  the  same,  varying  from  11  to  12| 
per  cent.  In  the  relative  proportion  of  the  ingredients,  however,  there  is  a 
considerable  difference  ;  there  being  much  more  butter,  and  less  casein,  in 
Human  milk  than  in  that  of  the  Cow  ;  so  that  the  former  would  be  most  nearly 
represented  by  the  cream  of  the  latter,  mingled  with  about  half  its  proportion 
of  skim  milk,  and  the  other  half  water.  The  cream  of  Human  Milk  has  been 
found  by  Sir  A.  Cooper  to  vary  in  proportion  to  the  milk,  from  one-fifth  to  one- 
third  of  the  whole  volume  ;  the  largest  amount  being  given  by  well-fed  women, 
free  from  mental  anxiety,  and  at  an  early  period  after  parturition.  It  is  curi- 
ous, however,  that  although  it  diminishes  to  as  little  as  one-seventh,  between 
the  fourth  and  ninth  months  of  lactation,  it  increases  again  between  the  twelfth 
and  the  eighteenth  ;  being  sometimes,  at  the  latter  period,  almost  a  third  of 
the  whole.  In  conformity  with  this  change  in  the  character  of  the  secretion, 
it  is  found  that  the  specific  gravity  increases  during  the  early  weeks,  as  the 
oleaginous  part  gives  place  to  the  albuminous  and  saccharine.  The  following 
table  exhibits  the  relative  proportion  of  the  different  ingredients,  in  the  Milk 
of  various  animals,  from  which  it  is  commonly  obtained.  It  appears  from 

Woman.         Cow.          Goat.          Sheep.          Ass.          Mare. 

Casein  .....  2-95  4-48  4-02  4-50  1-82  1-62 
Butter  .....  5-20  3-13  3-32  4-20  -Oil  traces 


6'34  *"  ™  *.00  6-08  8.75 
Saline  Matters  .  .  0-45  0-60  0-58  0-68  0-34)  ftQ  fi{> 
Water  .....  85-06  87-02  86-80  85-62  91-655 

this,  that,  whilst  the  milk  of  the  Cow,  Goat,  and  Sheep  do  not  differ  from  each 
other  in  any  very  prominent  degree,  that  of  the  Ass  and  Mare  is  a  fluid  of  very 
dissimilar  character,  containing  a  comparatively  small  proportion  of  casein  and 
butter,  and  abounding  in  sugar.  Hence  it  is,  that  it  is  much  more  disposed 
to  ferment  than  other  milk  ;  indeed,  the  sugar  of  Mare's  milk  is  so  abundant, 
that  the  Tartars  prepare  from  it  a  spirituous  liquor,  to  which  they  give  the 
name  of  koumiss.  It  appears  from  these  details  that  no  milk  more  nearly 
approaches  that  of  the  Human  female  than  that  of  the  Sheep  and  Goat  ;  these 

respiration,  eliminate  part  of  the  oily  matter  in  the  form  of  carbonic  acid  and  water; 
whilst  rest  and  warmth,  by  diminishing  this  drain,  favour  its  passage  into  the  milk.  — 
The  proportion  of  Casein,  on  the  other  hand,  is  increased  by  exercise;  which  would 
seem  to  show  that  this  ingredient  is  derived  from  the  disintegration  of  Muscular  tissue,  — 
and  thus  adds  strength  to  the  Author's  view  (§  468),  that  of  the  matter  thus  set  free,  a 
part  only  is  destined  to  immediate  excretion,  and  that  a  part  may  again  be  subservient  to 
the  operations  of  Nutrition.  Dr.  Playfair's  experience  on  this  head  seems  to  correspond 
with  the  results  of  common  observation  in  Switzerland,  where  the  cattle  pasture  in  very 
exposed  situations,  and  are  obliged  to  use  a  great  deal  of  muscular  exertion.  The  quan- 
tity of  Butter  yielded  by  them  is  very  small;  whilst  the  Cheese  is  in  unusually  large 
proportion.  But  these  very  cattle,  when  stall-fed,  give  a  large  quantity  of  Butter  and 
very  little  Cheese. 


MAMMARY  GLAND SECRETION  OF  MILK.  547 

both  possess,  however,  a  larger  proportion  of  casein,  which  forms  a  peculiarly 
dense  curd  ;  and  the  milk  of  the  Goat  is  tainted  with  the  peculiar  odour  of  the 
animal,  which  is  more  intense  if  the  individual  be  dark-coloured.  The  milk 
of  the  Cow  will  usually  answer  very  well  for  the  food  of  the  infant ;  care  being 
taken  to  dilute  it  properly,  according  to  the  age  of  the  child. 

689.  The  change  which  naturally  takes  place,  from  the  condition  of  Colos- 
trum to  that  of  true  Milk,  during  the  first  week  of  lactation,  is  a  very  im- 
portant one.     The  Colostrum  has  a  purgative  effect  upon  the  child,  which  is 
very  useful  in  clearing  its  bowels  of  the  meconium  that  loads  them  at  birth  ; 
and  thus  the  necessity  of  any  other  purgative  is  generally  superseded.    Occa- 
sionally, however,  the  coloslric  character  is  retained  by  the  milk,  during  an 
abnormally  long  period  ;  and  the  health  of  the  infant  is  then  severely  affected. 
It  is  important  to  know  that  this  may  occur,  even  though  the  milk  may  pre- 
sent all  the  usual  appearance  of  the  healthy  secretion ;  but  the  microscope 
at  once  detects  the  difference.*     The  return  to  the  character  of  the  early 
milk,  which  has  been  stated  to  take  place  after  the  expiration  of  about  twelve 
months,  seems  to  indicate  that  Nature  designs  the  secretion  no  longer  to  be 
encouraged.     The  mother's  milk  cannot  then  be  so  nutritious  to  the  child  as 
other  food;t  and  every  medical  man  is  familiar  with  the  injurious  conse- 
quences, to  which  she  renders  herself  liable  by  unduly  prolonging  lactation.^ 

690.  From  what  has  been  stated  of  the  close  correspondence  between  the 
elements  of  the  Blood  and  those  of  the  Milk,  it  is  evident  that  we  can  scarcely 
expect  to  trace  the  existence  of  the  latter,  as  such,  in  the  circulating  fluid. 
To  what  degree  the  change,  in  which  their  elaboration  consists,  is  accom- 
plished in  the  Mammary  gland,  or  during  the  course  of  the  circulation,  there 
is  no  certain  means  of  ascertaining.     The  recent  discovery  of  the  usual  pre- 
sence of  the  organic  compound  named  kiestine  (which  is  nearly  related  to 
casein),  in  the  urine  of  pregnant  women,  seems  to  indicate  that  the  conver- 
sion of  albumen  into  casein  takes  place  in  the  blood, — this  curious  excretion 
being  the  means  of  preventing  its  accumulation  in  the  circulating  fluid,  pre- 
viously to  the  time  when  it  is  secreted  by  the  mammae. §     It  is  evident  that 
this  secretion  cannot  serve  as  the  channel  for  the  deportation  of  any  element, 
the  accumulation  of  which  would  be  injurious  to  the  system  ;  since  it  does  not 
occur  in  the  male  at  all ;  and  in  the  female  at  particular  times  only.     Yet 
there  is  reason  to  believe  that  if,  whilst  the  process  is  going  on,  it  be  suddenly 
checked,  the  retention  of  the  material  in  the  blood,  or  the  re-absorption  of  the 
secreted  fluid,  is  attended  with  injurious  consequences.     Thus  if,  when  the 
milk  is  first  secreted,  the  child  be  not  put  to  the  breast,  an  accumulation  takes 
place,  which,  if  not  relieved,  occasions  great  general  disturbance  of  the  system. 
The  narrowness  of  the  orifices  of  the  milk-tubes  obstructs  the  spontaneous 
exit  of  the  fluid,  especially  in  primiparss  ;  the  reservoirs  and  ducts  become 
loaded  ;  further  secretion  is  prevented  ;  and  a  state  of  congestion  of  the  ves- 
sels of  the  gland,  tending  to  inflammation,  is  induced.     The  accompanying 
fever  is  partly  due,  no  doubt,  to  the  local  disturbance  ;  but  in  part,  also,  there 
seems  reason  to  believe,  to  the  re-absorption  of  the  milk  into  the  blood  ;  this 
cannot  but  be  injurious,  since,  although  but  little  altered,  the  constitution  of 
milk  is  essentially  different,  especially  in  regard  to  the  quantity  of  crystal liz- 

*  See  Donne,  "  Du  Lait,  et  en  particulier  celui  des  Nourrices  ;"  and  Brit,  and  For. 
Med.  Review,  vol.  vi.  p.  181. 

f  On  the  whole  subject  of  Infant  Nutrition,  the  Author  would  strongly  recommend  the 
excellent  little  work  of  Dr.  A.  Combe,  formerly  referred  to. 

$  One  of  these,  which  has  particularly  fallen  under  the  Author's  notice,  is  debility  of 
the  retina,  sometimes  proceeding  to  complete  amaurosis;  this,  if  treated  in  time,  is  most 
commonly  relieved  by  discontinuance  of  lactation,  generous  diet,  and  quinine. 

§  See  Dr.  Golding  Bird,  in  Guy's  Hosp.  Rep.,  vol.  v. 


548  OF  SECRETION. 

able  matter  (sugar)  which  it  contains.  The  instances  of  the  vicarious  secre- 
tion of  milk  are  not  numerous  ;  and  in  no  "instance  is  there  any  proof  that  the 
elements  of  the  fluid  were  pre-existent  in  the  blood.  Some  of  the  most  curious 
are  those  in  which  it  has  been  poured  out  from  a  gland  in  the  groin  ;  but  it 
is  probable  that  this  was  in  consequence  of  the  existence  of  a  real  repetition, 
in  that  place,  of  the  true  mammary  structure, — this  being  the  situation  of  the 
mammae  of  many  of  the  inferior  animals,  of  which  the  analogues  in  Man  are 
usually  undeveloped. 

691.  The  following  is  a  more  unequivocal  case  of  vicarious  secretion  ;  and 
it  is  peculiarly  interesting  as  exhibiting  the  injurious  effects  of  the  re-absorp- 
tion of  the  secretion,  and  the  relief  which  the  system  experienced  when  it  was 
separated  from  the  blood  by  the  new  channel.     "  A  lady  of  delicate  constitu- 
tion (with  a  predisposition  to  pneumonia)  was  prevented  from  suckling  her 
child,  as  she  desired,  by  the  following  circumstance.     Soon  after  her  delivery 
she  had  a  severe  fever,  during  which  her  breasts  became  very  large  and  hard  ; 
the  nipples  were  swollen  and  firm ;  and  there  was  evidently  an  abundant 
secretion  of  milk ;  but  neither  the  sucking  of  the  infant,  nor  any  artificial 
means,  could  draw  a  single  drop  of  fluid  from  the  swollen  glands.     It  was 
clear  that  the  milk-tubes  were  closed  ;  and  as  the  breasts  continued  to  grow 
larger  and  more  painful,  purgatives  and  other  means  were  employed  to  check 
the  secretion  of  milk.     After  three  days  the  fever  somewhat  diminished,  and 
was  replaced  by  a  constant  cough,  which  was  at  first  dry,  but  soon  after  was 
followed  by  the  expectoration  of  simple  mucus.     After  this,  the  cough  dimi- 
nished in  severity,  and  the  expectoration  became  easy ;  but  the  sputa  were  no 
longer  mucous,  but  were  composed  of  a  liquid,  which  had  all  the  physical 
characters  of  genuine  milk.     This  continued  for  fifteen  days  ;  the  quantity  of 
milk  expectorated  amounting  to  three  ounces  or  more  in  the  twenty-four  hours. 
The  breasts  gradually  diminished  in  size  :  and  by  the  time  that  the  expecto- 
ration ceased,  they  had  regained  their  natural  dimensions.     The  same  com- 
plete obstacle  to  the  flow  of  milk  from  the  nipples  recurred  after  the  births  of 
four  children  successively,  with  the  same  sequelae.     After  the  sixth,  she  had 
the  same  symptoms  of  fever,  but  this  time,  they  were  not  followed  by  bron- 
chitis or  the  expectoration  of  milk ;  she  had  in  their  stead  copious  sweatings, 
which,  with  other  severe  symptoms,  reduced  her  to  a  cachectic  state,  and 
terminated  fatally  in  a  fortnight."* 

692.  Of  the  quantity  of  Milk  ordinarily  secreted  by  a  good  Nurse,  it  is  im- 
possible to  gain  any  definite  idea;  as  the  amount  which  can  be  artificially 
drawn  affords  no  criterion  of  that  which  is  secreted  at  the  time  of  the  draught 
(§  426).     The  quantity  which  can  be  squeezed  from  either  breast  at  any  one 
time,  and  which,  therefore,  must  have  been  contained  in  its  tubes  and  reser- 
voirs, is  about  two  ounces.     The  amount  secreted  is  greatly  influenced  by  the 
mental  and  physical  condition  of  the  female,  and  also  by  the  quantity  and  cha- 
racter of  the  ingesta.     In  regard  to  the  influence  of  the  mental  state  upon  this 
secretion,  ample  details  have  already  been  given  (Chap.  vn.).     With  respect 
to  the  physical  state  most  favourable  to  the  production  of  an  ample  supply  of 
this  important  fluid,  it  may  be  stated  generally,  that  sound  health,  a  vigorous 
but  not  plethoric  constitution,  regular  habits,  moderate  but  not  fatiguing  exer- 
cise, and  an  adequate  but  not  "excessive  amount  of  nutritious  food,  furnish  the 
conditions  most  required.     It  is  seldom  that  stimulating  liquors,  which  are  so 
commonly  indulged  in,  are  any  thing  but  prejudicial;  but  the  unmeasured 
condemnation  of  them  in  which  some  writers  have  indulged,  is  certainly  inju- 
dicious ;  as  experience  amply  demonstrates  the  improvement  in  the  condition 

*  Bulletino  delle  Scienze  Mediche,  Apr.,  1839;  and  Brit,  and  For.  Med-  Review,  Jan., 
1840. 


SALIVARY  GLANDS  AND  PANCREAS.  549 

both  of  mother  and  infant,  which  occasionally  results  from  the  moderate  em- 
ployment of  them. — The  influence  of  various  Medicines  upon  the  Milk,  is 
another  important  question,  which  has  not  yet  been  sufficiently  investigated. 
As  a  general  rule,  it  appears  that  the  most  soluble  saline  compounds  pass  into 
the  milk  as  into  other  secretions ;  but  there  are  many  exceptions.  Common 
salt,  the  sesquicarbonate  of  soda,  sulphate  of  soda,  iodide  of  potassium,  oxide 
of  zinc,  tris-nitrate  of  bismuth,  and  sesquioxide  of  iron,  have  been  readily  de- 
tected in  the  milk,  when  these  substances  were  experimentally  administered 
to  an  ass ;  and  ordinary  experience  shows,  that  the  human  infant  is  affected 
by  many  of  these,  when  they  are  administered  to  the  mother.  The  influence 
of  mercurial  medicines  taken  by  the  mother,  in  removing  from  the  infant  a 
syphilitic  taint  possessed  by  both,  is  also  well  known.  The  vegetable  purga- 
tives, especially  castor  oil,  senna,  and  colocynth,  have  little  effect  upon  the 
milk ;  hence  they  are  to  be  preferred  to  the  saline  aperients,  when  it  is  not 
desired  to  act  upon  the  bowels  of  the  child. 

V.  Salivary  Glands  and  Pancreas. 

693.  The  structure  of  the  Salivary  Glands  and  Pancreas  in  Man,  bears 
considerable  resemblance  to  that  of  the  Mammary  glands.     In  some  of  the 
lower   tribes,   however,   they  are  much   simpler. 

Thus,  in  the  Echinodermata  and   in  Insects,  the  Fig.  162. 

Salivary  glands  have  the  character  of  prolonged 
coeca,  more  or  less  convoluted ;  and  the  Pancreas 
of  Fishes  presents  itself  in  the  form  of  a  cluster  of 
short  coeca  round  the  pyloric  extremity  of  the  sto- 
mach, and  opening  into  it  by  distinct  orifices.  The 
accompanying  figure  will  give  a  sufficient  idea  of 
the  structure  of  these  glands  in  Man ;  the  vesicles 
are  very  minute,  having  a  diameter  only  about 
three  times  greater  than  that  of  the  capillary  blood- 
vessels. Their  development  commences  from  a 
simple  canal,  sending  off  bud-like  processes,  which 
opens  from  the  mouth,  and  lies  amidst  a  cellular 
blastema.  As  development  proceeds,  the  canal  be- 
comes more  and  more  ramified,  increasing  at  the 

,,    -I        i  i  ,  .   ,      .  Lobule  of  parotid  gland  of  a 

expense  of  the  blastema,  which  is  at  last  almost    new.borninfant  ejected  with  mer- 

wholly  absorbed ;  so  that  the  substance  of  the  gland    cury.  Magnified  so  diameters. 

consists  of  the  ducts,  with  their  ramifications  and 

follicular  terminations,  and  of  the  blo<5d-vessels  which  are  distributed  upon 

these. 

694.  The  salivary  secretion  is  by  no  means  necessarily  constant,  being 
almost  or  completely  suspended  by  cessation  of  the  movement  of  the  masticator 
muscles  and  tongue,  if  unexcited  by  any  nervous  stimulus.     Hence  it  is,  that 
the  secretion  is  checked  during  sleep  ;  so  that,  if  the  mouth  be  kept  open,  its 
surface  is  almost  dried  up  by  the  atmosphere.     The  mode  in  which  the  secre- 
tion is  excited  through  the  influence  of  the  nervous  system  has  already  been 
considered  (§§  425-6).     The  quantity  of  saliva  formed  during  the  twenty-four 
hours  has  been  estimated  at  about  15  or  20  ounces  ;  but  on  this  point  it  is  evi- 
dently impossible  to  speak  with  certainty.    The  fluid  obtained  from  the  mouth 
is  of  a  more  viscous  character  than  the  true  saliva  secreted  by  the  glands,  being 
mingled  with  mucus.     The  salivary  fluid  varies  as  to  its  chemical  re-action  ; 
being  sometimes  slightly  acid,  and  sometimes  slightly  alkaline  ;  but  it  is  seldom 
precisely  neutral.     According  to  Huenefeld,  it  will  at  the  same  time  strike  a 
blue  colour  with  reddened  litmus  paper,  and  turn  blue  litmus  paper  red ;  but 


550  OF  SECRETIOX. 

the  saliva  examined  directly  before  and  during  the  act  of  eating,  is  always 
alkaline.  It  may  be  doubted  whether  the  add  reaction  is  not  due  to  the  mucus 
of  the  mouth;  which,  at  times  when  only  a  small  amount  of  saliva  is  excreted, 
is  not  neutralized  by  its  alkali.  Its  specific  gravity  varies  from  1-006  to  1-009. 
It  contains  a  small  number  of  corpuscles,  which  seem  to  be  partly  epithelium- 
cells  from  the  mucous  surface  of  the  mouth,  and  partly  the  secreting  cells  of 
the  salivary  vesicles.  The  solid  matter  contained  in  Saliva  is  estimated  by  Ber- 
zelius  at  about  1  per  cent.  The  animal  principles  of  which  this  is  composed 
are  osmazome,  mucus,  and  a  peculiar  substance  termed  salivary  matter,  which 
is  soluble  in  water,  insoluble  in  alcohol,  and  yet  is  different  from  either  albu- 
men or  gelatin.  Clear  Saliva,  when  submitted  to  the  influence  of  galvanism, 
is  found  to  exhibit  a  faint  coagulum ;  and  hence  it  has  been  supposed  to  con- 
tain albumen.  The  presence  of  this  substance,  however,  is  doubtful.  A  con- 
siderable proportion  of  saline  and  earthy  matter  exists  in  the  solid  residue  of 
saliva ;  this  is  nearly  of  the  same  character  as  that  which  the  blood  contains, 
being  chiefly  composed  of  the  phosphate  of  lime  and  soda,  the  chlorides  of 
sodium  and  potassium,  and  the  lactates  of  soda  and  potash.  One  remarkable 
property  of  the  salivary  secretion,  is  its  formation  of  a  rust-red  precipitate 
when  mixed  with  a  solution  of  a  per-salt  of  iron.  This  is  supposed  to  be  due 
to  the  presence  in  it  of  the  principle  termed  sulpho-cyanogen.  The  tartar  which 
collects  on  the  human  teeth  consists  principally  of  the  earthy  phosphates,  the 
particles  of  which  are  held  together  by  about  20  per  cent,  of  animal  matter ; 
and  nearly  the  same  may  be  said  of  the  salivary  concretions  which  occasionally 
obstruct  the  ducts.* — It  appears  from  the  recent  experiments  of  Schulze,  Leh- 
mann,  and  others  on  the  continent,  and  of  Dr.  Wrightt  in  this  country,  that  the 
peculiar  animal  .matter  of  the  saliva  has  a  decided  effect  in  metamorphosing 
certain  alimentary  substances,  and  thus  performs  the  first  part  of  the  digestive 
process.  It  appears  unquestionable,  that  starch  may  be  converted  into  sugar, 
and  sugar  into  lactic  acid,  by  its  agency ;  and  that  if  concentrated,  it  has  a 
certain  solvent  power  for  casein,  animal  flesh,  and  other  albuminous  substances. 
But  these  facts  by  no  means  justify  the  conclusion  which  has  been  drawn 
from  them, — that  the  Saliva  is  the  real  agent  in  Digestion,  and  that  no  solvent 
fluid  is  secreted  by  the  stomach  itself;  a  conclusion  to  which  many  well-known 
facts  are  opposed,  and  completely  subverted  by  the  observations  of  Dr.  Beau- 
mont, by  whom  the  secretion  of  gastric  fluid  has  been  seen  to  be  poured  out 
from  the  walls  of  the  stomach. 

695.  The  Pancreatic  Secretion  of  Man  cannot,  of  course,  be  readily  obtained 
for  analysis ;  that  which  is  procured  from  the  lower  animals,  however,  probably 
gives  a  sufficiently  correct  idea  of  its  character.  It  seems  to  be  of  a  nearly 
similar  nature  with  saliva,  but  contains  a  much  larger  proportion  of  solid  mat- 

*  [From  analyses,  conducted  on  the  same  plan  as  those  of  the  blood,  Enderlin  (Annalen 
der  Chemie  und  Pharmacie,  Marz,  1844)  concludes  that  the  saliva,  like  the  blood,  contains 
no  lactate,  carbonate,  or  acetate;  but  that  its  alkaline  reaction  is  due  to  tribasic  phosphate 
of  soda,  which  serves  also  as  the  solvent  of  the  mucous  and  proteine-compounds.    The 
analysis  of  the  ashes  obtained  from  a  very  large  quantity,  afforded,  in  100  parts  : 
Tribasic  phosphate  of  soda  (3  Na.'O,  P  2,  O  5)     .  .  .       28.122 

Chlorides  of  sodium  and  potassi-um          ....       61-93 

Sulphate  of  soda    .  .  .  .  .  .  .2-315 

Phosphate  of  lime  "^ 

"  magnesia    V-  .  .  .  .         5-509 

"  iron  3 

He  believes,  from  this,  that  the  saliva  must  take  a  very  important  part  in  digestion.  And 
it  is  but  reasonable  to  connect  these'-dis.cdveries  of  the  basic  phosphate  of  the  saliva  and 
the  acid  phosphate  of  the  gastric  fluid,  with  the  fact  observed  by  Schultz  and  Lehmann, 
and  more  clearly  by  Dr.  Wright,  (see  Ia1*t  .Report,  p.  12,  and  Lancet,  1842-3)  that  the  alka- 
linity of  the  saliva  bears  a  direct  proportfon  to  the  acidity  of  the  gastric  secretion. — M.  C.] 
f  Lancet,  March  5,  1842,  et  seg. 


THE  TESTIS SPERMATIC  FLUID.  551 

ter ;  in  that  of  the  Dog  as  much  as  8-72  has  heen  found,  and  in  that  of  the 
Sheep  between  4  and  5  per  cent.  In  the  pancreatic  fluid  of  the  Horse,  on  the 
other  hand,  the  quantity  of  solid  matter  seems  to  be  less  than  in  the  saliva. 
Of  the  residuum  obtained  by  evaporation,  half  appears  to  consist  of  albumen  ; 
there  is  also  a  small  amount  of  osmazome,  and  apparently  of  casein.  A  free 
acid,  probably  the  acetic,  exists  in  this  fluid ;  the  salts  which  it  contains  are 
nearly  the  same  as  those  of  the  saliva. 

VI.  Lachrymal  Gland. 

698.  The  Lachrymal  glands  and  their  secretion  may  be  next  mentioned ; 
but  neither  require  any  lengthened  description.  The  gland  in  Man  is  formed 
very  much  on  the  plan  of  the  Parotid,  being  composed  of  branched  canals  ter- 
minating in  follicles,  the  ultimate  ramifications  of  the  several  branches  forming 
lobules  or  divisions  of  the  glands.  The  lachrymal  fluid  has  not  recently  un- 
dergone any  accurate  analysis ;  and  all  that  can  be  stated  respecting  it  is  the 
general  fact,  that  the  quantity  of  solid  matter  in  it  is  extremely  small,  and  that 
this  consists  chiefly  of  saline,  and  either  mucous  or  albuminous  compounds. 
It  seems  probable  that  the  secretion  of  the  lachrymal  gland  itself  is  very  little 
else  than  the  serum  of  the  blood,  deprived  of  a  great  part  of  its  albumen ;  and 
that  the  mucus  of  the  tears  is  secreted  from  the  surface  of  the  conjunctival 
membrane.  This  secretion  has  a  slightly  alkaline  re-action.  It  is  being  con- 
stantly formed  in  moderate  amount,  for  the  purpose  of  cleansing  the  surface  of 
the  eye  from  the  impurities  which  would  otherwise  rest  upon  it ;  and  it  is  then 
absorbed  by  the  open  orifices  of  the  nasal  duct,  and  carried  into  the  nose,  as 
fast  as  it  is  poured  out.  The  cause  of  this  absorption  does  not  seem  very  clear. 
Capillary  attraction  is  probably  in  part  concerned ;  and  it  has  been  thought 
that  the  momentary  partial  vacuum  occasioned  by  the  inspiratory  effort  in  all 
the  air-passages,  will  cause  the  emptying  of  the  nasal  duct  below,  and  a  con- 
sequent in-draught  above.  The  influence  of  the  nervous  system  upon  this 
secretion  has  been  already  adverted  to  (§§  425,  426). 

VII.  The  Testis.^- Spermatic  Fluid. 

697.  In  the  Testes  we  return  to  the  tubular  form  of  glandular  structure, 
which  so  remarkably  distinguishes  the  Kidney  from  all  the  other  glands 
hitherto  mentioned.  The  external  forms  presented  by  these  glands  throughout 
the  Animal  kingdom,  are  extremely  various  ;  but  their  composition  is  for  the 
most  part  very  uniform.  The  object  is  sometimes  attained  by  a  simple  but 
much  elongated  canal ;  sometimes  by  shorter  branched  tubes ;  and  in  other 
instances,  again,  by  numerous  aggregated  cosca,  which  are  often  rounded  into 
cells.  In  regard  to  this,  as  to  many  other  glands,  it  may  be  stated  that,  whilst 
its  general  form  in  Insects  is  that  of  prolonged  tubes,  the  required  extension  of 
surface  is  given  in  the  Mollusca  by  the  multiplication  of  cells,  so  that  the  struc- 
ture has  a  compact  spongy  character.  It  is  interesting  to  remark  that,  in  some 
of  the  lowest  Fishes,  this  organ  consists  of  a  mass  of  vesicles  which  have  no 
efferent  duct ;  and  that  the  secretion  formed  within  these  escapes  by  the  rup- 
ture of  the  vesicles,  allowing  it  to  escape  into  the  abdominal  cavity,  whence  it 
passes  by  openings  that  lead  directly  to  the  exterior.  In  these  Fishes,  the  ova 
are  discharged  from  the  ovarium  in  a  very  similar  manner ;  a  modification  of 
which  plan  is  followed  in  all  the  higher  Vertebrata, — the  ovum  being  in  them 
also  discharged,  by  the  rupture  of  its  containing  vesicle  or  ovisac,  into  the 
abdominal  cavity,  but  immediately  received  and  conveyed  away  by  the  funnel- 
shaped  internal  prolongation  of  the  external  orifice,  which  is  known  as  the 
fimbriated  extremity  of  the  Fallopian  tube.* 

*  See  Principles  of  General  and  Comparative  Physiology,  §  641. 


552 


OF  SECRETION. 


a.  The  Testis  in  Man  has  in  every  respect,  however,  a  distinctly  glandular  character. 
It  consists  of  several  lobules,  which  are  separated  from  each  other  by  processes  of  the 
tunica  albuginea  that  pass  down  between  them,  and  also  by  an  extremely  delicate  mem- 
brane (described  by  Sir  A.  Cooper  under  the  name  of  tunica  vasculosa)  consisting  of 
minute  ramifications  of  the  spermatic  vessels  united  by  areolar  tissue.  Each  lobule  is 
composed  of  a  mass  of  convoluted  Tubuli  Seminiferi,  throughout  which  blood-vessels 
are  minutely  distributed.  The  lobules  differ  greatly  in  size,  some  containing  one,  and 
others  many  of  the  tubuli;  the  total  number  of  the  lobules  is  estimated  at  about  450  in 
each  testis,  and  that  of  the  tubuli  at  840.  The  convolutions  of  the  tubuli  are  so  arranged, 
that  each  lobule  forms  a  sort  of  cone,  the  apex  of  which  is  directed  towards  the  Rete 
Testis.  It  is  difficult  to  trace  the  free  extremities  of  the  Seminiferous  tubes,  owing  to 


[Fig.  163. 


[Fig.  164. 


The  Testicle  injected  with  mercury;  1,  tunica 
albuginea;  2,  seminiferous  tubes;  3,  the  rete  vas- 
culosum  testis ;  4,  a  globule  of  mercury  which  has 
ruptured  the  tubes;  5,  the  vasa  efferentia  which 
form  the  coni  vasculosi ;  6,  coni  vasculosi  forming 
the  head  of  the  epididymis ;  7,  epididymis ;  8,  glo- 
bus  minor  of  the  epididymis ;  9,  vas  deferens.] 


A  view  of  the  minute  structure  of  the  Testis; 
1, 1,  tunica  albuginea;  2,  2,  corpus  highmorianum; 
3,  3,  tubuli  seminiferi  convoluted  into  lobules ;  4, 
vasa  recta ;  5,  rete  testis ;  6,  vasa  efferentia ;  7,  coni 
vasculosi  constituting  the  globus  major  of  the  epi- 
didymis ;  8,  body  of  the  epididymis ;  9,  its  globus 
minor;  10, vas  deferens ;  11,  vasculum  aberrans  or 
blind  duct.] 


the  frequency  of  their  anastomoses  with  each  other;  in  this  respect,  therefore,  the 
structure  of  the  testis  accords  closely  with  that  of  the  Kidney.  The  diameter  of  the 
Tubuli  is  for  the  most  part  very  uniform;  in  the  natural  condition  they  seem  to  vary 
from  about  the  T^th  to  the  T4<y*th  of  an  inch ;  but  when  injected  with  mercury  they  are 
distended  to  a  size  nearly  double  the  smaller  of  these  dimensions.  When  they  have 
reached  to  within  a  line  or  two  of  the  Rete  Testis,  they  cease  to  be  convoluted,  several 
unite  together  into  tubes  of  larger  diameter,  and  these  enter  the  rete  testis  under  the 
name  of  tubuli  redi.  The  rete  testis  consists  of  from  seven  to  thirteen  vessels,  which  run 
in  a  waving  course,  anastomose  with  each  other,  and  again  divide,  being  all  connected 
together.  The  vasa  efferentia  which  pass  to  the  head  of  the  epididymis  are  at  first 
straight,  but  soon  become  convoluted,  each  forming  a  sort  of  cone,  of  which  the  apex  is 
directed  towards  the  rete  testis,  the  base  to  the  head  of  the  epididymis.  The  number  of 
these  is  stated  to  vary  from  nine  to  thirty;  and  their  length  to  be  about  eight  inches.  The 
epididymis  itself  consists  of  a  very  convoluted  canal,  the  length  of  which  is  about 
twenty-one  feet.  Into  its  lower  extremity,  that  is,  the  angle  which  it  makes  where  it  ter- 
minates in  the  vas  deferens,  is  poured  the  secretion  of  the  vasculum  aberrans  or  appen- 
dix; which  seems  like  a  testis  in  miniature,  closely  resembling  a  single  lobule  in  its 
structure.  Its  special  function  is  unknown. 
b.  The  Testicles  originate  in  the  Embryo,  from  the  lower  part  of  the  Corpora  Wolffiana 


THE  TESTIS SPERMATIC  FLUID. 

Fig.  165. 


553 


Human  Testis,  injected  with  mercury  as  completely  as  possible ;  1, 1,  lobules  formed  of  the  seminiferous 
tubes;  2,  rete  testis;  3,  vasa  efferentia;  4,  flexures  of  the  efferent  vessels  passing  into  the  head.  5,  5,  of  the 
epididymis;  6,  body  of  the  epididymis ;  7.  appendix ;  8,  cauda;  9,  vas  deferens.  (After  Lauth.) 

Fig.  166. 


Plan  of  the  structure  of  the  Testis  and  Epididymis ;  a,  a,  seminiferous  tubes ;  a*,  a*,  their  anastomoses 
the  other  references  as  in  the  last  figure. 

(§  667,  c) ;  arising  from  their  lower  and  inner  sides,  whilst  the  Kidneys  spring  from  their 
upper  and  outer  parts.  They  make  their  first  appearance  in  the  Chick  about  the  fourth 
day,  as  delicate,  striae  on  the  Wolffian  bodies ;  and  at  this  period  no  difference  can  be 
detected  between  the  Testes  and  the  Ovaria,  which  originate  in  precisely  the  same  manner. 
Like  the  kidneys,  the  germ-preparing  organs  increase  in  proportion  with  the  diminution 
47 


554  OF  SECRETION. 

in  the  temporary  structures  ;  at  first  their  efferent  ducts  open  into  those  of  the  Wolffian 
bodies,  but  they  are  subsequently  separated  by  the  formation  of  a  partition,  like  that 
which  separates  the  rectum  from  the  cloaca.  In  the  Human  embryo,  the  rudiments  of  the 
sexual  organs, — whether  testes  or  ovaria, — first  present  themselves  soon  after  the  kidneys 
make  their  appearance,  that  is,  towards  the  end  of  the  seventh  week.  They  are  at  first 
much  prolonged,  and  seem  to  consist  of  a  kind  of  soft,  homogeneous  blastema,  in  which 
the  tubular  structure  subsequently  develops  itself.  The  Ovary  at  that  period  has  the 
same  aspect  and  texture ;  but  its  subsequent  course  of  development  is  different.  The 
Testis  gradually  assumes  its  permanent  form;  the  epididymis  appears  in  the  tenth  week; 
and  the  gubernaculurn,  (a  membranous  process  from  the  filamentous  tissue  of  the 
scrotum,  analogous  to  the  round  ligament  arising  from  the  labium,  and  attached  to 
the  ovary  of  the  female.)  which  is  originally  attached  to  the  vas  deferens,  gradually 
fixes  itself  to  the  lower  end  of  the  tesiis  or  epididymis.*  The  Testes  begin  to  de- 
scend at  about  the  middle  period  of  pregnancy;  at  the  seventh  month  they  reach  the 
inner  ring;  in  the  eighth  they  enter  the  passage;  and  in  the  ninth  they  usually  de- 
scend into  the  scrotum.  The  cause  of  this  descent  is  not  very  clear.  It  can  scarcely 
be  due  merely,  as  some  have  supposed,  to  the  contraction  of  the  gubernaculum; 
since  that  does  not  contain  any  fibrous  structure,  until  after  the  lowering  of  the  testes 
has  commenced.  It  is  well  known  that  the  testes  are  not  always  found  in  the  scrotum  at 
the  time  of  birth,  even  at  the  full  period.  Upon  an  examination  of  97  new-born  infants, 
Wrisberg  found  both  testes  in  the  scrotum  in  67, — one  or  both  in  the  canal  in  17,— in  8 
one  testis  in  the  abdomen, — and  in  3  both  testes  within  the  cavity.  Sometimes  one  or 
both  testes  remain  in  the  abdomen  during  the  whole  of  life;  but  this  circumstance  does 
not  seem  to  impair  their  function.  This  condition  is  natural,  indeed,  in  the  Ram. 

698.  The  fluid  secreted  by  the  Testes  is  thick,  tenacious,  and  of  a  grayish 
or  yellowish  colour.     It  is  mingled,  during  or  before  emission,  with  fluid 
secreted  by  the  Prostate,  Cowper's  glands,  &c.;  and  it  cannot,  therefore,  be 
obtained  pure,  but  by  drawing  it  from  the  Testicle  itself ;  hence  no  accurate 
analysis  can  be  made  of  it  in  the  Human  subject.     The  so-called  Spermatozoa 
and  Seminal  Granules,  which  form  the  most  important  and  characteristic  parts 
of  the  Semen,  are  so  intimately  connected  with  the  Reproductive  Function, 
that  they  will  be  more  appropriately  described  under  that  head  (Chap.  XIV). 
It  may  be  here  remarked,  however,  that  they  correspond  most  exactly  with 
other  Secretions,  in  their  mode  of  production ;  for,  as  will  be  shown  hereafter, 
they  are  elaborated  by  cells,  which  lie  within  the  tubuli,  and  which  rupture  so 
to  set  them  free,  when  they  are  mature  (§  735).     The  peculiar  odour  which 
the  Semen  possesses,  does  not  appear  to  belong  to  the  proper  spermatic  fluid ; 
but  is  probably  derived  from  one  or  other  of  the  secretions  with  which  it  is 
mingled.     The  chemical  analyses  which  have  been  made  of  this  fluid  are  all 
defective,  inasmuch  as  they  do  not  distinguish  the  real  secretion  of  the  testes 
from  the  mucus,  prostatic  fluid,  &c.,  with  which  it  is  mingled.     It  may  be 
stated,  however,  that  it  has  an  alkaline  reaction,  and  contains  albumen,  with 
a  peculiar  animal  principle  termed  Spermatine  ;  and  also  saline  matter,  con- 
sisting chiefly  of  muriates  and  phosphates,  especially  the  latter,  which  form 
crystals  when  the  fluid  has  stood  for  some  little  time. 

VIII.  Cutaneous  and  Mucous  Follicles. 

699.  Having  now  described  the  structure  and  functions  of  the  principal 
Glands,  which  are  composed  of  aggregated  masses  of  secreting  cells  or  tubes, 
we  may  proceed  to  those  in  which  the  glandule  are  more  scattered,  but  are 
still,  in  their  aggregate  amount,  of  sufficient  importance  to  claim  particular 
notice.     This  is  especially  the  case  in  the  Skin,  and  its  internal  prolongations, 
forming  Mucous  Membranes.   ^The  Skin  is  the  seat  of  various  secretions;  for 

*  Mr.  Mayo  mentions  (Physiology,  p.  430)  a  curious  malformation  that  came  under  his 
notice,  which  is  explained  by  this  fact.  The  left  testis  had  not  descended,  and  lay  upon 
the  edge  of  the  psoas  muscle  immediately  within  the  internal  ring;  while  the  cord  was 
drawn  down  into  the  scrotum  through  the  persistence  of  the  original  attachment  of  the 
gubernaculum,  forming  a  long  loop. 


CUTANEOUS  AND  MUCOUS  FOLLICLES. 


555 


Fig.  167. 


each  of  which  it  is  provided  with  special 
organs.  Of  these  the  most  important  is  the 
Perspiration ;  which  is  formed  in  small 
glandular  organs  seated  just  beneath  the 
cutis,  and  diffused  over  the  whole  surface  of 
the  body.  The  efferent  ducts  of  these 
Glandulse  open  by  minute  pores  in  the 
Epidermis,  which  are  seen  in  elevated  lines 
on  the  skin  of  the  palm  of  the  hand  and 
the  sole  of  the  foot ;  they  penetrate  the 
epidermis  rather  obliquely,  so  that  a  sort 
of  little  valve  is  formed  by  it,  which  is  lifted 
up  by  the  excreted  fluid  as  it  issues.  The 
ducts  pass  through  the  Epidermis  and  Cutis 
in  a  spiral  direction ;  and  then  enter  the 
glands,  which  consist  of  the  convolutions  of 
the  ducts,  more  or  less  subdivided,  on  which 
blood-vessels  are  distributed.  Where  the 
Epidermis  is  thin,  the  canal  is  straighter. 

700.  The  Secretion  of  fluid  by  these 
Glands  is  continually  taking  place  ;  but  this 
fluid,  being  usually  carried  off  in  the  form 
of  vapour  as  fast  as  it  is  separated,  does  not 
accumulate  and  become  sensible.  If,  how- 
ever, from  the  increased  amount  of  the  se- 
cretion, or  from  the  condition  of  the  sur- 
rounding air,  the  whole  fluid  thus  poured 
out  should  not  evaporate,  it  accumulates  in 
minute  drops  upon  the  surface  of  the  skin. 
Thus  the  Sudoriferous  excretion  may  take 
the  form  either  of  sensible  or  insensible 
transpiration  ;  the  latter  being  constant,  the 
former  occasional.  It  is  difficult  to  obtain 
enough  of  this  secretion  for  analysis,  free 
from  the  sebaceous  and  other  matters  which 
accumulate  on  the  surface  of  the  skin;  and 
its  character  can  only,  therefore,  be  stated 
approximately.  It  has  usually  an  acid  re- 
action, which  seems  due  to  the  presence  of 
lactic  acid ;  and  to  this  we  are  probably  to 
attribute  the  sour  smell  which  it  has,  espe- 
cially in  some  disordered  states  of  the  sys- 
tem. The  proportion  of  solid  matter  was 
considered  by  Renard  to  be  about  l-10th ; 
but  according  to  Anselmino  it  varies  be- 
tween 5  and  H  per  cent.  The  greatest 
part  of  it  consists  of  animal  matter,  which  is  apparently  a  protein-compound 
in  a  state  of  incipient  decomposition.  The  remainder  consists  of  saline  com- 
pounds ;  of  which  the  chlorides  of  potassium  and  sodium  appear  to  be  pretty 
constantly  present ;  whilst  the  muriate  of  ammonia,  free  acetic  acid,  and 
acetate  of  soda,  have  also  been  said  to  occur  in  it.~ The  proportion  of  these 
ingredients  would  probably  be  found  larger  in  the  fluid  of  the  Sudoriferous 
glands,  if  we  had  the  means  of  collecting  it  separately  ;  for  of  the  whole  fluid 
which  passes  off  from  the  surface  of  the  Skin,  only  a  small  proportion  can  be 
properly  said  to  be  secreted  by  the  Sudoriferous  glands ;  the  greater  part, 


Sudoriferous  Gland  from  the  palm  of  the 
hand,  magnified  40  diameters;  1 , 1,  contorted 
lubes,  composing  the  gland,  and  uniting  into 
two  excretpry.  ducts,  2,  2,  which  unite  into 
one  spiral  canal,  that  perforate^  the  epider- 
mis at  3,  and  opens  on  its  Surface  at  4;  the 
gland  is  imbedded  in  fat-vesiclea,  which  are 
seen  at  5,  5.  (After  Wagner.) 


556  OF  SECRETION. 

under  ordinary  circumstances,  being  the  product  of  simple  Evaporation,  by 
which,  of  course,  nothing  but  pure  watery  vapour  is  dissipated. 

701.  The  entire  amount  of  fluid  which  is  insensibly  lost  from  the  Cutaneous 
and  Pulmonary  surfaces,  is  estimated  by  Seguin  at  18  grains  per  minute  ;  of 
which  11  grains  pass  off  by  the  skin,  and  7  by  the  lungs.     The  maximum 
loss  by  Exhalation,  cutaneous  and  pulmonary,  during  twenty-four  hours,  (ex- 
cept under  very  peculiar  circumstances,)  is  5  Ibs.;  the  minimum  1§  Ib.     It 
varies  greatly,  according  to  the  condition  of  the  atmosphere,  and  that  of  the 
body  itself.     The  manner  and  degree  in  which  it  is  influenced  by  atmospheric 
conditions,  will  be  better  discussed  under  the  head  of  Animal  Heat  (§731); 
since  this  influence  has  a  most  important  effect  in  the  regulation  of  the  tem- 
perature of  the  body.     As  already  pointed  out,  the  Urinary  excretion  is  in 
great  degree  vicarious  with  it,  in  regard  to  the  amount  of  fluid  discharged, — 
the  Urine  being  more  watery  in  proportion  as  the  Cutaneous  Exhalation  is 
diminished  in  amount,~and  vice  versa  (§  668).     But  we  are  also  to  look  at 
these  two  excretions  as  vicarious,  in  regard  to  the  deportation  (or  getting  rid) 
of  the  products  of  the  waste  of  the  system.     The  share  which  the  Skin  has  in 
this  office  has  probably  been  generally  underrated.     There  is  reason  to  believe 
that  at  least  100  grains  of  azotized  mater  are  excreted  from  it  daily;  and  any 
cause  which  checks  this  excretion  must  throw  additional  labour  on  the  kid- 
neys, and  will  be  likely  to  produce  disorders  of  their  function.     (See  §  714.) 

702.  The  Exhalant  action  of  the  Skin  is  influenced  by  general  conditions 
of  the  vascular  and  nervous  systems,  which  are  as  yet  ill  understood.     It  is 
quite  certain,  however,  that  through  the  influence  of  the  latter  the  secretion 
may  be  excited  or  suspended ;  this  is  seen  on  the  one  hand  in  the  state  of 
syncope,  and  in  the  effects  of  depressing  emotions,  especially  fear,  and  its 
more  aggravated  condition,  terror;  and  on  the  other  in  the  dry  condition  of 
the  skin  during  states  of  high  nervous  excitement.     It  is  very  probable  that, 
in  many  forms  of  fever,  the  suppression  of  the  perspiration  is  a  cause  rather 
than  an  effect  of  disordered  vascular  action;    for  there  are  several  morbid 
conditions  of  large  parts  of  the  surface,  in  which  the  suppression  of  the  trans- 
piration appears  to  be  one  of  the  chief  sources  of  danger,  having  a  tendency 
to  produce  congestion  and  inflammation  of  internal  organs.     From  the  recent 
experiments  of  Dr.  Fourcault,*  it  appears  that  complete  suppression  of  the 
Perspiration  in  animals,  by  means  of  a  varnish  applied  over  the  skin,  gives 
rise  to  a  state  termed  by  him  Cutaneous  Asphyxia;    which  is  marked  by 
imperfect  arterialization  of  the  blood,  and  considerable  fall  of  temperature, 
(§§  543,  726) ;  and  which,  as  it  produces  death  in  the  lower  animals,  would 
probably  do  the  same  in  Man.     A  partial  suppression  by  the  same  means 
gives  rise  to  Febrile  symptoms,  and  to  Albuminuria. 

703.  The  Skin  is  likewise  furnished  with  numerous  Sebaceous  glands,  also 
distributed  more  or  less  closely  throughout  the  whole  surface  of  the  body.— 
By  these  an  Adipose  secretion  is  poured  forth,  which  keeps  the  skin  from 
being  dried  and  cracked  by  the  action  of  the  sun  and  air.     It  is  especially 
abundant  in  the  races  which  are  formed  to  inhabit  warm  climates.     Some  of 
these  glandulse  are  simple  follicles  lined  with  secreting  cells,  and  contained 
in  the  substance  of  the  Skin  itself;    whilst  others  are  formed  out  of  similar 
follicles,  more  or  less  branched,  elongated,  and  convoluted ;  and  others,  again, 
seem  to  consist  of  little  else  than  clusters  of  Fat  cells,  from  one  part  of  which 
an  excretory  duct  arises ;  these  last  commonly  open  into  the  passage  by  which 
the  Hair  makes  its  way  outwards. — Besides  these,  there  are  other  glands 
situated  in  particular  parts  of  the  body,  and  having  special  functions.     Such 
are  the  Ceruminous  glands  situated  beneath  the  skin  of  the  auditory  meatus ; 

*  Comptes  Rendus  de  1'Acadcmie,  May,  1844;  and  Lancet,  June  8,  1844. 


CUTANEOUS  AND  MUCOUS  FOLLICLES. 

Fig.  168. 


557 


Cutaneous  Glands  of  external  Meatus  Auditorius.  !•  Section  of  the  skin,  magnified  3  diameters;  2,  2, 
hairs;  3,  3,  superficial  sebaceous  glands;  1, 1,  larger  and  deeper-seated  glands,  by  which  the  cerumen  is 
secreted.  3.  A  hair,  perforating  the  epidermis  at  3;  1, 1,  sebaceous  glands,  with  their  excretory  ducts,  2,  2; 
4,  base  of  the  hair,  in  its  double  follicle,  5,  5.  3.  Cerumen  gland,  formed  by  the  contorted  tube,  1, 1,  of  the 
excretory  duct,  2;  3,  vascular  trunk  and  ramifications. — The  last  two  figures  highly  magnified.  (After 
Wagner.) 

these  are  closely  analogous  in  form  to  the  sudoriferous  glands,  as  the  accom- 
panying figure  shows  ;  but  their  secretion  is  very  different,  being  nearly  solid, 
and  having  somewhat  of  a  resinous  character. — It  is  probable  that  by  similar 
glands  are  elaborated  the  Odorous  secretions,  which  are  exuded  from  particu- 
lar parts  of  the  surface,  especially  the  axillae.  In  many  of  the  lower  animals, 
such  glands  may  be  detected,  having  a  structure  of  considerable  complexity. 
The  Odorous  secretion  would  appear  to  be  elaborated  from  the  blood  by  a 
simple  chemical  change :  for  it  may  be  made  evident,  even  in  blood  that  has 
been  dried  up,  by  treating  it  with  sulphuric  acid.  This  aromatic  principle 
differs  sufficiently  in  the  blood  of  different  animals,  to  enable  a  person  with  a 
delicate  sense  of  smell  to  determine  from  what  animal  any  specimen  has  been 
procured ;  and  this  fact  has  been  applied  with  success  to  juridical  investiga- 
tions. It  has  even  been  stated  that  the  blood  of  the  Human  male  may  be 
distinguished  from  that  of  the  Female,  by  its  more  powerful  odour ;  but  this 
does  not  appear  to  be  the  case, — at  least  with  sufficient  certainty  for  medico- 
legal  inquiries.* 

704.  Besides  the  crypts  or  follicles,  which  have  been  spoken  of  as  gene- 
rally existing  in  Mucous  Membranes  (§  640),  there  exist,  in  that  of  the  Intes- 
tinal canal,  numerous  glandulae  in  various  parts,  for  the  elaboration  of  particu- 
lar secretions.  In  the  Stomach,  for  example,  a  large  number  of  these  secreting 
organs,  some  of  them  possessing  rather  a  complex  structure,  are  included  in 
the  thickness  of  its  walls,  composing,  indeed,  the  greater  part  of  the  mucous 
membrane.  If  this  be  divided  by  a  section  perpendicular  to  its  surface,  it  is 
seen  to  be  made  up  of  a  number  of  tubuli  closely  applied  to  each  other,  their 
blind  extremities  being  in  contact  with  the  submucous  tissue,  and  their  open 

*  See  Annales  d'Hygiene,  vol.  i.  pp.  267  and  548  ;  vol.  ii.  p.  217;  vol.  x.  p.  160,  &c.v 

47* 


558 


OF  SECRETION. 


Fig.  170. 


A  view  of  the  Mesocolon  in  its  connection  with  the  Mesentery,  as 
well  as  the  connections  of  the  Colon  with  the  Mesocolon — the  opening 
of  the  Ileum  into  the  Coecum.  and  the  passage  of  the  Duodenum  from 
the  superior  to  the  inferior  part  of  the  abdomen ;  1,  the  peritoneum  of 
the  lumbar  region,  and  the  origin  of  the  left  lumbar  mesocolon ;  2,  the 
left  lumbar  portion  of  the  mesocolon ;  3,  the  transverse  mesocolon ;  4,  the 
right  lumbar  mesocolon;  5,  the  union  of  the  mesocolon  with  the  mesen- 
tery ;  6,  the  mesentery;  7,  7,  the  folds  of  the  mesentery  cut  off  from  the 
small  intestines;  8,  lower  end  of  the  ileum;  9,  the  ccecum;  10, 10,  the 
ascending  colon;  11,  the  transverse  colon;  12,  the  descending  colon; 
13,  the  sigmoid  flexure;  14,  the  anterior  muscular  band  of  the  colon; 
]5,  the  duodenum,  passing  from  the  superior  to  the  inferior  portion  of  the 
abdomen;  10,  the  colon  ending  in  the  rectum;  17,  section  of  the  ileum.] 


Section  of  the  coats  of  the 
Stomach,  near  the  pylorus, 
showing  the  gastric  glands; 
1,  magnified  3  times ;  2,  mag- 
nified 20  times.  (After  Wag- 
ner.) 


ends  being  directed  towards  the  cavity  of  the  stomach.  In  some  situations, 
these  tubuli  are  short  and  straight ;  in  other  parts  they  are  no  longer,  and 
present  an  appearance  of  irregular  dilatation  or  partial  convolution.  This, 
indeed,  is  their  usual  character,  especially  towards  the  cardiac  orifice  of  the 


Fig.  171. 


Fig.  172. 


Glands  in  the  coats  of  the  Stomach,  magnified  45  diameters ; 
1,  gastric  gland  from  the  middle  of  the  stomach ;  2.  another  of 
more  complex  structure,  and  appearing  to  contain  mucus,  from 
the  neighbourhood  of  the  pylorus.  (After  Wagner.) 


Portion  of  the  mucous  membrane  of 
the  stomach,  showing  entrances  to  the 
secreting  tubes,  in  pits  upon  its  surface. 
(After  Boyd.) 


CUTANEOUS  AND  MUCOUS  FOLLICLES. 


559 


[Fig.  173. 


stomach.  On  the  other  hand,  towards  the  pyloric  extremity  they  have  a  much 
more  complex  structure.  Between  the  tubuli,  blood-vessels  pass  up  from  the 
sub-mucous  tissue,  and  form  a  vascular  network  on  its  surface.  From  the 
examination  of  these  horizontal  sections  of  the  mucous  membrane  at  various 
depths,  Dr.  Todd*  has  ascertained  that  the  tubuli  are  arranged  in  bundles  or 
groups,  surrounded  and  bound  together  by  a  fine  areolar  membrane;  the  size 
of  the  bundles,  and  the  number  of  tubules  contained  in  them,  vary  considera- 
bly. The  tubes  do  not,  in  general,  open  directly  upon  the  surface,  but  into 
the  bottom  of  small  depressions  or  pits,  which  may  be  seen  to  cover  the  mem- 
brane. These  pits  are  more  or  less  circular  in  form,  and  are  separated  from 
one  another  by  partition-like  elevations  of  the  membrane,  which  vary  in  depth ; 
and  sometimes  even  by  pointed  processes,  that  have  been  mistaken  by  some 
anatomists  for  villi.  The  diameter  of  these  pits  varies  from  about  l-100th  to 
1 -250th  of  an  inch;  it  is  always  greatest  near  the  pylorus.  When  the  sur- 
face of  the  membrane,  cleansed  from  mucus  and  epithelium-scales,  is  examined 
with  a  sufficient  magnifying  power,  it  is  seen  that  from  three  to  five  perfora- 
tions exist  in  the  bottom  of  each  pit ;  and  these  are  the  openings  of  the  secret- 
ing tubes.  The  Gastric  fluid,  elaborated  by  this  Apparatus,  having  been 
already  made  a  subject  of  special  consideration,  (§  449,  et  seq.,)  need  not  be 
here  described. 

705.  The  whole  Mucous  sur- 
face of  the  Intestinal  canal  is  fur- 
nished with  glandular  follicles  of 
a  very  similar  character;  of  which 
some  approach  those  of  the  sto- 
mach in  complexity  of  structure, 
whilst  others  evidently  corre- 
spond with  the  crypts  of  ordinary 
Mucous  Membrane.  An  innu- 
merable multitude  of  pores  are 
easily  seen,  by  the  aid  of  a  simple 
lens,  to  cover  the  whole  internal 
surface  of  the  large  Intestine; 
and  these  are  the  entrances  to 
tubular  follicles,  closely  resem- 
bling those  of  the  stomach,  but 

more  simple  in  structure.    Their 

ccEcal  extremities  abut  against  the 

sub-mucous  tissue:   towards  the 

end  of  the  Rectum,  however,  they 

are  much  prolonged,  and  consti- 
tute a  peculiar  layer  between  the 

mucous  and  muscular  coats ;  the 

tubes,  which  are  there  visible  to 

the  naked  eye,  being  erect,  pa- 
rallel,  and   densely   crowded. — 

These  glands  probably  form  the 

peculiarly   thick   and    tenacious 

mucus  of  the  large  intestine.    In 

the  small  intestine,  on  the  other 

hand,  the  coeca  are  less  deep  and 

their    apertures    are    smaller. — 

These  apertures  are,  for  the  most 


A  section  of  the  Ileum,  inverted  so  as  to  show  the  ap- 
pearance and  arrangement  of  the  villi  on  an  extended 
surface,  as  well  as  the  follicles  of  Lieberkiihn;  the  whole 
seen  under  the  -rhicroscope.  A  close  examination  of  this 
cut  will  show  a  great  number  of  black  points  in  the  spaces 
between  the  projections  of  villi :  these  are  the  follicles  of 
Lieberkiihn.] 


*  Gulstonian  Lectures  on  the  Physiology  of  the  Stomach,  in  Medical  Gazette,  1839. 
See  also  Dr.  Sprott  Boyd's  Inaugural  Dissertation  on  the  Mucous  Membrane  of  the  Sto- 
mach, in  Edinb.  Med.  and  Surg.  Journal,  vol.  xlvi. 


560 


OF  SECRETION. 


Fig.  174. 


Fig.  175. 


Mucous  coat  of  small  intestines  as  altered  in 
fever;  the  follicles  of  Lieberkiilm  filled  with 
tenacious  white  secretions.  (After  Boehm.) 


One  of  the  glandulse  majores  simplices, 
viewed  from  above,  and  seen  in  section; 
from  the  large  intestine.  (After  Boehm.) 


176. 


part,  situated  around  the  bases  of  the  villi :  in  the  foetus  and  newly-born  child, 
they  are  so  abundant  as  to  be  almost  in  contact ;  but  in  the  adult,  the  intervals 
increase,  so  as  to  occupy  more  space  than  the  apertures.  The  glandulae  of 
the  small  intestine  have  long  been  known  under  the  name  of  the  follicles  of 
Lieberklihn ;  they  become  particularly  evident  when  the  mucous  membrane 
is  inflamed,  being  then  filled  with  an  opaque  whitish  secretion,  which  is  absent 
in  the  healthy  state.  Besides  the  foregoing  descriptions  of  solitary  glandulae, 
the  Cfficum  and  the  lower  part  of  the  Rectum  contain  a  number  of  simple  and 
large  follicles,  which  produce  slight  rounded  elevations  on  the  surface  of  the 
mucous  membrane ;  the  centre  of  each  of  these  elevations  is  perforated  by  an 
aperture  of  the  follicle;  and  around  this  are  seen  the  orifices  of  the  tubular 
cosca,  which  closely  envelop  the  globular  follicle.  These  seem  most  abun- 
dant where  the  largest  quantity  of  mucus  is  required.  They  have  been  con- 
founded with  the  glands  of  Brunner ;  but  are  rather  analogous  to  the  solitary 
Peyerian  glands  presently  to  be  noticed. 

706.  The  true  glands  of  Brunner  are  chiefly  situated  in  the  Duodenum ; 

and  they  lie  not  in  the  mucous  but  in  the  sub-mucous 
tissue,  where  they  form  a  continuous  layer  of  white 
bodies  surrounding  the  whole  intestine.  Their  size, 
unless  diseased,  is  scarcely  that  of  a  hemp-seed ;  each 
consists  of  numerous  minute  lobules,  of  which  the 
ducts  open  into  a  common  excretory  tube ;  and  in  the 
lobules  may  be  distinguished  the  minute  ramifications 
of  these  ducts,  with  clusters  of  follicles  forming  acini, 
of  which  about  six  hundred  are  computed  to  exist  in 
each.  Hence  these  glands  are  of  complex  structure, 
much  resembling  that  of  the  Salivary  glands  and  Pan- 
creas, and  entirely  differing  from  all  the  other  glan- 
dulse of  the  walls  of  the  alimentary  canal.  Of  the 
peculiar  nature  of  their  secretion  nothing  is  known. 

707.  The  so-called  Peyerian  glands  constitute,  when  aggregated  together, 
large  patches  on  the  mucous  membrane  of  the  small  intestine,  where  they  are 
known  as  the  glandule  agminatas  ;  and  it  is  to  these  alone  that  Peyer's  name 
is  usually  applied.    Similar  bodies,  however,  known  as  the  glandulse  solitarise, 
exist  separately  in  the  lower  part  of  the  small  intestines ;  where  they  have 
been  confounded  with  the  glands  of  Brunner,  which  do  not  extend  beyond  the 
commencement  of  the  Jejunum.     The  glands  of  Peyer,  when  examined  in  a 
healthy  mucous  membrane,  present  the  appearance  of  circular  white  slightly- 
raised  spots,  about  a  line  in  diameter,  over  which  the  membrane  is  usually 
less  set  with  villi,  and  very  often  entirely  free  from  them.     Each  of  these 
white  spots,  of  which  a  large  number  are  contained  in  the  agminated  glands, 


Conglomerate  gland  of  Brun- 
ner, from  commencement  of 
duodenum ;  magnified  an  hun- 
dred limes.  (After  Boehm.) 


CUTANEOUS  AND  MUCOUS  FOLLICLES. 

[Fig-  177.  Fig.  i78. 


561 


A  section  of  the  small  Intestine  containing  some  Portion  of  one  of  the  patches  of  Peyer's  glands 

of  the  glands  of  Peyer,  as  shown  under  the  micro-  from  the  end  of  the  ileum,  highly  magnified;  the 

scope.    These  glands  appear  to  be  small  lenticular  villi  are  also  displayed.    (After  Boehra.) 

excavations,  containing,  according  to  Boehm,  a 
white,  milky  and  rather  thick  fluid,  with  nume- 
rous round  corpuscles  of  various  sizes,  but  mostly 
smaller  than  blood  globules.  The  meshes  seen  in 
the  cut  are  the  ordinary  tripe-like  folds  of  the  mu- 
cous coat,  and  not  the  venous  texture  spoken  of 
under  the  follicles.] 

is  surrounded  by  a  zone  of  openings  like  those  of  Lieberkuhn's  follicles,  which 
lead,  as  do  those,  into  tubular  coeca.  On  rupturing  the  surface  of  one  of  the 
white  bodies,  there  is  found  beneath  it  a  cavity,  corresponding  in  extent  with 
the  spot,  and  of  considerable  depth ;  but  this  cavity  has  usually  no  excretory 
opening;  and  the  tubular  follicles,  by  which  it  is  surrounded,  have  no  connec- 
tion with  it.  The  cavity  contains  a  grayish-white  mucous  matter,  interspersed 
with  cells  in  various  stages  of  development.  There  is  reason  to  believe  that 
at  certain  periods,  an  excretory  orifice  is  formed,  by  a  sort  of  dehiscence  in 
the  wall  of  the  cavity,  through  which  the  secreted  product  of  the  vesicle  may 
be  poured  forth.  These  glandulae  may  be  likened,  on  this  view,  to  the  ulti- 
mate follicles  of  the  ordinary  glands  (e.  g.,  the  Mammary  or  Lachrymal); 
except  that  the  latter  have  a  permanent  communication  with  their  excretory 
duct.  The  membrane  which  covers  in  the  cavity  is  extremely  thin,  and  is 
very  liable  to  be  destroyed  by  ulceration ;  hence  it  is  that,  after  inflammation 
of  the  membrane,  the  patches  of  Peyer  are  seen  as  a  congeries  of  shallow  open 
cells  or  follicles.  The  particular  use  of  these  bodies  is  entirely  unknown.* — 
The  general  function  of  the  Intestinal  Glandulae  has  already  been  adverted  to 
(§  447).  It  is  impossible,  for  obvious  reasons,  to  collect  their  secretion  for 
analysis;  but  there  are  many  reasons  for  regarding  the  Intestinal  surface 
(which  may  be  considered  in  the  light  of  an  expanded  gland)  as  a  most  import- 
ant means  of  eliminating  putrescent  matters  from  the  Blood;  whether  their 
presence  in  it  results  from  the  normal  waste  of  the  system  in  health,  or  from 

*  For  more  minute  details  regarding  the  structure  of  the  intestinal  glands,  see  the  Dis- 
sertation of  Dr.  Boehm,  "  De  Glandularum  Intestinarium  Structure  penitiori:"  of  which 
an  abstract  will  be  found  in  the  British  and  Foreign  Medical  Review,  vol.  i.,  and  also  in 
Mr.  Solly's  work  already  referred  to. 


662  OF  SECRETION. 

the  action  of  morbific  causes.     In  the  latter  case,  the  utility  of  Purgative  medi- 
cines, in  removing  the  products  of  decomposition,  is  obvious. 

IX.   The.  Spleen,  and  Supra-Renal  Capsules. 

708.  It  remains  for  us  to  consider  certain  other  bodies,  which,  from  their 
having  a  somewhat  glandular  aspect,  are  usually  ranked  among  the  secreting 
organs  ;  but  which  have  neither  excretory  ducts,  nor  any  thing  that  can  be 
considered  as  truly  glandular  in  their  structure.  Of  these,  the  largest  and 
most  important  in  the  adult  is  the  Spleen. 

a.  This  organ  is  essentially  composed  of  a  fibrous  membrane,  which  constitutes  its 
exterior  envelop,  and  which  sends  prolongations  in  all  directions  across  its  interior,  so 
as  to  divide  it  into  a  number  of  minute  cavities  of  irregular  form.  According  to  Dr. 
Evans, — whose  account  of  the  structure  of  this  organ  is  the  most  recent,  and  apparently 
the  most  complete,* — these  splenic  cells  communicate  freely  with  each  other,  and  with  the 
Splenic  Vein.  They  are  lined  by  a  membrane,  which  is  continuous  with  that  which 
lines  the  splenic  vein;  and  this  membrane  is  so  reflected  upon  itself,  as  to  leave  oval  or 
circular  foramina,  by  which  each  cell  opens  into  others,  or  into  the  splenic  vein.  The 
cells,  whose  usual  diameter  is  estimated  by  Dr.  E.  at  from  half  to  one-third  of  a  line,  are 
generally  traversed  by  filaments  of  elastic  tissue,  imbedded  in  which  a  small  artery  and 
vein  may  be  frequently  observed;  over  these  filaments,  the  lining  membrane  is  reflected 
in  folds;  and  in  this  manner  each  cell  is  incompletely  divided  into  two  or  more  smaller 
compartments.  There  is  no  direct  communication  between  the  splenic  artery  and  the 
interior  of  the  cells;  but  its  branches  are  distributed  through  the  intercellular  paren- 
chyma (which  will  be  presently  described) ;  and  the  small  veins,  which  collect  the  blood 
from  the  capillaries  of  the  organ,  convey  it  into  these  cavities,  from  which  it  is  conveyed 
away  by  the  splenic  vein.  The  cells  may  be  readily  injected  from  the  splenic  vein  with 
either  air  or  liquid, — provided  they  are  not  filled  with  coagulated  blood ;  and  they  are  so 
distensible,  that  the  organ  may  be  made  to  dilate  to  many  times  its  original  size,  with 
very  little  force.  This  is  especially  the  case  in  the  Spleen  of  the  Herbivora;  for  the 
Spleen  of  a  Sheep  weighing  four  ounces  may  be  easily  made  to  contain  30  ounces  of 
water.  That  of  Man,  however,  is  less  capable  of  this  kind  of  enlargement. — According 
to  Dr.  Evans,  the  cells  of  the  spleen  never  contain  any  thing  but  blood  ;f  and  he  notices 
that  a  frequent  condition  of  the  Human  Spleen  after  death,  which  is  sometimes  described 
as  a  morbid  appearance,  consists  in  the  filling  of  the  cells  with  firmly  coagulated  blood, 
which  gives  a  granular  appearance  to  the  organ. 

b..  The  partitions  between  the  cells  are  formed,  not  only  by  the  membranes  already 
mentioned,  but  by  the  peculiar  parenchyma  of  the  Spleen ;  which  forms  a  larger  part  of 
the  organ  in  Man  than  in  the  Herbivorous  Mammalia.  It  presents  a  half  fluid  appear- 
ance to  the  eye;  but  when  an  attempt  is  made  to  tear  it,  considerable  resistance  is  ex- 
perienced, in  consequence  of  its  being  intersected  by  what  appear  to  be  minute  fibres. 
When  a  small  portion  of  it  is  pressed,  a  liquid  is  separated;  which  is  that  commonly 
known  as  the  Liquor  Lienis,  or  Splenic  blood;  and  which  is  usually  described  (but 
erroneously,  according  to  Dr.  E.)  as  filling  the  cells  of  the  Spleen.  This  liquid,  when 
diluted  with  serum  and  examined  under  the  Microscope,  is  found  to  contain  two  kinds 
of  corpuscles, — one  sort  being  apparently^identical  with  ordinary  blood-corpuscles, — and 
the  other  with  the  globules  characteristic  of  the  lymph  and  abundant  in  the  lymphatic 
glands.  The  remaining  fibrous  substance  consists  entirely  of  capillary  blood-vessels 
and  lymphatics,  with  minute  corpuscles,  much  smaller  than  blood-corpuscles,  varying 
in  size  from  about  l-6000th  to  l-7000th  of  an  inch,  of  spherical  form,  and  usually  cor- 
rugated on  the  surface.  These  lie  in  great  numbers  in  the  meshes  of  the  sanguiferous 
capillaries;  and  the  minute  lymphatics  are  described  by  Dr.  E.  as  connected  with  the 
splenic  corpuscles,  and  apparently  arising  from  them.— Lying  in  the  midst  of  the  paren- 
chyma are  found  a  large  number  of  bodies,  of  about  a  third  of  a  line  in  diameter,  which 
are  evidently  in  close  connection  with  the  vascular  system;  these  have  long  been  known 


*  Lancet,  April  6,  1844. 

•j-  "  It  differs  in  no  respect  from  venous  blood  taken  out  of  any  other  part  of  the  portal 
system.  I  have  found  it  fluid  or  coagulated,  as  in  other  parts  of  the  venous  system  ;  and 
I  have  frequently  pulled  out  from  the  splenic  vein  colourless  coagula.  Occasionally  a 
number  of  globules  may  be  distinguished  in  it,  resembling  those  found  in  the  paren- 
chyma ;  but  in  these  cases  the  organ  appears  to  have  suffered  injury,  and  these  matters 
appear  to  have  got  into  the  cells  and  vein  in  consequence."  Loc.  cit. 


THE  SPLEEN,  AND  SUPRA-RENAL  CAPSULES.  563 

as  the  Malpighian  bodies  of  the  spleen,  after  the  name  of  their  discoverer;  but  since  his 
time,  their  existence  has  been  denied,  or  other  appearances  have  been  mistaken  for  them. 
According  to  Dr.  E.,  they  in  all  respects  resemble  the  mesenteric  or  lymphatic  glands  in 
miniature, — consisting  as  they  do  of  convoluted  masses  of  blood-vessels  and  lymphatics, 
united  together  by  elastic  tissue,  so  as  to  possess  considerable  firmness;  and  they  further 
correspond  with  them  in  this, — that  the  lymph  they  contain,  which  was  quite  transparent 
in  their  afferent  lymphatics,  now  becomes  somewhat  milky,  from  containing  a  large 
number  of  Lymph-globules. 

709.  In  regard  to  the  functions  of  the  Spleen,  great  uncertainty  exists. 
That  the  Spleen  performs  no  action  essential  to  life,  has  been  repeatedly  proved 
by  the  experimental  removal  of  it  in  many  of  the  lower  animals,  and  by  the 
accidental  loss  of  it  in  Man,  of  which  several  cases  are  on  record  ;  for  after  the 
immediate  effects  of  the  wound  were  recovered  from,  the  vital  functions  were 
performed  with  no  perceptible  interruption,  and  health  appeared  to  be  com- 
pletely restored.     Hence  the  Spleen  must  be  regarded  as  an  organ  of  duplex 
character,  and  probably  of  double  function.     The  cellated  structure  may  be 
considered  as  a  multilocular  reservoir,  capable  of  great  distension,  and  lined 
with  a  continuation  of  the  inner  membrane  of  the  vein ;  receiving  blood  on 
the  one  hand,  from  the  veins  of  the  interior  of  the  organ,  and  transmitting  it 
onward  to  the  Vena  Portae  ;  and  on  the  other  hand,  acting  as  a  reservoir  for 
the  venous  blood  of  the  abdomen,  when,  from  any  cause,  its  passage  into  the 
Vena  Cava  is  obstructed.     The  splenic  parenchyma,  on  the  other  hand,  must 
be  regarded  as  a  complex  Lymphatic  tissue,  essentially  resembling  that  of  the 
lymphatic  glands,  but  differently  arranged.     In  those  animals  in  which  it  pre- 
dominates, as  in  Man,  the  artery  is  large  ;  on  the  other  hand,  where  the  cellated 
structure  is  most  developed,  as  in  the  Herbivora,  the  Vein  is  very  large,  and 
the  artery  comparatively  small. — Nothing  completely  analogous  to  a  Spleen  is 
found  in  Invertebrated  animals ;    and  from  the  absence  of  the  Lymphatic 
system  in  them,  it  is  evident  that  the  parenchymatous  portion  can  have  no 
existence  as  such.     Something  analogous  to  the  cellated  portion  of  the  Spleen, 
however,  exists  in  the  venous  system  of  many  Cephalopoda ;  and  this  circum- 
stance is  an  additional  proof  of  the  duplicity  of  the  character  of  this  remarkable 
organ. — Out  of  the  numberless  theories  of  its  operation,  which  have  been  at 
different  times  brought  forwards,  the  one  which  is  most  satisfactory  to  the 
Author,  and  which  corresponds  best  with  the  account  just  given  of  its  cellated 
structure,  is  that  which  regards  it  as  a  sort  of  diverticulum  or  reservoir ; 
which  may  serve  to  relieve  the  Portal  Venous  system  from  undue  distension, 
under  a  great  variety  of  circumstances.     This  system  is  well  known  to  be 
destitute  of  valves ;  so  that  the  Splenic  vein  has  free  communication  with  the 
whole  of  it.     Hence  the  Spleen  will  be  a  ready  diverticulum  for  the  venous 
blood,  when  the  secreting  action  of  the  Liver  is  feeble,  so  that  the  Portal  cir- 
culation receives  a  partial  check  (§  662),    That  any  cause  of  congestion  of  the 
Portal  system  peculiarly  affects  the  Spleen,  has  been  proved  by  experiment ;  for 
after  the  Portal  Vein  has  been  tied,  the  spleen  of  an  animal,  which  previously 
weighed  only  2  oz.,  has  been  found  to  weigh  a  pound  and  a  quarter,  or  ten 
times  as  much.     Now  it  is  evident  that  congestion  of  the  Portal  system  is  liable 
to  occur  when  the  alimentary  canal  is  distended  with  food  ;  and  this  from  two 
causes, — the  pressure  on  the  Intestinal  veins,  and  the  quantity  of  fluid  absorbed 
by  these  veins.     Hence  it  may  be  conceived,  that  the  Spleen,  by  affording  a 
reservoir  into  which  the  superfluous  Venous  blood  may  be  directed,  serves  an. 
important  purpose  in  preventing  congestion  of  other  organs.     From  the  obser- 
vations of  Mr.  Dobson,*  it  appears  that  the  Spleen  has  its  maximum  volume 
at  the  time  when  the  process  of  chymification  is  t  at  an  end, — namely,  about 
five  hours  after  food  is  taken ;  and  that  it  is  small  and  contains  little  blood 

*  London  Medical  and  Physical  Journal,  Oct.  1820. 


564  OF  SECRETION. 

seven  hours  later,  when  no  food  has  been  taken  in  the  interval.  Hence  he 
inferred,  that  this  organ  is  the  receptacle  for  the  increased  quantity  of  Blood 
which  the  system  acquires  from  the  food,  and  which  cannot,  without  danger, 
be  admitted  into  the  blood-vessels  generally  ;  and  that  it  regains  its  previous 
dimensions,  after  the  volume  of  the  circulating  fluid  has  been  reduced  by 
secretion.  This  view  is  confirmed  by  the  fact  noticed  by  several  observers, — 
that  the  Spleen  rapidly  increases  in  bulk  after  the  ingestion  of  a  large  quantity 
of  fluid,  which  is  absorbed  rather  by  the  Veins  than  by  the  Lacteals.  It  has 
been  further  stated  in  support  of  this  theory,  that  animals  from  which  the 
Spleen  has  been  removed,  are  very  liable  to  die  of  apoplexy,  if  they  take  a 
large  quantity  of  food  at  a  time  ;  but  that,  if  they  eat  moderately  and  frequently, 
they  do  not  suffer  in  this  manner.  The  use  of  the  Spleen  as  a  diverticulum 
for  the  internal  Venous  circulation,  is  further  borne  out  by  its  liability  to  be- 
come enlarged  in  consequence  of  intermittent  fever ;  during  the  cold  stage  of 
which,  a  great  quantity  of  blood  is  driven  from  the  surface  towards  the  internal 
organs ;  and  it  may  be  easily  imagined  that,  if  there  were  no  such  reservoir, 
the  congestions  in  these  would  be  much  more  dangerous  than  those  which 
actually  do  occur.  The  permanent  enlargement  of  the  organ  is,  of  course,  on 
this  idea  of  its  use,  a  result  of  its  frequent  distension.  That  the  function  of  the 
Spleen  is  in  some  way  connected  with  that  of  Digestion,  appears  from  the  fact 
of  the  small  size  of  this  organ  in  the  foetal  state. 

710.  The  Supra-Renal  Capsules,  like  the  Kidneys,  consist  of  two  distinct 
kinds  of  substance, — a  cortical  and  medullary.  The  cortical  substance  is  of  a 
yellowish  colour,  and  consists  of  straight  parallel  fibres  arranged  side  by  side. 
Of  these  straight  fibres,  a  large  part  are  branches  of  arteries  which  enter  this 
body  at  every  point  of  its  exterior,  from  a  capillary  net-work  covering  its  sur- 
face ;  and  others  are  corresponding  branches  of  veins,  that  receive  the  blood 
from  these  arteries,  and  convey  it  into  a  venous  plexus,  of  which  the  medullary 
substance  is  chiefly  composed.  By  the  union  of  the  veins  of  this  plexus,  is 
formed  the  large  central  vein  of  the  organ ;  and  this  is  the  only  cavity  which 
it  contains.  No  apparatus  of  secreting  tubes  or  cells  can  be  detected  in  it ; 
and  its  function  is  entirely  unknown.  The  interspaces  of  the  vessels  are 
filled  up  by  a  sort  of  pulp,  which,  according  to  Mr.  Gulliver  (Op.  cit.  p.  103), 
is  composed  of  very  minute  oil-like  spherules,  very  unequal  in  their  size, 
varying  from  1 -24,000th  to  1 -6,000th  of  an  inch  in  diameter,  their  average 
size  being  about  l-10,000th.  These  spherules  are  but  little  affected  by 
chemical  reagents,  and  their  nature  is  very  uncertain.  In  many  Ruminant 
animals,  the  minute  spherules  are  less  plentiful ;  their  place  being  supplied  by 
corpuscles  that  somewhat  resemble  Lymph-globules  in  size,  but  are  often  of  a 
reddish  colour,  and  occasionally  of  an  oval  figure.  These  are  sometimes 
found  in  the  Human  subject  also,  particularly  in  early  life.  The  blood  of  the 
Supra-Renal  vein  has  been  observed  to  contain  numerous  minute  spherules, 
which  cannot  be  distinguished  from  those  of  the  gland ;  similar  particles, 
however,  may  be  detected  in  the  blood  of  other  parts ;  and  the  identity  of  these 
is  still  a  matter  of  doubt.  The  Supra-Renal  capsules,  as  already  mentioned 
(§  667),  attain  a  large  size  very  early  in  foetal  life  ;  surpassing  the  true  Kid- 
neys in  dimension,  up  to  the  tenth  or  twelfth  week.  As  is  the  case  in  the 
Spleen,  the  Lymphatics  are  of  large  size;  these  terminate  in  the  lumbar 
glands.  Their  Arteries  are  derived  from  the  aorta,  the  renal,  and  the  phrenic ; 
their  veins  open  into  the  vena  cava  on  the  right  side,  and  into  the  renal  vein 
on  the  left.  The  only  use  that  can  be  assigned  to  them  with  any  probability, 
is  that  of  serving  as  a  means  of  conveying  into  the  Veins  the  blood  transmitted 
through  the  Renal  Artery ;  when  from  any  cause  the  secreting  function  of  the 
Kidneys  is  partly  or  entirely  checked,  and  their  capillary  circulation  in  con- 
sequence stagnated.  This  idea  seems  to  derive  confirmation  from  the  fact, 


THYMUS  AND  THYROID  GLANDS.  565 

that  these  organs  have  proportionally  the  largest  size  during  the  development 
of  the  Kidneys,  when  their  secreting  function  can  scarcely  be  supposed  to 
have  commenced. 

X.  Thymus  and  Thyroid  Glands. 

711.  The  Thymus  Gland,  also,  is  largest  in  the  Foetus,  in  proportion  to  the 
size  of  the  body ;  but  it  continues  to  grow  after  birth,  and  remains  of  considera- 
ble size  during  the  first  year ;  after  which  it  remains  stationary,  or  gradually 
diminishes.  It  seldom,  however,  entirely  disappears,  as  is  usually  stated ;  and 
several  cases  are  mentioned  by  Krause,  in  which  it  remained  in  the  adult  of 
the  full  size  it  possessed  at  birth :  but,  as  the  rest  of  the  body  has  undergone 
an  increase  to  the  amount  of  twenty  times  its  original  weight,  the  Thymus 
may  be  said  to  have  relatively  diminished  to  the  same  amount. — According  to 
the  accurate  examination  of  its  structure,  recently  made  by  Sir  A.  Cooper,  it 
is  composed  of  lobules,  which  may  be  drawn  out  and  separated  from  one  ano- 
ther in  the  manner  of  a  string  of  beads,  when  their  enveloping  capsule  has 
been  removed.  These  lobules  vary  in  size  from  that  of  the  head  of  a  pin  to 
that  of  a  pea;  in  their  usual  position,  they  are  disposed  around  a  large  central 
cavity  or  reservoir.  When  a  thin  slice  is  cut  from  one  of  the  lobules,  a  num- 
ber of  small  cavities  are  seen  in  it ;  and  these  are  filled  with  a  white  granular 
fluid.  These  cavities  open  into  a  larger  one  at  the  base  of  each  lobule ;  and 
the  cavities  of  the  different  lobules  are  connected  by  a  channel,  which  passes 
from  one  to  the  other,  and  which  has  occasional  openings  leading  into  a  com- 
mon reservoir.  This  reservoir,  however,  has  no  efferent  duct ;  and  no  means 
of  exit  can  be  detected  for  its  contents,  except  that  afforded  by  the  Lymphatics, 
which  are  large,  and  terminate  directly  in  the  Vena  Cava;  their  immediate 
connection  with  the  cavities  of  the  gland  has  not,  however,  been  demonstrated. 
The  fluid  of  the  Thymus  Gland  is  whitish,  having  the  appearance  of  chyle  or 
cream ;  it  contains  a  large  number  of  corpuscles,  which  are  described  by  Mr. 
Wilson,*  as  being  "  smaller  than  the  blood-corpuscles,  globular  and  oval  in 
form,  irregular  in  outline,  variable  in  size,  and  provided  with  a  small  central 

Fig.  179. 


A  section  of  the  Tliymus  gland  at  the  eighth  month,  showing  its  anatomy;  from  a  preparation  of  Sir  A, 
Cooper's;  1,  the  cervical  portions  of  the  gland ;  the  independence  of  the  two  lateral  glands  is  well  marked; 
2  secretory  follicles  seen  upon  the  surface  of  the  section;  these  are  observed  in  all  parts  of  the  section; 
3, 3,  the  pores  or  openings  of  the  secretory  follicles  and  pouches ;  they  are  seen  covering  the  whole  internal 
surface  of  the  great  central  cavity  or  reservoir.  The  continuity  of  the  reservoir  in  the  lower  or  thoracic 
portion  of  the  gland  with  the  cervical  portion,  is  seen  in  the  figure. 

*  Anatomist's  Vade-Mecum  .p.  526. 

48 


566  OF  SECRETION. 

nucleus."  Mr.  Gulliver  considers  them  identical  (as  Hewson  did  long  ago) 
with  the  chyle  and  lymph-globules.  In  the  Human  fetus,  the  fluid  of  the 
Thymus  Gland  can  scarcely  be  obtained  in  quantity  sufficient  for  analysis  :  but 
it  has  been  found  by  Mr.  F.  Renaud,*  that,  on  treating  the  sliced  gland  with 
ether,  a  considerable  quantity  of  oil  was  obtained  from  it ;  so  that  the  resem- 
blance in  its  composition  to  chyle  or  milk  is  very  close.  In  the  Thymic  fluid 
of  the  Calf,  which  exists  in  greater  abundance,  the  following  ingredients  were 
found.  One  hundred  parts  of  the  fluid  contained  sixteen  of  solid  matter;  and 
this  consisted  of  incipient  Fibrin,  Albumen,  Mucus  and  Muco-extractive  mat- 
ter, Muriate  and  Phosphate  of  Potass,  Phosphate  of  Soda,  and  a  trace  of  Phos- 
phoric acid. 

712.  Of  the  nature  of  the  function  of  the  Thymus  Gland,  nothing  is  cer- 
tainly known.  By  Hewson  it  was  regarded  as  an  appendage  to  the  system  of 
lymphatic  glands ;  and  this  doctrine  is  advocated  by  Mr.  Gulliver.  It  is 
remarked  by  Miiller,  that  it  appears  quite  vain  to  attempt  to  explain  by  hypo- 
thesis, how  the  organ  can  contribute  to  the  formation  of  the  blood  in  the  foetus 
and  child ;  and  that  "  every  hypothesis  which  regards  it  as  an  organ  adapted 
to  the  necessities  of  foetal  life,  and  not  to  those  of  the  child,  must  be  incorrect." 
This  last  observation  appears  to  be  pointed  at  the  theory  not  long  since  put 
forth  by  Mr.  Tyson,t  that  the  office  of  the  Thymus  is  to  receive,  during  Foetal 
life,  the  blood  which  is  afterwards  sent  to  the  Lungs;  yet  in  support  of  this 
theory  something  may  still  be  said.  It  is  well  known  that,  although  the  Re- 
spiratory function  is  established  at  birth,  it  does  not  for  some  time  come  into 
full  activity.  The  lungs  are  small  in  proportion  to  the  size  of  the  body ;  the 
amount  of  oxygen  consumed  is  much  less  than  in  the  adult  state ;  and  the 
power  of  generating  heat  is  comparatively  feeble  (§  728).  During  infancy 
and  childhood,  the  Digestive  apparatus  is  undergoing  rapid  development ;  but 
the  Lungs  do  not  make  the  same  comparative  progress.  About  the  period  of 
puberty,  however,  their  evolution  becomes  much  more  rapid,  and  their  function 
more  energetic ;  so  that,  at  this  time,  as  is  well  known,  disorders  of  their 
function,  leading  to  structural  changes,  are  more  common  than  at  any  other 
period  of  life.  Now  the  relative  disappearance  of  the  Thymus  Gland,  pari 
passu  with  the  evolution  of  the  lungs,  does  appear  to  indicate  that  there  is 
something  vicarious  or  reciprocal  in  their  function.  Moreover,  it  has  been 
shown  that  one  of  these  vascular  masses,  somewhat  resembling  glands  in 
structure,  but  having  no  secreting  ducts,  is  found  in  connection  with  the  two 
other  principal  excretory  organs, — the  Liver  and  the  Kidneys.  It  may  be 
said,  however,  in  reply,  that  the  lungs  do  not  receive  their  principal  supply  of 
blood  from  the  arterial  system,  but  from  the  venous ;  so  that,  although  the  two 
organs  are  in  proximity,  there  is  no  direct  vascular  connection  between  them. 
This  objection,  however,  has  less  force  when  it  is  remembered,  that,  up  to  the 
time  of  birth, — the  period  during  which  the  Thymus  gland  is  of  greatest  pro- 
portional size, — little  or  no  blood  proceeds  to  the  Lungs  through  the  Pulmonary 
arteries ;  but  that  they  are  then  chiefly,  if  not  entirely,  supplied  by  the  Bron- 
chial arteries ;  and  these  come  off'  from  the  thoracic  aorta  at  no  great  distance 
from  the  Internal  Mammary  arteries,  which  supply  the  Thymus  gland,  and  are 
the  lowest  branches  of  the  Subclavian.  It  is  through  the  Bronchial  arteries 
that  the  blood  is  conveyed,  on  which  the  nutrition  of  the  Lungs  depends,  during 
the  whole  of  life ;  and  the  history  of  the  development  of  these  organs,  com- 
pared with  that  of  the  Thymus  gland,  seems  to  indicate  that,  just  as  the  flow 
of  blood  through  the  one  diminishes,  that  which  takes  place  through  the  other 
increases.  It  is,  however,  also  true  (as  remarked  by  Mr.  Gulliver)  that  the 

*  Edinburgh  Monthly  Journal,  March,  1843. 
f  London  Medical  and  Surgical  Journal,  1833. 


GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES.  567 

Thymus  gland  diminishes  in  proportion  to  the  diminished  activity  of  the  gene- 
ral nutritive  functions;  and  that  its  fluid  decreases,  andjDecomes  less  rich  in 
globules,  when  the  supply  of  food  is  insufficient,  or  the  animal  is  prevented  by 
other  causes  (such  as  over-fatigue)  from  duly  assimilating  it.  At  present,  the 
question  of  the  specific  use  of  this  body  must  be  left  in  uncertainty.  It  may 
be  surmised,  however,  from  the  very  striking  analogy  which  it  bears  to  the 
Spleen,  that  its  function  is  double;  and  that,  whilst  it  serves  as  a diverticulum 
for  blood,  it  also  performs  some  office  in  connection  with  the  Lymphatic  system. 
It  would  be  interesting  to  examine  if,  in  those  animals  in  which  the  Spleen 
has  been  extirpated,  the  Thymus  Gland  undergoes  any  increase  in  size. 

713.  The  Thyroid  Gland  appears  to  have  a  structure  analogous  to  that  of 
the  Thymus  ;  but  less  is  known  respecting  it.  When  incised,  small  cells  may 
be  detected  in  it :  but  no  connection  has  yet  been  traced  between  them,  nor  is 
there  any  common  reservoir.  Like  the  Thymus,  this  body  has  no  excretory 
duct,  but  is  provided  with  large  Lymphatics,  which  directly  enter  the  great 
veins.*  Though  proportionally  larger  in  the  foetus  than  in  the  adult,  it  remains 
of  considerable  size  during  the  whole  of  life,  and  is  supplied  with  arteries  of 
large  calibre.  The  fluid  which  the  cells  contain  is  viscid  and  nearly  colour- 
less, sometimes  having  a  yellowish  tinge ;  when  put  into  rectified  spirit,  it 
becomes  solid  but  not  opaque ;  and  it  probably  contains,  therefore,  some  modi- 
fication of  albumen.  The  Thyroid  body  is  the  seat  of  that  enlargement  of  the 
neck  which  is  known  as  goitre  or  bronchocele.  In  the  commencement  of  this 
disease,  there  seems  at  first  to  be  simply  distension  of  the  cells  resulting  from 
increased  secretion  ;  so  that,  when  the  body  is  cut  into,  no  change  of  structure 
is  observed  in  it  but  such  as  results  from  the  enlargement  of  the  cells,  which 
are  of  various  sizes,  usually  from  that  of  a  pea  downwards,  and  are  filled  with 
a  more  or  less  viscid  fluid.  In  more  advanced  cases,  however,  other  alterations 
are  commonly  met  with,  resulting  probably  from  the  altered  vascular  action 
generated  by  the  primary  affection ;  so  that,  when  the  tumour  is  cut  into,  stea- 
tomatous,  cartilaginous,  or  even  ossific  deposits  are  found  in  it. 


CHAPTER   XIII. 

GENERAL    REVIEW    OF    THE    NUTRITIVE    PROCESSES.—ANIMAL    HEAT. 

I.  Review  of  the  Nutritive  Processes,  with  Practical  Applications. 

714.  THE  detailed  survey  which  has  been  now  taken  of  the  different  Func- 
tional operations  concerned  in  maintaining  the  life  of  the  individual,  may  sug- 
gest to  us  some  general  views  that  have  important  practical  applications.  In 
the  first  place,  it  has  been  shown,  that  the  province  of  the  Animal  is  not  to 
combine  Inorganic  elements  into  Organic  compounds,  fit  to  be  applied  to  the 
purposes  of  Nutrition  ;  but  to  use  those  which  are  prepared  for  it  by  the  Plant. 
The  nutritive  materials  thus  obtained  may  be  divided  into  two  great  classes, 
the  azotized  and  the  non-azotized.  The  former  have  been  shown  (§  457)  to 
be  so  nearly  identical  in  composition  with  the  proximate  principles  of  which 

*  See  King,  in  Guy's  Hospital  Reports,  vol.  i. 


568  GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 

the  Animal  body  is  composed,  that  no  great  amount  of  chemical  transformation 
can  be  required  to  prepare  them  for  being-  appropriated  by  it.  The  latter  are 
altogether  different  in  character ;  and  whether  or  not  they  can,  by  any  process 
of  transformation,  be  made  subservient  to  the  nutrition  of  the  Azotized  tissues, 
it  is  unquestionable  that  their  ordinary  use  is  to  serve  as  the  materials  for  the 
Respiratory  process,  and  for  the  maintenance  of  Animal  heat.  The  demand 
for  these  several  articles  in  the  system  will  depend,  in  regard  to  the  former, 
upon  the  amount  of  Tissue  which  has  been  disintegrated  and  needs  repair; 
and  with  respect  to  the  latter,  upon  the  amount  of  heat  which  it  is  necessary 
to  generate,  to  keep  up  the  temperature  of  the  body  to  its  regular  standard. 
Hence  a  highly-azotized  diet  is  most  required  when  the  greatest  amount  of 
muscular  exertion  is  being  used ;  whilst  a  diet  in  which  non-azotized  sub- 
stances are  predominant  will  serve  to  sustain  the  Animal  Heat  in  a  cold  atmo- 
sphere. The  adjustment  of  the  diet  to  the  wants  of  the  system  is  a  matter  of 
the  greatest  importance  for  the  preservation  of  health.  If  too  great  an  amount 
of  azotized  food  be  ingested,  and  the  superfluity  be  thrown  upon  the  Kidneys 
to  eliminate  (§  679),  disorder  of  the  Urinary  Secretion  is  almost  certain,  sooner 
or  later,  to  manifest  itself.  The  quantity  of  Lithic  Acid,  in  particular,  under- 
goes considerable  increase;  and,  by  the  removal  of  its  bases  through  the 
increased  production  of  other  acids,  it  is  very  likely  to  pass  out  in  an  insoluble 
state,  giving  rise  to  Gravelly  deposits.  Or  it  may  accumulate  in  the  Blood, 
and  there  combine  with  Soda;  forming  a  salt,  which  is  deposited  in  various 
parts  (especially  in  the  neighbourhood  of  the  smaller  joints),  forming  concre- 
tions, which  are  commonly  known  under  the  name  of  "  chalk-stones."  These 
deposits  usually  take  place,  however,  after  severe  attacks  of  a  peculiar  Inflam- 
mation known  as  Gout :  and  this  inflammation  seems  to  be  dependent  upon 
the  accumulation  of  Lithate  of  Soda  in  the  Blood. — Over  this  disease,  a  careful 
regulation  of  the  diet  exercises  a  powerful  control.  A  patient  affected  with 
the  Lithic  Acid  diathesis  may  palliate,  if  not  altogether  cure,  his  disorder,  by 
rigorously  abstaining  from  the  use  of  any  superfluous  amount  of  azotized  com- 
pounds as  food ;  and  by  subsisting  as  much  as  possible  upon  those  belonging 
to  the  Farinaceous  group.  It  is  by  no  means  every  case,  however,  that  is 
capable  of  alleviation  by  treatment  of  this  sort ;  in  fact,  it  can  seldom  be  rigo- 
rously enforced,  except  in  early  life,  or  at  any  rate  when  the  constitution  is 
unbroken  by  disease  or  intemperance.  Not  unfrequently  it  will  be  found, 
that  the  persistence  in  a  diet  of  this  kind  occasions  so  much  disorder  of  the 
stomach,  as  to  be  quite  out  of  the  question. — On  the  other  hand,  in  the  "  stru- 
mous  diathesis,"  there  would  seem  to  be  a  low  condition  of  those  vital  powers, 
which  are  concerned  in  the  conversion  of  the  Albuminous  materials  prepared 
by  the  Digestive  process,  into  the  Fibrinous  matter  which  is  ready  for  assimi- 
lation;* so  that,  by  a  perversion  of  the  ordinary  nutrient  actions,  Albuminous 

*  Some  very  interesting  observations  have  been  recently  made  on  the  state  of  the 
Blood  soon  after  a  meal,  by  Dr.  Buchanan.  These  are  confirmatory  of  the  belief  gene- 
rally entertained, — that  the  milky  appearance  sometimes  presented  by  the  Serum  (§  580) 
is  due  to  the  admixture  of  Chyle.  He  found  that,  when  a  full  meal  was  taken  after  a 
long  fast,  and  a  small  quantity  of  blood  was  drawn  previously  to  the  meal  and  at  inter- 
vals subsequently,  the  Serum,  which  was  quite  limpid  in  the  blood  first  drawn,  showed 
an  incipient  turbidity  about  half  an  hour  afterwards;  and  that  its  turbidity  increased  for 
about  six  hours  subsequently;  after  which  it  usually  began  to  clear.  The  period  at 
which  the  discoloration  is  greatest,  however,  and  the  length  of  time  during  which  it  con- 
tinues, vary  according  to  the  digestibility  of  the  food. — The  crassamentum  also  frequently 
exhibited  a  pellucid  fibrinous  crust;  sometimes  interspersed  with  white  dots.  These 
experiments  indicate,  therefore,  that  the  process  of  assimilation  has  been  but  imperfectly 
performed,  when  the  new  materials  of  blood  are  introduced  into  the  circulating  system; 
but  that,  in  the  state  of  health,  the  first  stage  of  this  assimilation  is  usually  completed  (as 
shown  by  the  returning  transparency  of  the  Serum)  a  few  hours  after  the  ingestion  of  the 
food.  The  persistence  of  this  milky  appearance,  however,  when  there  is  impaired  appe- 


GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES.  569 

Tubercle  is  deposited  in  the  interstices  of  the  tissues,  instead  of  these  tissues 
being  themselves  regenerated  by  Organizable  Fibrin ;  and  the  same  may  take 
place  in  a  more  rapid  manner,  in  consequence  of  that  disturbance  of  the 
nutrient  processes  which  is  known  in  healthy  constitutions  as  Inflammation 
(§  606).  It  is  obvious,  then,  that  the  treatment  of  the  Strumous  Diathesis 
should  be  directed  towards  the  invigoration  of  the  general  powers  of  the  sys- 
tem; and  although,  when  disease  of  the  Chest  has  once  established  itself,  a 
warm  moist  atmosphere  may  be  necessary  as  a  preventive  of  inflammatory 
affections,  it  is  a  great  mistake  to  imagine  that  such  a  plan  is  applicable  to 
those  in  whom  there  is  merely  a  strumous  predisposition ;  for  this  should  be 
combatted  by  such  means  as  are  calculated  rather  to  brace  than  to  relax  the 
system, — especially  out-door  exercise,  a  nutritious  diet,  in  which  easily-digested 
protein-compounds  should  predominate,  and  an  airy  and  well-ventilated  habita- 
tion. There  can  be  no  doubt  that  the  Tuberculous  Cachexia  is  encouraged, 
and  even  developed,  by  injudicious  management  during  the  early  ages  of  life, 
in  many  cases  where  it  might  have  been  avoided.* 

715.  Equally  important  is  the  regulation  of  the  diet  in  regard  to  its  non- 
azotized  constituents.  If  these  are  in  excess,  the  elimination  of  them  from  the 
Blood  falls  especially  upon  the  Liver  (§  664) ;  and  a  continued  excess  gives 
rise  to  disorders  in  its  function,  which  a  diminution  in  the  quantity  of  Farina- 
ceous or  Oleaginous  matter  ingested  would  prevent  or  cure.  This  is  especially 
liable  to  happen  to  Europeans  proceeding  to  warm  climates,  who  are  not 
warned  by  their  decrease  of  appetite  that  there  is  no  longer  a  necessity  for  the 
same  supply ;  but  force  themselves  to  eat  much  more  than  they  have  any  real 
occasion  for. — There  is  a  very  remarkable  condition  of  the  system,  in  which 
there  is  a  tendency  to  the  presence  of  a  large  amount  of  Sugar  within  the 
vessels ;  either  through  the  absence  of  power  to  convert  that  which  has  been 
taken  in ;  or  through  the  actual  production  of  that  compound,  as  a  result  of 
the  waste  of  the  system.  From  Dr.  Buchanan's  recent  experiments!  it  ap- 
pears that  Sugar  may  be  detected  in  the  Serum  of  healthy  blood,  drawn  soon 
after  a  meal;  but  that  it  soon  becomes  untraceable, — probably  in  consequence 
of  its  being  carried  off  by  the  respiratory  process.  In  the  disease  termed 
Diabetes,  or  the  "saccharine  diathesis,"  there  is  a  much  larger  amount  of 
Sugar  in  the  Blood;  and  this  appears  to  be  constantly  present,  as  if,  from 
some  cause,  its  elimination  by  the  usual  channel  were  retarded.  The  Sugar 
makes  its  appearance,  also,  in  the  Urine ;  the  Kidneys  taking  on  the  unusual 
office  of  separating  this  compound,  that  it  may  not  accumulate  in  the  Blood. 
Some  late  researches  on  the  exclusive  employment  of  azotized  principles  as 
articles  of  diet,  in  the  treatment  of  the  Saccharine  diathesis,  have  given 
very  favourable  results.  The  plan  was  long  since  proposed  by  Dr.  Rollo ; 
and  when  the  diseased  condition  has  been  uncomplicated  by  other  maladies 
(as  is  not  unfrequently  the  case),  the  rigorous  enforcement  of  such  a  diet  has 
been  attended  with  success  in  numerous  instances.  One  of  the  greatest  diffi- 
culties in  the  application  of  the  system,  however,  has  arisen  from  the  longing 
which  the  patients  experience  for  Vegetable  food ;  since  this  tempts  them  to 
gratify  their  appetites,  to  the  complete  prejudice  of  the  remedial  system, — a 

tite,  and  the  quantity  of  food  taken  is  inconsiderable,  must  be  regarded  as  a  sign  of  dis- 
ease. Although  the  opaque  matter,  when  it  rises  to  the  surface,  has  very  much  the 
appearance  of  cream,  yet  it  appears  that  it  may  contain  a  large  proportion  of  a  protein- 
compound;  the  relative  amounts  of  which,  and  of  oily  matter,  seem  to  depend  in  part 
upon  the  constituents  of  the  food  ingested.  It  is  probably  from  a  check  to  the  normal 
assimilating  processes,  by  which  these  substances  are  ordinarily  withdrawn  from  the 
Blood,  that  various  forms'of  diseased  action  originate. 

*  See  the  excellent  works  of  Sir  James  Clark,  in  which  the  importance  of  Hygienic 
treatment  is  strongly  insisted  on. 

f  Loc.  cit. 

48* 


570  GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 

very  small  amount  of  farinaceous  matter  4  being  sufficient  to  cause  the  re- 
appearance of  the  Sugar,  after  it  had  seemed  to  be  entirely  got  rid  of.  It  has 
been  recently  proposed  by  M.  Bouchardat  to  gratify  this  longing  to  a  certain 
degree,  by  allowing  the  use  of  bread  made  of  wheaten  flour,  from  which 
nearly  all  the  Fecula  has  been  separated, — the  Gluten  only  being  left,  with 
such  a  small  amount  of  Fecula  as  may  serve  to  make  it  rise  in  fermentation ; 
so  that  it  is  as  free  from  unazotized  constituents  as  the  average  of  animal 
substances.  This  plan  is  stated  to  have  been  very  successfully  practised.* 

716.  From  what  has  been  stated  in  Chap.  ix.  respecting  the  nature  of  the 
Function  of  Circulation,  it  is  evident  that  primary  disorders  of  that  function 
are  not  nearly  so  frequent  as  they  are  ordinarily  supposed  to  be  ;  and  that  the 
proximate  cause  of  morbid  phenomena  is  seldom  to  be  found  in  them.  By 
the  action  of  the  Heart  and  Blood-vessels,  the  nutrient  fluid,  which  has  been 
prepared  from  the  alimentary  materials  submitted  to  the  digestive  apparatus, 
is  conveyed  to  the  tissues  which  it  is  to  nourish ;  but  the  true  process  of 
Nutrition  is  independent  of  this,  and  may  take  place  after  the  motion  of  the 
fluid  has  ceased,  just  as  it  commences  before  any  movement  shows  itself.  For 
the  tissue  which  exists  in  the  Embryo,  during  the  early  period  of  its  develop- 
ment, and  also  in  any  newly-forming  part,  is  destitute  of  vessels,  consisting 
only  of  cells;  and  these  grow  and  reproduce  themselves  at  the  expense  of  the 
nutritive  materials  supplied  to  them  from  without,  just  as  does  the  whole  mass 
of  a  Cellular  Plant.  Moreover  it  has  been  shown  (§  511),  that  the  activity  of 
the  nutrient  processes  has  much  to  do  with  the  movement  of  the  fluid  through 
the  smaller  vessels,  and  is  a  cause  rather  than  a  consequence  of  it.  If  the 
action  of  the  Heart  cease,  the  whole  circulation  must  obviously  come  to  a 
stand  ere  long ;  but  in  many  animals  the  Capillary  movement  may  continue 
for  some  time  after  the  general  circulation  has  been  checked ;  and  so  long  as 
blood  is  supplied  to  the  parts,  so  long  may  their  nutrition  continue,  provided 
other  circumstances  be  favourable.  It  is  unquestionably  true,  that  the  cessa- 
tion of  the  Circulation  is  usually  the  immediate  cause  of  Death;  and  that, 
when  the  suspension  is  permanent,  the  loss  of  the  vitality  of  the  system,  con- 
sidered both  as  a  whole,  and  as  made  up  of  distinct  parts,  is  a  necessary 
consequence.  But  still,  we  find  that  the  cause  of  this  cessation  seldom  origi- 
nates in  the  Circulating  apparatus  itself.  Putting  aside  those  forms  of  Death 
in  which  all  the  vital  actions  appear  to  be  suspended  at  once  (as  in  NecrsBmia, 
§  592,  and  in  Cooling  of  the  body,  §  730,)  we  find  the  two  chief  modes  to  be 
Syncope  and  Asphyxia.  In  the  former,  the  Circulation  comes  to  a  stand, 
simply  through  want  of  power  in  the  propelling  organs  to  move  the  blood ; 
this  want  of  power  may  result  from  a  variety  of  causes.  Long-continued 
deficiency  in  the  quantity  or  depravation  of  the  quality  of  the  blood  may  have 
induced  insufficient  nutrition  of  the  Heart ;  and  its  muscular  power  may  thus 
be  gradually  lost.  This  is  a  very  common  mode  of  Death,  as  a  sequence  of 
exhausting  disease;  more  commonly,  however,  the  cessation  of  the  Heart's 
action  is  sudden,  and  results  from  some  impression  propagated  to  it  through 
the  Nervous  system ;  thus  mental  emotion,  sudden  loss  of  blood,  concussion  of 
the  nervous  centres,  injuries  extensively  involving  the  nervous  ramifications, 
&c.,  seem  to  have  an  immediately  depressing  effect  on  the  Heart's  action ; 
and  in  many  of  these  cases,  the  Circulation  is  checked  not  merely  at  the 
centre  but  also  at  the  periphery,' — the  vitality  of  the  system  at  large,  and  of 
the  Blood,  being  equally  affected  with  that  of  the  heart  (§§  513,  583).  The 
Heart's  action  may  be  checked  by  causes  whose  action  is  purely  local ;  as 
appears  from  Mr.  Blake's  experiments  formerly  referred  to  (§  491). — But  it  is 
probably  seldom,  in  any  ordinary  condition  of  the  system,  that  such  local 

*  See  Comptes  Rendues  de  1'Academie  Royale,  1841. 


GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES.  571 

action  can  occur;  and  a  disturbed  state  of  the  Circulation  is  therefore  to  be 
generally  looked  upon  rather  as  a  result  than  as  a  cause  of  diseased  action* 
An  extreme  case  of  such  a  disturbance,  which,  when  sufficiently  prolonged, 
is  attended  with  fatal  results,  is  to  be  found  in  Asphyxia ;  in  which  the  cessa- 
tion of  the  action  of  the  Lungs  induces  a  stagnation  of  the  Blood  in  their 
capillaries ;  and  as,  in  warm-blooded  animals,  the  whole  current  of  Blood  has 
to  pass  through  the  Lungs,  before  proceeding  again  to  the  system,  a  total  sus- 
pension of  the  Circulation  necessarily  results  from  this  interruption  (§§  508  and 
546-8).  Now  if  we  take  this  (which  it  appears  reasonable  to  do)  as  a  type  of 
a  great  number  of  morbid  conditions  of  different  organs,  we  are  led  to  see  why 
a  serious  disturbance  of  the  movement  in  any  one  part  should  affect  the  entire 
circulating  apparatus,  and  should  thus  influence  its  flow  through  almost  every 
other  organ.  There  are  no  other  organs,  however,  in  which  a  stagnation  can 
be  so  serious  as  in  the  Lungs ;  since  there  are  none  through  which  the  whole 
current  flows.  The  Liver  ranks  next  in  importance,  since  all  the  venous  blood 
collected  from  the  Chylopoietic  viscera  passes  through  it;  and  every  practical 
man  is  aware  how  frequently  derangement  of  the  circulation  through  the 
Liver,  originating  in  an  unhealthy  state  of  the  gland  itself,  is  a  cause  of  serious 
disorders  in  the  abdominal  viscera. — Minor  irregularities  in  the  Circulation, 
in  various  parts,  nof  unfrequently  become  causes  of  serious  inconvenience. — 
Thus,  few  conditions  are  more  common,  especially  amongst  persons  of  active 
minds  but  inert  habits,  than  undue  determination  of  blood  to  the  Head,  con- 
joined with  torpor  of  the  circulation  through  the  Skin,  especially  that  of  the 
extremities,  which  are  ordinarily  cold.  The  obvious  indication  here  is  to 
endeavour  to  restore  the  balance  of  the  Circulation,  and  excitement  of  the  flow 
of  blood  through  the  Skin,  by  frictions,  moderately  stimulating  applications, 
exercise,  &c.,  will  commonly  prove  of  great  utility. 

717.  There  are  many  disorders  commonly  regarded  as  affections  of  the 
Circulation,  which  evidently  consist  in  reality  of  a  morbid  alteration  in  the 
Nutritive  processes :  among  these  there  can  be  little  doubt  that  we  are  to  rank 
local  Determinations  and  Congestions,  which  result  from  an  exalted  or  dimi- 
nished activity  of  the  formative  actions ;  and  Inflammation,  in  which  these 
actions  are  perverted.  Much  has  been  said  and  written,  to  very  little  purpose, 
respecting  the  essential  nature  of  this  process ;  it  has  been  attributed  by  some 
to  disordered  action  of  the  vessels,  and  by  others  to  an  injurious  impression  on 
the  nerves, — the  fact,  that  Inflammation  may  occur  in  tissues  which  contain 
neither  vessels  nor  nerves  having  been  entirely  overlooked.  The  only  view  of 
the  character  of  Inflammation  that  seems  likely  to  account  for  its  phenomena, 
is  that  which  regards  it  as  essentially  consisting  in  a  disturbance  of  the  due 
relation  between  the  living  Tissue,  and  the  nutrient  materials  contained  in  the 
Blood  (§§  608-8).  That  there  must  be  a  certain  relation  or  adaptiveness,  be- 
tween the  substance  of  the  Tissues,  and  the  materials  at  whose  expense  they 
are  formed,  appears  sufficiently  evident.  In  the  Inflammatory  diathesis  there 
is  an  increased  tendency  in  the  Blood  to  the  generation  of  Fibrin ;  and  this, 
by  disturbing  the  due  relation  between  the  nutritive  fluid  and  the  solid  tissues, 
may  become  a  cause  of  local  disease, — the  morbid  action  which  results  from 
this  condition  of  the  Blood,  being  determined  to  a  particular  part  by  some 
extraneous  causes.  In  this  morbid  action,  Fibrinous  matter  is  effused,  either 
into  the  substance  of  the  tissue  affected,  or  upon  its  surface ;  there  is  a  ten- 
dency to  organization,  but  in  both  cases  its  degree  may  vary, — a  perfectly 
formed  tissue  being  produced,  or  a  degeneration  taking  place  into  Pus-globules, 
according  to  circumstances  (§  609).  Inflammation  may  result,  however,  from 
causes  purely  local,  and  primarily  affecting  the  solid  Tissues ;  here,  therefore, 
the  disturbance  of  the  normal  relation  is  on  'the  other  side,  yet  the  production 
of  an  increased  amount  of  Fibrin  is  still  a  character  of  the  disease.  Whether 


572  GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 

the  blood  moves  faster  or  slower  in  an  Inflamed  part, — whether  the  Capillaries 
are  contracted  or  dilated, — are  questions,  therefore,  of  little  moment,  in  com- 
parison with  those  which  affect  the  actions  of  Nutrition  and  Secretion,  to  which 
the  fluid,  in  its  passage  through  the  parts  in  question,  ought  to  be  subservient. 
The  same  may  be  remarked  of  those  productions  which  have  been  termed 
Heterologous  transformations  of  tissue ;  but  which  are  rather  to  be  regarded 
as  new  growths,  that  have  appropriated  the  nutriment  designed  for  the  support 
of  the  proper  tissues,  and  have  therefore  become  developed  at  the  expense  of 
these.  It  is  quite  as  absurd  to  attempt  to  account  for  the  growth  of  Scirrhus, 
Carcinoma,  &c.,  by  any  peculiar  action  of  the  vessels  of  the  part,  as  it  would 
be  to  attribute  the  secretion  of  fatty  matter  by  the  cells  of  one  tissue,  or  of 
phosphate  of  lime  by  those  of  another,  to  the  peculiar  distribution  of  their  ves- 
sels. The  progress  of  research  obviously  leads  to  the  conclusion,  that  in  every 
part  of  the  living  body  there  is  an  inherent  and  independent  vitality,  which 
enables  it  to  grow  and  maintain  its  normal  structure  and  constitution,  so  long  as 
it  is  supplied  with  the  requisite  materials  ;  and  that  changes  in  the  character  of 
the  tissue  can  be  referred  to  nothing  else  than  to  alterations  in  its  properties, 
resulting  from  external  agencies,  or  to  alterations  in  the  materials  supplied  for 
its  renewal.  Of  these  two  morbific  causes,  the  latter  is  undoubtedly  the  most 
frequent ;  and  the  tendency  which  is  now  gaining  ground,  to  seek  in  the  Blood 
for  indications  of  pathological  changes,  when  there  is  no  obvious  general  dis- 
turbance of  the  system,  will  probably  lead  to  a  greatly  increased  knowledge 
of  the  real  nature  of  diseased  states ;  in  spite  of  the  opposition  which  any 
return  to  the  Humoral  Pathology  is  sure  to  excite  in  the  midst  of  those  who 
regard  it  as  an  exploded  and  pernicious  system. 

717.  The  Sympathy  between  different  parts  of  the  system,  which  especially 
manifests  itself  in  the  tendency  to  simultaneous  affection  with  the  same  Dis- 
ease, affords  an  excellent  illustration  of  this  principle.  Of  those  Sympathetic 
actions,  which  result  from  the  Nervous  connections  of  the  various  organs,  this 
is  not  the  place  to  speak  ;  since  we  are  at  present  concerned  with  those  per- 
versions of  the  Nutritive  processes  which  give  rise  to  Inflammatory  and  other 
diseases.  Where  a  certain  tissue  throughout  the  body  is  similarly  affected, 
there  is  strong  reason  to  presume  that  the  morbific  cause  is  conveyed  to  it  in 
the  Blood ;  this  is  the  case,  for  example,  with  regard  to  the  Mucous  membranes, 
which  all  manifest  a  tendency  to  Inflammation,  when  Arsenic  has  been  received 
into  the  system :  and  certain  forms  of  the  disease  commonly  termed  Influenza, 
are  marked  by  a  similar  disposition.  The  same  may  be  said  in  regard  to  In- 
flammation of  the  Fibrous  membranes,  Areolar  tissue,  Serous  membranes,  and 
other  structures.  It  has  been  considered  a  sufficient  account  of  these  consen- 
taneous affections,  to  say  that  they  result  from  Sympathy, — a  mere  verbal 
quibble,  which  explains  nothing.  If,  on  the  other  hand,  we  regard  the  disease 
as  a  perversion  of  the  ordinary  processes  of  Nutrition,  Secretion,  &c.,  and  as 
dependent  upon  an  abnormal  condition  of  the  Blood  (such  as  is  induced  by 
the  introduction  of  a  poison  into  it),  the  rationale  of  the  sympathetic  disturb- 
ance becomes  apparent  ;< — since  all  the  tissues  of  the  same  kind  will  of  neces- 
sity be  similarly  affected,  although  some  local  cause  may  occasion  one  to  suffer 
more  severely  than  another.  In  the  ingenious  paper  by  Dr.  W.  Budd  already 
referred  to  (§  590),  the  perfect  correspondence  which  not  unfrequently  mani- 
fests itself  between  the  diseased  actions  on  the  two  sides  of  the  body,  is  adduced 
in  support  of  the  same  view,  to  which  it  is  made  to  afford  very  striking  con- 
firmation. The  fact  that  this  kind  of  Sympathy  not  unfrequently  manifests 
itself  between  tissues  having  an  analogous  structure,  but  very  different  func- 
tion, is  another  argument  in  favour  of  the  same  view  ;  of  this  fact,  the  sympathy 
of  which  every  practical  man  is  aware,  between  the  Skin  and  Mucous  mem- 
branes, is  a  very  good  example.  The  sympathy  of  the  different  tissues  forming 


ANIMAL  HEAT.  573 

any  individual  organ,  by  which  disease  in  one  becomes  a  cause  of  disorder  in 
the  rest,  is,  however,  to  be  very  differently  explained.  We  have  examples 
of  this  in  Inflammatory  affections  of  the  Mucous  membranes,  which  usually 
extend  themselves  to  the  remaining  constituents  of  the  organs  of  which  they 
form  a  part ;  and  in  those  of  the  Serous  membranes,  which  almost  always 
follow  inflammation  of  the  organs  they  invest.  Here  the  local  disturbance  of 
one  part  appears  sufficient  to  account  for  the  extension  of  it  to  another  that  is 
closely  connected  with  it  by  vessels  and  nerves ;  this  has  been  termed  the 
Sympathy  of  Contiguity.  The  Fibrous  membranes  are  less  liable  to  be  affected 
in  this  manner  than  are  most  other  tissues ;  and  the  reason  appears  simply 
this, — that  there  is  usually  less  vascular  connection  between  them  and  the 
adjacent  parts  than  there  is  in  the  case  of  the  Serous  membranes.  Hence  the 
Fibrous  membranes  frequently  act  as  insulators,  preventing  the  spread  of  dis- 
ease to  adjacent  parts. 

718.  The  general  characters  of  the  processes  of  Nutrition  and  Secretion  are 
so  nearly  allied,  that  what  has  been  stated  of  the  Pathological  states  of  the 
former,  is  nearly  as  applicable  to  those  of  the  latter.  Although  it  is  unquestion- 
able that  disordered  Secretion  may  result  from  a  purely  local  cause,  acting  on  the 
solid  tissue  of  the  part  affected,  yet  there  is  also  increasing  reason  to  believe,  that 
in  a  large  number  of  cases,  the  abnormal  character  of  the  product  is  in  reality 
a  result  of  the  abnormal  state  of  the  Blood  from  which  it  is  separated ;  and 
that  the  organ  itself  is  still  performing  a  healthy  function,  in  separating  from 
the  blood  that  which  would  be  injurious  to  it.     This  leads  us  to  refer  such 
disorders  to  causes  much  more  remote  than  those  which  were  formerly  sup- 
posed to  operate ;  but  they  are  undoubtedly  nearer  the  true  ones.     Such  a 
view  has  been  prosecuted  by  Dr.  Prout  in  regard  to  the  abnormal  conditions 
of  the  Urine,  with  great  success  ;  and  there  can  be  little  doubt  that  it  is  also 
applicable  to  the  Biliary  secretion,  on  the  true  chemical  nature  of  which  there  is 
scarcely  yet  an  agreement  among  Chemists,  and  whose  pathological  conditions, 
therefore,  are,  and  must  long  remain,  comparatively  obscure.     It  is  obvious 
that,  if  the  Assimilation  of  Nutritive  matter  be  in  any  respect  wrongly  per- 
formed, the  products  of  the  Decomposition  of  the  Tissues  (in  which  these 
secretions  probably  originate,  §  648)  must  also  be  different ;  and  our  remedial 
measures  must  often  be  directed,  therefore,  not  so  much  to  the  Secreting  organ, 
as  towards  the  previous  operations.— These  hints,  which  may  to  some  appear 
of  too  abstract  a  character  to  be  of  any  practical  value,  are  introduced  here  for 
the  purpose  of  directing  the  intelligent  Student  in  the  path  that  will  conduct 
him  to  fields  of  inquiry  scarcely  yet  trodden,  and  fertile  in  the  most  valuable 
results.     In  the  present  unsettled  state  of  opinion  upon  many  of  the  highest 
questions  in  Pathology,  it  would  be  absurd  to  attempt  to  lay  down,  in  a  dog- 
matic form,  what  is;  but  much  may  be  done,  by  purifying  the  science  of  what 
is  not ;  and  here  a  sound  Physiology  affords  most  valuable  assistance.* 

II.  Animal  Heat. 

719.  All  the  vital  actions  that  have  been  considered  in  the  preceding  pages 
require  a  certain  amount  of  Heat,  as  a  condition  of  their  performance ;  and  in 
the  more   elevated  tribes  of  animals,  in  which  (for  the  very  purposes  of  their 
creation)  a  high  degree  of  constancy  and  regularity  is  required  in  these  actions, 
there  is  a  provision  within  themselves  for  the  maintenance  of  their  tempera- 
ture at  a  certain  standard.     We  shall  inquire  in  the  first  place  into  the  amount 
of  Heat  thus  generated  by  Man ;  and  then  into  the  sources  of  its  production. 

*  The  Author  would  particularly  refer  to  Dr.  Williams's  Principles  of  Medicine,  as 
giving  the  best  general  view  of  this  subject  that  has  yet  been  published,— in  this  country 
at  least. 


574 


GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 


720.  Our  present  knowledge  of  the  Temperature  of  the  Human  body  under 
different  circumstances,  is  chiefly  due  to  the  investigations  of  Dr.  J.  Davy. — 
Much  additional  information  may  be  expected,  however,  from  inquiries  which 
are  at  present  in  progress.  Dr.  Davy's  observations*  have  included  114  indi- 
viduals of  both  sexes,  of  different  ages,  and  among  various  races,  in  different 
latitudes,  and  under  various  temperatures  ;  the  external  temperature,  however, 
was  in  no  instance  very  low,  and  the  variations  were  by  no  means  extreme. 
The  mean  of  the  ages  of  all  the  individuals  was  27  years.  The  following  is 
a  general  statement  of  the  results,  the  temperature  of  the  body  being  ascer- 
tained by  a  thermometer  placed  under  the  tongue. 
Temperature  of  the  air  60°  Average  temperature  of  the  body 


78° 
79-5° 

80° 

82° 


98-28° 
98-15° 
98-85° 
99-21° 
99-67° 


99-9° 

Mean  of  all  the  experiments  74°       Mean  of  all  the  experiments  100° 

Highest  temperature  of  air  82°       Highest  temperature  of  body  102° 

Lowest  temperature  of  air    60°       Lowest  temperature  of  body  96-5" 

From  this  we  see  that  the  variations  noted  by  Dr.  Davy,  which  were  evidently 
in  part  the  consequence  of  variations  in  external  temperature,  but  which  were 
also  partly  attributable  to  individual  peculiarities,  amounted  to  5|  degrees ;  the 
lower  extreme  would  probably  undergo  still  further  depression,  if  the  inquiries 
were  carried  on  in  very  cold  climates. — The  Temperature  of  the  body  may  be 
affected  by  internal  as  well  as  by  external  causes ;  thus  in  diseases  which  in- 
volve an  accelerated  pulse  and  an  augmented  respiration,  the  temperature  is 
generally  higher  than  usual,  even  though  a  large  portion  of  the  lung  may  be 
unfit  for  its  function.  This  is  often  remarkably  seen  in  the  last  stages  of 
Phthisis,  when  the  inspirations  are  extremely  rapid,  and  the  pulse  so  quick  as 
scarcely  to  admit  of  being  counted ;  the  skin,  in  such  cases,  often  becomes 
almost  painfully  hot.  On  the  other  hand,  in  diseases  of  the  contrary  charac- 
ter, such  as  Asthma  and  the  Asiatic  Cholera,  the  temperature  of  the  body  falls, 
sometimes  to  the  extent  of  20  degrees.  The  following  observations  have  been 
made  on  this  subject  by  M.  Donne  ;t  it  is  much  to  be  desired,  however,  that 
fuller  data  could  be  collected  on  the  subject.  In  a  case  of  Puerperal  Fever, 
the  pulse  being  168,  and  the  respiration  48  per  minute,  the  temperature  was 
104°.  In  a  case  of  Hypertrophy  of  the  Heart,  the  pulse  being  150,  and  the 
respirations  34,  the  temperature  was  103°.  In  a  case  of  Typhoid  Fever,  the 
pulse  being  136,  and  the  respirations  50,  the  temperature  was  104°.  And  in 
a  case  of  Phthisis,  the  pulse  being  140,  and  the  respirations  62,  the  tempera- 
ture was  102°.  On  the  other  hand,  in  a  case  of  Jaundice,  in  which  the  pulse 
was  but  52,  the  temperature  was  only  96-40° ;  but  the  same  temperature  was 
observed  in  a  case  of  Diabetes,  in  which  the  pulse  was  84.  The  limited  re- 
sults of  Mons.  D.'s  experiments,  whilst  they  clearly  indicate  that  a  general 
relation  exists  between  the  temperature  of  the  body  and  the  rapidity  of  the 
pulse,  also  show  that  this  relation  is  by  no  means  invariable,  but  that  it  is  liable 
to  be  affected  by  several  causes,  of  which  our  knowledge  is  as  yet  very  limited. 
Dr.  Dunglison  speaks  of  having  frequently  seen  the  thermometer  at  106°  in 
Scarlatina  and  Typhus  ;  and  Dr.  Edwards  mentions  a  case  of  Tetanus,  in  which 
it  rose  to  110!  4 

*  Phil.  Trans.  1814;  republished  in  Anatomical  and  Physiological  Researches. 
f  Archives  Generales,  Oct.,  1835  ;  and  Brit,  and  For.  Med.  Rev.,  vol.  ii.,  p.  248. 
i  [An  extensive  series  of  observations  has  been  made  by  M.  Roger§  on  the  temperature 
of  children  in  health  and  various  diseases. 


§  Arch.  Gen.  de  Medecine,  Juillet,  Aout,  &c.,  1844. 


ANIMAL  HEAT.  575 

721.  Although  there  appears  to  be,  for  all  species  of  animals,  a  distinct  limit 
to  the  variations  of  bodily  temperature,  under  which  their  vital  operations  can 
be  carried  on,  this  limitation  does  not  prevent  animals  from  existing  in  the 
midst  of  great  diversities  of  external  conditions  ;  since  they  have  within  them- 
selves the  power  of  compensating  for  these,  in  a  very  extraordinary  degree. — 
This  power  seems  to  exist  in  Man  to  a  higher  amount  than  in  most  other  ani- 
mals ;  since  he  can  not  only  support  but  enjoy  life  under  extremes,  either  of 
which  would  be  fatal  to  many.     In  many,  parts  of  the  tropical  zone,  the  ther- 
mometer rises  every  day  through  a  large  portion  of  the  year  to  110°;  and  in 
British  India  it  is  said  to  be  seen  occasionally  at  130°.     On  the  other  hand,  the 
degree  of  cold  frequently  sustained  by  Arctic  voyagers,  and  quite  endurable 
under  proper  precautions,  appears  much  more  astonishing ;  by  Capt.  Parry, 
the  thermometer  has  been  seen  as  low  as  — 55°,  or  87°  below  the  freezing 
point;  by  Capt.  Franklin  at  — 58°,  or  90°  below  the  freezing  point;  and  by 
Capt.  Back  at  — 70°,  or  102°  below  the  freezing  point.     In  both  cases,  the 
effect  of  the  atmospheric  temperature  on  the  body  is  greatly  influenced  by  the 
condition  of  the  air  as  to  motion  or  rest ;  thus,  every  one  has  heard  of  the 
almost  unbearable  oppressiveness  of  the  sirocco  or  hot  wind  of  Sicily  and  Italy, 
the  actual  temperature  of  which  is  not  higher  than  has  often  been  experienced 
without  any  great  discomfort,  when  the  air  is  calm :  and  on  the  other  side,  it 
may  be  mentioned  that,  in  the  experience  of  many  Arctic  voyagers,  a  tempe- 
rature of  — 50°  may  be  sustained,  when  the  air  is  perfectly  still,  with  less 
inconvenience  than  is  caused  by  air  in  motion  at  a  temperature  fifty  degrees 
higher.     This  is  quite  conformable  to  what  might  be  anticipated  on  physical 
principles. 

722.  Again,  the  degree  of  moisture  contained  in  a  heated   atmosphere, 

In  nine  examinations  of  infants  from  one  to  twenty  minutes  after  birth,  the  temperature, 
(observed  in  these  and  in  all  the  other  cases,  in  the  axilla),  was  from  99-95  to  95-45.  Im- 
mediately after  birth  the  temperature  was  at  the  highest;  but  it  quickly  fell  to  near  the 
lowest  of  those  above  stated;  but,  by  the  next  day,  it  was  again  completely  or  nearly 
what  it  was  before.  The  rapidity  of  the  pulse  and  of  respiration  appeared  to  have  no 
certain  relation  to  the  temperature. 

In  thirty-three  infants  of  from  one  to  seven  days  old,  the  most  frequent  temperature  was 
98-6;  the  average  was  98-75;  the  maximum  (in  one  case  only)  102-2;  the  minimum  (also 
observed  only  once)  96°-8.  All  the  infants  were  healthy.  The  frequency  of  respiration 
had  no  evident  or  constant  relation  to  the  temperature.  A  few  of  the  infants  were  of  a 
weakly  habit;  their  average  was  97-7:  the  others  were  strong,  and  their  average  tempe- 
rature was  99°-534.  The  age  of  the  infant  (in  this  short  period)  had  no  influence  on  its 
temperature  ;  neither  had  its  sex.  nor  its  state  of  sleep  or  waking,  nor  the  period  after 
suckling. 

In  twenty-four  children,  chiefly  boys,  from  four  months  to  fourteen  years  old,  the  most 
frequent  temperature  was  above  98°-6 ;  the  average  was  98°-978;  the  minimum  was 
98°-15  ;  the  maximum  99°-95.  The  average  temperature  of  those  six  years  old  or  under, 
was  98°-798;  of  those  above  six  years  old,  99°-158.  The  average  number  of  pulsations 
in  the  minute  was  in  those  under  six  years  old  102 ;  in  those  above  that  age  77 ;  yet  the  tem- 
perature of  the  latter  was  higher  than  that  of  the  former,  or  of  younger  infants.  There 
was  no  evident  relation  between  the  temperature  and  the  frequency  of  respiration;  nor, 
in  a  few  examinations,  was  the  temperature  affected  in  a  regular  way,  by  active  exercise 
for  a  short  time,  or  by  the  stage  of  digestion. 

As  already  said,  in  all  the  examinations  from  which  these  results  were  obtained,  the 
thermometer  was  held  in  the  axilla ;  comparative  examinations  proved  that  the  tempera- 
ture of  the  axilla,  (though  lower  than  that  of  internal  organs,)  was  higher  than  that  of 
any  other  part  of  the  surface  of  the  skin.  Of  the  other  parts  examined,  the  warmest  was 
the  abdomen,  then  in  succession,  the  cavity  of  the  mouth,  the  bend  of  the  arm,  the  hands, 
the  feet;  of  which  last,  the  average  temperature,  in  four  examinations,  was  only  87°-35. 
(These  results  correspond  sufficiently  with  those  obtained  by  Dr.  John  Davy.) 

In  diseased  states,  (to  the  illustration  of  which  the  greater  part  of  the  memoir  is  de- 
voted,) the  temperature  of  the  skin  in  children  may  descend  to  74°-3,  and  may  ascend  to 
108°-5.  Its  range  of  variation  is  therefore  much  greater  than  in  adults,  in  whom  M.  An- 
dral  found  it  to  vary  in  different  diseases  not  more  than  from  95°  to  107°-6.] 


576  GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 

makes  a  great  difference  in  the  degree  of  elevation  of  temperature,  which  may 
be  sustained  without  inconvenience.  Many  instances  are  on  record,  of  a  heat 
of  from  250°  to  280°  being  endured  in  dry  air  for  a  considerable  length  of 
time,  even  by  persons  unaccustomed  to  a  particularly  high  temperature  ;  and 
persons  whose  occupations  are  such  as  to  require  it,  can  sustain  a  much 
higher  degree  of  heat,  though  not  perhaps  for  any  long  period.  The  workmen 
of  the  late  Sir  F.  Chantrey  have  been  accustomed  to  enter  a  furnace  in  which 
his  moulds  were  dried,  whilst  the  floor  was  red-hot,  and  a  thermometer  in  the 
air  stood  at  350°  ;  and  Chabert,  the  "  Fire-king,"  was  in  the  habit  of  entering 
an  oven  whose  temperature  was  from  400°  to  000°.  It  is  possible  that  these 
feats  might  be  easily  matched  by  many  workmen  who  are  habitually  exposed 
to  high  temperatures  ;  such  as  those  employed  in  Iron-foundries,  Glass-houses, 
and  Gas-works.  In  all  these  instances,  the  dryness  of  the  air  facilitates  the 
rapidity  of  the  vapourization  of  the  fluid,  of  which  the  heat  occasions  the  secre- 
tion by  the  cutaneous  glands  ;  and  the  large  amount  of  caloric  which  becomes 
latent  in  the  process,  is  for  the  most  part  withdrawn  from  the  body,  the  tem- 
perature of  which  is  thus  kept  down.  Exposure  to  a  very  elevated  tempera- 
ture, however,  if  continued  for  a  sufficient  length  of  time,  does  produce  a 
certain  elevation  of  that  of  the  body ;  as  might  be  expected  from  the  state- 
ments already  made  in  regard  to  the  variation  in  the  heat  of  the  body  which 
changes  in  atmospheric  temperature  (§  720).  In  the  experiments  of  MM. 
Berger  and  Delaroche,  it  was  found  that,  after  the  body  had  been  exposed  to  air 
of  120°  during  17  minutes,  a  thermometer  placed  in  the  mouth  rose  nearly  6 
degrees  above  the  ordinary  temperature ;  it  may  be  remarked,  however,  that  as 
the  body  was  immersed  in  a  close  box,  from  which  the  head  projected  (in 
order  to  avoid  the  direct  influence  of  the  heated  air  on  the  temperature  of  the 
mouth),  the  air  had  probably  become  charged  with  the  vapour  exhaled  from 
the  surface,  and  had  therefore  somewhat  of  the  effects  of  a  moist  atmosphere. 
At  any  rate,  the  temperature  of  the  body  does  not  appear  to  rise,  under  any 
circumstances,  to  a  degree  very  much  greater  than  this.  In  one  of  the  expe- 
riments of  Drs.  Fordyce  and  Blagden,  the  temperature  of  a  Dog,  that  had 
been  shut  up  for  half  an  hour  in  a  chamber  of  which  the  temperature  was 
between  220°  and  236°,  was  found  to  have  risen  from  101°  to  about  108°. 
MM.  Delaroche  and  Berger  tried  several  experiments  on  different  species  of 
animals,  in  order  to  ascertain  the  highest  temperature  to  which  the  body  could 
be  raised  without  the  destruction  of  life,  by  enclosing  them  in  air  heated  from. 
122°  to  201°,  until  it  died :  the  result  was  very  uniform,  the  temperature  of  the 
body  at  the  end  of  the  experiment  only  varying  in  the  different  species  between 
11°  and  13°  above  their  natural  standard:  whence  it  may  be  inferred,  that  an 
elevation  to  this  degree  must  be  fatal.  This  elevation  would  be  attained  com- 
paratively soon  in  a  moist  atmosphere ;  partly  because  of  the  greater  conducting 
power  of  the  medium ;  but  principally  "on  account  of  the  check  which  is  put 
upon  the  vapourization  of  the  fluid  secreted  by  the  skin.  Even  here,  however, 
custom  and  acquired  constitution  have  a  very  striking  influence ;  for  whilst 
the  inhabitants  of  this  country  are  unable  to  sustain,  during  more  than  10  or 
12  minutes,  immersion  in  a  vapour-bath  of  the  temperature  of  110°  or  120°. 
the  Finnish  peasantry  remain  for  half  an  hour  or  more  in  a  vapour-bath  the 
temperature  of  which  finally  rises  to  158°  or  167°. — Accurate  experiments 
are  yet  wanting,  to  determine  the  influence  of  humidity  on  the  effects  of  cold 
air.  From  experiments  on  young  Birds  incapable  of  maintaining  their  own 
temperature,  of  which  some  were  placed  in  cold  dry  air,  and  others  in  cold 
air  charged  with  moisture,  it  was  found  by  Dr.  Edwards  that  the  loss  of  heat 
was  in  both  instances  the  same ;  the  effect  of  the  evaporation  from  the  surface 
in  the  former  case,  being  counterbalanced  by  the  depressing  influence  of  the 


ANIMAL  HEAT.  577 

cold  moisture.     This  influence,  the  existence  of  which  is  a  matter  of  ordinary 
experience,  is  probably  exerted  directly  upon  the  nervous  system. 

723.  Having  thus  considered  the  general  facts  which  indicate  the  faculty 
possessed  by  the  living  system,  in  the  higher  Animals,  of  keeping  up  its  tem- 
perature to  an  elevated  standard,  and  of  preventing  it  from  being  raised  much 
beyond  it  by  any  degree  of  external  heat,  we  have  next  to  inquire  to  what  this 
faculty  is  due.     We  shall  be  more  likely  to  arrive  at  accurate  results  in  such 
an  inquiry,  the  more  comprehensive  our  survey  is  of  the  phenomena  to  which 
it  relates.*     The  most  recent  experiments  on  the  temperature  of  Plants  (those 
made  by  MM.  Becquerel  and  Breschet  with  the  thermo-multiplier)  have  de- 
monstrated, that  in  those  parts  in  which  the  vital  processes  are  taking  place 
with  activity,  a  sensible  amount  of  caloric  is  being  constantly  evolved.     The 
amount  of  this  evolution  of  heat  is  generally  very  low, — not  more,  in  fact,  than 
a  single  degree  (Fahr.) ;  and  as  it  does  not  more  than  counterbalance  the  effect 
of  the  evaporation,  which  is  continually  taking  place  from  the  surface,  there 
is  no  sensible  difference  between  the  temperature  of  the  plant  and  that  of  the 
surrounding  air.     At  the  time  of  Flowering,  however,  a  much  greater  degree 
of  heat  is  generated  in  many  plants ;  especially  in  those  in  which  a  large 
number  of  flowers  are  crowded  together,  as  in  the  case  of  the  Arum  tribe  : 
thus  a  thermometer  placed  in  the  midst  of  twelve  spadixes  has  been  seen  to 
rise  to  121°,  whilst  the  temperature  of  the  air  was  only  66°.     During  the 
Germination  of  seeds,  again,  a  considerable  development  of  heat  takes  place  ; 
this,  which  is  soon  carried  off  from  a  single  seed,  becomes  very  sensible  when 
a  large  number  are  heaped  together,  as  in  malting ;  the  thermometer  plunged 
into  a  heap  of  germinating  barley  having  been  seen  to  rise  to  110°. 

724.  These  facts  are  of  more  importance  than  might  appear  at  first  sight ; 
for  they  indicate  unequivocally,  that  the  source  of  the  heat  is  to  be  looked  for 
in  the  Organic  functions  not  in  those  of  Animal  life.     The  evolution  of  Calo- 
ric has  been  attributed  by  many  physiologists  to  the  Nervous  system ;  the 
influence  which  this  system  evidently  possesses  over  the  function,  being  mis- 
taken for  the  efficient  cause  of  it.     As  has  been  remarked  on  several  former 
occasions,  however, — the  fact  that  any  change  takes  place  in  Vegetables  to 
the  same  degree  (under  certain  conditions)  with  that  in  which  it  ever  presents 
itself  in  Animals,  is  a  sufficient  proof  that  it  cannot  be  dependent  upon  nervous 
agency,  although  it  may  be  influenced  by  it.     Moreover,  it  may  be  remarked, 
that  the  production  of  Heat  is  an  operation  of  an  entirely  physical  character, 
and  that  it  may  be  referred  to  physical  causes  ;  whilst  the  operations  in  which 
the  Nervous  system  is  concerned,  are  such  as  we  cannot  liken  in  any  degree 
to  physical  phenomena,  and  are  of  a  purely  vital  character.     In  our  inquiry 
into  the  sources  of  the  Heat  evolved  by  living  beings,  we  are  limited,  there- 
fore, to  those  which  can  operate  in  the  Vegetable  kingdom ;  and  on  examining 
into  the  phenomena  which  present  any  relation  to  this,  we  are  at  once  struck 
with  the  fact,  that  an  absorption  of  Oxygen  from  the  air,  with  an  extrication  of 
Carbonic  acid,  is  continually  taking  place  (constituting  the  true  Respiratory 
process  of  Plants,  §  522) ;  and  that  these  changes  occur  with  excessive  activity, 
at  the  very  periods  at  which  the  evolution  of  Heat  is  most  remarkable, — those, 
namely,  of  germination  and  flowering.     The  quantity  of  Oxygen  consumed 
by  flowers  is  enormous, — those  of  the  Arum  Italicum  having  been  found  to 
convert  40  times  their  own  bulk  of  that  gas  into  Carbonic  acid,  between  the 
periods  of  their  first  appearance  and  their  final  decay ;  and  of  this,  the  far 
larger  proportion  is  consumed  by  the  sexual  apparatus,  which  has  been  found 
to  consume  132  times  its  own  bulk  of  Oxygen  in  24  hours.   That  this  change 

*  This  subject  is  more  fully  treated  in  the  Author's  Principles  of  General  and  Com- 
parative Physiology,  §§  548 — 567. 
49 


578  GENERAL  REVIEW  OF  THE  NUTRITIVE  PROCESSES. 

is  a  condition  necessary  for  the  production  of  Heat,  is  fully  proved  by  the  fact, 
that  no  caloric  is  evolved  when  the  flowers  are  excluded  from  the  contact  of 
Oxygen  ;  whilst  the  substitution  of  pure  oxygen  for  atmospheric  air  occasions 
the  elevation  of  temperature  to  be  more  rapid  and  considerable  than  usual.* 
The  same  may  be  said  of  the  heat  liberated  by  seeds  in  the  act  of  Germina- 
tion :  a  large  amount  of  oxygen  is  absorbed,  and  of  carbonic  acid  given  out 
during  this  process ;  and  the  evolution  of  Heat  may  be  easily  shown  to  be  as 
dependent  upon  this  change  as  in  the  instance  just  quoted.  It  is  the  opinion 
of  some  physiologists,  that  the  production  of  heat  under  these  circumstances 
is  dependent  upon  a  real  process  of  Combustion ;  the  carbon  of  the  Plant 
uniting  with  the  oxygen  of  the  air,  and  thereby  giving  out  caloric,  as  it  does 
in  the  ordinary  burning  of  charcoal.  Perhaps  this  account  is  rather  too 
simple.  It  is  well  known  that  most  chemical  changes,  especially  those  in 
which  there  is  an  alteration  in  the  form  of  the  agents  concerned,  are  attended 
with  a  change  of  temperature  ;  and  it  is  not  unreasonable  to  suppose,  that,  of 
those  Molecular  alterations  which  have  been  shown  to  be  so  continually  oc- 
curring in  the  living  system,  some  may  be  connected  with  the  disengagement 
of  heat  peculiar  to  it.  For  the  continuance  of  these  alterations,  however,  the 
absorption  of  Oxygen  and  the  extrication  of  Carbonic  Acid  are  necessary  condi- 
tions ;  if  these  be  suspended,  therefore,  the  temperature  soon  falls. 

725.  When  the  phenomena  of  Calorification  in  Animals  are  carefully  ex- 
amined, they  are  found  to  harmonize  completely  with  this  view.  Throughout 
the  whole  kingdom,  an  exact  conformity  may  be  perceived  between  the  amount 
of  Oxygen  consumed  and  of  Carbonic  acid  given  off,  and  the  degree  of  Heat 
liberated.  In  the  cold-blooded  animals,  whose  temperature  is  almost  entirely 
dependent  upon  that  of  the  surrounding  medium,  the  respiration  is  feeble, 
being  carried  on,  for  the  most  part,  through  the  medium  of  water.  In  the 
warm-blooded  Vertebrata,  however,  which  have  the  power  of  keeping  up  the 
heat  of  their  bodies  to  an  elevated  standard,  even  when  that  of  the  surround- 
ing air  is  far  beneath  it,  the  quantity  of  oxygen  consumed  is  very  large  ;  and 
that  required  by  Birds  is  more,  in  proportion  to  their  size,  than  that  employed 
by  Mammalia;  as  we  should  expect  from  the  more  elevated  temperature  of 
the  former.  In  the  class  of  Insects  we  have  a  very  remarkable  illustration  of 
the  same  general  fact.  It  appears,  from  the  researches  of  Mr.  Newport,  that 
Insects,  during  their  larva  and  pupa  states,  and  even  in  their  perfect  condition 
when  at  rest,  are  to  be  regarded  as  truly  cold-blooded  animals  ;  their  tempera- 
ture rising  and  falling  with  that  of  the  surrounding  medium,  and  being  at  no 
time  more  than  a  degree  or  two  above  it.  In  a  state  of  activity,  however,  the 
temperature  of  the  body  attains  a  considerable  elevation, — frequently  as  much 
as  10°  or  15°  above  that  of  the  air.  It  must  be  remembered  that,  owing  to 
their  larger  extent  of  surface  in  proportion  to  their  bulk,  small  animals  are 
cooled  much  more  rapidly  than  large  ones ;  and  the  temperature  of  Insects 
would  probably  rise  much  higher,  if  it  were  not  for  the  loss  they  are  thus 
continually  experiencing,  which  is  greatly  increased  by  the  action  of  the 
wings.  In  one  of  Mr.  N.'s  experiments,  a  single  Humble-bee,  in  a  state  of 
violent  exckement,  communicated  to  three  cubic  inches  of  air  as  much  as  4° 
of  heat  within  five  minutes ;  its  own  temperature  being  raised  7°  in  the  same 
time.  When  several  individuals  in  a  state  of  excitement,  however,  are  clus- 
tered together,  so  that  the  loss  of  heat  is  prevented,  the  elevation  of  tempera- 
ture is  much  more  considerable ;  thus,  a  thermometer  introduced  among  seven 
"  Nursing-Bees"  stood  at  92^°,  whilst  the  external  air  was  only  70°;  and  the 
temperature  of  a  hive  was  raised  by  disturbing  it,  during  winter,  from  48!° 

*  See  the  very  interesting  experiments  of  MM.  Vrolik  and  Vriese,  in  the  Ann.  des  Sci. 
Nat.,  N.  S.  Botan.,  torn.  xi.  p.  551. 


DEVELOPMENT  OF  HEAT.  579 

to  102°,  the  temperature  of  the  air  being  only  34^  °  at  the  time  !  In  all  these 
instances,  the  amount  of  Oxygen  consumed  bears  an  exact  proportion  to  that 
of  the  Heat  evolved.  Even  in  higher  animals,  exercise  has  a  considerable 
effect  in  producing  an  elevation  of  temperature  ;  and,  that  this  is  not  merely 
due  to  the  acceleration  of  the  circulation,  is  shown  by  the  very  curious  fact, 
that  the  exercise  of  a  particular  muscle  will  cause  an  increase  in  the  heat 
liberated  from  it,  as  shown  by  needles  plunged  in  its  substance,  and  connected 
with  the  Thermo-Multiplier.*  It  may,  indeed,  be  stated  as  a  general  propo- 
sition, applicable  as  well  to  different  parts  of  the  same  being,  as  to  different 
individuals,  that  the  development  of  Heat  is  proportional  to  the  activity  of  the 
molecular  processes  which  constitute  the  functions  of  Nutrition,  Secretion, 
&c. ;  increasing  with  their  activity,  and  diminishing  with  their  torpor.  It  is 
very  easy  to  explain,  on  this  principle,  the  known  influence  of  the  Nervous 
system  on  the  calorific  function:  since,  although  the  molecular  changes  in  the 
organized  fabric  are  not  dependent  upon  the  agency  of  that  system,  they  are 
very  much  influenced  by  it ;  and  thus  we  can  readily  understand  how  a  state 
of  nervous  excitement  may  produce  an  elevation  of  temperature,  and  a  depres- 
sion of  nervous  power  occasion  a  cooling  of  the  body.  The  experiments  of 
Sir  B.  Brodie,  Chossat  and  others,-— in  which  a  greater  or  less  portion  of  the 
nervous  centres  was  removed,  and  the  animal  cooled  notwithstanding  the 
maintenance  of  the  circulation, — by  no  means  prove  that  the  Nervous  system 
is  directly  concerned  in  the  production  of  heat ;  since  in  all  such  experiments 
there  is  a  gradual  loss  of  those  other  vital  powers  which  are  concerned  in  the 
function  of  calorification.  From  the  experiments  of  Dr.  W.  Philip  and  Dr. 
Hastings,  it  appears  that  an  animal  whose  nervous  centres  have  been  re- 
moved, cools  much  faster  when  left  to  itself  than  when  Artificial  Respiration 
is  practised ;  and  that,  if  the  cooling  have  made  much  progress  before  the 
artificial  respiration  is  caused  to  commence,  the  temperature  may  be  raised ; 
— and  this,  too,  in  spite  of  the  very  imperfect  manner  in  which  natural  Respi- 
ration is  replaced  by  movements  artificially  effected. 

726.  That  the  maintenance  of  Animal  Heat  is  due  in  part  to  those  mole- 
cular changes,  to  which  the  extrication  of  Carbonic  acid  through  the  Skin  is 
subservient,  appears  from  the  following  experiments  recently  performed  by 
MM.  Becquerel  and  Breschet.  The  hair  of  Rabbits  was  shaved  off,  and  a 
composition  of  glue,  suet  and  resin,  forming  a  coating  through  which  air 
could  not  pass,  was  applied  over  the  whole  surface.  It  might  seem  natural 
to  suppose  that,  by  preventing  the  evaporation  of  the  sweat,  the  temperature 
of  the  tissues  would  be  very  sensibly  increased ;  and  that,  by  this  increase  of 
the  temperature  of  the  whole,  body,  a  high  state  of  fever  would  be  engendered, 
with  the  symptoms  of  which  the  animal  would  at  last  die.  But  the  contrary 
occurred.  In  the  first  Rabbit,  which  had  a  temperature  of  100°  before  being 
shaved  and  plastered,  it  had  fallen  to  89^°  by  the  time  the  material  spread 
over  him  was  dry.  An  hour  after,  the  thermometer,  placed  in  the  same  parts, 
(the  muscles  of  the  thigh  and  chest)  had  descended  to  76°.  In  another  Rab- 
bit, prepared  with  more  care,  by  the  time  that  the  plaster  was  dry,  the  tem- 
perature of  the  body  was  not  more  than  65°  above  that  of  the  surrounding 
medium,  which  was  at  that  time  625°;  and  an  hour  after  this  the  animal 
died.  These  experiments  place  in  a  very  striking  point  of  view  the  import- 
ance of  the  Cutaneous  surface  as  a  respiratory  organ,  even  in  the  higher  ani- 
mals :  and  they  enable  us  to  understand  how,  when  the  secreting  power  of 
the  Lungs  is  nearly  destroyed  by  disease,  the  heat  of  the  body  is  kept  up  to 
its  natural  standard  by  the  action  of  the  Skin.  A  valuable  therapeutic  indi- 

*  See  the  experiments  of  MM.  Becquerel  and  Breschet,  in  Ann.  des  Sci.  Nat.,  N.  S. 
Zool.,  torn.  vi. 


580  GENERAL  REVIEW  OF  THE  NUTRITIVE  FUNCTIONS. 

cation,  also,  is  derivable  from  the  knowlecjge  which  we  thus  gain,  of  the  im- 
portance of  the  Cutaneous  Respiration ;  for  it  leads  us  to  perceive  the  desira- 
bleness of  keeping  the  skin  moist,  in  those  febrile  diseases  in  which  there  are 
great  heat  and  dryness  of  the  surface,  since  secretion  cannot  properly  take 
place  through  a  dry  membrane.  Of  the  relief  afforded  by  cold  or  tepid  spong- 
ing in  such  cases,  experience  has  given  ample  evidence. 

727.  It  has  been,  and  still  is,  a  prevalent  opinion  amongst  Physiologists  of 
the  Chemical  school,  that  the  process  of  Calorification  is  one  of  ordinary  Com- 
bustion ;  being  entirely  dependent  upon  the  union  of  Carbon  and  Hydrogen, 
— either  directly  furnished  by  the  non-azotized  constituents  of  the  food,  or 
derived  from  the  disintegration  of  the  tissues  (§  433), — with  the  Oxygen 
obtained  from  the  atmosphere.     It  may  be  questioned,  however,  on  several 
grounds,  whether  this  is  a  sufficient  account  of  it.     From  the  experiments  of 
Dulong  and  Despretz  (between  which  there  is  a  close  agreement),  it  appears 
that  more  Heat  is  given  off  from  the  bodies  of  warm-blooded  animals  than 
can  be  accounted  for  by  the  union  of  the  amount  of  Carbon  and  Hydrogen, 
contained  in  the  Carbonic  acid  and  Watery  vapour  exhaled  by  them  during  a 
given  time,  with  their  equivalents  of  Oxygen.     According  to  Dulong,  the 
combustion  of  the  Carbon  alone  would  not  account  for  more  than  half  of  the 
caloric  liberated  by  Carnivorous  animals,  or  for  more  than  seven-tenths  of  that 
set  free  by  Herbivorous  species  ;  and,  even  when  the  Hydrogen  was  also 
taken  into  account,  the  amount  of  heat  accounted  for  was  only  from  3-4ths  to 
4-5ths  of  that  which  is  developed  in  the  same  space  of  time.     The  results 
obtained  by  Despretz  were  very  similar ;  for  he  found  that  the  Heat  that 
would  be  generated  by  the  union  with  Oxygen  of  a  given  amount  of  Carbon 
and  Hydrogen,  was  only  from  3-4ths  to  9-10ths  of  that  which  would  be  set 
free  by  an  animal,  in  the  time  necessary  to  exhale  from  the  skin  and  lungs  a 
corresponding  amount  of  Carbonic  acid  and  of  Watery  vapour.   Although  the 
attempt  has  been  made  by  Liebig  to  invalidate  these  results,  yet  there  are 
other  reasons  that  tend  to  the  same  conclusions.     Thus  we  have  no  proof 
whatever  that  the  Watery  vapour  which  passes  off  from  the  Lungs,  is,  any 
more  than  that  transpired  from  the  skin,  a  product  of  the  Combustion  of  Hy- 
drogen ;  it  is  just  as  likely  to  be  a  simple  product  of  exhalation  from  the 
Blood,  recently  diluted  by  the  introduction  of  Chyle,  which  contains  a  large 

proportion  of  fluid.  Again,  there  are  many  other  uses  for  the  Oxygen  ab- 
~sorbed  from  the  air  (according  to  Liebig's  own  showing)  within  the  system  ; 
such,  for  example,  as  the  oxidation  of  the  Sulphur  and  Phosphorus,  which 
pass  off  in  the  form  of  acids  by  the  Urine ;  or  the  combination  of  Oxygen,  in 
various  proportions,  with  Protein,  in  its  metamorphosis  into  the  elements  of 
the  various  tissues.  Hence  it  is  evident  that  the  Chemical  doctrine,  in  its 
present  form,  is  insufficient  to  explain  the  phenomena  of  Animal  Calorifica- 
tion ;  but  there  can  be  little  doubt  that  an  increased  knowledge  of  the  Molecu- 
lar changes  which  go  on  within  the  system,  will  afford  a  solution  of  the  diffi- 
culty.— At  present,  then,  it  may  be  stated  as  a  general  fact,  that  the  production 
of  Animal  Heat  is  due  to  the  various  changes  in  Chemical  composition  that 
are  continually  taking  place  within  the  system  ;  of  which  changes,  the  absorp- 
tion of  Oxygen,  and  the  disengagement  of  Carbonic  Acid,  are  the  two  chief 
external  manifestations : — and  that  the  degree  of  Caloric  liberated  bears  a 
close  relation  to  the  activity  of  these  changes,  either  in  regard  to  the  body  at 
large,  or  to  any  portion  of  it. 

728.  The  researches  of  Dr.  Edwards  upon  Animal  Heat  have  brought  to 
light  some  very  interesting  facts  regarding  the  diversity  which  exists  as  to  the 
power  of  generating  heat  in  the  same  species  of  animal  at  different  ages, 
and  at  different  periods  of  the  year.     It  appears  to  be  a  general  fact  that  the 
younger  the  animal  the  less  is  its  independent  calorifying  power.     The  de- 


DEVELOPMENT  OF  HEAT. 


581 


velopment  of  the  embryo  of  oviparous  animals  is  entirely  dependent  upon  the 
amount  of  external  warmth  supplied  to  it ;  and  there  are"  many  kinds  of  Birds, 
which,  at  the  time  they  issue  from  the  egg,  are  so  deficient  in  the  power  of 
generating  heat,  that  the  temperature  rapidly  falls,  when  they  are  removed 
from  the  nest  and  placed  in  a  cold  atmosphere.  It  was  shown  by  collateral 
experiments,  that  the  loss  of  heat  was  not  to  be  attributed  to  the  absence  of 
feathers,  nor  to  the  extent  of  surface  exposed  in  comparison  with  the  bulk  of 
the  body;  and  that  nothing  but  an  absolute  deficiency  in  the  power  of  gene- 
rating it  would  account  for  the  fall  of  temperature.  This  is  quite  conformable 
to  facts  well  ascertained  in  regard  to  Mammalia.  The  foetus,  during  intra- 
.  uterine  life,  has  little  power  of  keeping  up  its  own  temperature  ;  and  in  many 
cases  it  is  much  dependent  on  external  warmth,  for  some  time  after  birth. 
The  degree  of  this  dependence,  however,  differs  greatly  in  the  various  species 
of  Mammalia,  as  among  Birds  ;  being  less,  in  proportion  as  the  general  deve- 
lopment is  advanced.  Thus,  young  Guinea-pigs,  which  can  run  about  and 
pick  up  food  for  themselves  almost  as  soon  as  they  are  born,  are  from  the  first 
independent  of  parental  warmth;  whilst,  on  the  other  hand,  the  young  of 
Dogs,  Cats,  Rabbits,  &c.,  which  are  born  blind,  and  which  do  not,  for  a  fort- 
night or  more,  acquire  the  same  development  with  the  preceding,  rapidly  lose 
their  heat  when  withdrawn  from  contact  with  the  body  of  the  mother.  In  the 
Human  species  it  is  well  known,  that  external  warmth  is  necessary  for  the 
Infant ;  but  the  fact  is  too  often  neglected  (under  the  erroneous  idea  of  hard- 
ening the  constitution)  during  the  early  years  of  childhood.  It  is  to  be  care- 
fully remembered,  that  the  development  of  Man  is  slower  than  that  of  any 
other  animal ;  and  that  his  calorifying  power  is  closely  connected  with  his  gene- 
ral bodily  vigour.  In  the  case  of  children  born  very  prematurely,  the  greatest 
attention  must  be  given  to  the  sustenance  of  the  heat  of  the  body  (§  756);  and 
though  the  infant  becomes  more  independent  of  it  as  development  advances,  it 
is  many  years  before  the  standard  can  be  maintained  without  assistance, 
throughout  the  ordinary  vicissitudes  of  external  temperature.  The  calorify- 
ing power,  which  is  fully  possessed  by  adults,  decreases  again  in  advanced 
age.  Old  people  complain  that  their  "  blood  is  chill;"  and  they  suffer  greatly 
from  exposure  to  cold,  the  temperature  of  their  whole  body  being  lowered  by 
it. — These  facts  have  a  very  interesting  connection  with  the  results  of  statisti- 
cal inquiries,  as  to  the  average  number  of  deaths  at  different  seasons,  recorded 
by  M.  Q,uetelet.* 


First 
Month. 

2-3 
Years. 

8-12 
Years. 

25-30 
Years. 

50-65 
Years. 

90  Years 
and  above. 

January 

1-39 

1-22 

1-08 

1-05 

1-30 

1-58 

February 

1-28 

1-13 

•06 

1-04 

1-22 

1-48 

March 

1-21 

1-30 

•27 

I'll 

1-11 

1-25 

April 

1-02 

1-27 

1-34 

1-06 

1-02 

0-96 

May 

0-93 

1-12 

•21 

1-02 

0-93 

0-84 

June 

0-83 

0-94 

0-99 

1-02 

0-85 

0-75 

July 

0-78 

0-82 

0-88 

0-91 

0-77 

0-64 

August 

0-79 

0-73 

0-82 

0-96 

0-85 

0-66 

September     - 
October 

0-86 
0-91 

0-76 
0-78 

0-81 
0-76 

0-95 
0-93 

0-89 
0-90 

0-76 
0-74 

November 

0-93 

0-91 

0-80 

0-97 

1-00 

1-03 

December 

1-07 

1-01 

0-96 

0-97 

1-15 

1-29 

We  see  from  this  table  that,  during  the  first  month  of  infant  life,  the  external 
temperature  has  a  very  marked  influence ;  for  the  average  mortality  during 


*  Essai  de  Physique  Sociale,  torn,  i.,  p.  197. 
49* 


583  GENERAL  REVIEW  OF  THE  NUTRITIVE  FUNCTIONS. 

each  of  the  three  summer  months  being  80,J;hat  of  January  is  nearly  140,  and 
the  average  of  February  and  March  is  125.  This  is  confirmed  by  the  result 
obtained  by  MM.  Villerme  and  Milne-Edwards  in  their  researches  on  the  mor- 
tality of  the  children  conveyed  to  the  Foundling  Hospitals  in  the  different 
towns  in  France ;  for  they  not  only  ascertained  that  the  mortality  is  much  the 
greatest  during  the  first  three  months  in  the  year,  but  also  that  it  varies  in  dif- 
ferent parts  of  the  kingdom,  according  to  the  relative  severity  of  the  winter. 
As  childhood  advances,  however,  the  winter  mortality  diminishes,  whilst  that 
of  the  spring  undergoes  an  increase  ;  this  is  probably  due  to  the  greater  preva- 
lence of  certain  epidemics  at  the  latter  season ;  for  the  same  condition  is 
observed,  in  a  still  more  remarkable  degree,  between  the  ages  of  8  and  12 
years, — the  time  when  children  are  most  severely  affected  by  such  epidemics. 
As  the  constitution  requires  greater  vigour,  and  the  bodily  structure  attains  its 
full  development,  the  influence  of  the  season  upon  mortality  becomes  less  appa- 
rent ;  so  that,  at  the  age  of  from  25  to  30  years,  the  difference  between  the 
summer  and  winter  mortality  is  very  slight.  This  difference  reappears,  how- 
ever, in  a  very  marked  degree,  at  a  later  period,  when  the  general  vigour,  and 
the  calorifying  power,  undergo  a  gradual  diminution.  Between  the  ages  of 
50  and  65  it  is  nearly  as  great  as  in  early  infancy ;  and  it  gradually  becomes 
more  striking,  until,  at  the  age  of  90  and  upwards,  the  deaths  in  January  are 
158  for  every  64  in  July  (a  proportion  of  2£  to  1) ;  and  the  average  of  the 
three  winter  months  is  145,  whilst  that  of  the  three  summer  months  is  only 
68,  or  less  than  one-half. 

729.  Not  only  does  the  same  individual  possess  different  degrees  of  calori- 
fying power,  at  different  periods  of  his  life ;  but  also  at  different  parts  of  the 
year.     Dr.  Edwards  found  that  Sparrows,  when  exposed  for  some  time  to  a 
temperature  of  32°  during  the  summer,  rapidly  lost  heat,  the  refrigeration 
during  3  hours  being  from  6  to  21  degrees;  but  that,  when  they  were  placed 
in  the  same  circumstances  during  winter  (after  having  been  accustomed  to  a 
warm  temperature),  the  refrigeration  was  much  less,  not  being  in  any  instance 
more  than  2°  in  3  hours.     Although  it  would  be  difficult  to  prove  the  fact 
experimentally  in  regard  to  Man,  there  can  be  little  doubt  that  he  shares  with 
the  other  Mammalia  in  this  variation.     It  is  well  known  that  the  general 
vigour  of  the  system  is  less  in  summer  than  in  winter ;  in  hot  climates,  than 
in  moderately  cold.     Moreover,  we  continually  experience  the  great  discom- 
forts of  a  cold  day  in  summer;  when,  our  system  not  being  prepared  for  it, 
we  can  less  readily  maintain  our  temperature  at  its  normal  standard.     The 
practical  inference, — that  we  should  be  much  on  our  guard  against  exposure 
to  low  temperatures  during  summer, — is  one  of  much  importance ;  and  its 
value  has  been  fully  confirmed  by  experience.     The  same  principle  may  also 
be  applied  to  the  explanation  of  the  well-known  fact,  that  those  who  have  been 
long  resident  in  warm  climates  feel  the  cold  acutely ;  whilst  those  who  have 
been  inured  to  cold  are  able  to  resist  it  much  better  than  those  who  are  exposed 
to  it  for  the  first  time.     The  former  have  a  continued  summer  constitution ; 
and  their  system  not  being  called  upon  by  its  external  conditions  to  produce 
much  heat,  the  power  is  after  a  time  partially  lost.     On  the  other  hand,  those 
who  live  in  cold  climates  have  a  perpetual  winter  constitution  (as  it  were) 
established ;  and  the  amount  of  heat  generated  by  them  is  much  greater.     It 
will  be  obvious  that  this  must  be  the  case,  if  Man's  capability  of  living  under 
the  greatest  varieties  of  climate  be  sufficiently  considered.     From  Dr.  E.'s 
experiments  it  appears,  that  every  month  makes  an  evident  difference  in  the 
seasonal  degree ;  the  heat  lost  by  Sparrows  in  August  being  much  less  than 
that  lost  by  birds  of  the  same  species  in  July. 

730.  Our  knowledge  of  the  dependence  of  all  the  vital  processes  in  warm- 
blooded animals,  upon  the  Heat  of  their  bodies, — and  of  the  dependence  of 


DEVELOPMENT  OF  HEAT.  583 

their  Calorifying  power  upon  the  due  supply  of  material  for  the  Chemical 
changes  which  generate  Heat,— has  lately  received  some  very  remarkable 
additions  from  the  experiments  of  M.  Chossat.*  He  found  that  Birds,  when 
totally  deprived  of  food  and  drink,  suffered  a  progressive,  though  slight,  daily 
diminution  of  temperature.  This  diminution  was  not  so  much  shown  by  a 
fall  of  their  maximum  heat,  as  by  an  increase  in  the  diurnal  variation,  which 
he  ascertained  to  occur  even  in  the  normal  state.  The  amount  of  this  varia- 
tion, in  Birds  properly  supplied  with  food,  is  about  1^°  Fahr.  daily;  the 
maximum  being  about  noon,  and  the  minimum  at  midnight.  In  the  inaniti- 
ated  state,  however,  the  average  variation  was  about  6°,  gradually  increasing 
as  the  animal  became  weaker:  moreover,  the  gradual  rise  of  temperature, 
which  should  have  taken  place  between  midnight  and  noon,  was  retarded ; 
whilst  the  fall  subsequently  to  noon  commenced  much  earlier  than  in  the 
healthy  state  :  so  that  the  average  of  the  whole  day  was  lowered  by  about  4^° 
between  the  first,  and  the  penultimate  days  of  this  condition.  On  the  last  day, 
the  production  of  Heat  diminished  very  rapidly,  and  the  thermometer  fell  from 
hour  to  hour,  until  death  supervened ;  the  whole  loss  on  that  day  being  about 
25°  Fahr.,  making  the  total  depression  about  295°.  This  depression  appears, 
from  the  considerations  to  be  presently  stated,  to  be  the  immediate  cause  of 
Death. — On  examining  the  amount  of  loss  sustained  by  the  different  organs  of 
the  body,  it  was  found  that  93  per  cent,  of  the  Fat  had  disappeared,- — all,  in 
fact,  which  could  be  removed ;  whilst  the  Nervous  Centres  scarcely  exhibited 
any  diminution  in  weight.  The  loss  of  weight  of  the  whole  body  averaged 
about  40  per  cent. ;  and  that  of  the  various  other  component  tissues  was  very 
much  what  might  have  been  anticipated.  From  the  constant  coincidence 
between  the  entire  consumption  of  the  Fat,  and  the  depression  of  Tempera- 
ture,— joined  to  the  fact  that  the  duration  of  life  under  the  inanitiating  process 
evidently  varied  (other  things  being  equal)  with  the  amount  of  Fat  previously 
accumulated  in  the  body, — the  inference  seems  irresistible,  that  the  Calorify- 
ing power  depended  chiefly,  if  not  entirely,  on  the  materials  supplied  by  this 
substance.  The  maintenance  of  the  normal  amount  of  matter  in  the  Nervous 
centres  is  a  very  remarkable  fact ;  and  seems  to  countenance  the  idea  formerly 
suggested,  that  the  substances  peculiar  to  Nervous  tissue  may  be  formed  from 
Fatty  matter  rather  than  from  a  Protein-compound  (§  77).  Whenever,  there- 
fore, the  store  of  combustible  matter  in  the  system  was  exhausted, — whether 
by  the  Respiratory  process  alone,  or  by  this  in  conjunction  with  the  conversion 
of  Adipose  matter  into  the  materials  for  the  Nervous  or  other  tissues,— the 
inanitiated  animals  died,  by  the  cooling  of  their  bodies  consequent  upon  the 
loss  of  Calorifying  power.  That  this  is  the  real  explanation  of  the  fact,  is 
shown  by  the  results  of  a  series  of  very  remarkable  experiments  performed  by 
M.  Chossat,  with  a  view  of  testing  the  correctness  of  this  view.  When  inani- 
tiated animals,  whose  death  seemed  impending,  (in  several  instances  death 
actually  took  place,  whilst  the  preliminary  processes  of  weighing,  the  applica- 
tion of  the  thermometer,  &c.,  were  being  performed,)  were  subjected  to  artifi- 
cial heat,  they  were  almost  uniformly  restored  from  a  state  of  insensibility  and 
want  of  muscular  power  to  a  condition  of  comparative  activity ;  their  tempera- 
ture rose,  their  muscular  power  returned,  they  flew  about  the  room  and  took 
food  when  it  was  presented  to  them ;  and,  if  the  artificial  assistance  was  suffi- 
ciently prolonged,  and  they  were  not  again  subjected  to  the  starving  process, 
most  of  them  recovered,  'if  they  were  left  to  themselves  too  early,  however, 
the  digestive  process  was  not  performed,  and  they  ultimately  died.  Up  to  the 
time  when  they  began  to  take  food,  their  weight  continued  to  diminish ;  the 

*  Rec.herches  Experimentales  sur  1'Inanition,  Paris,  1843.    See,  also,  the  Brit,  and  For. 
Med.  Rev.  for  April,  1>44. 


584  GENERAL  REVIEW  OF  THE  NUTRITIVE  FUNCTIONS. 

secretions  being  renewed,  under  the  influence  of  artificial  heat,  sometimes  to 
a  considerable  amount.  It  is  not  until  Digestion  has*  actually  taken  place 
(which,  owing  to  the  weakened  functional  power,  is  commonly  many  hours 
subsequently  to  the  ingestion  of  the  food),  that  the  animal  regains  its  power  of 
generating  heat ;  so  that,  if  the  external  source  of  heat  is  withdrawn,  the  body 
at  once  cools :  and  it  is  not  until  the  quantity  of  food  actually  digested  is  suffi- 
cient to  support  the  wants  of  the  body,  that  its  independent  power  of  Calorifica- 
tion returns.  It  is  to  be  remembered  that,  in  such  cases,  the  resources  of  the 
body  are  on  the  point  of  being  completely  exhausted,  when  the  attempt  at  re- 
animation  is  made  ;  consequently  it  has  nothing  whatever  to  fall  back  upon ; 
and  the  leaving  it  to  itself  at  any  time  until  fresh  resources  have  been  pro- 
vided for  it,  is  consequently  as  certain  a  cause  of  death  as  it  would  have  been 
in  the  first  instance. — It  can  scarcely  be  questioned,  from  the  similarity  of  the 
phenomena,  that  Inanitiation,  with  its  consequent  depression  of  temperature, 
is  the  immediate  cause  of  death  in  various  Diseases  of  Exhaustion ;  and  it 
seems  probable  that  there  are  many  cases,  in  which  the  depressing  cause  is  of 
a  temporary  nature,  and  in  which  a  judicious  and  timely  application  of  artifi- 
cial Heat  might  prolong  life  until  it  has  passed  off, — just  as  artificial  Respira- 
tion is  serviceable  in  cases  of  Narcotic  Poisoning  (§  74).  It  is  especially, 
perhaps,  in  those  forms  of  Febrile  disease,  in  which  no  decided  lesion  can  be 
discovered  after  death,  that  this  view  has  the  strongest  claim  to  reception  ;  but 
many  other  cases  will  occur  to  the  intelligent  Practitioner.* 

731.  Having  thus  considered  the  means,  by  which  the  degree  of  Heat 
necessary  for  the  performance  of  the  functions  of  the  Human  system  is  gene- 
rated, we  have  to  inquire  how  its  temperature  is  prevented  from  being  raised 
too  high ;  in  other  words,  what  Frigorifying  means  there  are,  to  counter- 
balance the  influence  of  causes,  which  in  excess  would  otherwise  be  fatal,  by 
raising  the  heat  of  the  body  to  an  undue  degree.  How  is  it,  for  example,  that 
when  a  person  enters  a  room  whose  atmosphere  is  heated  to  one  or  two  hundred 
degrees  above  his  body,  the  latter  does  not  partake  of  the  elevation,  even  though 
exposed  to  the  heat  for  some  time  ?  Or,  since  the  inhabitants  of  a  climate 
where  the  thermometer  averages  100°  for  many  weeks  together,  are  continu- 
ally generating  additional  heat  in  their  own  bodies,  how  is  it  that  this  does  not 
accumulate,  and  raise  them  to  an  undue  elevation  ?  The  means  provided  by 
Nature  for  cooling  the  body  when  necessary,  are  of  the  simplest  possible  cha- 
racter. From  the  whole  of  its  soft  moist  surface,  simple  Evaporation  will  take 
place  at  all  times,  as  from  an  inorganic  body  in  the  same  circumstances  ;  and 
the  amount  of  this  will  be  regulated  merely  by  the  condition  of  the  atmosphere, 
as  to  warmth  and  dryness.  The  more  readily  watery  vapour  can  be  dissolved 
in  atmospheric  air,  the  more  will  be  lost  from  the  surface  of  the  body  in  this 
manner.  In  cold  weather,  very  little  is  thus  carried  off,  even  though  the  air 
be  dry ;  and  a  warm  atmosphere,  already  charged  with  dampness,  will  be 
nearly  as  ineffectual.  But  simple  evaporation  is  not  the  chief  means  by  which 
the  temperature  of  the  body  is  regulated.  The  Skin,  as  already  mentioned 
(§  699),  contains  a  large  number  of  glandulse,  the  office  of  which  is  to  secrete 
an  aqueous  fluid  ;  and  the  amount  of  this  Exhalation  appears  to  depend  solely 

*  The  beneficial  result  of  the  administration  of  Alcohol  in  such  conditions,  and  the 
large  amount  in  which  it  may  be  given  with  impunity,  may  probably  be  accounted  for 
on  this  principle.  That  it  is  a  specific  stimulus  to  the  Nervous  system,  cannot  be  doubted 
from  its  effects  on  the  healthy  body;  but  that  it  serves  as  a  fuel  to  keep  up  the  Calorify- 
ing  process,  appears  equally  certain.  Now  its  great  efficacy  in  such  cases  seems  to 
depend  upon  the  readiness  with  which  it  will  be  taken  into  the  Circulation,  by  a  simple 
act  of  Endosmotic  Imbibition,  when  the  special  Absorbent  process,  dependent  upon  the 
peculiar  powers  of  the  cells  of  the  villi  (§  462),  are  in  abeyance.  There  is  no  other 
combustible  fluid,  whose  density,  relatively  to  that  of  the  Blood,  will  permit  of  its  rapid 
Absorption  by  the  simple  physical  process  adverted  to. 


OF  REPRODUCTION.  585 

or  chiefly  upon  the  temperature  of  the  surrounding  air.  Thus,  when  the 
external  heat  is  very  great,  a  considerable  amount  of  fluid  is  transuded  from 
the  skin  ;  and  this,  in  evaporating,  converts  into  latent  heat  a  large  quantity  of 
the  free  caloric,  which  would  otherwise  raise  the  temperature  of  the  body.  If 
the  atmosphere  be  hot  and  dry,  and  also  be  in  motion,  both  Exhalation  and 
Evaporation  go  on  with  great  rapidity.  If  it  be  cold,  both  are  checked, — the 
former  almost  entirely  so ;  but  if  it  be  dry,  some  evaporation  still  continues. 
On  the  other  hand,  in  a  hot  atmosphere,  saturated  with  moisture,  Exhalation 
continues,  though  Evaporation  is  almost  entirely  checked ;  and  the  fluid  poured 
out  by  the  exhalant  glands  accumulates  on  the  skin.  There  is  reason  to  believe 
that  the  secretion  continues,  even  when  the  body  is  immersed  in  water,  pro- 
vided its  temperature  be  high. — We  learn  from  these  facts  the  great  import- 
ance of  not  suddenly  checking  Exhalation,  by  exposure  of  the  surface  to  cold, 
when  the  secretion  is  being  actively  performed ;  since  a  great  disturbance  of 
the  circulation  will  be  likely  to  ensue,  similar  to  that  which  has  been  already 
mentioned,  as  occurring  when  other  important  secretions  are  suddenly  sus- 
pended. 


CHAPTER    XIV. 

OF    REPRODUCTION. 

I.   General  character  of  the  Function. 

732.  THE  Function  of  Reproduction  has  been  commonly  regarded  as  so 
entirely  different  in  character  from  the  ordinary  Nutritive  processes,  that  no 
analogy  can  be  drawn  between  them.  The  results  of  late  inquiries,  however, 
leave  no  doubt  that  the  difference  between  them  is  extremely  small,— having, 
in  fact,  a  relation  rather  to  the  object  of  the  action,  than  to  the  mode  in  which 
it  is  performed.  In  the  ordinary  function  of  Nutrition,  there  is  a  continual 
regeneration  or  reproduction  of  the  tissues  and  organs  of  the  body ;  but  the 
new  parts  are  destined  still  to  constitute  the  same  whole.  On  the  other  hand, 
in  Reproduction,  the  newly-formed  parts  are  destined  from  the  first  to  be  cast 
off  from  the  parent  structure,  and  to  become  new  individuals.  Still  their 
origin  is  essentially  the  same  in  both  instances ;  as  appears  from  the  mode  in 
which  the  multiplication  of  the  lower  Plants  and  Animals  takes  place.  Thus 
in  the  simplest  Cryptogamia,  such  as  the  Yeast  Fungus,*  every  single  cell 
may  be  regarded  as  a  distinct  individual ;  since  it  is  capable  of  living  by  itself, 
and  of  generating  new  cells  ;  and  thus  the  production  of  a  new  cell,  in  con- 
nection with  the  original  one,  may  be  regarded  as  alike  an  act  of  Nutrition 
and  of  Reproduction.  So  again  in  the  Hydra  and  other  Polypes,  the  remark- 
able power  of  reparation  which  is  manifested  in  their  Nutritive  operations, 
may  be  employed  in  generating  new  individuals ;  since,  when  the  body  is 
divided  into  numerous  parts,  each  one  of  these  has  the  power  of  developing 
all  the  rest  of  the  structure,  and  thus  of  becoming  a  complete  animal  (§  21). 

*  See  Principles  of  General  and  Comparative  Physiology,  §  98. 


586  OF' REPRODUCTION. 

Still  we  find  in  most  Plants,  and  in  all  Animals,  some  portion  of  the  structure 
specially  designed  to  form  and  to  set  free  germs,  which  are  destined  to  become 
new  individuals ;  and  it  is  in  the  liberation  and  development  of  these,  that  the 
function  of  Reproduction  essentially  consists.  In  Plants  it  is  very  evident  that 
these  germs  differ  but  little  from  those  which  elsewhere  produce  new  cells 
(§  557) ;  and  that  the  first  aspect  of  the  new  being  is  neither  more  nor  less 
than  a  single  cell,  in  which  all  the  other  cells  of  the  structure  subsequently 
originate.  In  the  Cryptogamia,  the  cell-germs  are  contained  in  what  is  termed 
the  spore ;  and  when  liberated  from  the  parent,  they  are  developed  into  cells 
without  any  further  assistance  than  that  which  they  derive  from  the  air, 
moisture,  &c.,  that  surround  them.  In  Flowering  Plants,  on  the  other  hand, 
the  cell-germs  are  converted  into  a  new  set  of  organs,  in  which  they  are  sup- 
plied with  nutriment  previously  elaborated  for  them  by  the  parent ;  and,  in 
this  manner,  they  are  enabled  to  attain  an  ultimate  development,  which  is 
much  higher  than  that  of  the  Cryptogamia.  It  is  now  well  established,  that 
the  pollen-grain  of  Phanerogamia  is  analogous  to  the  spore  of  Cryptogamia ; 
since  it  contains  the  reproductive  granules,  which  are  the  germs  of  the  first 
cells  of  the  new  individual.  When  the  pollen-grains  are  cast  upon  the  stig- 
matic  surface,  they  project  one  or  more  long  tubes,  which  insinuate  themselves 
down  the  soft  loose  tissues  of  the  style,  and  reach  the  ovarium.  Into  these 
tubes,  the  granules  which  the  pollen-grain  contained  are  seen  to  pass ;  and 
they  are  thus  conveyed  into  the  ovules,  the  foramina  of  which  are  penetrated 
by  the  extremities  of  the  pollen-tubes.  The  ovules  previously  contained 
nothing  but  starchy  matter :  but  from  the  time  that  the  pollen-tubes  have 
thus  implanted  (as  it  were)  their  contents  in  their  cavity,  they  may  be  con-s 
sidered  as  fecundated.  The  subsequent  growth  of  the  embryo  from  the  first- 
formed  cells,  takes  place  according  to  the  principles  already  stated,  under  the 
head  of  Nutrition ;  and  thus  it  is  seen,  that  the  mysterious  process  of  Repro- 
duction evidently  consists,  in  Flowering  Plants,  of  nothing  else  than  the 
implantation  of  a  cell-germ  prepared  by  the  male  organs,  in  a  nidus  or  recep- 
tacle adapted  to  aid  its  early  development,  which  nidus  constitutes  the  essen- 
tial part  of  the  female  system. 

733.  There  is  now  good  reason  to  believe  that  in  no  Animals  is  the  Re- 
productive apparatus  less  simple  than  it  is  in  the  higher  Plants : — that  is  to 
say,  in  every  instance,  two  sets  of  organs,  a  germ-preparing  and  a  germ- 
nourishing ',  are  present.  These  organs  differ  much  in  form  and  complexity 
of  structure,  in  the  various  tribes  of  Animals ;  but  their  essential  function  is 
the  same  in  all.  Those  which  are  termed  male  organs  prepare  and  set  free 
certain  bodies,  which,  having  an  inherent  power  of  motion,  have  been  sup- 
posed to  be  independent  Animalcules,  and  have  been  termed  Spermatozoa ; 
there  is  but  little  reason,  however,  to  regard  them  in  this  light,  since  ciliated 
epithelium-cells  may  exhibit  as  much  activity ;  and  there  is  no  evidence  that 
their  function  is  any  higher  than  that  of  the  pollen-tube  of  Plants,  which  con- 
veys into  the  ovulum  the  germs  of  the  first  cells  of  the  embryo.  This  view 
of  the  character  of  the  Spermatozoa  rests  alike  upon  the  nature  of  their 
movements,  and  the  mode  of  their  production.*  Dr.  Barry's  observations  on 
the  history  of  the  Ovum,  and  on  the  nature  of  the  act  of  Fecundation  (which 
will  be  presently  given  in  some  detail)  have  left  scarcely  any  doubt,  that  this 
act  consists  in  the  introduction  of  some  new  element  into  the  Ovule,  through 
the  medium  of  the  Spermatozoa ;  the  arrival  of  which  at  the  surface  of  the 
ovary  had  been  more  than  once  previously  seen,  and  the  penetration  of  which 
to  the  ovum  there  was  good  reason  to  suspect ;  and  these  have  been  confirmed 
by  the  observations  of  Dr.  A.  Farre  on  the  Ovum  of  the  Earth-worm,  which 

*  See  Principles  of  General  and  Comparative  Physiology,  §  006. 


ACTION  OF  THE  MALE.  587 

lie  has  distinctly  seen  to  be  penetrated  by  Spermatozoa.  The  act  of  Fecun- 
dation is  evidently  analogous,  therefore,  in  Animals,  to  the  process  which  has 
been  described  as  taking  place  in  the  Flowering  Plants.  In  many  of  the 
lower  tribes  of  Animals,  the  spermatic  fluid  effused  by  an  individual  of  one 
sex  comes  into  direct  contact  with  the  ova  previously  deposited  by  the  other ; 
but  in  all  the  higher  tribes,  as  in  Man,  the  act  of  fecundation  is  performed 
before,  or  shortly  after  the  ova  quit  the  ovarium.  With  these  general  views, 
we  shall  now  be  prepared  to  consider  the  share  which  each  sex  has  in  the 
Function  of  Reproduction. 

II.  Action  of  the  Male. 

734.  The  Spermatic  fluid  secreted  by  the  Testes  of  the  Male  (§  700),  differs 
from  all  other  secretions,  in  containing  a  large  number  of  very  minute  bodies, 
only  discernible  with  a  higher  power  of  the  Microscope  ;  and  these,  in  ordi- 
nary cases,  remain  in  active  motion  for  some  time  after  they  have  quitted  the 
living  body.     The  Human  Spermatozoon  (of  which  representations  are  given 
in  Plate  I.,  Fig.  18),  consists  of  a  little  oval  flattened  body  from  the  l-600th  to 
the  l-800th  of  a  line  in  length,  from  which  proceeds  a  long  filiform  tail,  gradu- 
ally tapering  to  the  finest  point,  of  l-50th  or  at  most  l-40th  of  a  line  in  length. 
The  whole  is  perfectly  transparent ;  and  nothing  that  can  be  termed  structure 
can  be  satisfactorily  distinguished  within  it.*     The  movements  are  principally 
executed  by  the  tail,  which  has  a  kind  of  vibratile  undulating  motion.     They 
may  continue  for  many  hours  after  the  emission  of  the  fluid ;  and  they  are  not 
checked  by  its  admixture  with  other  seminal  secretions,  such  as  the  urine  and 
the  prostatic  fluid.     Thus,  in  cases  of  nocturnal  emission,  the  Spermatozoa 
may  not  unfrequently  be  found  actively  moving  through  the  urine  in  the  morn- 
ing ;  and  those  contained  in  the  seminal  fluid  collected  from  females  that  have 
just  copulated,  are  frequently  found  to  live  many  days.     Their  presence  may 
be  readily  detected  by  a  Microscope  of  sufficient  power,  even  when  they  have 
long  ceased  to  move,  and  are  broken  into  fragments;  and  the  Physician' and 
the  Medical  Jurist  will  frequently  derive  much  assistance  from  an  examination 
of  this  kind.     Thus,  cases  are  of  no  uncommon  occurrence,  especially  among 
those  who  have  been  too  much  addicted  to  sexual  indulgence,  in  which  seminal 
emissions  take  place  unconsciously  and  frequently,  and  produce  great  general 
derangement  of  the  health ;  and  the  true  nature  of  the  complaint  is  obscure, 
until  the  fact  has  been  detected  by  ocular  examination.     Again,  in  charges 
of  rape,  in  which  evidence  of  actual  emission  is  required,  a  microscopic  exami- 
nation of  the  stiffened  spots  left  on  the  linen  will  seldom  fail  in  obtaining  proof, 
if  the  act  have  been  completed:  in  such  cases,  however,  we  must  not  expect 
to  meet  with  more  than  fragments  of  Spermatozoa?;  but  these  are  so  unlike  any 
thing  else,  that  little  doubt  need  be  entertained  regarding  them.     It  has  been 
proposed  to  employ  the  same  test  in  juridical  inquiries  respecting  doubtful 
cases  of  death  by  suspension;  seminal  emissions  being  not  unfrequent  results 
of  this  kind  of  violence  :  but  there,  are  many  obvious  objections  which  should 
prevent  much  confidence  being  placed  in  it.t 

735.  The  mode  of  Evolution  of  Spermatozoa,  which  has  been  recently  dis- 
covered by  Wagner,  is  so  different  from  the  ordinary  method  of  production 
amongst  Animalcules,  as  of  itself  to  indicate  that  the  former  cannot  be  referred 

*  It  has  been  asserted  that  distinct  oral  and  anal  orifices,  with  appearances  of  internal 
organs,  have  been  seen  in  the  Spermatozoa  of  certain  Mammalia:  but  these  observations 
have  not  been  confirmed;  and  they  are  not  borne  out  by  the  attentive  examination  of  the 
larger  Spermatozoa  of  other  animals. 

|  See  the  Author's  Article  "Asphyxia,"  in  the  Library  of  Practical  Medicine,  and  the 
authorities  there  referred  to. 


588  OF  REPRODUCTION. 

to  the  same  category  with  the  latter.  It  may  be  best  studied  in  those  animals 
which  only  have  a  periodical  fertility ;  and  the  Passerine  Birds  are  among  the 
most  convenient  subjects  for  the  purpose.  During  the  winter,  the  testes  are 
small  and  almost  bloodless,  and  no  trace  of  Spermatozoa  can  be  detected  within 
them ;  on  the  return  of  spring,  however,  they  undergo  great  enlargement  and 
become  almost  gorged  with  blood,  and  the  gradual  steps  of  the  evolution  of  the 
Spermatozoa  may  be  easily  observed.  The  fluid  drawn  from  them  is  first  seen 
to  contain  a  number  of  granular  corpuscles,  resembling  those  known  as  the 
Seminal  Granules- in  the  human  semen  (delineated  at  #,  Fig.  18,  Plate  I.) ; 
and  in  a  short  time  there  are  seen,  in  addition  to  these,  numerous  rounded 
transparent  vesicles,  at  first  having  but  one  nucleus,  and  afterwards  presenting 
several.  v  These  nuclei  bear  a  close  resemblance  to  the  granular  corpuscles  just 
mentioned  ;  and  it  is  probable  that  the  former  are  to  be  regarded  as  cytoblasts, 
from  which  the  Spermatoferous  cells  (shown,  as  existing  in  the  human  semen, 
in  Fig.  19,  Plate  I.)  are  evolved.  The  nuclei  seem  afterwards  to  resolve  them- 
selves into  a  fine  granular  matter,  which  is  diffused  through  the  whole  vesicle 
or  "cyst  of  evolution;"  and  in  this,  a  linear  arrangement  soon  becomes  per- 
ceptible. The  lines  become  more  and  more  distinct,  and  are  at  last  seen  to  be 
evidently  produced  by  the  arrangement  of  the  Spermatozoa,  which  lie  side  by 
side  within  the  vesicle ;  and  the  form  of  this  changes  from  a  sphere  to  a  long 
oval.  After  a  time  they  break  forth,  but  still  adhere  to  each  other  for  a  short 
period,  forming  bundles,  such  as  may  often  be  met  with  in  the  human  semen, 
when  taken  directly  from  the  testis  (Fig.  20,  Plate  I.).*  That  the  Spermatozoa 
are  the  essential  elements  of  the  spermatic  fluid,  has  been  reasonably  inferred 
from  several  circumstances,  such  as  their  absence  or  imperfect  development  in 
hybrid  animals,  which  are  nearly  or  entirely  sterile :  and  the  fact  that  Fecun- 
dation essentially  consists  in  the  direct  communication  of  one  of  them  with  a 
certain  -point  in  the  Ovum,  appears  too  well  established  to  admit  of  further 
doubt.  Regarding  the  uses  of  the  other  constituents  of  the  Semen,  no  suffi- 
cient account  can  be  given. 

736.  The  power  of  procreation  does  not  usually  exist  in  the  Human  Male, 
until  the  age  of  from  14  to  16  years ;  and  it  may  be  considered  probable  that 
no  Spermatozoa  are  produced  until  that  period,  although  a  fluid  is  secreted  by 
the  testes.  At  this  epoch,  which  is  ordinarily  designated  as  that  of  Puberty, 
a  considerable  change  takes  place  in  the  bodily  constitution :  the  sexual  organs 
undergo  a  much-increased  development ;  various  parts  of  the  surface,  especially 
the  chin  and  the  pubes,  become  covered  with  hair ;  the  larynx  enlarges,  and 
the  voice  becomes  lower  in  pitch,  as  well  as  rougher  and  more  powerful;  and 
new  feelings  and  desires  are  awakened  in  the  mind.  Instances,  however,  are 
by  no  means  rare,  in  which  these  changes  take  place  at  a  much  earlier  period ; 
the  full  development  of  the  generative  organs,  with  manifestations  of  the  sexual 
passion,  having  been  observed  in  children  of  but  a  few  years  old.  The  pro- 
creative  power  may  last,  if  not  abused,  during  a  very  prolonged  period. 
Undoubted  instances  of  virility  at  the  age  of  more  than  100  years  are  on 
record ;  but  in  these  cases,  the  general  bodily  vigour  was  preserve4  in  a  very 
remarkable  degree.  The  ordinary  rule  seems  to  be,  that  sexual  power  is  not 
retained  by  the  male  in  any  considerable  degree,  after  the  age  of  60  or  65 
years.  To  the  use  of  the  sexual  organs  for  the  continuance  of  his  race,  Man 
is  prompted  by  a  powerful  Instinctive  desire,  which  he  shares  with  the  lower 
animals.  This  Instinct,  like  the  others  formerly  alluded  to  (§§  259 — 63),  is 
excited  by  sensations ;  and  these  may  either  originate  in  the  sexual  organs 
themselves,  or  may  be  excited  through  the  organs  of  special  sensation.  Thus 

*  For  a  fuller  account,  with  illustrations,  of  the  development  of  the  Spermatozoa,  and 
its  analogy  with  the  formation  of  other  tissues,  see  Princ.of  Gen.  and  Comp.Phys.§§  430 
and  607. 


ACTION  OF  THE  MALE.  589 

in  Man  it  is  most  powerfully  aroused  by  impressions  conveyed  through  the 
sight  or  the  touch  :  in  many  other  animals,  the  auditory  and  olfactive  organs 
communicate  impressions  which  have  an  equal  power ;  and  it  is  not  improba- 
ble that,  in  certain  morbidly-excited  states  of  feeling,  the  same  may  be  the  case 
in  ourselves.  That  local  impressions  have  also  very  powerful  effect  in  exciting 
sexual  desire,  must  have  been  within  the  experience  of  almost  every  one;  the 
fact  is  most  remarkable,  hotvever,  in  cases  of  Satyriasis,  which  disease  is  gene- 
rally found  to  be  connected  with  some  obvious  cause  of  irritation  of  the  gene- 
rative system,  such  as  pruritus,  active  congestion,  &c.  That  some  part  of  the 
Encephalon  is  the  seat  of  this  as  of  other  instinctive  propensities,  appears  from 
the  considerations  formerly  adduced ;  but  that  the  Cerebellum  is  the  part  in 
which  this  function  is  specially  located,  cannot  be  regarded  as  by  any  means 
sufficiently  proved  (§§  274 — 8).  The  instinct,  when  once  aroused,  (even 
though  very  obscurely  felt,)  acts  upon  the  mental  faculties  and  moral  feelings  : 
and  thus  becomes  the  source,  though  almost  unconsciously  so  to  the  individual, 
of  the  tendency  to  form  that  kind  of  attachment  towards  one  of  the  opposite 
sex,  which  is  known  as  love.  This  tendency  cannot  be  regarded  as  a  simple 
passion  or  emotion,  since  it  is  the  result  of  the  combined  operations  of  the 
reason,  the  imagination,  and  the  moral  feelings ;  and  it  is  in  the  engraftment 
(so  to  speak)  of  the  psychical  attachment  upon  the  mere  corporeal  instinct 
that  a  difference  exists  between  the  sexual  relations  of  Man  and  those  of  the 
lower  animals.  In  proportion  as  the  Human  being  makes  the  temporary 
gratification  of  the  mere  sexual  appetite  his  chief  object,  and  overlooks  the 
happiness  arising  from  spirtual  communion,  which  is  not  only  purer  but  more 
permanent,  and  of  which  a  renewal  may  be  anticipated  in  another  world, — 
does  he  degrade  himself  to  the  level  of  the  brutes  that  perish.  Yet  how 
lamentably  frequent  is  this  degradation ! 

738.  When,  impelled  by  sexual  excitement,  the  Male  seeks  intercourse  with 
the  Female,  the  erectile  tissue  of  the  genital  organs  becomes  turgid  with  blood 
(§  519),  and  the  surface  acquires  a  much-increased  sensibility ;  this  is  espe- 
cially acute  in  the  Glans  penis.  By  the  friction  of  the  Glans  against  the 
rugous  walls  of  the  Vagina,  the  excitement  is  increased ;  and  the  impression 
which  is  thus  produced  at  last  becomes  so  strong,  that  it  produces,  through  the 
medium  of  the  Spinal  Cord,  a  reflex  contraction  of  the  muscles  which  surround 
the  Vesicula3  Seminales  (§  203).  These  receptacles  discharge  their  contents 
(partly  consisting  of  semen  and  partly  of  a  secretion  of  their  own)  into  the 
Urethra ;  and  from  this  they  are  expelled  with  some  degree  of  force,  and  with 
a  kind  of  convulsive  action,  by  its  own  Compressor  muscles.  Now  although 
the  sensations  concerned  in  this  act  are  ordinarily  most  acutely  pleasureable, 
there  appears  sufficient  evidence  that  they-are  by  no  means  essential  to  its  per- 
formance; and  that  the  impression  which  is  conveyed  to  the  Spinal  Cord 
need  not  give  rise  to  a  sensation,  in  order  to  produce  the  reflex  contraction  of 
the  Ejaculator  muscles  (§  182).  The  high  degree  of  nervous  excitement 
which  the  act  of  coition  involves,  produces  a  subsequent  depression  of  cor- 
responding amount ;  and  the  too  frequent  repetition  of  it  is  productive  of  con^ 
sequences  very  injurious  to  the  general  health.  This  is  still  more  the  case 
with  the  solitary  indulgence,  which  (it  is  to  be  feared)  is  practised  by  too  many 
youths  ;  for  this,  substituting  an  unnatural  degree  of  one  kind  of  excitement, 
for  that  which  is  wanting  in  another,  cannot  but  be  still  more  trying  to  the 
bodily  powers.  The  secretion  of  seminal  fluid  being,  like  other  secretions, 
very  much  under  the  control  of  the  nervous  system,  will  be  increased  by  the 
continual  direction  of  the  mind  towards  objects  which  awaken  the  sexual  pro- 
pensity (§  426,  note) ;  and  thus,  if  intercourse  be  very  frequent,  a  much  larger 
quantity  will  altogether  be  produced,  although  the  amount  emitted  at  each 
period  will  be  less.  The  formation  of  the  secretion  seems  of  itself  to  be  a 
50 


590  OF  REPRODUCTION. 

much  greater  tax  upon  the  corporeal  powers,  than  might  have  been  supposed 
a  priori  ;  and  it  is  a  well-known  fact,  that'the  highest  degree  of  bodily  vigour 
is  inconsistent  with  more  than  a  very  moderate  indulgence  in  sexual  inter- 
course ;  whilst  nothing  is  more  certain  to  reduce  the  powers,  both  of  body  and 
mind,  than  excess  in  this  respect.  These  principles,  which  are  of  great 
importance  in  the  regulation  of  the  health,  are  but  results  of  the  general  law, 
which  prevails  equally  in  the  Vegetable  and  Animal  kingdoms, — that  the 
Development  of  the  Individual,  and  the  Reproduction  of  the  Species,  stand  in 
an  inverse  ratio  to  each  other. 

III.  Action  of  the  Female. 

739.  The  essential  part  of  the  Female  Generative  System  is  that  in  which 
the  Ova  are  prepared ;  the  other  organs  are  merely  accessory,  and  are  not  to 
be  found  in  a  large  proportion  of  the  Animal  kingdom.  In  many  of  the  lower 
animals,  the  Ovaria  and  Testes  are  so  extremely  like  each  other,  that  the  dif- 
ference between  them  can  scarcely  be  distinguished  ;  and  the  same  has  already 
been  stated  regarding  the  condition  of  these  organs  in  Man,  at  an  early  period 
of  development  (§  697  b).  The  fact  is  one  of  no  small  interest.  In  the  lower 
animals,  the  Ovarium  consists  of  a  loose  tissue  containing  many  cells,  in  which 
the  Ova  are  formed,  and  from  which  they  escape  by  the  rupture  of  the  cell- 
walls  ;  in  the  higher  animals,  as  in  the  Human  female,  the  tissue  of  the  Ova- 
rium is  more  compact,  forming  what  is  known  as  the  stroma  ;  and  the  Ova, 
except  when  they  are  approaching  maturity,  can  only  be  distinguished  in  the 
interstices  of  this,  by  the  aid  of  a  high  magnifying  power.  We  owe  to  Dr. 
Barry  the  discovery  of  the  earliest  stages  in  the  production  of  the  Ovum  and 
its  accessory  parts,  in  Mammalia  and  other  Vertebrata.  In  order  to  understand 
his  account,  however,  it  will  be  necessary  that  the  parts  of  which  the  ovum 
consists  should  be  previously  understood. — Taking  the  Fowl's  Egg  as  a  fami- 
liar illustration,  it  must  be  remarked,  in  the  first  place,  that  neither  the  albumen 
which  forms  the  white,  nor  the  shell-membrane  with  its  testaceous  covering, 
exists  in  the  Ovarian  Ovum ;  xthese  portions  being  added  during  its  passage 
along  the  oviduct.  The  parts  which  we  have  to  analyze,  are  the  Yolk-mem- 
brane and  its  contents.  Within  the  Yolk-membrane  we  find,  in  the  first  place, 
the  Yolk  itself ;  a  substance  consisting  in  part  of  albuminous  granules,  and  in 
part  of  oily  globules.  Towards  the  centre,  the  character  of  the  Yolk  in  some 
degree  changes ;  its  colour  being  lighter,  and  the  granules  presenting  more 
the  appearance  of  cells,  with  minuter  globules  in  their  interior.  The  central 
portion  is  termed  the  discus  vitellinus.  Occupying  the  centre  of  the  yolk 
(in  the  immature  ovulum)  is  a  large  cell,  very  distinct  in  aspect  from  the 
rest,  and  having  a  well-marked  nucleus  upon  its  walls.  This  is  termed  the 
germinal  vesicle;  and  the  nucleus,  the  germinal  spot. — The  Mammalian 
Ovum  contains  exactly  the  same  parts  ;  but  the  yolk  is  much  smaller  in  pro- 
portion, and  corresponds  in  character  rather  with  the  discus  vitellinus  than 
with  the  whole  yolk  of  the  Bird's  egg.  The  Ovum  in  all  Vertebrated  animals 
is  produced  within  a  capsule  or  bag,  the  exterior  of  which  is  in  contact  with 
the  stroma  of  the  ovarium ;  this  has  been  termed  in  Mammalia,  the  Graafian 
follicle,  after  the  name  of  its  first  discoverer ;  but  the  more  general  and  appro- 
priate designation  of  Ovisac  has  been  given  to  it  by  Dr.  Barry,  who  has  shown 
that  it  exists  in  other  classes  of  Vertebrata.  Between  the  Ovum  and  the 
Ovisac,  in  Oviparous  animals,  there  is  scarcely  any  interval ;  but  in  the  Mam- 
malia, a  large  amount  of  granular  matter  is  present ;  and  this  arranges  itself 
into  some  peculiar  structures  discovered  by  Dr.  Barry,  and  presently  to  be 
described.  The  membrane  which  surrounds  the  yolk  in  Mammalia  has  re- 
ceived, on  account  of  its  thickness  and  peculiar  transparency,  the  designation 


ACTION  OF  THE  FEMALE.  591 

of  zona  pellucida. — The  several  parts  of  the  Ovum  now  described  are  shown 
in  Fig.  5,  Plate  I. 

740.  From  the  researches  of  Dr.  Barry  on  the  early  development  of  the 
Ovum,  it  appears  that  the  Germinal  Vesicle  is  the  part  which  can  first  be  dis- 
tinctly traced.  In  Fig.  1  (Plate  I.)  is  seen  a  representation  of  one  of  its  inci- 
pient stages  in  the  Rabbit ;  there  is  nothing  here  visible,  but  a  collection  of 
very  transparent  vesicles,  surrounded  by  a  mass  of  dark  granules.  In  the 
succeeding  stage,  represented  in  Fig.  2,  some  of  the  vesicles  have  enlarged, 
and  the  granules  immediately  surrounding  them  have  become  developed  into 
cells.  A  more  advanced  condition  is  represented  (on  a  smaller  scale)  in  Fig. 
3 ;  in  which  a  distinct  spot  (b)  is  seen  on  the  central  vesicle  (a\  marking  it  as 
the  Germinal  Vesicle  ;  whilst  many  of  the  granules  surrounaing  it  have  be- 
come cells,  and  have  taken  on  a  very  regular  arrangement.  After  a  time,  a 
membrane  forms  around  each  cluster  of  granules,  separating  it  from  the  stroma 
of  the  ovarium  ;  this  is  the  Ovisac.  At  a  later  period,  a  separation  takes  place 
between  the  inner  and  outer  portions  of  the  mass  of  granular  matter,  included 
between  the  ovisac  and  the  germinal  vesicle  ;  and  the  separation  is  completed 
by  the  development  of  a  membrane,  which  envelops  the  inner  stratum.  This 
stratum  becomes  the  Yolk,  and  includes  most  of  the  oil-particles  which  pre- 
viously existed  within  the  ovisac ;  whilst  the  portion  of  the  granular  mass, 
exterior  to  this,  gives  origin  in  Mammalia  to  certain  structures  of  a  very  pecu- 
liar character,  which  seem  to  be  concerned  in  the  liberation  of  the  ovum  from 
the  Graafian  follicle  or  Ovisac.  The  appearance  of  the  Human  Ovisac  and  its 
contents  is  seen  in  Fig.  4.  The  granules  immediately  surrounding  the  Ovum 
assume  the  appearance  of  cells  ;  and  these  unite  to  form  a  sort  of  membrane, 
to  which  the  name  of  tunica  granulosa  has  been  given.  This  is  seen  at  tg 
(Fig.  7).  The  granules  lining  the  Ovisac  also  combine  themselves  into  a 
membranous  structure ;  to  which  Dr.  Barry  has  given  the  designation  of 
membrana  granulosa  (gg,  Fig.  6).  These  are  connected  by  four  band-like 
extensions  of  the  same  cellulo-membranous  structure,  which  seem  to  suspend 
the  ovum  in  its  place ;  and  these  ar,e  called  retinacula  (rr,  Figs.  6  and  7). 
The  space  between  the  Tunica  Granulosa  and  the  Membrana  Granulosa,  which 
is  not  occupied  by  the  Retinacula,  is  filled  with  fluid,  in  which  few  or  no  cells 
can  be  seen.  The  uses  of  this  structure,  so  far  as  they  are  apparent,  will  be 
described,  when  the  processes  by  which  the  Ovum  escapes  from  the  Ovary  are 
detailed.  The  Ovisac  does  not  form  the  entire  structure  which  has  been  de- 
scribed as  the  Graafian  follicle ;  for  this  consists  of  two  layers,  of  which  the 
inner  one  is  the  true  Ovisac,  whilst  the  outer  results  from  a  thickening  and 
condensation  of  the  surrounding  layer  of  the  Stroma  of  the  Ovarium.  It  is  the 
outer  layer  only  which  is  vascular  ;  the  inner  presents  no  trace  of  structure  ; 
and  the  increase  of  the  ovum  must  take  place  by  simple  imbibition,  through 
it,  of  the  supply  of  nutritive  matter  brought  into  contact  with  its  exterior.  The 
Ovarium  may  be  seen,  even  in  the  foetal  animal,  to  contain  immature  Ova;  in 
which  the  several  parts  can  be  clearly  distinguished.  At  a  later  period,  how- 
ever, the  number  of  Ova  greatly  increases ;  and  the  development  of  some  ad- 
vances, whilst  others  degenerate.  According  to  the  recent  valuable  inquiries 
of  Dr.  Ritchie,*  it  appears  that,  even  during  the  period  of  childhood,  there  is 
a  continual  rupture  of  Ovisacs,  and  discharge  of  Ova,  at  the  surface  of  the 
Ovarium.  The  Ovaria  are  studded  with  numerous  minute  copper-coloured 
maculee ;  and  their  surface  presents  delicate  vesicular  elevations,  which  are 
occasioned  by  the  most  matured  ovisacs  :  the  dehiscence  of  these  takes  place 
by  minute  punctiform  openings  in  the  peritoneal  coat ;  and  no  cicatrix  is  left. 
At  the  period  of  puberty,  the  stroma  of  the  ovarium  is  crowded  with  Ovisacs; 

*  London  Medical  Gazette,  1844. 


592  OF  REPRODUCTION. 

which  are  still  so  minute,  that  in  the  Ox  (according  to  Dr.  Barry's  computa- 
tion) a  cubic  inch  would  contain  200  millions  of  them.  The  greatest  advance 
is  seen  in  those  which  are  situated  nearest  the  surface  of  the  Ovarium ;  and 
in  these  the  Graafian  follicle  with  its  two  coats,  may  be  distinctly  traced.  It  is 
curious  that  the  outer  wall  (which  is  itself  a  part  of  the  condensed  stroma  of 
the  ovarium),  should  contain  an  immense  number  of  minute  ovisacs  ;  so  that 
this,  in  the  adult  animal,  is  the  most  convenient  situation  in  which  to  view 
them:  these  ovisacs  have  been  termed  by  Dr.  Barry  "  parasitic  ovisacs."  In 
those  animals  whose  aptitude  for  conception  is  periodical,  the  development  of 
the  Ova  to  such  a  degree  that  they  become  prepared  for  fecundation,  is  peri- 
odical also.  This  development  becomes  evident,  when  the  parts  are  examined 
in  an  animal  which  is  "  in  heat,"  by  the  projection  of  the  Graafian  follicles 
from  the  surface ;  and  it  consists  not  merely  in  an  increase  of  size,  but  in  cer- 
tain internal  changes  presently  to  be  described. 

741.  In  the  Human  female,  the  period  of  Puberty,  or  of  commencing  apti- 
tude for  procreation,  is  usually  between  the  13th  and  the  16th  year:  it  is 
earlier  in  warm  climates  than  in  cold,*  and  in  densely-populated  manufac- 
turing towns,  than  in  thinly-peopled  agricultural  districts.  The  mental  and 
bodily  habits  of  the  individual  have  also  a  considerable  influence  upon  the 
time  of  its  occurrence ;  girls  brought  up  in  the  midst  of  luxury  or  sensual 
indulgence  undergoing  this  change  earlier  than  those  reared  in  hardihood  and 
self-denial.  The  changes  in  which  Puberty  consists,  are  for  the  most  part 
connected  with  the  Reproductive  system.  The  external  and  internal  organs 
of  generation  undergo  a  considerable  increase  of  size ;  the  mammary  glands 
enlarge ;  and  a  deposition  of  fat  takes  place  in  the  mammae  and  on  the  pubes, 
as  well  as  over  the  whole  surface  of  the  body, — giving  to  the  person  that 

[*  It  has  been  stated,  by  almost  all  physiological  writers,  that  women  reach  maturity, 
and  that  menstruation  commences  much  earlier  in  hot  climates,  particularly  between 
the  tropics,  than  in  temperate  and  very  cold  countries.  Haller  states  that  in  the  warm 
regions  of  Asia,  the  catamenia  appear  from  the  8th  to  the  10th  year;  and  in  Switzerland, 
Britain,  and  other  temperate  regions,  at  the  age  of  12  or  13,  and  later  the  farther  we 
ascend  towards  the  north.  The  same  view  has  been  held  by  nearly  all  subsequent 
writers  on  the  subject,  and  they  infer  that  animals,  like  plants,  reach  maturity  sooner  in 
hot  than  in  cold  climates.  Dewees  says  that  menstruation  occurs  later  in  our  northern 
than  in  our  southern  states.  From  many  elaborate  and  interesting  papers  which  have 
been  published  within  a  few  years,  especially  from  those  of  Mr.  Roberton  of  Manchester, 
it  would  seem  that  the  natural  period  of  puberty  in  women  occurs  in  a  much  more 
extended  range  of  ages,  and  is  much  more  equally  distributed  through  that  range  than 
others  have  alleged,  and  that,  in  other  countries,  the  parallel  between  plants  and  fruits 
does  not  hold  good. 

At  Gottingen,0siander  ascertained  the  ages  at  which  137  women  began  to  menstruate. 
In  21  of  these  the  catamenia  appeared  at  14;  in  32  at  15;  in  24  at  16;  9  at  12;  and  1 
not  before  the  24th  year.  The  Indian  girls  in  Canada,  and  in  our  north-western  states 
and  territories,  begin  to  menstruate  frequently  at  12,  13  and  14.  From  the  statement  of 
Baron  Humboldt,  the  same  is  equally  true  of  the  Kornacs,  and  the  tribes  of  northern 
Asia,  where  girls  of  10  years  are  sometimes  found  mothers.  The  notion  that  women  in 
Lapland  do  not  menstruate  till  20,  and  then  only  during  summer,  is  founded  on  a  mistake 
in  Linnaeus's  Flora  Lapponica.  Tooke  states  that  the  Sclavonian,  or  native  Russians, 
reach  puberty  at  an  early  age;  and  Dr.  Robert  Lee,  who  was  in  the  Crimea,  and  all  the 
Russian  provinces  along  the  Black  Sea,  and  in  the  Ukraine,  and  whose  opportunities  of 
observation  were  extensive,  says  that  his  conviction  is,  that  over  the  whole  south  of 
Russia  the  period  of  puberty  is  the  same  as  in  Great  Britain ;  and  that  women  cease  to 
bear  children  at  the  same  age.  The  same  would  appear  to  hold  good  in  Java,  and  in  all 
the  islands  of  the  Indian  Archipelago,  and  in  Sierra  Leone;  and  the  difference  said  to 
exist  in  Arabia  in  this  respect  is  due  to  the  early  marriages,  and  universal  licentiousness 
and  depravity  of  morals  in  that  country.  It  would  appear  from  observations  made  in 
the  West  India  Islands,  that  menstruation  occurs  there  about  the  same  period,  and  that 
the  alleged  difference  in  this  respect  between  the  negress  and  the  white  female  does  not 
exist.— M.  C.] 


ACTION  OF  THE  FEMALE.  593 

roundness  and  fulness  which  are  so  attractive  to  the  opposite  sex,  at  the 
period  of  commencing  Womanhood.  The  first  appearance  of  the  Catamenia 
usually  occurs  whilst  these  changes  are  in  progress,  and  is  a  decided  indica- 
tion of  the  arrival  of  the  period  of  Puberty;  but  it  is  not  unfrequently  delayed 
much  longer ;  and  its  absence  is  by  no  means  to  be  regarded  as  a  proof  of 'the 
want  of  aptitude  for  procreation,  since  many  women  have  borne  large  families 
without  having  ever  menstruated.  The  Catamenial  discharge  appears  nor- 
mally to  consist  of  blood  deprived  of  its  fibrin;  the  fluid  being  composed  of 
serum,  in  which'red  corpuscles  are  suspended,  and  being  readily  distinguish- 
able from  true  blood  by  its  want  of  power  to  clot.  When  clots  are  found  in 
it,  therefore,  a  morbid  condition  of  the  secreting  surface  must  be  inferred.  The 
interval  which  usually  elapses  between  the  successive  appearances  of  the 
secretion  is  about  four  weeks ;  and  the  duration  of  the  flow  is  from  three  to 
six  days.*  There  is,  however,  great  variety  in  this  respect  among  the  inhabi- 
tants of  different  climates,  and  among  individuals:  in  general,  the  appearance 
is  more  frequent,  and  the  duration  of  the  flow  greater,  among  the  residents  in 
warm  countries,  and  among  individuals  of  luxurious  habits  and  relaxed  frame, 
than  among  the  inhabitants  of  colder  climes,  or  among  individuals  inured  to 
bodily  exertion.  The  first  appearance  of  the  discharge  is  usually  preceded 
and  accompanied  by  considerable  general  disturbance  of  the  system ;  espe- 
cially pain  in  the  loins  and  a  sense  of  fatigue  in  the  lower  extremities ;  and 
its  periodical  return  is  usually  attended  with  the  same  symptoms,  which  are 
more  or  less  severe  in  different  individuals. 

742.  Much  discussion  has  taken  place  respecting  the  causes  and  purposes 
of  the  Menstrual  flow ;  and  recent  inquiries  have  thrown  much  light  upon 
them.  The  state  of  the  Female  Generative  system  during  its  continuance, 
appears  to  be  analogous  to  the  heat  of  the  lower  animals  ;  many  of  which  have 
a  sero-sanguinolent  discharge  at  that  period.  There  is  good  reason  to  believe 
that  in  Women  the  sexual  feeling  becomes  stronger  at  that  epoch ;  and  it  is 
quite  certain  that  there  is  a  greater  aptitude  for  Conception,  immediately  before 
and  after  Menstruation,  than  there  is  at  any  intermediate  period.  Observa- 
tions to  this  effect  were  made  by  Hippocrates,  and  were  confirmed  by  Boer- 
haave  and  Haller ;  indeed  coitus  immediately  after  menstruation  appears  to 
have  been  frequently  recommended  as  a  cure  for  sterility,  and  to  have  proved 
successful.  It  is  well  known  that,  among  many  of  the  lower  animals,  the  Ova 
are  entirely  extruded  by  the  Female,  before  the  Spermatic  fluid  of  the  Male 
reaches  them ;  and  that  even  in  Birds,  this  occasionally  takes  place.  This 
question  has  been  recently  made  the  subject  of  special  inquiry  by  M.  Raci- 
borski ;  who  affirms  that  the  exceptions  to  the  rule— -that  Conception  occurs 
immediately  before  or  after,  or  during  Menstruation — are  not  more  than  6  or  7 
per  cent.  Indeed,  in  his  latest  work  on  this  subject,!  he  gives  the  details  of 
15  cases,  in  which  the  date  of  Conception  could  be  accurately  fixed,  and  the 
time  of  the  last  appearance  of  the  Catamenia  was  als6  known ;  and  in  all  but 
one  of  them,  the  correspondence  between  the  two  periods  was  very  close. 
Even  in  the  exceptional  case,  the  Catamenia  made  their  appearance  shortly 
after  the  Coitus  ;  which  took  place  at  about  the  middle  of  the  interval  between 
the  two  regular  periods.  When  Conception  occurs  immediately  before  the 
Menstrual  period,  the  Catamenia  sometimes  appear,  and  sometimes  are  absent ; 
if  they  appear,  their  duration  is  generally  less  than  usual.  The  fact  that  Con- 
ception often  takes  place  immediately  before  the  last  appearance  of  the  Cata- 

[*  It  would  appear,  from  the  statistical  researches  of  M.  Brierre  de  Boismont,  that  the 
two  periods  at  which  the  largest  number  of  females  menstruate,  are  the  8th  and  3d  days. 
A  women  who  menstruates  eight  days  for  thirty  years,  (the  usual  period  of  uterine  life,) 
will  consume  eight  years  in  this  function. — M.  C.] 

t  Sur  la  Ponte  des  Mammiferes.    Paris,  1844. 

50* 


594  OF  REPRODUCTION. 

menia  (and  not  after  it,  as  commonly  imagined),  is  one  well  known  to  practi- 
cal men.  Numerous  cases  have  been  collected  by  Mr.  Girdwood,  Dr.  Robert 
Lee,  MM.  Gendrin,  Negrier,  Raciborski,  and  others,  in  which  the  Menstrual 
period  was  evidently  connected  with  the  maturation  and  discharge  of  Ova ; 
but  the  most  complete  observations  yet  made  upon  this  subject,  are  undoubtedly 
those  of  Dr.  Ritchie  (loc.  cit.).  He  states  that  about  the  period  of  Puberty  a 
marked  change  usually  takes  place  in  the  mode  in  which  the  Ovisacs  discharge 
their  contents ;  but  that  this  change  does  not  necessarily  occur  simultaneously 
with  the  first  appearance  of  the  Catamenia ;  as  in  some  cases  the  conditions 
which  obtain  in  the  period  before  puberty,  are  extended  into  that  of  menstrua- 
tion. The  Ovaries  now  receive  a  much  larger  supply  of  blood ;  and  the  Ovi- 
sacs show  a  great  increase  in  bulk  and  vascularity  ;  so  that,  when  they  appear 
at  the  surface  of  the  ovary,  they  present  themselves  as  pisiform  turgid  eleva- 
tions ;  and  the  discharge  of  their  contents  leaves  a  much  larger  cicatrix,  and 
is  accompanied  by  an  effusion  of  blood  into  their  cavity,  with  other  subsequent 
changes,  to  be  presently  described.  It  would  appear,  however,  that  although 
such  a  discharge  takes  place  most  frequently  at  the  Menstrual  period,  yet  that 
the  two  occurrences  are  not  necessarily  co-existent :  for  Menstruation  may 
take  place  without  any  such  rupture  ;  whilst,  on  the  other  hand,  the  matura- 
tion and  discharge  of  mature  ova  may  occur  in  the  intervals  of  Menstruation, 
and  even  at  periods  of  life  when  that  function  is  not  taking  place.  The  essen- 
tial condition  of  Menstruation  itself  would  appear  to  be  the  increased  turges- 
cence  of  the  vessels  of  the  Uterus  ;  and  the  appearance,  on  its  internal  surface, 
of  a  meshwork  of  deciduous  villous  vessels,  which  may  remain  for  at  least  two 
weeks.  It  is  evident  that  this  is  a  preparation  for  the  formation  of  the  Decidua 
(§  748). — The  duration  of  the  period  of  aptitude  for  procreation,  as  marked  by 
the  persistence  of  the  Catamenia,  is  more  limited  in  Women  than  in  Men ; 
usually  terminating  at  about  the  45th  year ;  it  is  sometimes  prolonged,  how- 
ever, for  ten  or  even  fifteen  years  longer ;  but  cases  are  rare  in  which  women 
above  50  years  of  age  have  borne  children.  There  is  usually  no  Menstrual 
flow  during  Pregnancy  and  Lactation ;  in  fact,  the  cessation  of  the  Catamenia 
is  generally  one  of  the  first  signs,  indicating  that  Conception  has  taken  place. 
But  it  is  by  no  means  uncommon  for  them  to  appear  once  or  twice  subse- 
quently to  Conception ;  and  in  some  women,  there  is  a  regular  monthly  dis- 
charge, though  probably  not  of  the  usual  secretion,  through  the  whole  period. 
Some  very  anomalous  cases  are  recorded,  in  which  the  Catamenia  never 
appeared  at  any  other  time  than  during  Pregnancy ;  and  were  then  regular. 
The  absence  of  the  Catamenia  during  Lactation  is  by  no  means  constant,  espe- 
cially if  the  period  be  prolonged ;  when  the  Menstrual  discharge  recurs,  it 
may  be  considered  as  indicating  an  aptitude  for  Conception ;  and  it  is  well 
known  that,  although  Pregnancy  seldom  recurs  during  the  continuance  of  Lac- 
tation, the  rule  is  by  no  means  invariable. 

743.  The  function  of  the  Female,  during  the  coitus,  is  entirely  of  a  passive 
character.  When  the  sexual  feeling  is  strongly  excited,  there  is  a  considera- 
ble degree  of  turgescence  in  the  erectile  tissue  surrounding  the  vagina,  and 
composing  the  greater  part  of  the  nymphas  and  the  clitoris ;  and  there  is  also 
an  increased  secretion  from  the  mucous  follicles.*  But  these  changes  are  by 

[*  The  glands  of  Duverney  have  been  lately  (1840)  very  accurately  described  by  Pro- 
fessor Tiedemann,  his  attention  having  been  directed  to  these  organs  by  the  late  Dr. 
Fricke,  of  Hamburg.  These  glands  are  situated  at  either  side  of  the  entrance  of  the 
vagina,  beneath  the  integument  covering  the  inferior  part  of  the  vagina,  as  well  as  the 
superficial  perineal  fascia,  and  the  constrictor  vaginas  muscle.  The  space  they  occupy 
lies  between  the  lower  end  of  the  vagina,  the  ascending  ramus  of  the  ischium,  the  crus 
clitoridis,  and  the  erector  clitoridis  muscle.  Superiorly  are  the  fibres  of  the  levator  ani 
which  are  attached  to  the  ischium,  and  behind  these  are  the  transversi-perinei  muscles. 
They  are  surrounded  by  very  loose  cellular  tissue.  They  are  rounded,  but  somewhat 


ACTION  OF  THE  FEMALE.  595 

no  means  necessary  for  effectual  coition;  since  it  is  a  fact  well  established, 
that  fruitful  intercourse  may  take  place,  when  the  female  is  in  a  state  of  nar- 
cotism, of  somnambulism,  or  even  of  profound  ordinary  sleep.  It  has  been 
supposed  by  some,  that  the  os  uteri  dilates,  by  a  kind  of  reflex  action,  to  receive 
the  semen;  but  of  this  there  is  no  evidence.  The  introduction  of  a  small 
quantity  of  the  fluid  just  within  the  Vagina,  appears  to  be  all  that  is  absolutely 
necessary  for  conception;  for  there  are  many  cases  on  record,  in  which  pivj- 
nancy  has  occurred,  in  spite  of  the  closure  of  the  entrance  to  the  vagina  by  a 
strong  membrane,  in  which  but  a  very  small  aperture  existed.  That  the  Sper- 
matozoa make  their  way  towards  the  Ovarium,  and  fecundate  the  Ovum  either 
before  it  entirely  quits  the  Ovisac  or  very  shortly  afterwards,  appears  to  be  the 
general  rule  in  regard  to  the  Mammalia ;  and  the  question  naturally  arises, — 
by  what  means  do  they  arrive  there  ?  It  has  been  supposed  that  the  action  of 
the  cilia,  which  line  the  Fallopian  tubes,  might  account  for  their  transit ;  but 
the  direction  of  this  is  from  the  Ovaria  towards  the  Uterus,  and  would  there- 
fore §be  opposed  to  it.  A  peristaltic  action  of  the  Fallopian  tubes  themselves 
may  generally  be  noticed  in  animals  killed  soon  after  sexual  intercourse  ;  and 
in  those  which  have  a  two-horned  membranous  Uterus,  such  as  is  evidently 
but  a  dilatation  of  the  Fallopian  tube,  this  partakes  of  the  same  movement,  as 
may  be  well  seen  in  the  Rabbit :  in  animals,  however,  which  have  a  single 
Uterus  with  thicker  walls  (as  in  the  Human  female),  it  must  evidently  be  una- 
vailable. Among  the  tribes  whose  Ova  are  fertilized  out  of  the  body,  the 
power  of  movement  inherent  in  the  Spermatozoa  is  obviously  the  means  by 
which  they  are  brought  in  contact  with  the  Ova :  and  it  does  not  seem  unrea- 
sonable to  suppose,  that  the  same  is  the  case  in  regard  to  the  higher  classes  ; 
and  that  the  transit  of  these  curious  particles,  from  the  Vagina  to  the  Ovaries, 
is  effected  by  the  same  kind  of  action  as  that  which  causes  them  to  traverse 
the  field  of  the  microscope. — We  shall  now  consider  the  changes  in  the  Ovum 
and  its  appendages,  by  which  it  is  prepared  for  fecundation. 

744.  Up  to  the  period  when  the  Ovum  is  nearly  brought  to  maturity,  it  re- 
mains in  the  centre  of  the  Ovisac  or  inner  layer  of  the  Graafian  follicle  ;  and 
it  is  supported  in  its  place  by  the  Retinacula,  which  connect  its  Tunica  Gra- 
nulosa  with  the  Membrana  Granulosa  that  lines  the  ovisac.  (See  Fig.  6,  Plate 
I.).  The  Ovum  then  begins  to  move  towards  the  periphery  of  the  Graafian 
follicle ;  and  always  towards  that  point  of  it  which  is  nearest  the  surface  of 
the  Ovary.  This  movement  appears  to  be  due,  in  the  first  instance,  to  the 

elongated,  being  flat  and  bean-shaped.  Their  long  diameter  is  from  5  to  10  lines;  their 
transverse  diameter  2J  to  4|  lines,  and  they  are  from  2J  to  3  lines  thick.  The  excretory 
duct  is  at  the  antorior  edge  of  the  superior  part  of  the  gland,  and  runs  beneath  the  con- 
strictor vaginse,  horizontally  forwards  and  inwards,  to  the  inner  face  of  the  nympha, 
opening  in  front  of  the  carunculse  myrtiformes,  in  the  midst  of  a  number  of  small  mucous 
follicles.  These  glands  were  first  discovered  by  Duverney  in  the  cow,  about  the  middle 
of  the  seventeenth  century.  Bartholinus  subsequently  found  them  in  the  human  female, 
and  his  observations  were  confirmed  by  Duverney,  Morgagni,  Santorini,  Peyer,  &c. 
Haller  denied  their  existence;  and  such  structure  seems  to  have  been  forgotten  until 
they  were  again  described  by  Mr.  Taylor  (Dublin  Journal,  vol.  xiii.,  1838).  They  are 
analogous  to  Cowper's  glands  in  the  male  according  to  Tiedemann,  and  like  them  are 
sometimes  wanting,  and  differ  in  size.  In  advanced  age  they  are  said  to  diminish  in 
size,  and  even  disappear.  They  are  present  in  the  females  of  all  animals,  where  Cow- 
per's glands  exist  in  the  males.  They  secrete  a  thick,  tenacious,  grayish-white  fluid, 
which  is  emitted  in  large  quantities,  at  the  termination  of  the  sexual  act,  most  likely  from 
the  spasmodic  contraciion  of  the  constrictor  vaginae  muscle,  under  which  they  lie.  Its 
admixture  with  the  male  semen  is  supposed  to  probably  have  some  connection  with 
impregnation,  and  it  has  been  suggested  that  it  may  be  the  vehicle  of  the  fecundating 
principle  of  the  semen.  These  glands  were  probably  known  to  the  ancients,  and  it  is. 
doubtless  their  secretion  which  Hippocrates  and  others  describe  as  the  female  semen. — 
M.  C.] 


596  OF  REPRODUCTION. 

shortening  of  the  Retinacula  in  that  direction ;  and  whilst  the  Ovum  lies 
against  the  membrane  of  the  Ovisac,  a  gradual  thinning  of  the  latter  seems  to 
take  place.  At  the  same  time  an  important  change  is  occurring  in  the  outer 
wall  of  the  Graafian  follicle,  especially  at  the  part  most  deeply  imbedded  in 
the  Ovary  ;  its  vascularity  is  greatly-increased,  and  its  substance  appears  thick- 
ened. This  thickening  is  probably  due  to  the  deposition  of  blood  in  a  state 
ready  to  become  more  highly  organized,  upon  the  exterior  of  the  Ovisac ;  and 
the  consequence  of  it  is,  that  considerable  pressure  is  made  upon  the  contents  of 
the  follicle,  the  effect  of  which  is,  of  course,  exerted  most  upon  the  thinnest 
part  of  it.  Thus,  a  sort  of  vis  a  tergo  is  exercised  against  the  Ovum  and  the 
Disc  (consisting  of  the  tunica  granulosa  and  the  central  part  of  the  retinacula) 
in  which  it  is  imbedded ;  and  the  whole  is  forced,  by  the  rupture  of  the  Graa- 
fian follicle,  into  the  funnel-shaped  entrance  of  the  Fallopian  tube, — the  Re- 
tinacula being  gradually  detached  from  the  Membrana  Granulosa,  which  is 
left  behind.  This  action  is  represented  in  Fig.  8,  Plate  I.  What  becomes  of 
the  Ovisac  is  not  certain.  Dr.  Barry  affirms  that  he  has  sometimes  known  it 
to  be  subsequently  expelled  from  the  ovary ;  but  it  appears  more  commonly  to 
coalesce  with  the  surrounding  envelop,  and  to  constitute,  together  with.it,  the 
lining  of  the  cavity,  which  is  usually  found  in  the  Corpus  Luteum.  The  sub- 
stance known  under  this  name  is  found  in  the  Ovary,  after  the  Ovum  has 
escaped  from  it ;  and  the  importance  of  the  question,  how  far  its  presence  may 
be  regarded  as  an  indication  that  Conception  has  taken  place,  requires  that  we 
should  have  clear  ideas  respecting  its  nature.  The  term  Corpus  Luteum  has 
been  usually  applied  to  a  reddish-yellow  substance,  glandular  in  aspect,  friable 
in  consistence,  and  very  vascular ;  which  occupies  a  larger  or  smaller  part  of 
the  Ovary,  from  which  the  germ  has  escaped,  according  to  the  length  of  time 
that  has  elapsed  since  conception.  At  first  it  is  usually  so  large,  as  to  occasion 
a  considerable  projection  on  the  surface  of  the  Ovary  ;  its  form  is  oval,  or  resem- 
bles that  of  a  bean.  When  cut  across,  its  dimensions  are  usually  found  to  be 
from  4  to  5-8ths  of  an  inch  in  its  long  diameter,  and  from  3  to  4-8ths  in  its 
short ;  and  it  thus  occupies  from  a  fourth  to  a  half  of  the  whole  area  of  the 
ovarium;  but  these  dimensions  are  not  unfrequently  exceeded.  The  centre 
of  this  substance  is  hollow ;  and  by  a  proper  acquaintance  with  this  character, 
the  true  Corpus  Lujeum  may  be  distinguished  from  substances  bearing  a  gene- 
ral resemblance  to  it,  but  very  different  in  their  character.  The  following  is 
Dr.  Montgomery's  account  of  it.  "Its  centre  exhibits  either  a  cavity  or  a  radi- 
ated or  branching  white  line,  according  to  the  period  at  which  the  examination 
is  made.  If  within  the  first  three  or  four  months  after  conception,  we  shall,  I 
believe,  always  find  the  cavity  still  existing,  and  of  such  a  size  as  to  be  capable 
of  containing  a  grain  of  wheat  at  least,  and  very  often  of  much  greater  dimen- 
sions ;  this  cavity  is  surrounded  by  a  strong  white  cyst ;  and  as  gestation  pro- 
ceeds, the  opposite  parts  of  this  cyst  approximate,  and  at  length  close  together, 
by  which  the  cavity  is  completely  obliterated,  and  in  its  place  there  remains  an 
irregular  white  line,  whose  form  is  best  expressed  by  calling  it  radiated  or  stel- 
liform.  This  »is  visible  as  long  as  any  distinct  trace  of  the  Corpus  Luteum 
remains."*  The  true  Corpus  Luteum  is  further  distinguished  by  its  capability 
of  being  injected  from  the  vessels  of  the  Ovary ;  which  is  not  the  case  with 
Tubercular  deposits,  or  other  substances  which  may  simulate  it.  After  Deli- 
very, the  size  of  the  Corpus  Luteum  rapidly  diminishes;  and  in  a  few  months 
it  ceases  to  be  recognizable  as  such.  The  cicatrix  by  which  the  Ovum  has 
escaped  is  visible  for  some  time  longer ;  but  this,  too,  according  to  the  careful 
researches  of  Dr.  Montgomery,  cannot  be  distinguished  at  a  subsequent  period. 
Hence  there  is  no  correspondence  between  the  number  of  Corpora  Lu  tea  found 

*  Signs  of  Pregnancy,  p.  226. 


ACTION  OF  THE  FEMALE.  597 

in  the  ovaries  of  a  woman,  or  of  Cicatrices  on  their  surface,  and  the  number 
of  children  she  may  have  borne.  The  number  of  Corpora  Lutea  must  always 
be  less,  when  there  have  been  many  conceptions ;  but  the  number  of  Cicatrices 
may  be  greater;  for  several  causes,  such  as  the  escape  of  unimpregnated  ova, 
or  the  bursting  of  little  abscesses,  may  give  rise  to  such  appearances.  Much 
discussion  has  taken  place  amongst  EmbryologistsTas  to  whether  the  substance 
of  the  Corpus  Luteum  is  deposited  within  the  Graafian  follicle,  externally  to 
it,  or  between  its  layers.  The  first  is  the  opinion  of  Baer,  Bischoff,  and  others ; 
who  regarded  it  as  a  growth  from  the  inner  layer  of  the  Graafian  follicle.  The 
second  is  the  opinion  of  Dr.  R.  Lee  and  Mr.  Wharton  Jones.  The  third  is  the 
doctrine  taught  by  Drs.  Montgomery  and  Barry ;  the  former  regarding  it,  how- 
ever, as  deposited  between  the  two  layers,  of  which  the  eel lulo- vascular  layer 
of  the  Graafian  follicle  (which  are  both  derived  from  the  condensed  stroma  of 
the  ovarium)  consist;  whilst  the  latter  maintains  that  the  deposit  takes  place 
between  the  true  Ovisac  and  ifs  Ovarian  envelops.  The  recent  inquiries  of 
Dr.  Ritchie*  throw  great  light  on  this  question  ;  by  showing  that  a  great  variety 
of  changes  may  take  place,  after  the  discharge  of  the  Ovum  from  the  Ovisac ; 
amongst  which  may  be  included  all  the  appearances  described  by  the  several 
writers  just  quoted.  The  following  is  an  abstract  of  the  results  of  Dr.  R.'s 
researches. 

a.  The  appearances  presented  by  the  Ovaries,  Graafian  follicles,  and  by  the  blood  which 
is  contained  in  the  latter  subsequent  to  their  rupture,  vary  according  to  the  time  at  which 
they  are  examined,  and  the  absorbing  power  of  the  individual. — In  cases  of  the  recent 
discharge  of  an  Ovum,  the  Peritoneal  coat  of  the  Ovary  is  marked  by  a  jagged  slit  or 
opening,  having  a  florid  vascular  areola;  in  those  of  longer  standing,  the  opening  is  cov- 
ered over,— with  the  exception  of  a  minute  circular  foramen  in  the  centre,  or  (where  the 
slit  has  been  of  great  length)  of  two  such  openings, — with  new  tissue,  surrounded  by  a 
claret-coloured  margin;  and  in  those  still  more  ancient,  the  whole  is  healed  up  into  a 
cicatrix,  which  is  more  or  less  superficial  and  free  from  discoloration,  according  to  its 
age. 

6.  With  respect  to  the  Blood,  which  is  generally  contained  in  the  ruptured  follicles,  it 
is  seen  first  as  a  florid  coagulum  ;  next,  having  only  its  centre  scarlet-coloured,  and  its 
periphery  more  or  less  black,  and  perhaps  furrowed;  frequently  the  clot  has  a  gamboge 
colour  from  the  decomposition  of  its  red  corpuscles,  or  has  become  pale  from  their  ab- 
sorption;  and  lastly,  the  clot  is  found  in  different  stages  of  absorption.  But  it  sometimes 
also  happens, — and  that  indifferently  in  every  variety  of  the  uterine  state, — that  the  rup- 
tured follicles  are  found  empty,  or  containing  only  an  aqueous  fluid. 

c.  The  coats  of  the  ruptured  Follicles  have  been  found  in  four  different  general  condi- 
tions, apparently  dependent  on  their  relative  degree  of  organization;  and  each  class  pre- 
senting, also,  modifications  of  their  respective  characteristics,  proceeding  in  part  from 
the  same  cause,  and  in  part  also  from  changes  connected  with  the  period  of  their  progress 
in  which  they  were  examined. 

I.  The  first  class  was  distinguished  by  the  attenuated  state  of  the  coats  of  the  ruptured 
Follicle;  and  by  the  total  absence  of  any  organic  changes  in  these,  different  from  their 
condition  previous  to  their  discharge.  The  only  alterations  observable  resulted  from  the 
mechanical  dyeing  of  their  coats  of  an  inky-black,  or  of  a  yellow  colour,  proceeding  from 
their  contact  with  decomposed  blood. — This  first  class  of  appearances  was  found  indif- 
ferently in  all  ages  and  states,  subsequent  to  puberty. 

IF.  The  second  general  class  of  ruptured  Follicles  was  characterized,  in  addition  to  the 
appearances  just  described,  by  organic  changes  in  their  coats;  consisting,  progressively, 
of  an  increased  vascularity,  a  thickening,  a  whitening  of  the  colour,  and  finally,  a  cor- 
rugation of  their  tissue.  The  white  bodies  thus  formed,  to  which  Dr.  R.  has  given  the 
designation  of  Corpora  Albida,  may  exist  under  two  distinct  forms : — 1.  As  soft  bodies  of 
a  yellowish  fatty  aspect,  having  the  outer  coat  much  thickened,  whilst  their  inner  remains 
as  a  delicate  diaphanous  pellicle;  these,  after  a  lengthened  period,  present  themselves  as 
yellowish-white,  and  generally  globular  bodies,  more  or  less  fissured 'from  their  contrac- 
tion, and  sometimes  in  process  of  absorption,  having  a  granular-looking  structure,  and 
seldom  being  divisible  into  laminae  by  simple  dissection: — and  2.  As  dense  bodies  of  a 
whitish,  shining,  firm  structure,  their  inner  coat  being  the  seat  of  these  changes,  and 

*  Loc.  cit. 


598  OF  REPRODUCTION. 

their  outer  adhering  loosely  as  a  transparent  pellicular  layer;  the  inner  layer  presents 
itself  as  a  thick,  opaque,  deeply-wrinkled  or  corrugated,  and  rocky  cyst,  or  is  sometimes 
partially  diaphanous,  and  of  a  shining  pearly  aspect,  and  very  white  colour ;  and  it  some- 
times contains  a  yellow,  greenish,  transparent  fluid,  or  a  clot  of  blood,  either  unchanged, 
or  converted  into  a  yellow  or  black  pigment.  This  second  variety  appears  to  be  the 
Corpus  Luteum  of  Baer. — These  white  bodies,  or  Corpora  Albida,  were  found  by  Dr.  R. 
in  every  variety  of  uterine  condition,  subsequent  to  the  establishment  of  menstruation, 
but  never  before  it;  and  the  dense  kind,  especially,  were  persistent  for  a  long  period. — 
They  had  no  necessary  connection  with  the  gravid  condition;  but  they  were  occasionally 
(especially  the  dense  variety)  the  only  specialty  observable  in  the  ovaries  of  the  puerperal 
female,  some  time  after  delivery. 

III.  The  third  class  was  characterized  by  the  presence  of  an  organized,  yellow-coloured, 
brain-like,  granular  matter;  forming  bodies  to  which  Dr.  R.  has  given  the  name  of  Cor- 
pora Cephaluidea.    These  differed,  according  as  the  cerebriform  matter  was  deposited 
between  the  layers  of  ruptured  Follicles,  having  transparent  pellicular  walls,  as  in  Class 
I.,  or  having  either  their  inner  or  outer  coat  thickened,  as  in  Class  II. ;— or  according  as 
the  cerebriform  matter  was  deposited  externally  to  the  two  inner  layers  of  the  Follicle. — 
The  former  of  those  varieties  was  found  by  Dr.  Ritchie  in  menstruating  females;  also 
during  the  first  months  of  the  gravid  state;  and  sometimes  even  in  the  period  of  lacta- 
tion.    In  some  instances  only  one  or  two  of  the  cerebriform  bodies  were  found,  but  some- 
times five  or  six.     Their  structure,  especially  in  the  more  perfectly-organized  specimens, 
presented  a  striking  resemblance  to  the  convoluted  reddish-yellow  surface  of  the  brain, 
covered  by  its  inner  membranes,  and  painted  with  its  scarlet-coloured  and  dark  vessels. 
These  cephaloid  bodies  undergo  diminution  in  proportion  to  their  age,  and  the  absorbing 
power  of  the  female.     In  those  possessed  of  only  thin  coats,  or  having  the  outer  layer  as 
the  seat  of  the  thickening,  the  inner  walls  of  the  cysts  speedily  contracted  and  coalesced; 
so  that  their  centres  exhibited  a  delicate  opaque  streak:  or,  in  those  better  developed,  a 
serrated,  curved,  and  well-marked  white  line,  according  as  the  cyst  was  of  elliptical  or  of 
a  globular  form.     This  variety  of  cerebriform  cyst  was  met  with  in  a  recent  state  indif- 
ferently in  immediate  connection  with  the  existence  of  menstruation,  and  during  the  first 
seven  months  of  pregnancy ;  and  in  this  latter  case,  by  undergoing  a  conversion  in  its 
form  presently  to  be  noticed  (IV.),-they  constituted  the  Corpora  Lutea  of  Dr.  Montgomery. 
— In  the  second  variety  of  Cephaloid  bodies,  the  two  inner  layers  of  the  Graafian  Follicle 
were   converted  into  a  dense  white  body,  surrounded  by  an  envelop  of  yellow  matter. — 
Such  cysts  (the  Corpora  Lutea  of  Dr.  Lee)  were  never  observed  as  an  effect  of  menstrua- 
tion simply,  but  were  met  with  exclusively  in  the  gravid  female;  although  they  were  seen 
(as  were  also  the  cephaloid  bodies  of  the  preceding  order),  presenting  double  in  some 
cases  of  single  conception.    This  form  of  Cephaloid  bodies  was  generally  distinguished 
by  large,  persistent,  white,  glistening  cavities.     The  granular  cephaloid  matter  was  some- 
times found  quite  absorbed  within  a  few  days  after  parturition;  but  in  other  instances  it 
underwent  the  metamorphosis  characteristic  of  the  next  class. 

IV.  The  fourth  general  state  of  the  ruptured  Graafian  follicle  was  peculiar  to  the  im- 
pregnated and  lactating  female,  in  the  period  between  the  eighth  and  thirteenth  months 
after  conception;  and  appeared  to  be  a  conversion  of  the  Corpora  Cephaloidea  already 
described,  arising  out  of  a  higher  and  more  perfect  organization.     Down  to  the  seventh 
month  of  pregnancy,  the  cysts  contained  in  the  Ovaries  did  not  differ  in  any  respect  from 
the  cerebriform  bodies  found  in  the  unimpregnated  state;  except  that  they  were  some- 
times plumper,  more  vascular,  better  developed,  and  had  their  inner  layer  more  frequently 
thickened.     A  change  in  the  hue  of  the  granular  matter  then  commences,  which  becomes 
more  decided  as  time  elapses;  so  that  by  the  end  of  the  first  month  after  delivery,  it  be- 
comes of  a  decided  rose  colour,  changing  to  a  still  more  florid  hue  on  exposure  to  air. — 
Its  cavity  also  contracts,  so  as  to  leave  but  a  stellated  point,  or  a  curved  groove:  and  a 
fibrous  appearance  (probably  dependent  on  the  traction  thus  exercised),  is  seen  in  ihe 
surrounding  substance.     Although  these  bodies,  termed  by  Dr.  Ritchie  Corpora  min/,are 
found  exclusively  in  the  later  months  of  pregnancy,  or  in  the  puerperal  state,  yet  they 
are  not  always  present  in  those  conditions. 

The  number  of  cases  examined  by  Dr.  Ritchie  is  not,  perhaps,  sufficient  to 
enable  us  to  found  any  positive  statements  upon  the  results  of  his  examination 
of  them;  but  the  following  inductions  appear  highly  probable. — 1.  That  the 
presence  of  Corpora  Rubra  may  be  regarded  as  indicative,  not  only  of  con- 
ception, but  also  of  an  advanced  stage  of  pregnancy,  or  of  recent  delivery ; 
but  that  their  absence  is  not  to  be  regarded  as  any  proof  to  the  contrary. — 
2.  That  the  presence  of  Corpora  Cephaloidea  of  the  second  order  is  to  be 


ACTION  OF  THE  FEMALE.  599 

regarded  as  indicative  of  conception. — 3.  That  the  presence  of  the  Corpora 
Cephaloidea  of  the  first  order,  or  of  Corpora  Mbida,  cannot  be  regarded  as  in 
the  least  degree  indicative  of  Conception ;  as  they  may  result  from  the  simple 
discharge  of  an  Ovum,  in  the  ordinary  course  of  those  changes  to  which  the 
Ovarium  is  subject.— The  excess  of  Corpora  Albida  above  every  other  appear- 
ance is  due,  not  merely  to  their  being  an  ordinary  result  of  the  discharge  of 
unimpregnated  Ova ;  but  also  to  the  frequency  of  their  production  as  degene- 
rated forms  (so  to  speak)  of  the  Corpora  Cephaloidea  and  Corpora  Rubra  of 
the  gravid  female  ;  and  also  to  their  occasional  existence  as,  from  the  first,  the 
only  Ovarian  change  following  upon  Conception. 

745.  The  object  of  the  changes  which  have  been  already  described,  is  to 
bring  the  Ovum  within  reach  of  the  fecundating  influence  ;  and  to  convey  it 
into  the  Uterus  after  it  has  been  fertilized.  We  have  now  to  consider  the 
changes  in  the  Ovum  itself,  which  take  place  during  the  same  epoch.  At 
about  the  same  period  that  the  Ovum  moves  towards  the  periphery  of  the 
Graafian  follicle,  the  Germinal  Vesicle  moves  towards  the  periphery  of  the 
yolk-bag;  and  it  always  takes  up  its  position  at  the  precise  point  of  the  Zona 
Pellucida  which  is  nearest  the  Ovisac,  and  which  is  closest,  therefore,  to  the 
surface  of  the  Ovary.  Moreover,  the  Germinal  Spot  is  always  on  that  part 
of  the  Germinal  Vesicle,  which  is  in  closest  contact  with  the  Zona  Pellucida. 
(See  «,  Figs.  9  and  10,  Plate  I.)  Thus,  the  Germinal  Spot  is  very  near  the 
exterior  of  the  Ovary ;  but  is  separated  from  it  by  the  peritoneal  coat  of  the 
latter,  by  a  thin  layer  of  its  stroma  forming  the  external  layer  of  the  Graafian 
follicle,  by  the  ovisac  forming  its  internal  membrane,  and  by  the  zona  pellu- 
cida.  We  have  already  seen  how  the  obstacle  interposed  by  the  three  former 
to  the  entrance  of  the  Spermatozoon,  is  overcome  ;  we  shall  presently  find  that 
the  Zona  Pellucida  undergoes  a  similar  change. — Whilst  the  Ovum  is  being 
prepared  for  fecundation,  a  series  of  very  important  actions  take  place  in  the 
Germinal  Vesicle.  The  exterior  or  peripheral  portion  of  the  Spot,  which 
previously  consisted  of  a  collection  of  very  minute  granules,  begins  to  develop 
itself  into  a  ring  of  new  cells  of  extreme  delicacy  (Fig.  9,  «) ;  these  gradually 
enlarge,  and  a  second  ring  of  cells  is  developed  within  it,  pushing  the  first- 
formed  cells  further  away  from  the  centre.  Many  successive  rings  of  cells  are 
thus  formed ;  and  at  last  the  whole  Germinal  Vesicle  is  filled  with  them,  as 
shown  at  6,  Fig.  10.  Still  there  remains  a  pellucid  space  in  the  centre  of  the 
Germinal  Spot  (resembling  that  seen  at  a,  Fig.  12)  ;  in  which  no  cells  are 
developed.  The  first-formed  cells  that  have  been  pushed  outwards,  are  so 
much  compressed  by  those  subsequently  formed,  as  frequently  to  undergo 
liquefaction ;  and  during  the  time  that  the  Ova  are  being  matured  for  fertili- 
zation, there  is  a  continual  new  production  of  cells  at  the  centre,  and  a  degene- 
ration at  the  circumference. — At  the  same  time,  the  Yolk  undergoes  changes 
somewhat  analogous  ;  for  it  ceases  to  contain  separate  oil-globules  ;  and  large 
elliptical  discs  or  cells  are  seen  in  it,  especially  just  beneath  the  Zona  Pel- 
lucida (Fig.  9,  c).*  Here,  too,  the  formation  of  new  cells  takes  place  from 
the  periphery  towards  the  centre ;  the  peripheral  ones  gradually  undergo 
liquefaction,  as  is  seen  in  the  outer  layer  of  those  in  Fig.  10,  which  are 
becoming  indistinct ;  and  they  are  replaced  by  a  new  layer  pushed  outwards 
from  the  centre.  The  same  process  subsequently  continues  in  the  Yolk,  for 
some  time  after  fecundation ;  and  this  not  only  in  regard  to  the  yolk  as  a 
whole,  but  in  respect  to  its  individual  cells,  as  is  shown  in  Fig.  11,  where 
concentric  rings  of  new  cells  are  seen  in  each  of  the  parent  vesicles.  Even 
in  the  most  advanced  of  these  secondary  cells,  another  generation  may  be 

*  It  is  to  be  remembered  that  the  observations  of  Dr.  Barry  here  quoted,  were  made  on 
the  Rabbit:  and  are,  therefore,  probably  applicable  equally  to  other  Mammalia,  but  not  to 
Oviparous  Animals. 


600  OF  REPRODUCTION. 

seen,  and  these  are  developed  upon  the  same  plan  with  those  of  the  Germinal 
Vesicle :  thus  in  Fig.  12,  the  pellucid  centre  of  the  original  nucleus  of  the 
parent  disc  is  seen  at  a,  and  is  surrounded  by  several  concentric  rings  of  cells, 
increasing  in  size  from  within  outwards  ;  and  at  b  is  represented  the  condition 
of  the  outer  and  older  cells,  in  which  the  same  process  is  undergoing  repetition. 
(Although  the  figure  only  represents  one  secondary  cell  as  in  the  act  of  pro- 
ducing others,  the  others  of  the  same  age  are  alike  engaged  in  the  process  of 
multiplication.)  The  foregoing  history  is  equally  applicable  to  the  cells  from 
which  the  Embryo  subsequently  originates ;  and  it  is  probably  the  general 
mode  in  which  the  process  takes  place. 

746.  At  the  time  when  the  interior  of  the  Germinal  Vesicle  is  being  prepared 
for  the  reception  of  the  fecundating  influence,  the  portion  of  the  Zona  Pellucida 
against  which  it  lies  becomes  attenuated ;  and  a  chink  then  forms  in  it,  just 
above  what  was  the  pellucid  centre  of  the  Germinal  Spot.     Through  this 
chink,  the  Spermatozoon  can  reach  the  Germinal  Vesicle  ;  and  that  it  does  so, 
we  are  now  entitled  to  affirm,  not  only  from  analogy,  but  also  from  actual 
observation  (§  733).     What  is  the  nature  of  the  influence  communicated  by  it 
is  less  certain ;  but  from  the  known  character  of  the  process  of  fecundation  in 
Plants,  we  shall  have  little  difficulty  in  concluding,  that  it  deposits  in  the 
Germinal  Vesicle  the  rudiments  of  the  first  cells,  which  are  subsequently  to 
be  developed  into  the  Embryonic  structure.     It  is  certain  that  none  of  the 
cells  previously  contained  in  the  Germinal  Vesicle  subsequently  form  part  of 
it ;  in  fact,  they  all  liquefy  after  a  time,  and  disappear  entirely.     But  in  the 
previously  pellucid  centre  of  what  was  the  Germinal  Spot,  two  new  cells  are 
seen  after  fecundation ;  these  enlarge  at  the  expense  of  the  rest ;  and  from 
them  all  the  permanent  structures  originate.     This  pair  of  cells  is  seen  at  «, 
Figs.  13  and  14;  in  the  former  some  of  the  cells  of  the  Germinal  Vesicle  are 
still  left ;  in  the  latter  they  have  been  all  absorbed.     The  Germinal  Vesicle 
returns  after  fecundation  to  the  centre  of  the  Yolk,  being  at  first  entirely  con- 
cealed by  its  discs  (Fig.  11) ;  and  the  cleft  in  the  Zona  Pellucida  soon  closes, 
so  as  to  be  no  longer  distinguishable.     The  two  new  cells  and  the  other  con- 
tents of  the  Germinal  Vesicle,  undergo  such  a  rapid  increase  in  size,  that  they 
soon  fill  the  whole  interior  of  the  Zona  Pellucida ;  and  the  cells  of  the  Yolk 
being  reduced  by  the  pressure  into  a  liquid  form,  their  elements  are  absorbed 
by  the  new  cells  of  the  Embrj^onic  structure.     This,  at  least,  is  the  case  in  the 
Mammalia;  among  which  the  Yolk  performs  but  a  very  subordinate  part, 
having  only  to  serve  for  the  development  of  the  Embryo  during  a  very  brief 
period. — In  each  of  the  two  primary  Germ-cells  (as  they  may  be  called)  a 
series  of  changes  takes  place,  exactly  conformable  to  that  already  described 
as  occurring  in  the  Germinal  Vesicle ;  that  is  to  say, — a  ring  of  new  cells 
originates  in  the  margin  of  its  nucleus, — this  increases  in  size,  and  is  pushed 
outwards  by  another  ring  nearer  the  centre,  this  again  by  another,  and  so  on, — 
and  at  last,  two  cells  appear  in  the  pellucid  central  space,  which  are  developed 
at  the  expense  of  all  the  rest,  and  are  to  be  regarded  as  the  real  permanent 
offspring  of  the  parent.     These  changes  may  be  seen  in  progress  in  Figs.  13 
and  14 ;  in  the  former,  the  original  cells  of  the  Germinal  Vesicle  have  not 
quite  disappeared,  although  their  liquefaction  is  in  progress  ;  in  the  latter,  no 
vestige  of  them  is  left,  the  whole  cavity  being  occupied  by  the  twin-cells. 

747.  These  changes  commence  during  the  passage  of  the  Ovum  along  the 
Fallopian  tube  ;  and  during  its  transit  to  the  Uterus,  it  receives  a  very  import- 
ant addition,  that  of  the   Chorion.      According  to  Dr.  Barry,  the  Choriori 
originates  as  a  layer  of  cells,  the  remains  of  which  may  be  frequently  seen, 
when  the  membrane  is  otherwise  complete  (as  in  Fig.  14,  Plate  I.) ;  and  the 
space  between  the  Chorion  and  the  Zona  Pellucida  is  occupied  by  a  quantity 
of  gelatinous-looking  fluid,  which  he  supposes  to  be  drawn  within  the  former 


ACTION  OF  THE  FEMALE. 


601 


by  imbibition  (Fig.  13).  Mr.  Wharton  Jones,  on  the  other  hand,  (who  was 
the  first  to  observe  this  stage  of  the  process,  and  to  maintain  that  the  Chorion 
is  formed  in  the  Fallopian  tube,)  asserts  that  the  gelatinous  matter  is  first 
deposited  around  the  Zona  Pellucida ;  and  that  the  Chorion  is  subsequently 
formed  from  or  upon  it.  It  appears  to  the  Author,  that  the  gelatinous  envelop 
is  strictly  analogous  to  the  white  of  the  Bird's  egg ;  and  that  the  Chorion 
corresponds  with  its  enveloping  membrane,  and  is  probably  formed  in  the  same 
manner.  The  gelatinous-looking  envelop  is  probably  of  an  albuminous 
nature  in  reality  ;  and  the  texture  of  the  Chorion,  which  is  seen  to  be  fibrous, 
as  soon  as  it  can  be  clearly  distinguished,  is  probably  derived  from  the  Fibrin 
poured  out  from  the  lining  of  the  Fallopian  tube.  The  appearance  of  cells 
noticed  by  Dr.  Barry,  corresponds  with  what  is  witnessed  in  other  fibrinous 
effusions  (§  560).  From  the  surface  of  the  Chorion,  a  large  number  of  villous 
prolongations  afterward  shoot  forth ;  these  serve  as  absorbing  radicles,  and 
form  the  channel  through  which-  the  Embryo  is  nourished  by  the  fluids  of  the 
Parent,  until  a  more  perfect  communication  is  formed. 

748.  We  have  now  to  speak  of  the  changes  in  the  Uterus,  which  take  place 
in  consequence  of  Conception,  and  which  prepare  it  to  receive  the  Ovum.  Of 
these  the  most  important  is  the  formation  of  the  Membrana  Decidua,  so  called 
from  its  being  cast  off  at  each  parturition.  This  membrane  has  been  usually 
supposed  to  be  a  new  formation ;  and  has  been  described  as  originating  in 
coagulable  lymph  thrown  out  on  the  inner  surface  of  the  Uterus,  into  which 
vessels  are  prolonged  from  the  subjacent  surface.  It  appears,  however,  from 
the  late  researches  of  Dr.  Sharpey  and  Prof.  Weber,*  that  this  is  not  the  true 
account  of  it ;  and  that  the  Decidua  is  really  composed  of  the  inner  portion  of 
the  Mucous  membrane  itself,  which  undergoes  a  considerable  change  in  its 
character.  The  Mucous  membrane  of  the  Uterus  had  been  observed  by  Dr. 
J.  Reid  to  possess,  on  its  free  surface,  a  tubular  structure  ;  not  very  unlike 
that  which  has  been  described  as  existing  in  the  lining  membrane  of  the 
stomach  (§  704  and  Fig.  170).  This  tubular  portion  becomes  thickened  and 


Fig.  160. 


Fig.  181. 


Section  of  the  Uterus,  showing  the  position 
of  the  decidua  vera;  a,  cervix;  &,  6,  orifices 
of  Fallopian  tubes;  c,  decidua  vera;  d,  ca- 
vity of  uterus. 


Section  of  the  Uterus,  at  entrance  of  ovum 
/,  surrounded  by  its  chorion  g;  a,  cervix; 
6,  6,  Fallopian  tubes;  c,  decidua  vera;  d,  ca- 
vity of  uterus  ;  e,  decidua  reflexa. 


51 


*  Mailer's  Physiology,  pp.  1574-1580. 


602  OF  REPRODUCTION. 

increased  in  vascularity,  within  a  short  time  after  conception ;  and  when  the 
inner  surface  of  a  newly-impregnated  Uteriis  is  examined  with  a  low  magnify- 
ing power,  the  orifices  of  its  tubes  are  very  distinctly  seen,  being  lined  with  a 
white  epithelium.  The  blood-vessels  form  a  very  minute  network,  which 
extends  in  loops  from  the  subjacent  portion  of  the  membrane  (as  seen  in  Fig. 
17,  Plate  I.).  Of  the  orifices  of  the  glandular  follicles,  some  afterwards  become 
widened  and  enlarged  for  the  reception  of  the  foetal  villi.  The  thickness  of 
the  Decidua,  when  fully  formed,  is  from  one  to  three  lines ;  its  inner  surface 
is  smooth  ;  whilst  that  in  connection  with  the  Uterus  is  rough,  in  consequence 
of  the  varying  length  of  the  tubes,  and  of  the  vascular  connections  of  the  two 
structures.  It  has  not  yet  been  explained  how  the  Decidua  is  formed  con- 
tinuously over  the  upper  orifice  of  the  Cervix  Uteri,  and  over  the  orifices  of 
the  Fallopian  tubes,  as  is  frequently,  though  by  no  means  uniformly,  the  case ; 
and  it  seems  as  if  a  new  production  must  there  take  place.  The  formation  of 
the  Uterine  Decidua  occurs  whether  the  Ovum  reach  the  Uterus  or  not ;  it 
being  probably  invariable*  in  cases  of  extra-uterine  pregnancy,  even  though  a 
Decidua  is  formed  around  the  Ovum  in  the  place  of  its  lodgment.  Besides 
the  Decidua  lining  the  Uterus,  however,  another  membrane,  continuous  with 
this,  furnishes  a  proper  envelop  to  the  Ovum  ;  and  this  has  been  termed  the 
Decidua  reflexa.  The  formation  of  this  is  usually  explained,  in  conformity 
with  the  account  of  Dr.  W.  Hunter,  after  the  following  manner.  The  Ovum, 
on  passing  from  the  Fallopian  tube  into  the  Uterus,  pushes  before  it  a  portion 
of  the  Decidua  Vera,  as  represented  in  Fig.  181 ;  and  this  portion  is  gradually 
extended,  by  the  subsequent  growth  of  the  Ovum,  so  as  at  last  to  surround  it 
completely.  If  this  were  precisely  the  case,  however,  the  structure  of  the 
two  membranes  ought  to  be  the  same,  which  it  is  not ;  for,  according  to  the 
observations  of  Dr.  Sharpey,t  the  Decidua  Reflexa  is  destitute,  in  great  part 
of  its  surface,  of  the  small  orifices  which  characterize  the  Vera ;  and  these  are 
confined  chiefly,  though  not  entirely,  to  a  zone  of  the  membrane  surrounding 
the  angle  of  reflexion,  that  is,  to  the  part  next  to  the  Decidua  Vera.  It  would 
seem  more  probable,  therefore,  that  the  Decidua  Reflexa  is  almost  entirely  a 
new  production,  the  growth  of  which  is  simultaneous  with  the  enlargement  of 
the  ovum  ;  and  that  the  Decidua  Vera  has  no  more  share  in  its  formation  than  as 
supplying,  through  its  vessels,  the  necessary  materials.  As  the  ovum  increases 
in  size,  the  Decidua  Reflexa  w^hich  covers  it,  comes  into  contact  with  the  Decidua 
Vera,  which  lines  the  Uterus;  and  the  fluid  that  previously  filled  the  cavity 
disappears  by  absorption  ;  this  usually  happens  during  the  third  month.  After 
this  period,  it  is  difficult  and  frequently  impossible,  to  distinguish  the  two 
layers ;  and  even  in  aborted  ova  of  an  earlier  age,  the  Decidua  Reflexa  is  not 
always  to  be  found,  on  a  careful  examination  ;  so  that  its  very  existence  has 
been  denied  by  some.  At  one  part  of  its  surface,  the  Ovum  is  covered  neither 
by  the  Decidua  vera,  nor  by  the  Decidua  reflexa ;  this  is  where  the  former 
was  originally  detached  from  the  wall  of  the  Uterus,  by  the  Ovum,  and  where 
it  becomes  continuous  with  the  latter.  It  is  at  this  point  that  the  Placenta  is 
subsequently  formed.  The  deficiency  is  supplied,  however,  by  a  new  pro- 
duction, very  analogous  in  structure  to  the  Decidua  Reflexa,  and  continuous 
with  the  reflected  fold  of  the  Decidua  Vera ;  this  is  termed  (from  its  formation 
being  supposed  to  take  place  at  a  later  period)  the  Decidua  Serotina  (Fig. 
186/). 

*  The  doctrine  of  the  formation  of  the  Decidua,  here  adopted  on  the  authority  of  the 
two  accomplished  Anatomists  mentioned  above,  tends  to  reconcile  the  contradictory  ob- 
servations which  have  been  recorded  on  this  interesting  point ;  for  in  those  cases  in  which 
nothing  but  an  increase  of  thickness  and  sponginess  in  the  Mucous  membrane  of  the 
Uterus  was  observable,  the  very  change  was  in  progress,  in  which  the  formation  of  the 
Decidua  consists. 

f  Loc.  cit. 


ACTION  OF  THE  FEMALE.  003 

749.  The  formation  of  the  Placenta  commences  by  the  penetration  of  the 
ramified  villi,  or  filamentous  processes  of  the  Chorion,  into  the  tubuli  of  the 
Decidua ;  the  villi  thus  serve  as  roots,  which  suck  up  and  convey  to  the 
embryo  the  nourishment  secreted  for  it  by  the  maternal  structures.  The 
mode  in  which  these  villi,  at  first  consisting  merely  of  cells,  become  connected 

with  the  vessels  of  the  Foetus,  will  be  explained  hereafter  (§  704).     This, 

the  earliest  and  simplest  mode  by  which  the  FoBtus  effects  a  new  connection 
with  the  parent, — is  the  only  one  in  which  it  ever  takes  place  in  the  lower 
Mammalia,  which  are  hence  properly  designated  as  "  non-placental,"  rather 
than  as  ovo-viviparous  (§  55).  In  the  higher  Mammalia,  however,  there  soon 
occurs  a  great  extension  of  the  vascular  tufts  of  the  foetal  Chorion,  at  certain 
points  ;  and  a  corresponding  adaptation,  on  the  part  of  the  Uterine  structure, 
to  afford  them  an  increased^  supply  of  nutritious  fluid.  These  specially-pro- 
longed portions  are  scattered,  in  the  Ruminantia  and  some  other  Mammalia, 
over  the  whole  surface  of  the  Chorion,  forming  what  are  termed  the  Cotyle- 
dons ;  but  in  the  higher  orders,  and  in  Man,  they  are  concentrated  in  one 
spot,  forming  the  Placenta.  In  some  of  the  lower  tribes,  the  maternal  and  the 
foetal  portions  of  the  Placenta  may  be  very  easily  separated ;  the  former  con- 
sisting of  the  thickened  Decidua ;  and  the  latter  being  composed  of  the  pro- 
longed and  ramifying  vascular  tufts  of  the  Chorion,  dipping  down  into  it. 
But  in  the  Human  Placenta,  the  two  elements  are  mingled  together  through 
its  whole  substance.  On  looking  at  its  Foetal  surface,  we  perceive  that  the 
umbilical  vessels  diverge  in  every  direction  from  the  point  at  which  they 
enter  it ;  and  their  subdivisions  ramify  very  minutely,  forming  a  large  part  of 
its  substance.  The  terminal  ramifications  are  represented  by  Dr.  J.  Reid*  as 
having  the  form  represented  in  Fig.  23,  (Plate  I.),  each  consisting  of  an  artery 
and  vein  bound  up  together ;  thus  closely  resembling  the  arrangement  of  the 
vessels  of  the  gills  in  aquatic  animals.  By  Weber,  however,  a  somewhat 
different  description  of  the  terminations  of  the  foetal  vessels  is  given ;  each 
villus  being  represented  by  him  as  consisting  of  a  capillary  vessel  communi- 
cating with  the  artery  and  vein,  and  making  several  turns  upon  itself,  so  as  to 
form  a  series  of  loops.  It  is  of  little  practical  importance  which  statement  is 
the  most  correct ;  since  the  essential  fact,  that  each  villus  contains  the  termi- 
nal connecting  branch  of  an  artery  and  a  vein,  is  recognized  in  both.t  The 
Maternal  portion  of  the  Placenta  may  be  regarded,  according  to  Dr.  J.  Reid, 
as  consisting  of  a  large  sac  formed  by  a  prolongation  of  the  inner  coat  of  the 
Uterine  vessels ;  against  the  foetal  surface  of  this  sac,  the  tufts  just  described 
may  be  said  to  push  themselves,  so  as  to  dip  down  into  it,  carrying  before 
them  a  portion  of  its  thin  wall,  which  constitutes  a  sheath  to  each  tuft.  In 
this  manner,  the  whole  interior  of  the  placental  cavity  is  intersected  by  nume- 
rous tufts  of  foetal  vessels,  disposed  in  fringes,  and  bound  down  by  reflexions 
of  the  delicate  membrane  that  forms  its  proper  wall;  just  as  the  intestines  are 
held  in  their  places  by  reflexions  of  the  peritoneum  that  covers  them.  This 
view  was  suggested  to  Dr.  R.  by  the  very  interesting  fact,  thatt  he  tufts  of 
foetal  vessels  not  unfrequently  extend  beyond  the  uterine  surface  of  the  Pla- 
centa, and  dip  down  into  the  uterine  sinuses  ;  where  they  are  still  covered, 

*  Edinburgh  Med.  and  Surg.  Journal,  Jan.,  1841. 

|  By  Mr.  F.  Renaud,  the  variation  in  the  appearance  of  the  placental  tufts  is  attributed 
to  the  degree  of  imbibition  which  has  taken  place  through  the  enveloping  membrane. 
When  examined  without  either  injection  or  immersion  in  fluid,  each  tuft  is  seen  to  con- 
tain a  long  convoluted  capillary,  originating  in  the  umbilical  artery  and  terminating  in 
the  vein.  In  its  normal  condition,  this  seems  to  transmit  but  one  row  of  blood  corpus- 
cles; but  several  may  be  forced  along  it  by  the  aid  of  a  little  pressure.  When  immersed 
in  fluid,  the  tuft  becomes  distended  into  the  form  represented  by  Dr.  Reid,  owing  to  the 
imbibition  of  fluid.  This  may  probably  be  their  condition  whilst  in  action.  Edinburgh 
Monthly  Journal,  March,  1843. 


604  OF  REPRODUCTION. 

and  held  in  their  places,  by  the  same  reflected  membrane.  The  blood  is  con- 
veyed into  the  Placental  cavity  by  the  "  curling  arteries"  of  the  Uterus  ;  and 
is  returned  from  it  by  the  large  veins,  that  are  commonly  designated  as 
sinuses.*  The  foetal  vessels,  being  bathed  in  this  blood,  as  the  branchiae  of 
aquatic  animals  are  in  the  water  that  surrounds  them,  not  only  enable  the 
festal  blood  to  exchange  its  venous  character  for  the  arterial,  by  parting  with 
its  carbonic  acid  to  the  Maternal  blood,  and  receiving  oxygen  from  it ;  but 
they  also  serve  as  rootlets,  by  which  certain  nutritious  elements  of  the  Ma- 
ternal blood  (probably  those  composing  the  liquor  sanguinis)  are  taken  into 
the  system  of  the  Foetus.  There  is  no  more  direct  communication  between 
the  Mother  and  Foetus  than  this ;  all  the  observations  which  have  been  sup- 
posed to  prove  the  existence  of  real  vascular  continuity,  having  been  falsified 
by  the  extravasation  of  fluid,  consequent  upon  the  force  used  in  injecting  the 
vessels.  Moreover,  the  different  size  of  the  blood-corpuscles  in  the  Foetus 
and  in  the  Parent  (§  575)  shows  the  non-existence  of  any  such  communication .t 
750.  The  formation  of  the  Placenta,  in  the  manner  just  described,  com- 
mences in  the  latter  part  of  the  second  month  ;  during  the  third,  it  acquires 
its  proper  character ;  and  it  subsequently  goes  on  increasing,  in  accordance 
with  the  growth  of  the  ovum.  Towards  the  end  of  the  term  of  gestation, 
however,  it  becomes  more  dense  and  less  vascular ;  owing,  it  would  seem,  to 
the  obliteration  of  several  of  the  minuter  vessels,  which  are  converted  into 
hard  fibrous  filaments.  The  vessels  of  the  Uterus  undergo  great  enlargement 
throughout,  but  especially  at  the  part  to  which  the  Placenta  is  attached ;  and 
the  blood  in  moving  through  them  produces  a  peculiar  murmur,  which  is 
usually  distinctly  audible  at  an  early  period  of  Pregnancy,  and  may  be  re- 
garded (when  due  care  is  taken  to  avoid  sources  of  fallacy)  as  one  of  its  most 
unequivocal  positive  signs.  The  Placental  bruit  is  thus  described  by  Dr. 
Montgomery.;}:  "  The  characters  of  this  phenomenon  are,  a  low  murmuring 
or  somewhat  cooing  sound,  resembling  that  made  by  blowing  gently  over  the 
lip  of  a  wide-mouthed  phial,  and  accompanied  by  a  slight  rushing  noise,  but 
without  any  sensation  of  impulse.  The  sound  is,  in  its  return,  exactly 
synchronous  with  the  pulse  of  the  mother  at  the  time  of  examination;  and 
varies  in  the  frequency  of  its  repetitions,  with  any  accidental  variation  which 
may  occur  in  the  maternal  circulation.  Its  situation  does  not  vary  during  the 
course  of  the  same  pregnancy ;  but  in  whatever  region  of  the  uterus  it  is  first 
heard,  it  will  in  future  be  found,  if  recognized  at  all, — for  it  is  liable  to  inter- 
missions,—at  least  we  shall  occasionally  be  unable  to  hear  it  where  we  have 
already  heard  it  a  short  time  before,  and  where  we  shall  shortly  again  recog- 
nize it.  According  to  my  experience,  it  will  be  most  frequently  heard  about 
the  situation  of  the  Fallopian  tube  of  the  right  side  ;  but  it  may  be  detected  in 
any  of  the  lateral  or  anterior  parts  of  the  uterus."  That  the  cause  of  this 
sound  exists  in  the  Uterus  itself,  is  distinctly  proved  by  the  fact,  that  it  has 
been  heard  when  that  organ  was  so  completely  anteverted,  that  the  fundus 

*  A  plan  of  Dr.  Reid's  idea  of  this  structure  is  shown  in  Fig.  24,  (Plate  I.) 
f  That  the  Placenta  is  not  absolutely  necessary  to  the  nutrition  of  the  Human  foetus,  any 
more  than  to  that  of  the  non-placental  Mammalia,  is  a  doctrine  that  has  been  maintained 
by  several  physiologists  of  eminence;  in  consequence  of  the  not  very  unfrequent  occur- 
rence of  cases,  in  which  it  has  been  very  imperfectly  formed,  so  as  to  be  manifestly 
unfit,  at  least  in  great  degree,  for  the  performance  of  its  functions :  and  it  cannot  but  be 
admitted  that  there  is  much  evidence  in  support  of  this  view.  In  those  cases,  however, 
in  which  the  Placenta  has  been  from  the  first  imperfectly  formed,  the  nutrition  of  the 
foetus  has  manifestly  suffered;  whilst  in  those  in  which  a  degeneration  of  its  structure 
has  taken  place  (as  by  the  deposition  of  calcareous  matter),  there  is  no  evidence  that,  up 
to  a  late  period  of  pregnancy,  the  foetus  may  not  have  been  nourished  through  its  means. 
For  a  collection  of  such  cases,  see  Dr.  Dunglison's  Physiology,  vol.  ii.  [p.  448]. 
t  Op.  cit.  p.  121. 


ACTION  OF  THE  FEMALE. 

hung  down  between  the  patient's  thighs.  A  sound  so  much  resembling  this, 
as  to  be  scarcely  distinguishable  from  it,  may  be  occasioned,  however,  by  a 
cause  of  a  very  different  nature, — namely,  an  abdominal  tumour,  pressing 
upon  the  aorta,  iliac  arteries,  or  enlarged  vessels  of  its  own  ;  and,  in  doubtful 
cases,  it  is  necessary  to  give  full  weight  to  the  possibility  of  such  an  explana- 
tion. The  sound  may  be  imitated  at  any  time,  by  pressing  the  stethoscope 
on  the  iliac  arteries.  The  Placental  bruit  has  been  not  unfrequently  heard  in 
the  llth  week  ;  but  it  cannot  generally  be  detected  before  the  fourth  month, 
when  the  fundus  uteri  rises  above  the  anterior  wall  of  the  pelvis. 

751.  The  amount  of  the  peculiar  tissue  of  the  Uterus  (§  375)  greatly  in- 
creases during  pregnancy ;  and  from  the  recent  observations  of  Dr.  R.  Lee, 
it  appears  that  a  corresponding  increase  takes  place  in  the  size  of  the  Nervous 
Ganglia.     At  the  same  time  the  Mammary  gland  and  its  appendages  undergo 
a  fuller  development ;  and  from  this  a  valuable,  but  not  unequivocal  indication 
of  pregnancy  may  be  drawn.     Occasional  shooting  pains  in  the  Mammae  are 
not  unfrequently  experienced  within  a  short  period  after  conception;    and 
more  continued  tenderness  is  also  not  unusual.     A  sense  of  distension  is  very 
commonly  experienced  at  about  the  end  of  the  second  month ;  and  from  that 
time  a  distinct  "  knottiness"  usually  begins  to  present  itself,  increasing  with 
the  advance  of  Pregnancy.     In  many  instances,  however,  these  mammary 
sympathies  are  entirely  absent ;  and  they  may  be  simulated  by  changes  that 
take  place  in  consequence  of  various  affections  of  the  Uterus.     A  change  of 
colour  in  the  areola  is  a  very  common,  but  not  an  invariable  occurrence  in 
the  early  months  of  pregnancy ;  but  another  sign  is  afforded  by  the  areola  and 
nipple,  which  is  of  more   value   because  more   constant, — namely,  a  puffy 
turgescence,  and  an  increased  development  of  the  little  glandular  follicles, 
or  tubercles,  which  commonly  secrete  a  dewy  moisture.— The  presence  or 
absence  of  kiestine  in  the  Urine  (§  690)  also  may  probably  be  regarded  as  a 
valuable  diagnostic  sign.     This  substance  appears  on  the  surface  of  the  fluid, 
after  it  has  stood  two  or  three  days,  in  the  form  of  a  thin  pellicle  of  a  some- 
what fatty  aspect ;    it  is  preceded  by  a  sediment  which  has  very  much  the 
appearance  of  cotton  wool ;  and  it  disappears  when  the  urine  is  decomposing, 
at  the  same  time  emitting  an  odour  like  that  of  putrid  cheese.* — Many  other 
changes  in  the  constitution  take  place  during  Pregnancy ;    indicated  by  the 
buffiness  of  the  blood,  the  irritability  of  the  stomach,  and  the  increased  excit- 
ability of  the  mind.     All  these,  however,  are  discussed  with  sufficient  ampli- 
fication, in  works  on  Obstetric  Medicine. 

752.  The  act  of  Conception,  being  one  of  a  purely  organic  nature,  is  not 
attended  with  any  consciousness  on  the  part  of  the  mother ;    but  there  are 
some  women,  in  whom  it  is  attended  with  certain  sympathetic  affections,  such 
as  faintness,  vertigo,  &c.,  that  enable  them  to  fix  upon  the  particular  time  at 
which  it  has  taken  place.     From  that  period,  however,  the  Mother  has  no 
direct  consciousness  of  the  change  going  on  in  the  Uterus  (save  by  the  effects 
of  its  increasing  pressure  on  other  parts),  until  the  occurrence  of  what  is 
termed  "  Quickening."     This  is  generally  described  as  a  kind  of  fluttering 
movement,  attended  with  some  degree  of  syncope  or  vertigo.     After  it  has 
once  occurred,  and  has  strongly  excited  attention,  it  is  occasionally  renewed 
once  or  twice,  and  then  gives  place  to  the  ordinary  movements  of  the  foetus. 
Not  unfrequently,  however,  no  movement  whatever  is  felt,  until  near  the  end 
of  the  term  of  gestation,  or  even  through  the  whole  of  it.     As  to  the  cause  of 
the  sensation,  Obstetricians  are  much  divided;    and  no  satisfactory  account 
has  been  given  of  it.     It  has  been  vulgarly  supposed  to  be  due  to  the  first 

*  [See  an  excellent  paper  on  this  subject  in  the  American  Journal  of  Medical  Sciences, 
No.  vii.  N.  S.;  by  Dr.  Elisha  Kane.— M.  C.] 

51* 

I 


606  OF  REPRODUCTION. 

movement  of  the  Foetus,  which  was  imagined  then  to  become  possessed  of  an 
independent  life :  and  the  English  law  recognizes  the  truth  of  this  doctrine, 
in  varying  the  punishment  of  an  attempt  to  procure  Abortion,  according  to 
whether  the  woman  be  "quick  with  child"  or  not ;  and  in  delaying  execution 
when  a  woman  can  be  proved  to  be  so,  though  it  is  made  to  proceed  if  she  is 
not,  even  if  she  be  unquestionably  pregnant.  Whether  or  not  the  first  sensible 
motions  of  the  Foetus  are  the  cause  of  the  peculiar  feeling  in  question,  there 
can  be  no  doubt  that  the  Embryo  has  as  much  independent  vitality  before,  as 
after,  the  quickening.  From  the  time  that  the  Ovum  quits  the  Ovary,  it 
ceases  to  be  a  part  of  the  Parent,  and  is  dependent  on  it  only  for  a  due  supply 
of  nourishment,  which  it  converts,  by  its  own  inherent  powers,  into  its  proper 
fabric.  This  dependence  cannot  be  said  to  cease  at  the  moment  of  quicken- 
ing ;  for  the  connection  must  be  prolonged  during  several  weeks,  before  the 
Fostus  can  be  said  to  be  capable  of  living  without  such  assistance.  The 
earliest  period  at  which  this  may  occur,  will  be  presently  considered  (§  756). 
753.  At  the  conclusion  of  about  nine  (solar)  months  from  the  period  of  con- 
ception, the  time  of  Parturition  arrives.  The  Uterus,  by  its  own  efforts,  and 
by  the  assistance  of  the  muscles  of  Expiration,  expels  its  contents ;  and  the 
membranes  of  the  Ovum  being  usually  ruptured  before  it  is  entirely  dis- 
charged, the  Foetus  comes  at  once  into  the  world.  Although  there  can  be  no 
doubt  that,  as  already  stated  (§  203),  the  contractile  fibres  of  the  Uterus  may 
be  called  into  effectual  action  without  Nervous  influence,  yet  it  is  equally  cer- 
tain that  Uterine  contractions  may  be  induced  through  the  Spinal  system  of 
nerves.  For  in  no  other  way  can  we  account  for  many  phenomena,  which 
are  obviously  of  a  reflex  character;  such  as  the  sudden  contraction  of  the 
Uterus,  previously  distended  and  inactive,  when  cold  is  applied  to  the  ex- 
ternal surface  of  the  body,  or  when  the  child  is  applied  to  the  nipple.  In  the 
first  stage  of  labour,  the  Uterine  contractions  appear  to  be  alone  concerned ; 
and  it  is  not  until  the  head  of  the  child  is  passing  through  the  Os  Uteri,  and 
is  entering  the  Vagina,  that  the  assistance  of  the  Expiratory  muscles  is  called 
in.  The  excitor  fibres,  which  convey  to  the  Spinal  Cord  the  stimulus  to  their 
actions,  must  originate,  therefore,  rather  in  the  Vagina  than  in  the  Uterus 
itself.  Whilst  the  fibres  of  the  fundus  and  body  of  the  Uterus  are  in  power- 
ful contraction,  those  of  the  Cervix  Uteri  and  Vagina  must  be  in  a  state  of 
dilatation ;  and  this  dilatation  appears  to  be  in  some  respects  different  from 
the  mere  yielding  to  the  pressure  of  the  child's  head.  A  slow  contraction  of 
the  fibres  of  the  fundus  and  body  of  the  Uterus,  and  a  yielding  of  those  of  the 
cervix,  usually  take  place  during  some  days  previous  to  Parturition ;  so  that 
the  child  lies  lower,  and  the  size  of  the  abdomen  diminishes.*  As  to  the 
reason  why  the  period  of  Parturition  should  be  just  nine  months  after  that  of 
Conception,  we  know  nothing  more  than  we  do  of  that  of  similar  facts  in  the 
physical  history  of  Man. — such  as  the  periodical  return  of  the  Catamenia, — 
the  renewal  of  the  Teeth, — the  recurrence  of  the  tendency  to  Sleep,  &c.  That 
it  is  immediately  dependent  upon  some  state  of  the  constitution,  rather  than 
upon  the  condition  of  the  Uterus,  appears  from  the  fact  that,  in  cases  of  Extra- 
uterine  pregnancy,  contractions  resembling  those  of  labour  take  place  in  its 
walls.  Moreover,  various  states  of  the  constitution,  especially  that  which  is 
designated  as  irritability,  may  induce  the  occurrence  of  the  parturient  efforts 
at  an  earlier  period ;  and  this  constitutes  Abortion,  or  Premature  delivery, 
according  to  the  viability  of  the  child.  There  are  some  women,  in  whom 
this  regularly  happens  at  a  certain  month,  so  that  it  seems  to  be  an  action 
natural  to  them ;  but  it  is  always  to  be  prevented,  if  possible,  being  injurious 

*  See  some  interesting  Papers  on  the  Physiology  of  Parturition,  by  Dr.  W.Tyler  Smith, 
in  the  Lancet,  July  6  and  13,  1.-44. 


ACTION  OF  THE  FEMALE.  GOT 

alike  to  the  mother  and  child ;  and  this  prevention  is  to  be  attempted  by  rest 
and  tranquillity  of  mind  and  body,  and  by  a  careful  avoidance  of  all  the  ex- 
citing causes  which  may  produce  Uterine  contractions  by  their  operation  on 
the  Nervous  system.  For  it  is  to  be  remembered  that,  although  the  muscular 
fibres  of  the  Uterus  are  capable,  like  those  of  the  alimentary  canal,  of  an  inde- 
pendent action,  they  are  likely  to  be  excited  to  operation  through  the  Nervous 
system,  and  especially  through  the  Sympathetic  (§  203).  The  same  action 
which  expels  the  Fretus  also  detaches  the  Placenta;  and  if  the  Uterus  con- 
tract with  sufficient  force  after  this  has  been  thrown  off,  the  orifices  of  the 
vessels  which  communicated  with  it  are  so  effectually  closed,  that  little  or  no 
hemorrhage  takes  place.  If,  however,  the  Uterus  does  not  contract,  or  relaxes 
after  having  contracted,  a  large  amount  of  blood  may  be  lost  in  a  short  time 
from  the  open  orifices.  For  some  little  time  after  Parturition,  a  sero-sanguine- 
ous  discharge,  termed  the  Lochia,  is  poured  out  from  the  Uterus;  and  this 
commonly  contains  shreds  of  the  Deciduous  membrane,  which  had  not  been 
previously  detached.  Within  a  few  weeks  after  delivery,  the  Uterus  regains 
(at  least  in  a  healthy  subject)  its  previous  condition;  and  it  is  probable  that 
the  portion  of  its  mucous  Membrane,  which  had  been  thrown  off  as  Decidua, 
is  very  early  reproduced. 

754.  Although  the  duration  of  Pregnancy  is  commonly  stated  at  nine  solar 
months,  it  would  be  more  correct  to  fix  the  period  at  40  weeks,  or  280  days ; 
which  exceeds  nine  months  by  from  5  to  7  days,  according  to  the  months  in- 
cluded.    This,  at  least,  is  the  average  result  of  observation,  in  cases  in  which 
the  period  of  Conception  could  be  fixed,  from  peculiar  circumstances,  with 
something  like  certainty.     The  mode  of  reckoning  customary  among  women, 
is  to  date  from  the  middle  of  the  month  after  the  last  appearance  of  the  Cata- 
menia  ;  but  it  is  certain  Conception  is  much  more  likely  to  take  place  soon 
after  they  have  ceased  to  flow,  or  even  before  their  access,  than  at  a  later  period 
(§  742) ;  so  that,  in  most  instances,  it  would  be  most  correct  to  expect  Labour 
at  forty  weeks  and  a  few  days  after  the  last  recurrence  of  the  Menses.     The 
period  of  Quickening  may  be  relied  on  in  some  women,  in  whom  it  occurs 
with  great  regularity  in  a  certain  week  of  Pregnancy ;  but  there  is  in  general 
great  latitude  as  to  the  time  of  its  occurrence.     The  usual  or  average  time  is 
probably  about  the  18th  week. 

755.  The  question  of  the  extreme  limits  of  Gestation  is  one  of  great  import- 
ance both  to  the  Practitioner  and  to  the  Medical  Jurist ;  but  it  is  one  which 
cannot  yet  be  regarded  as  satisfactorily  decided.     Many  persons,  whose  expe- 
rience should  give  much  weight  to  their  opinion,  maintain  that  the  regular 
period  of  40  weeks  is  never  exterlded  for  more  than  two  or  three  days;  whilst, 
on  the  other  hand,  there  are  numerous  cases  on  record,  which,  if  testimony  is 
to  be  believed  at  all,  (and  in  many  of  these,  the  character  and  circumstances 
of  the  parties  placed  them  above  suspicion,)  furnish  ample  evidence  that  Ges- 
tation may  be  prolonged  for  at  least  three  weeks  beyond  the  regular  term.* 
The  English  law  fixes  no  precise  limit ;  and  the  decisions  which  have  been 
given  in  our  courts,  when  questions  of  this  kind  have  been  raised,  have  been 
mostly  formed  upon  the  collateral  circumstances.  The  law  of  France  provides 
that  me  legitimacy  of  a  child  born  within  300  days  after  the  death  or  departure 
of  the  husband  shall  not  be  questioned ;  and  a  child  born  after  more  than  300 
days  is  not  declared  a  bastard,  but  its  legitimacy  may  be  contested.     By  the 
Scotch  law,  a  child  is  not  declared  a  bastard,  unless  born  after  the  tenth  month 
from  the  death  or  departure  of  the  husband. — The  analogical  evidence  drawn 
from  observations  on  the  lower  animals  is  extremely  strong.   The  observations 

*  A  good  collection  of  such  cases  will  be  found  in  Dr.  Montgomery's  excellent  work 
on  the  Signs  of  Pi  egnancy. 


608  OF  REPRODUCTION. 

of  Tessier,  which  were  continued  during  a  period  of  forty  years,  with  every 
precaution  against  inaccuracy,  have  furnished  a  body  of  results  which  seems 
quite  decisive.  In  the  Cow,  the  ordinary  period  of  gestation  is  about  the  same 
as  in  the  Human  female  ;  but  out  of  577  individuals,  no  less  than  20  calved 
beyond  the  298th  day,  and  of  these,  some  went  on  to  the  321st,  making  an 
excess  of  nearly  six  weeks.  Of  447  Mares,  whose  natural  period  of  gesta- 
tion is  about  335  days,  42  foaled  between  the  359th  and  the  419th  day,  the 
greatest  protraction  being  thus  84  days,  or  just  one-fourth  of  the  usual  term. 
Of  912  Sheep,  whose  natural  period  is  about  151  days,  96  yeaned  beyond  the 
153d  day  ;  and  of  these,  7  went  on  until  the  157th  day,  making  an  excess  of 
6  days.  Of  161  Rabbits,  whose  natural  period  is  about  30  days,  no  fewer  than 
25  littered  between  the  32d  and  35th ;  the  greatest  protraction  was  here  one- 
sixth  of  the  whole  period,  and  the  proportion  in  which  there  was  a  manifest 
prolongation  was  also  nearly  one-sixth  of  the  total  number  of  individuals.  In 
the  Incubation  of  the  common  Hen,  Tessier  found  that  there  was  not  unfre- 
quently  a  prolongation  to  the  amount  of  3  days,  or  one-seventh  of  the  whole 
period.  In  regard  to  Cows,  the  observations  of  Tessier  have  been  recently 
confirmed  by  those  of  Earl  Spencer,  who  has  published*  a  table  of  the  period 
of  gestation  as  observed  in  764  individuals  ;  he  considers  the  average  period 
to  be  284  or  285  days :  but  no  fewer  than  310  calved  after  the  285th  day  ; 
arid  of  these,  3  went  on  to  the  306th  day,  and  1  to  the  313th.  It  is  curious 
that,  among  the  calves  born  between  the  290th  and  300th  days,  there  was  a 
decided  preponderance  of  males, — these  being  74,  to  32  females  ;  whilst  all  of 
those  born  after  the  300th  day  were  females.!  These  variations  are  probably 
to  be  regarded  as  due,  not  so  much  to  a  prolongation  of  the  period  of  Utero- 
gestation,  as  to  various  circumstances  which  may  have  a  retarding  influence 
on  the  process  of  Fecundation,  and  on  the  transmission  of  the  Ovum  through 
the  Fallopian  tube.  These  have  been  well  pointed  out  by  Dr.  Montgomery.^ 
It  may  be  added  that,  in  Dr.  Barry's  observations  on  the  early  changes  that 
take  place  in  the  Ovum  of  Rabbits,  he  has  noticed  several  irregularities  of  this 
description.*— On  the  whole,  it  may  be  considered  that  in  regard  to  the  Human 
female,  the  French  law  is  a  very  reasonable  one.  It  is  probable,  from  the  cir- 
cumstances alluded  to  in  the  preceding  paragraph,  that  Gestation  is  protracted 
to  the  extent  of  a  week,  ten  days,  or  a  fortnight,  much  more  frequently  than 
is  commonly  supposed.  In  several  of  the  cases  in  which  the  protraction  ap- 
peared indubitable,  the  Infant  was  unusually  large  and  vigorous. 

756.  In  regard  to  the  shortest  period  at  which  Gestation  may  terminate, 
consistently  with  the  viability  of  the  Child,  there  is  a  still  greater  degree  of 
uncertainty.  Most  practitioners  are  of  opinion,  that  it  is  next  to  impossible 
for  a  Child  to  live  and  grow  to  maturity,  which  has  not  almost  completed  its 
seventh  month ;  but  it  is  almost  unquestionable  that  Infants  which  have  been 
born  at  a  much  earlier  period,  have  lived  for  some  months.  It  is  rare  in  such 
cases,  however,  that  the  date  of  Conception  can  be  fixed  with  sufficient  pre- 
cision, to  enable  a  definite  statement  to  be  given.  Of  the  importance  of  the 
question,  a  case  which  recently  occurred  in  Scotland  afFords  sufficient  proof. 

*  Journal  of  the  English  Agricultural  Society,  1839. 

f  It  appears,  however,  from  some  recent  statements  published  on  the  authority  of  Earl 
Spencer,  that  the  Male  may  exert  an  important  influence  on  the  period  of  gestation.  Of 
75  Cows  in  calf  by  a  particular  bull,  the  average  period  was  2884  days,  or  four  days 
more  than  the  usual  period.  Of  the  764  cows  previously  mentioned,  185  (nearly  one- 
fourth)  went  less  than  281  days;  whilst  not  one  of  the  cows  in  calf  to  this  bull  did  so. 
On  the  other  hand,  of  the  764  cows  first  mentioned,  111  (rather  more  than  one-seventh) 
went  above  289  days;  while  by  this  bull  29  out  of  75  (nearly  two-fifths)  went  above  289 
days. — Dr.  J.  C.  Hall,  in  Medical  Gazette,  May  6,  1842. 

t  Op.  cit.,  p.  272. 


ACTION  OF  THE  FEMALE.  609 

A  vast  amount  of  contradictory  evidence  was  adduced  on  this  trial ;  but,  on  the 
general  rule  of  accepting  positive  in  preference  to  negative  testimony,  it  seems 
that  we  ought  to  consider  it  possible,  that  a  child  may  live  for  some  months, 
which  has  been  born  at  the  conclusion  of  24  weeks  of  gestation.  In  the  case 
in  question,  the  Presbytery  decided  in  favour  of  the  legitimacy  of  an  Infant 
born  alive  within  25  weeks  after  marriage. — A  very  interesting  case  is  on 
record,*  in  which  the  mother  (who  had  borne  five  children)  was  confident  that 
her  period  of  gestation  was  less  than  19  weeks ;  the  facts  stated  respecting 
the  development  of  the  child  are  necessarily  very  imperfect,  as  it  was  imporr- 
ant  to  avoid  exposing  his  body,  in  order  that  his  temperature  might  be  kept 
up ;  but  at  the  age  of  three  weeks,  he  was  only  13  inches  in  length,  and  his 
weight  was  no  mor^e  than  29  oz.  At  that  time  he  might  be  regarded,  accord- 
ing to  the  calculation  of  the  mother,  as  corresponding  with  an  infant  of  22 
weeks  or  5£  months ;  but  the  length  and  weight  were  greater  than  is  usual  at 
that  period,  and  he  must  have  been  probably  born  at  about  the  25th  week.  It 
is  an  interesting  feature  in  this  case,  that  the  calorific  power  of  the  Infant  was 
so  low,  that  artificial  heat  was  constantly  needed  to  sustain  it ;  but  that,  under 
the  influence  of  the  heat  of  the  fire,  he  evidently  became  weaker,  whilst  the 
warmth  of  a  person  in  bed  rendered  him  lively  and  comparatively  strong. 
During  the  first  week  it  was  extremely  difficult  to  get  him  to  swallow ;  and  It 
was  nearly  a  month  before  he  could  suck.  At  the  time  of  the  report,  he  was 
four  months  old,  and  his  health  appeared  very  good. — Another  case  of  very 
early  viability  has  been  more  recently  put  on  record  by  Mr.  Dodd  :t  in  this, 
as  in  the  former  instance,  the  determination  of  the  child's  age  rests  chiefly  on 
the  opinion  of  the  mother ;  but  there  appears  no  reason  for  suspecting  any 
fallacy.  The  child  seems  to  have  been  born  at  the  20th  or  27th  week  of 
gestation;  and  having  been  placed  under  judicious  management,  it  has  thriven 
well. — One  of  the  most  satisfactory  cases  on  record,  is  that  detailed  by  Dr. 
Outrepont  (Professor  of  Obstetrics  at  Wurtzburgh),  and  stated  by  Dr.  Chris- 
tison  in  his  evidence  on  the  case  just  alluded  to.J  The  evidence  is  as  complete 
as  it  is  possible  to  be  in  any  case  of  the  kind  ;  being  derived  not  only  from  the 
date  assigned  by  the  Mother  to  her  Conception,  but  also  from  the  structure  and 
history  of  the  Child.  The  Gestation  could  have  only  lasted  27  weeks,  and 
was  very  probably  less.  The  length  of  the  child  was  13£  inches,  and  its 
weight  was  24  oz.  Its  development  was  altogether  slow  ;  and  at  the  age  of 
eleven  years,  the  child  seemed  no  more  advanced  in  body  or  mind  than  most 
other  lads  of  seven  years  old.  In  this  last  point  there  is  a  very  striking* 
correspondence  with  the  results  of  other  observations  upon  very  premature 
children,  made  at  an  earlier  age  :  and  these  all  harmonize  with  the  general 
principle  already  more  than  once  alluded  to,— *that  the  shorter  the  period 
during  which  the  early  development  of  the  embryo  takes  place  at  the  expense 
of  nourishment  supplied  by  the  parent,  the  lower  is  the  degree  of  development 
it  will  ultimately  attain  (§  54). — To  these  may  be  added  another  case  of  recent 
occurrence  in  America  ;  in  which  a  woman,  who  believed  herself  to  be  in  the 
sixth  month  of  pregnancy,  was  prematurely  delivered  in  consequence  of  a 
fall.  The  child  seemed  barely  alive,  showing  scarcely  any  motion,  and  being 
too  feeble  to  cry.  It  had  no  nails  on  its  hands  or  feet,  nor  hair  on  the  scalp ; 
and  the  cranium  was  imperfectly  ossified.  At  the  end  of  seven  weeks  it  was 
weighed  for  the  first  time,  and  found  to  weigh  only  26  oz.  When  ten  months 
old,  it  was  playful,  lively,  and  healthy ;  and  weighed  lOj  Ibs.  The  reporter 
of  this  case  regrets  that  he  did  not  take  more  particular  notice  of  the  state  of 

*  Edinb.  Med.  and  Surg.  Journal,  vol.  xi. 

f  Provincial  Medical  and  Surgical  Journal,  vol.  ii.  p.  474. 

$  Report  of  Proceedings  against  the  Rev.  Fergus  Jardine,  Edinb.,  1839. 


610  OF  REPRODUCTION. 

the  Child  at  birth,  which  he  was  prevented  from  doing  by  the  daily  expecta- 
tion of  its  death.* 

758.  There  is  another  question  regarding  the  Function  of  the  Female  in 
the  Reproductive  act,  which  is  of  great  interest  in  a  scientific  point  of  view, 
and  which  may  become  of  importance  in  Juridical  inquiries, — namely,  the 
possibility  of  Superfcetation,  that  is,  of  two  distinct  conceptions  at  an  interval 
of  greater  or  less  duration  ;  so  that  two  fetuses  of  different  ages,  the  offspring 
perhaps  of  different  parents,  may  exist  in  the  Uterus  at  the  same  time. — The 
simplest  case  of  Superfetation*  the  frequent  occurrence  of  which  places  it 
beyond  reasonable  doubt,  is  that  in  which  a  Female  has  intercourse  on  the 
same  day  with  two  Males  of  different  complexions,  and  bears  twins  at  the  full 
time ;  the  two  infants  resembling  the  two  parents  respectively.  Thus,  in  the 
slave-states  of  America,  it  is  not  uncommon  for  a  black  woman  to  bear  at  the 
same  time  a  black  and  a  mulatto  child ;  the  former  being  the  offspring  of  her 
black  husband,  and  the  latter  of  her  white  paramour.  The  converse  has  occa- 
sionally, though  less  frequently,  occurred;  a  white  woman  bearing  at  the 
same  time  a  white  and  a  mulatto  child.  There  is  no  difficulty  in  accounting 
for  such  facts,  when  it  is  remembered  that  nothing  has  occurred  to  prevent 
the  Uterus  and  Ovaria  from  being  as  ready  for  the  second  conception  as  for 
the  first;  since  the  orifice  of  the  former  is  not  yet  closed  up;  and,  at  the  time 
when  one  Ovum  is  matured  for  fecundation,  there  are  usually  more  in  the 
same  condition. — But  it  is  not  easy  thus  to  account  for  the  birth  of  two  children, 
each  apparently  mature,  at  an  interval  of  five  or  six  months;  since  it  might 
have  been  supposed  that  the  uterus  was  so  completely  occupied  with  the  first 
Ovum,  as  not  to  allow  of  the  transmission  of  the  seminal  fluid,  necessary  for 
the  fecundation  of  the  second.  In  cases  where  two  children  have  been  pro- 
duced at  the  same  time,  one  of  which  was  fully-formed,  whilst  the  other  was 
small  and  seemingly  premature,  there  is  no  occasion  whatever  to  imagine  that 
the  two  were  conceived  at  different  periods;  since  the  smaller  fetus  may  have 
been  "  blighted,"  and  its  development  retarded,  as  not  unfrequently  happens 
in  other  cases.  Nor  is  it  necessary  to  infer  the  occurrence  of  Superfetation 
in  every  case,  in  which  a  living  child  has  been  produced  a  month  or  two  after 
the  birth  of  another;  since  the  latter  may  have  been  premature,  whilst  the 
former  has  been  carried  to  the  full  term.  But  such  a  difference  can  scarcely 
be,  at  the  most,  more  than  2£  or  three  months ;  and  there  are  several  cases 
now  on  record,  in  which  the  interval  was  from  110  to  170  days,  whilst  neither 
of  the  children  were  premature  in  appearance;  so  that  the  possibility  of  a 
second  Conception,  when  the  Uterus  already  contains  an  Ovum  of  several 
months,  can  scarcely  be  denied,  however  improbable  it  may  seem. 

IV.  Development  of  the  Embryo. 

757.  Under  this  head  it  is  intended  to  state,  not  so  much  the  details  of  the 
process  of  Development,  as  those  leading  facts,  the  knowledge  of  which  is 
desirable  in  itself,  as  well  as  essential  to  the  due  comprehension  of  the  former. 
It  is  difficult  to  see  what  practical  benefit  can  result  from  a  minute  acquaint- 
ance with  all  the  steps  of  the  evolution  of  the  Embryo,  however  interesting 
these  may  be  in  a  scientific  point  of  view ;  and  the  time  of  the  ordinary  Stu- 
dent, on  which  there  are  so  many  pressing  calls,  may  be  much  better  occu- 
pied than  in  committing  them  to  memory.  In  the  following  sketch,  little 
will  be  said  respecting  the  later  stages  of  the  process,  or  the  development  of 
particular  organs,  since  these  have  been  already  noticed  under  their  several 
distinct  heads.  Our  attention  will  first  be  given  to  the  formation  of  the  Em- 

*  American  Journal  of  the  Medical  Sciences,  April,  1843. 


DEVELOPMENT  OF  THE  EMBRYO.  611 

bryonic  mass,  and  of  the  membranes  surrounding  the  Yolk-bag;  and  then  to 
the  origin  of  the  Vertebral  column,  Digestive  organs,  and  Circulating  apparatus. 

758.  The  Ovum,  when  it  quits  the  Ovariurn,  has  been  stated  to  contain 
within  the  Germinal  Vesicle,  two  cells  which  did  not  exist  there  previously  to 
fecundation :  and  from  each  of  these,  two  new  cells  are  subsequently  produced, 
which  in  their  turn  give  birth  to  eight  others  (§  745).     In  this  manner,  the 
number  of  vesicles  originating  in  the  twin-cells  of  the  Germ  is  continually 
increased,  until  at  last  they  become  too  numerous  to  be  counted,  and  form  a 
cluster  resembling  a  Mulberry  in  appearance;  this  mulberry-like  structure 
may  be  conveniently  termed  the  Germinal  Mass  (Plate  I.  Fig.  15,  a).     In  the 
centre  of  this  mass  there  is  found  a  peculiar  Cell,  differing  from  the  rest  in  its 
greater  size,  and  in  possessing  a  very  well  defined  annular  nucleus,  with  a  pel- 
lucid cavity  in  its  centre  (Fig.  16,  a,  b).     From  this  peculiar  Cell,  all  the  parts 
which  enter  permanently  into  the  composition  of  the  Embryo  are  developed ; 
the  vesicles  forming  the  exterior  of  the  germinal  mass  being  subservient  to  a 
merely  temporary  purpose.     This  central  or  Embryonic  Cell   is  gradually 
brought  to  the  surface  of  the  Germinal  Mass,  by  the  formation  of  a  cavity  (c) 
in  the  interior  of  the  latter ;  for  the  layer  of  cells  within  which  this  cavity  is 
formed,  progressively  extends  itself,  until  it  comes  into  contact  with  the  inner 
surface  of  the  Yolk-bag,  having  absorbed  the  yolk  into  the  hollow  thus  left. 
Thus  out  of  the  periphery  of  the  Mulberry-mass,  appears  to  be  formed  the 
exterior  layer  of  what  is  termed  the  Germinal  Membrane;  this  membrane  is 
first  seen  as  an  epithelium-like  layer  of  cells,  covering  the  Yolk;  but  beneath 
this  layer,  which  is  afterwards  known  as  the  serous  lamina  of  the  Germinal 
membrane,  two  others  are  subsequently  produced  from  the  central  portion  of 
the  Germinal  mass.     Now  it  is  highly  interesting  to  observe,  that  this  Ger- 
minal Membrane,  which  in  the  higher  animals  is  a  mere  temporary  structure, 
subservient  only  to  a  temporary  function,  forms,  in  the  lower  tribes,  the  greater 
part  of  the  permanent  fabric  of  the  body.     Thus,  in  the  Polypes,  the  cavity  in 
which  the  Yolk«s  enclosed  becomes  a  Stomach;  the  external  layer  of  the 
Germinal  Membrane  becomes  the  integument ;  whilst  the  internal  forms  the 
lining  of  the  Digestive  cavity,  of  which  the  mouth  is  formed  by  absorption  of 
its  wall  at  one  point.     Here  the  Yolk  is  directly  absorbed  and  assimilated  by 
the  surrounding  membrane.     In  the  higher  Oviparous  animals,  the  Germinal 
Membrane  serves  to  absorb  nutritious  matter  from  the  Yolk,  and  to  prepare  it 
for  the  use  of  the  Embryo  itself,  by  converting  it  into  Biood  (§  762) ;  but,  after 
the  Yolk  has  been  exhausted,  the  Yolk-bag  is  taken  into  the  body,  and  is 
gradually  removed  by  absorption.     In  Mammalia,  these  structures  are  of  less 
importance.     The  store  of  Yolk,  laid  up  for  the  nutrition  of  the  Embryo,  is 
comparatively  inconsiderable  ;  being  only  destined  to  serve  for  the  short  time 
that  elapses,  before  the   Ovum  forms  its  new  connection  with  the  Parent, 
through  the  medium  of  the  Chorion;  and  the  Yolk-bag  is  ultimately  separated 
from  the  Embryo,  and  thrown  off  as  useless.     Still  the  early  processes  are  the 
same  in  Mammiferous,  as  they  are  in  Oviparous  animals ;  and  the  Develop- 
ment of  Man,  of  a  Bird,  of  a  Reptile,  or  of  a  Fish,  takes  place,  up  to  a  certain 
point,  upon  the  same  general  plan. 

759.  The  Embryonic  Cell,  and  the  cluster  of  cells  that  surrounds  it,  having 
arrived  on  the  surface  of  the  Yolk  by  the  movement  just  described,  constitute 
what  is  known  in  the  Bird's  egg  under  the  name  of  the  Cicatricula.     This  is 
a  semi-opaque  disc,  composed  of  numerous  flattened  cells  ;  and  in  the  midst 
of  it  is  seen  a  round  transparent  space,  termed  the  Area  Pellucida,  which  is 
nothing  else  than  the  place  occupied  by  the  large  Embryonic  Cell,  now  become 
flattened,  and  still  retaining  its  clearness.     In  the  centre  of  this  is  seen  a  very 
faint  line,  which  is  termed  the  Primitive  Trace;  and  this  is  the  large  annular 
Nucleus  (Fig.  16,  b)  of  the  Embryonic  Cell,  now  become  elongated,  and  itself 


612  OF  REPRODUCTION. 

beginning  to  be  developed  into  cells.  The  same  process  then  takes  place 
within  the  Embryonic  Cell,  which  has  been  described  as  occurring  within  the 
Germinal  Vesicle  (§  745) ;  the  granules  forming  the  periphery  of  the  nucleus 
are  first  developed  into  cells,  and  these  are  pushed  outwards  by  a  new  series 
subsequently  generated  nearer  the  centre.  From  the  mass  of  cells  thus  formed, 
a  hollow  process  passes  down  into  the  Yolk  ;  and  this  gradually  extends  itself, 
in  the  s,ame  manner  as  did  that  formed  from  the  Mulberry-mass,  until  it  includes 
the  whole  Yolk,  and  cornes  into  contact  with  the  inner  surface  of  the  layer  of 
cells  already  mentioned  as  forming  the  serous  or  external  lamina  of  the  Ger- 
minal Membrane.  This  second  layer  of  cells  is  probably  that  which  forms 
the  vascular  lamina  of  the  Germinal  Membrane.  A  third  process  seems  to  be 
afterwards  sent  down,  from  a  part  of  the  nucleus  somewhat  interior  to  that 
from  which  the  last  proceeded ;  and  this  becomes  the  mucous  or  internal 
lamina  of  the  Germinal  Membrane. 

760.  The  cell-germs  forming  the  periphery  of  the  Nucleus  having  been 
thus  developed,  those  nearer  the  centre  then  begin  to  exhibit  a  corresponding 
activity.  Their  evolution  follows  exactly  the  same  plan  as  that  which  has 
been  described  in  regard  to  the  contents  of  the  Germinal  Vesicle  (§  745) ;  with 
the  exception  that  these  are  arranged  in  an  elongated  and  not  in  a  circular 
form.  The  shape  of  the  nucleus  at  this  time  may  be  compared  to  that  of  a 
pear ;  the  large  end  marking  the  situation  of  the  Head ;  whilst  the  prolonged 
portion  is  the  rudiment  of  the  body.  On  the  median  line  is  seen  a  groove, 
occupying  the  situation  in  which  the  Nervous  Centres  are  to  be  subsequently 
evolved  (Fig.  25,  Plate  II.).  These,  when  first  developed,  are  surrounded  by 
a  tubular  structure,  which  has  but  a  temporary  existence  in  the  higher  Ver- 
tebrata,  but  which  is  permanent  in  the  lower  Fishes  :  this  structure,  termed 
the  Chorda  Dorsalis,  is  found,  wherever  it  exists,  to  be  entirely  composed  of 
nucleated  cells.  From  the  cells  which  are  exterior  to  these,  is  produced  the 
Vertebral  Column ;  and  the  mode  in  which  this  originates  is  somewhat  as 
follows.  The  cells  on  either  side  of  the  central  space  (in  v^hich  the  elements 
of  the  nervous  system  are  not  yet  developed)  rise  up  in  a  ridge,  so  that  the 
central  space  becomes  a  groove ;  these  two  ridges  gradually  rise  up  and 
approach  one  another,  and  they  are  then  observed  to  contain,  in  what  sub- 
sequently becomes  the  thoracic  region,  a  few  pairs  of  small  opaque  plates. 
The  ridges  (termed  plicae  dorsales,  or  dorsal  laminae)  continue  inclining  towards 
each  other,  until  they  coalesce,  so  that  a  complete  tube  is  formed ;  and  in  this 
tube  an  indication  is  soon  perceived  of  a  division  into  vertebra?,  of  which  the 
plates  just  mentioned  are  the  incipient  arches  (Fig.  26,  Plate  II.).  Towards 
the  anterior  extremity,  however,  the  dorsal  laminae  do  not  at  once  close  in ; 
and  the  large  cells,  in  which  the  great  divisions  of  the  Encephalon  originate 
(§  214),  may  be  seen  between  them.  From  the  Dorsal  Lamina  on  either  side, 
a  prolongation  passes  outwards  and  then  downwards,  forming  what  is  known 
as  the  ventral  lamina;  in  this  are  developed  the  Ribs  and  the  transverse  pro- 
cesses of  the  Vertebrae ;  and  the  two  have  the  same  tendency  to  meet  on  the 
median  line,  and  thus  to  close  in  the  abdominal  cavity,  which  the  dorsal 
laminae  have  to  enclose  the  spinal  cord.  At  the  same  time  the  layers  of  the 
Germinal  Membrane,  which  lie  beyond  the  extremities  of  the  Embryo,  are 
folded  in,  so  as  to  make  a  depression  on  the  yolk ;  and  their  folded  margins 
gradually  approach  one  another  under  the  abdomen.  In  these  two  modes,  a 
cavity  is  formed  beneath  the  Embryonic  mass,  which  is  separated  from  the 
general  cavity  of  the  Yolk  by  the  folds  just  described  ;  but  these  still  leave  a 
passage  which,  in  the  Bird,  remains  of  considerable  size  until  a  much  later 
period,  but  which,  in  the  Mammiferous  Ovum,  is  soon  obliterated.  For  the  sac 
which  contains  the  yolk,  and  from  which  the  abdominal  cavity  is  pinched  off  (as 
it  were)  at  a  very  early  period,  is  destined,  in  the  Mammiferous  animal,  to  be 


DEVELOPMENT  OF  THE  EMBRYO. 


613 


entirely  cast  away ;  the  purpose  which  it  has  to  serve  being  one  of  a  very 
temporary  character. 

761.  Whilst  these  new  structures  are  being  produced,  a  very  remarkable 
change  is  taking  place  in  that  part  of  the  Serous  lamina  which  surrounds  the 
Area  Pellucida.  This  rises  up  on  either  side  in  two  folds ;  and  these  gradu- 
ally approach  one  another,  at  last  meeting  in  the  space  between  the  general 
envelop  and  the  embryo,  and  thus  forming  an  additional  investment  to  the 
latter.  As  each  fold  contains  two  layers  of  membrane,  a  double  envelop  is 
thus  formed ;  of  this,  the  outer  lamina  adheres  to  the  general  envelop ;  whilst 
the  inner  remains  as  a  distinct  sac,  to  which  the  name  of  Amnion  is  given. 
(See  Figs.  185,  186,  and  187.)  This  takes  place  during  the  third  day  in  the 
Chick ;  the  period  at  which  it  occurs  in  the  Human  Ovum  is  difficult  to  be 
ascertained,  owing  to  the  small  number  of  normal  specimens  which  have  come 
under  observation  at  a  sufficiently  early  period. 


Fig.  182. 


Fig.  183. 


Plan  of  early  uterine  Ovum.  Within  the 
external  ring,  or  zona  pellucida,  are  the 
serous  amina,  a;  the  yolk,  b;  and  the  inci- 
pient embryo,  c.  (After  Wagner.) 


Diagram  of  Ovum  at  later  stage;  the  digestive  cavity 
beginning  to  be  separated  from  the  yolk-sac,  and  the 
amnion  beginning  to  be  formed ;  a,  chorion ;  b,  yolk-sac ; 
c,  embryo ;  d  and  e,  folds  of  the  serous  layer  rising  up  to 
form  the  amnion.  (After  Wagner.) 


762.  During  the  same  period,  a  very  important  provision  for  the  future  sup- 
port of  the  Embryo  begins  to  be  made  ;  by  the  development  of  Blood-vessels 
and  the  formation  of  Blood.  Hitherto,  the  Embryonic  structure  has  been 
nourished  by  direct  absorption  of  the  alimentary  materials  supplied  to  it  by  the 
Yolk ;  in  the  same  manner  as  the  simplest  Cellular  plant  is  developed  at  the 
expense  of  the  carbonic  acid,  moisture,  &c.,  which  it  obtains  for  itself  from  the 
surrounding  elements.  But  its  increasing  size,  and  the  necessity  for  a* more 
free  communication  between  its  parts  than  any  structure  consisting  of  cells 
alone  can  permit,  call  for  the  development  of  Vessels,  through  which  the  nutri- 
tious fluid  may  be  conveyed.  These  vessels  are  first  seen  in  that  part  of  the 
Vascular  lamina  of  the  Germinal  Membrane  which  immediately  surrounds 
the  embryo ;  and  they  form  a  network,  bounded  by  a  circular  channel,  which 
is  known  under  the  name  of  the  Vascular  Area  (Fig.  27,  Plate  II.].  This 
gradually  extends  itself,  until  the  vessels  spread  over  the  whole  of  the  mem- 
brane containing  the  yolk.  The  first  blood-discs  appear  to  be  formed  from 
the  nuclei  of  the  cells,  whose  cavities  have  become  continuous  with  each  other 
to  form  the  vessels  (§  575) ;  and  from  these,  all  subsequent  blood-discs  are 
probably  generated.  This  network  of  blood-vessels  serves  the  purpose  of 
absorbing  the  nutritious  matter  of  the  Yolk,  and  of  conveying  it  towards  the 
embryonic  structures,  which  are  now  in  process  of  rapid  development.  The 
first  movement  of  the  fluid  is  towards  the  embryo ;  and  this  can  be  witnessed 
before  any  distinct  heart  is  evolved.  The  same  process  of  absorption  from  the 
52 


614  OF  REPRODUCTION. 

Yolk,  and  of  conversion  into  Blood,  probably  continues  as  long  as  there  is  any 
alimentary  material  left  in  the  sac.  The  Yolk-sac  is  early  separated  in  the 
Mammalia,  by  a  constriction  of  the  portion  which  is  continuous  with  the  abdo- 
men of  the  Embryo ;  and  it  is  known  from  that  time  under  the  name  of  the 
Umbilical  Vesicle.  The  communication,  however,  remains  open  for  a  time 
through  the  constricted  portion,  which  is  termed  the  Vitelline  Duct ;  and  even 
after  this  has  been  cut  off,  the  trunks  which  connected  the  circulating  system 
of  the  Embryo  with  that  of  the  Vascular  Area,  are  still  discernible ;  these  are 
called  Omphalo-Mesenteric,  Meseraic,  or  Vitelline  vessels.  It  was  formerly 
believed,  that  the  nutrient  matter  of  the  yolk  passes  directly  through  the  Vitel- 
line duct,  into  the  (future)  digestive  cavity  of  the  Embryo,  and  is  from  it 
absorbed  into  its  structure ;  but  there  can  now  be  little  doubt  that  the  Vitelline 
vessels  are  the  real  agents  of  its  absorption,  and  that  they  convey  it  to  the  tis- 
sues in  process  of  formation.  They  do,  in  fact,  correspond  to  the  Mesenteric 
veins  of  Invertebrated  animals,  which  are  the  sole  agents  in  the  absorption  of 
nutriment  from  their  digestive  cavity  (§  462) ;  and  the  yolk-bag,  as  already 
remarked,  is  the  temporary  stomach  of  the  Embryo, — remaining  as  the  per- 
manent stomach  in  the  Radiated  tribes.  Previous  to  the  ninth  day  of  incuba- 
tion (in  the  Fowl's  egg),  a  series  of  folds  are  formed  by  the  lining  membrane 
of  the  yolk-bag,  which  project  into  its  cavity ;  these  become  gradually  deeper 
and  more  crowded,  as  the  bag  diminishes  in  size  by  the  absorption  of  its  con- 
*tents.  The  Vitelline  vessels,  that  ramify  upon  the  yolk-bag,  send  into  these 
folds  (or  valvulae  conniventes)  a  series  of  inosculating  loops,  which  immensely 
increase  the  extent  of  this  absorbing  apparatus.  But  these  minute  vessels  are 
not  in  immediate  contact  with  the  yolk ;  for  there  intervenes  between  them  a 
layer  of  nucleated  cells,  which  is  easily  washed  away.  It  was  from  the  colour 
of  these,  communicated  to  the  vessels  beneath,  that  Haller  termed  the  latter 
vasa  lutea;  when  the  layer  is  removed,  the  vessels  present  their  usual  colour. 
There  seems  good  reason  to  believe  that  these  cells,  like  those  of  the  Intesti- 
nal Villi  in  the  adult  (§  461),  are  the  real  agents  in  the  process  of  absorbing 
and  assimilating  the  nutritive  matter  of  the  yolk;  and  that  they  deliver  this 
up  to  the  vessels,  by  themselves  undergoing  rupture  or  dissolution,  being 
replaced  by  new  layers. 

763.  The  formation  of  the  Heart  takes  place  in  the  Vascular  layer,  beneath 
the  upper  part  of  the  Spinal  Column ;  it  at  first  appears  as  a  mere  cavity  in 
its  substance,  surrounded  only  by  cells ;  but  its  walls  gradually  acquire  firm- 
ness and  distinctness,  and  become  sufficiently  powerful  to  propel  the  bk>od 
through  the  vessels  of  the  Embryo  and  those  of  the  Vascular  Area.  The  first 
appearance  of  the  Heart  in  the  Chick  is  at  about  the  27th  hour ;  the  time  of  its 
formation  in  Mammalia  has  not  been  distinctly  ascertained.  In  its  earliest 
form,  it  has  the  same  simple  character  which  is  presented  by  the  central  im- 
pelling cavity  of  the  lower  Invertebrata ;  being  a  mere  prolonged  canal,  which 
at  its  posterior  extremity  receives  the  veins,  and  at  its  anterior  sends  forth  the 
arteries.  After  a  short  time,  however,  it  becomes  bent  upon  itself  (Plate  II., 
Fig.  27,  d) ;  and  it  is  soon  subdivided  into  three  cavities,  which  exist  in  all 
Vertebrata, — a  simple  auricle  or  receiving  cavity,  a  simple  ventricle  or  pro- 
pelling cavity,  and  a  bulbus  arteriosus  at  the  origin  of  the  aorta.  The  cir- 
culation is  at  first  carried  on  exactly  upon  the  plan  which  is  permanently 
exhibited  by  Fishes.  The  aorta  subdivides  into  four  or  five  arches  on  either 
side  of  the  neck  ;  and  these  are  separated  by  slits  or  fissures,  much  resembling 
those  which  form  the  entrances  to  the  gill-cavities  of  Cartilaginous  Fishes. 
These  arches  reunite  to  form  the  descending  aorta,  which  transmits  branches 
to  all  parts  of  the  body.  Such  is  the  first  phase  or  aspect  of  the  Circulating 

*  Grainger  and  Dalrymple,  in  Baly's  translation  of  Muller's  Physiology,  pp.  1557-1560 


DEVELOPMENT  OF  THE  EMBRYO. 


615 


Apparatus,  which  is  common  to  all  Vertebrata  during  the  earliest  period  of 
their  development,  and  which  may  therefore  be  considered  as  its  most  general 
form.  It  remains  permanent  in  the  class  of  Fishes  ;  and  in  them  the  vascular 
system  undergoes  further  development  on  the  same  type,  a  number  of  minute 
tufts  being  sent  forth  from  each  of  the  arches,  which  enter  the  filaments  of  the 
gills,  and  serve  for  the  aeration  of  the  blood.  In  higher  Vertebrata,  however, 
the  plan  of  the  circulation  is  afterwards  entirely  changed,  by  the  formation  of 
new  cavities  in  the  heart,  and  by  the  production  of  new  vessels  ;  these  changes 
will  be  presently  described.  It  is  incorrect,  therefore,  to  speak  of  the  vascular 
arches  in  their  necks  as  branchial  arches  ;  since  no  branchiae  or  gills  are  ever 
developed  from  them.  The  clefts  between  them  may  be  very  distinctly  seen 
in  the  Human  Foetus  towards  the  end  of  the  first  month ;  during  the  second, 
they  usually  close  up  and  disappear. 

764.  With  the  evolution  of  a  Circulating  apparatus  adapted  to  absorb  nour- 
ishment from  the  store  prepared  for  the  use  of  the  Embryo,  and  to  convey  it 
to  its  different  tissues,  it  becomes  necessary  that  a  respiratory  apparatus  should 
also  be  provided,  for  unloading  the  blooo\  of  the  carbonic  acid  with  which  it 
becomes  charged  during  the  course  of  its  circulation.  The  temporary  Respi- 
ratory apparatus  now  to  be  described,  bears  a  strong  resemblance  in  its  own 
character,  and  especially  in  its  vascular  connections,  with  the  gills  of  the 
Mollusca ;  which  are  prolongations  of  the  external  surface  (usually  near  the 
termination  of  the  intestinal  canal),  and  which  almost  invariably  receive  their 
vessels  from  that  part  of  the  system.  This  apparatus  is  termed  the  Jlllantois. 
It  consists  at  first  of  a  kind  of  diverticulum  or  prolongation  of  the  lower  part 
of  the  Digestive'  cavity,  the  formation  of  which  has  been  already  described. 
This  is  at  first  seen  as  a  single  vesicle,  of  no  great  size  (Fig.  185,  g) ;  and  in 
the  Foetus  of  Mammalia,  which  is  soon  provided  with  other  means  of  aerating 
its  blood,  it  seldom  attains  any  considerable  dimensions.  In  Birds,  however, 
it  becomes  so  large  as  to  extend  itself  around  the  whole  Yolk-sac,  intervening 
between  it  and  the  membrane  of  the  shell ;  and  through  the  latter  it  comes 
into  relation  with  the  external  air.  The  accompanying  diagram  will  serve  to 
explain  its  origin  and  position  in  the  Human  ovum.  The  chief  office  of  the 
Allantois  in  Mammalia  is  to  convey  the  vessels  of- the  embryo  to  the  Chorion ; 


Fig.  184. 


The  Amnion  in  process  of  formation,  by  the 
arching  over  of  the  serous  lamina;  a,  the  cho- 
rion;  6,  the  yolk-bag,  surrounded  by  serous 
and  vascular  laminae;  c,  the  embryo;  d,  e  and 
f,  external  and  internal  folds  of  the  serous 
layer,  forming  the  amnion:  g,  incipient  allan- 
tois.  (After  Wagner.) 


Diagram  representing  a  Human  Ovum  in  second 
month;  a,  1,  smooth  portion  of  chorion ;  a,  2,  villous 
portion  of  chorion ;  fc,  &,  elongated  villi,  beginning  to 
collect  into  placenta;  b.  yolk-sac  or  umbilical  vesicle; 
c,  embryo;  /,  amnion  (inner  layer);  g,  allantois;  A, 
outer  layer  of  amnion,  coalescing  with  chorion.  (After 
Wagner.) 


616 


OF  REPRODUCTION. 


and  its  extent  bears  a  pretty  close  correspondence  with  the  extent  of  surface, 
through  which  the  Chorion  comes  into  vascular  connection  with  the  Decidua. 
Thus,  in  the  Carnivora,  whose  Placenta  extends  like  a  band  around  the  whole 
Ovum,  the  Allantois  also  lines  the  whole  inner  surface  of  the  Chorion,  except 
where  the  Umbilical  Vesicle  comes  in  contact  with  it.  On  the  other  hand,  in 
Man  and  the  Quadrumana,  whose  Placenta  is  restricted  to  one  spot,  the  Allan- 
tois is  small,  and  conveys  the  foetal  vessels  to  one  portion  only  of  the  Chorion. 
When  these  vessels  have  reached  the  Chorion,  they  ramify  in  its  substance, 
and  send  filaments  into  its  villi ;  and  in  proportion  as  these  villi  form  that  con- 
nection with  the  uterine  structure  which  has  been  already  described,  do  the 
vessels  increase  in  size.  They  then  pass  directly  from  the  Foetus  to  the 
Chorion ;  and  the  Allantois  being  no  longer  of  any  use,  shrivels  up,  and 
remains  as  a  minute  vesicle,  only  to  be  detected  by  careful  examination.  The 
same  thing  happens  in  regard  to  the  Umbilical  vesicle,  from  which  the  entire 
contents  have  been  by  this  time  exhausted ;  and  from  henceforth  the  Fretus  is 
entirely  dependent  for  the  materials  of  its  growth,  upon  the  supply  it  receives 
through  the  Placenta,  which  is  conducted  to  it  by  the  vessels  of  the  Umbilical 


Diagram  of  Human  Ovum,  at  the  time  of  formation  of  the  placenta;  a,  muco-gelalinous  substance,  block- 
ing up  os  uteri ;  6,  b,  Fallopian  tubes;  e,  c,  decidua  vera,  prolonged  at  c  2,  into  Fallopian  tube  ;  el,  cavity  of 
uterus,  almost  completely  occupied  by  ovum  (compare  with  fig.  161) ;  e,  e,  angles  at  which  decidua  vera  is 
reflected;/,  decidua  serotina;  g,  allantois;  A,  umbilical  vesicle;  i,  amuion;  &,  chorion,  lined  with  outer 
fold  of  serous  tunic.  (After  Wagner.) 


DEVELOPMENT  OF  THE  EMBRYO.  617 

Cord.     This  state  of  things  is  represented  in  the  preceding  diagram. — The 
Allantois  has  a  correspondence  in  situation  with  the  Urinary  Bladder ;  but  it 
is  only  the  lower  part  of  it,  pinched  off,  as  it  were,  from  the  rest,  that  remains 
as  such.     The  duct  by  which  it  is  connected  with  the  abdomen  gradually 
shrivels  ;  and  a  vestige  of  this  is  permanent,  forming  the  Urachus  or  suspen- 
sory ligament  of  the  Bladder,  by  which  it  is  connected  with  the  Umbilicus. 
Before  this  takes  place,  however,  the  Allantois  is  the  receptacle  for  the  secre- 
tion of  the  Corpora  Wolffiana,  and  of  the  true  Kidneys,  when  they  are  formed. 
765.  It  will  be  seen  from  the  preceding  diagram,  that  the  Umbilical  Cord 
receives  an  investment  from  the  Amnion,  which  forms  a  kind  of  tubular  sheath 
around  it ;  it  is  continuous  at  the  Umbilicus  with  the  integument  of  the  foetus ; 
and  at  the  point  where  the  cord  enters  the  Placenta,  it  is  reflected  over  its 
internal  or  foetal  surface.     The  Amnion  (which  thus  forms  a  short  sac,  like 
that  of  the  Pleura,  Arachnoid,  &c.)  contains  a  fluid  known  as  the  liquor 
amnii;  this  consists  of  water  holding  in  solution  a  small  quantity  of  albumen 
and  saline  matter,  and  resembling,  therefore,  very  dilute  serum.     During  the 
first  two  months  of  gestation,  the  Amnion  and  the  inner  surface  of  the  Chorion 
(which  is  really  the  reflected  layer  of  the  Amnion,  just  as  the  lining  of  the 
abdominal  cavity  is  formed  by  the  peritoneum),  are  separated  by  a  ^latinous- 
looking  substance;  which  may  perhaps  be  considered  as  representing  the 
white  of  the  egg  in  Birds ;  and  which  probably  aids  in  the  nutrition  of  the 
Embryo,  previously  to  the  formation  of  the  Placenta  (§  747).    This  is  absorbed 
during  the  second  month ;  and  the  Amnion  is  then  found  immediately  beneath 
the  Chorion.     In  the  Umbilical  Cord,  when  it  is  completely  formed,  the  fol- 
lowing parts  may  be  traced.     1.  The  tubular  sheath  afforded  by  the  Amnion. 
2.  The  Umbilical  Vesicle,  with  its  pedicle,  or  Omphalo-Enteric  duct.    3.  The 
Vasa  Omphalo-Meseraica,  or  mesenteric  vessels  of  the  Embryo,  by  which  the 
Yolk  was  absorbed  into  the  body  of  the  Foetus ;  these  accompany  the  pedicle. 
4.  The  Urachus,  and  remains  of  the  Allantois.     5.  The  Vasa  Umbilicalia, 
which,  in  the  later  period  of  gestation,  constitute  the  chief  part  of  the  Cord. 
These  last  vessels  consist  in  Man  of  two  Arteries  and  one  Vein.     The  Arte- 
ries are  the  main  branches  of  the  Hypogastric ;  and  they  convey  to  the  Pla- 
centa the  blood  which  has  to  be  aerated  and  otherwise  revivified,  by  being 
brought  into  relation  with  that  of  the  Mother.     The  Vein  returns  this  to  the 
Foetus,  and  discharges  a  part  of  it  into  the  Vena  Portae,  and  a  part  directly 
through  the  Ductus  Venosus  into  the  Aorta. 

766.  A  change  in  the  type  of  the  Circulating  system  of  the  Foetus,  from 
that  at  first  presented  by  it  (§  763),  takes  place  at  a  very  early  period.  At 
about  the  4th  week,  in  the  Human  Embryo,  a  septum  begins  to  be  formed  in 
the  Ventricle ;  and  by  the  end  of  the  8th  week  it  is  complete.  The  Septum 
Auriculorum  is  formed  at  a  somewhat  later  period,  and  it  remains  incomplete 
during  the  whole  of  foetal  life ;  it  is  partly  closed  by  the  valvular  fold  covering 
the  Foramen  Ovale,  which  fold  is  developed  during  the  third  month.  During 
the  same  period,  a  transformation  takes  place  in  the  arrangement  of  the  large 
vessels  proceeding  from  the  Heart;  which  ends  in  their  assumption  of  the 
form  they  present  until  the  end  of  Foetal  life ;  and  this  undergoes  but  a  slight 
alteration,  when  the  plan  of  the  circulation  is  changed  at  the  moment  of  the 
first  inspiration.  The  number  of  Aortic  arches  on  each  side,  which  was  five 
at  first,  soon  becomes  reduced  in  the  Mammalia  to  three,  by  the  obliteration  of 
the  two  highest  pairs,  the  Bulbus  Arteriosus  is  subdivided,  by  the  adhesion 
of  its  walls  at  opposite  points,  into  two  tubes,  of  which  one  becomes  the  Aorta 
and  the  other  the  Pulmonary  artery ;  and  of  the  three  pairs  of  (branchial) 
arches,  the  highest,  being  connected  with  the  Aortic  trunk,  contributes  to  the 
formation  of  the  subclavian  and  Carotid  arteries;  whilst  of  the  middle  pair, 
the  arch  on  the  right  side  is  obliterated,  the  other  becoming  the  arch  of  the 

52* 


618 


OF  REPRODUCTION. 


Aorta.  The  lowest  pair  arises  from  the  Pulmonary  trunk,  and  forms  the  Pul- 
monary artery  on  each  side ;  that  on  the  left  side,  however,  goes  on  to  join  the 
descending  Aorta  as  before,  and  thus  constitutes  the  Ductus  Arteriosus. ~-The 
following  is  the  course  of  the  circulation  of  the  blood  in  the  Foetus.  The  fluid 
brought  from  the  Placenta  by  the  Umbilical  Vein  is  partly  conveyed  at  once 
to  the  Vena  Cava  ascendens,  by  means  of  the  Ductus  Venosus,  and  partly 
flows  through  the  Vena  portae  into  the  Liver,  whence  it  reaches  the  ascending 
Cava  by  the  Hepatic  Vein.  Having  thus  been  transmitted  through  the  two 


U  0 


The  Foetal  Circulation;  1,  the  umbilical  cord,  consisting  of  the  umbilical  vein  and  two  umbilical  arteries ; 
proceeding  from  the  placenta  (2) ;  3,  the  umbilical  vein  dividing  into  three  branches ;  two  (4, 4)  to  be  distri- 
buted to  the  liver;  and  one  (5),  the  ductus  venosus,  which  enters  the  inferior  vena  cava  (6) ;  7,  the  portal 
vein,  returning  the  blood  from  the  intestines,  and  uniting  with  the  right  hepatic  branch;  8,  the  right  auricle; 
the  course  of  the  blood  is  denoted  by  the  arrow,  proceeding  from  8  to  9,  the  left  auricle ;  10,  the  left  ventricle  : 
the  blood  following  the  arrow  to  the  arch  of  the  aorta  (11),  to  be  distributed  through  the  branches  given  off 
by  the  arch  to  the  head  and  upper  extremities.  The  arrows,  12  and  13,  represent  the  return  of  the  blood 
from  the  head  and  upper  extremities  through  the  jugular  and  subclavian  veins,  to  the  superior  vena  cava 
(14),  to  the  right  auricle  (8),  and  in  the  course  of  the  arrow  through  the  right  ventricle  (15),  to  the  pulmonary 
artery  (16) ;  17,  the  ductus  arteriosus,  which  appears  to  be  a  proper  continuation  of  the  pulmonary  artery— 
the  offsets  at  each  side  are  the  right  and  left  pulmonary  artery  cut  off;  these  are  of  extremely  small  size  as 
compared  with  the  ductus  arteriosus.  The  ductus  arteriosus  joins  the  descending  aorta  (18, 18).  which 
divides  into  the  common  iliacs,  and  these  into  the  internal  iliacs,  which  become  the  umbilical  arteries  (19), 
find  return  the  blood  along  the  umbilical  cord  to  the  placenta;  while  the  other  divisions,  the  external  iliacs 
(20),  are  continued  intp  the  lower  extremities.  The  arrows  at  the  termination  of  these  vessels  mark  the 
return- of  the  venous  bloo(f  by  the  "veins  to  the  inferior  cava. 


DEVELOPMENT  OF  THE  EMBRYO.  619 

great  depurating  organs,  the  Placenta  and  the  foetal  Liver,  it  is  in  the  condi- 
tion of  arterial  blood ;  but,  being  mixed  in  the  vessels  with  that  which  has 
been  returned  from  the  trunk  and  lower  extremities,  it  loses  this  character  in 
some  degree  by  the  time  that  it  arrives  in  the  Heart.  In  the  right  Auricle, 
which  it  then  enters,  it  would  be  also  mixed  with  the  venous  blood  conveyed 
by  the  descending  Cava;  were  it  not  that  a  very  curious  provision  exists  to 
prevent  (in  great  degree,  if  not  entirely)  any  such  further  dilution.  The  Eusta- 
chian  valve  has  been  found,  by  the  experiments  of  Dr.  J.  Reid,*  to  serve  the 
purpose  of  directing  the  arterial  blood,  which  flows  upwards  from  the  ascend- 
ing Cava,  through  the  Foramen  Ovale,  into  the  left  Auricle,  whence  it  passes 
into  the  Ventricle:  whilst  it  also  directs  the  Venous  blood  that  has  been 
returned  by  the  descending  Cava,  into  the  right  Ventricle.  When  the  Ven- 
tricles contract,  the  Arterial  blood  which  the  left  contains  is  propelled  into  the 
ascending  Aorta,  and  supplies  the  branches  that  proceed  to  the  head  and  upper 
extremities,  before  it  undergoes  any  admixture ;  whilst  the  Venous  blood,  con- 
tained in  the  right  Ventricle,  is  forced  through  the  Pulmonary  artery  and 
Ductus  Arteriosus,  into  the  descending  Aorta,  mingling  with  the  arterial  cur- 
rent which  that  vessel  previously  conveyed,  and  passing  thus  to  the^trunk  and 
lower  extremities.  Hence  the  Head  and  superior  extremities,  whoPe  develop- 
ment is  required  to  be  in  advance  of  that  of  the  lower,  are  supplied  with  blood 
nearly  as  pure  as  that  which  returns  from  the  Placenta;  whilst  the  rest  of  the 
body  receives  a  mixture  of  this,  with  what  has  previously  circulated  through 
the  system ;  and  of  this  mixture  a  portion  is  transmitted  to  the  Placenta,  to  be 
renovated  by  coming  into  relation  with  the  maternal  fluid.  At  birth,  the 
course  of  the  current  is  entirely  changed  by  its  diversion  into  the  Lungs ; 
which  takes  pla&e  immediately  on  the  first  inspiration.  The  Ductus  Venosus 
and  Ductus  Arteriosus  soon  shrivel  into  ligaments;  the  Foramen  Ovale 
becomes  closed  by  its  valve ;  and  the  circulation,  which  was  before  carried  on 
upon  the  plan  of  that  of  the  higher  Reptiles,  now  becomes  that  of  the  complete 
Bird  or  Mammal.  It  is  by  no  means  unfrequent,  however,  for  some  arrest  of 
development  to  prevent  the  completion  of  these  changes ;  and  various  malfor- 
mations, involving  an  imperfect  discharge  of  the  function,  may  hence  result.! 
767.  The  Alimentary  Canal  has  been  shown  to  have  its  origin  in  the  Yolk- 
sac  or  Umbilical  Vesicle  ;  being  a  portion  pinched  off  (as  it  were)  from  that 
part  of  it  which  is  just  beneath  the  Spinal  Column  of  the  Embryo  (§  760). 
At  first  it  is  merely  a  long  narrow  tube,  nearly  straight,  and  communicating 
with  the  Umbilical  Vesicle  at  about  the  middle  of  its  length ;  thus  it  may  be 
regarded  as  composed  of  the  union  of  two,  an  upper  and  a  lower  division. 
At  first,  neither  Mouth  nor  Anus  exists ;  but  these  are  formed  early  in  the 
second  month,  if  not  before.  The  tube  gradually  manifests  a  distinction  into 
its  special  parts,  ^Esophagus,  Stomach,  Small  Intestine,  and  large  Intestine  ; 
and  the  first  change  in  its  position  occurs  in  the  Stomach,  which,  from  being 
disposed  in  the  line  of  the  body,  takes  an  oblique  direction.  The  curves  of 
the  large  and  small  intestines  present  themselves  at  a  later  period.  It  is  at 
the  lower  part  of  the  small  Intestine,  near^ts  termination  in  the  large,  that  the 
entrance  of  the  Omphalo-Enteric  duct  exists  ;  and  a  remnant  of  this  canal  i 
not  unfrequently  preserved  throughout  life,  in  the  form  of  a  small  pouch  or 
diverticulum  from  that  part  of  the  intestine.  The  various  Glandular  struc- 
tures connected  with  the  alimentary  canal,  originate  in  diverticula  from  its 
walls,  in  the  manner  already  described  in  regard  to  the  Liver  (§  655).  The 
Lungs  and  Respiratory  apparatus  are  formed  in  like  manner,  as  diverticula 
from  the  (Esophagus  (§  526). 

*  Edinb.  Med.  and  Surg.  Journal,  voK  xliii. 

j-  See  Principles  of  General  and  Compafative  Physiology,  chap.  vi. 


620  OF  REPRODUCTION. 

768.  The  mode  in  which  the  chief  organs  of  the  Human  embryo  originate 
having  been  thus  described,  and  sufficient  particulars  in  regard  to  their  subse- 
quent development  having  been  already  given  under  distinct  heads,  it  is  un- 
necessary here  to  add  more  on  this  very  interesting  but  complex  subject ; 
because  for  practical  purposes  there  is  little  or  no  advantage  to  be  gained 
from  the  most  perfect  acquaintance  with  it.  The  most  important  of  all  the 
facts  that  have  come  under  our  review,  is  that  which  has  been  stated  as  in  the 
highest  degree  probable,  if  not  yet  absolutely  proved,  in  regard  to  the  relative 
offices  of  the  Male  and  Female  in  this  hitherto  mysterious  process.  Accord- 
ing to  the  view  here  given,  the  Male  furnishes  the  germ  ;  and  the  Female 
supplies  it  with  Nutriment,  during  the  whole  period  of  its  early  development. 
There  is  no  difficulty  in  reconciling  such  a  doctrine  with  the  well-known  fact, 
that  the  offspring  commonly  bears  a  resemblance  to  both  parents  (of  which 
the  production  of  a  hybrid  between  distinct  species  is  the  most  striking  ex- 
ample) ;  since  numerous  phenomena  prove  that,  in  this  earliest  and  simplest 
condition  of  the  organism,  the  form  it  will  ultimately  assume  very  much  de- 
pends upon  circumstances  external  to  it ;  among  which  circumstances,  the 
kind  of  nutriment  supplied  will  be  one  of  the  most  important.*  Upon  the 
same  principle  we  may  account  for  the  influence  of  the  mental  condition  of 
the  Mother  upon  her  Offspring  during  a  later  period  of  pregnancy.  That 
such  influence  may  occur,  there  can  be  no  reasonable  doubt.  "  We  have 
demonstrative  evidence,"  says  Dr.  A.  Combe,t  "  that  a  fit  of  passion  in  a 
nurse  vitiates  the  quality  of  the  milk  to  such  a  degree,  as  to  cause  colic  and 
indigestion  [or  even  death]  in  the  suckling  infant.  If,  in  the  child  already 
born,  and  in  so  far  independent  of  its  parent,  the  relation  between  the  two  is 
thus  strong,  is  it  unreasonable  to  suppose  that  it  should  be  yet  stronger,  when 
the  infant  lies  in  its  mother's  womb,  is  nourished  indirectly  by  its  mother's 
blood,  and  is,  to  all  intents  and  purposes,  a  part  of  her  own  body  ?  ft  a  sud- 
den and  powerful  emotion  of  her  own  mind  exerts  such  an  influence  upon  her 
stomach  as  to  excite  immediate  vomiting,  and  upon  her  heart  as  almost  to 
arrest  its  motion  and  induce  fainting,  can  we  believe  that  it  will  have  no  effect 
on  her  womb  and  the  fragile  being  contained  within  it  ?  Facts  and  reasons, 
then,  alike  demonstrate  the  reality  of  the  influence ;  and  much  practical  ad- 
vantage would  result  to  both  parent  and  child,  were  the  conditions  and  extent 
of  its  operations  better  understood."  Among  facts  of  this  class,  there  is,  per- 
haps, none  more  striking  than  that  quoted  by  the  same  Author  from  Baron 
Percy,  as  having  occurred  after  the  siege  of  Landau,  in  1793.  In  addition  to 
a  violent  cannonading,  which  kept  the  women  for  some  time  in  a  constant 
state  of  alarm,  the  arsenal  blew  up  with  a  terrific  explosion,  which  few  could 
hear  with  unshaken  nerves.  Out  of  92  children  born  in  that  district  within 
a  few  months  afterwards,  Baron  Percy  states  that  16  died  at  the  instant  of 
birth  ;  33  languished  for  from  8  to  10  months,  and  then  died  ;  8  became  idio- 
tic, and  died  before  the  age  of  5  years ;  and  2  came  into  the  world  with 
numerous  fractures  of  the  bones  of  the  limbs,  caused  by  the  cannonading  and 
explosion.  Here,  then,  is  a  total  of  59  children  out  of  92,  or  within  a  trifle  of 
2  out  of  every  3,  actually  killed  through  the  medium  of  the  Mother's  alarm 
and  the  natural  consequences  upon  her  own  organization, — an  experiment, 
(for  such  it  is  to  the  physiologist)  upon  too  large  a  scale  for  its  results  to  be 
set  down  as  mere  "coincidences."  No  soundly-judging  Physiologist  of  the 
present  day  is  likely  to  fall  into  the  popular  error,  of  supposing  that  marks 
upon  the  Infant  are  to  be  referred  to  some  transient  though  strong  impression 
upon  the  imagination  of  the  Mother  ;  but  there  appear  to  be  a  sufficient  num- 

*  See  Principles  of  General  and  Comparative  Physiology,  §  665. 
t  On  the  Management  oflnfancy,  p.  76. 


DEVELOPMENT  OF  THE  EMBRYO.  621 

her  of  facts  on  record,  to  prove  that  habitual  mental  conditions  on  the  part  of 
the  Mother  may  have  influence  enough,  at  an  early  period  of  gestation,  to 
produce  evident  bodily  deformity,  or  peculiar  tendencies  of  the  mind.  But 
whatever  be  the  nature  and  degree  of  the  influence  thus  transmitted,  it  must 
be  such  as  can  act  by  modifying  the  character  of  the  nutritive  materials  sup- 
plied by  the  Mother  to  the  Foetus  ;  since  there  is  no  other  channel  by  which 
any  influence  can  be  propagated.  The  absurdity  of  the  vulgar  notion  just 
alluded  to,  is  sufficiently  evident  from  this  fact  alone ;  as  it  is  impossible  to 
suppose  that  a  sudden  fright,  speedily  forgotten,  can  exert  such  a  continued 
influence  on  the  nutrition  of  the  Embryo  as  to  occasion  any  personal  peculi- 
arity.* The  view  here  stated  is  one  which  ought  to  have  great  weight,  in 
making  manifest  the  importance  of  careful  management  of  the  health  of  the 
Mother,  both  corporeal  and  mental,  during  the  important  period  of  pregnancy ; 
since  the  constitution  of  the  offspring  so  much  depends  upon  the  impressions 
then  made  upon  its  most  impressible  structure. 

769.  It  is  frequently  of  great  importance,  both  to  the  Practitioner  and  to  the 
Medical  Jurist,  to  be  able  to  determine  the  age  of  a  Foetus,  from  the  physical 
characters  which  it  presents ;  and  the  following  table  has  been  framed  by  De- 
vergiet  in  order  to  facilitate  such  determination.  It  is  to  be  remarked,  how- 
ever, that  the  absolute  Length  and  Weight  of  the  Embryo  are  much  less  safe 
criteria  than  its  degree  of  Development, — as  indicated  by  the  relative  evolu- 
tion of  the  several  parts,  which  make  their  appearance  successively.  Thus  it 
is  very  possible  for  one  child,  born  at  the  full  time,  to  weigh  less  than  another, 
born  at  8  or  even  at  7  months:  its  length,  too,  may  be  no  greater;  but  the  posi- 
tion of  the  middle  point  of  the  body  will  usually  afford  sufficient  ground  for  the 
determination ;  since,  during  the  two  latter  months  of  pregnancy,  the  increas- 
ing development  of  the  lower  extremities  throws  it  lower  down. 

Embryo  3  to  4  weeks. — It  has  the  form  of  a  serpent; — its  length  from  three  to  five  lines ; 
its  head  indicated  by  a  swelling; — its  caudal  extremity,  (in  which  is  seen  a  white  line, 
indicating  the  continuation  of  the  medulla  spinalis,)  slender,  and  terminating  in  the  um- 
bilical cord ; — the  mouth  indicated  by  a  cleft ;  the  eyes  by  two  black  points ;  the  members 
begin  to  appear  as  nipple-like  protuberances; — the  liver  occupies  the  whole  abdomen; — 
the  bladder  is  very  large.  The  chorion  is  villous,  but  its  villosities  are  still  diffused  over 
the  whole  surface. 

Embryo  of  6  weeks. — Its  length  from  7  to  10  lines; — its  weight  from  40  to  75  grains; — 
face  distinct  from  cranium  ; — aperture  of  nose,  mouth,  eyes,  and  ears  perceptible; — head 
distinct  from  thorax; — hands  and  forearms  in  the  middle  of  the  length,  fingers  distinct; 
— legs  and  feet  situated  near  the  anus; — clavicle  and  maxillary  bone  present  a  point  of 
ossification; — distinct  umbilicus  for  attachment  of  cord,  which  at  that  time  consists' of 
the  omphalo-meseraic  vessels,  of  a  portion  of  the  urachus,  of  a  part  of  the  intestinal  tube, 
and  of  filaments  which  represent  the  umbilical  vessels.  The  placenta  begins  to  be  formed ; 
— the  chorion  still  separated  from  the  amnion;— the  umbilical  vesicle  very  large. 

Embryo  of  2  months. — Length  from  16  to  19  lines;  weight  from  150  to  300  grains  ;  the 
elbows  and  arms  detached  from  the  trunk; — heels  and  knees  also  isolated; — rudiments  of 
the  nose  and  of  the  lips; — palpebral  circle  beginning  to  show  itself; — clitoris  or  penis 
apparent;  anus  marked  by  a  dark  spot;  rudiments  of  lungs,  spleen,  and  supra-renal 
capsules ;— ccecum  placed  behind  the  umbilicus;— digestive  canal  withdrawn  into  the 
abdomen  ; — urachus  visible  :— osseous  points  in  the  frontal  bone  and  in  the  ribs.— Cho- 
rion commencing  to  touch  the  amnion  at  the  point  opposite  the  insertion  of  the  placenta; 
placenta  begins  to  assume  its  regular  form; — umbilical  vessels  commence  twisting. 

*  For  some  valuable  observations  on  this  subject,  see  Montgomery  on  the  signs  of 
Pregnancy.  Numerous  cases  have  been  recorded,  during  the  last  few  years  (especially 
in  the  Lancet  and  Provincial  Medical  Journal),  in  which  malformations  in  the  Infant 
appeared  distinctly  traceable  to  strong  impressions  made  on  the  mind  of  the  Mother, 
some  months  previously  to  parturition;  these  impressions  having  been  persistent  during 
the  remaining  period  of  pregnancy,  and  giving  rise  to  a  full  expectation  on  the  part  of 
the  Mother,  that  the  child  would  be  affected  in  the  particular  manner  which  actually 
occurred. 

f  Medecine  Legale,  vol.  i.,  p.  495. 


622  OF  REPRODUCTION. 

Embryo  of  3  months. — Length  from  2  to  2|  inches; — weight  from  1  oz.  to  1£  oz. 
(Troy)  ;— head  voluminous; — eyelids  in  contact  by  their  free  margin;  membrana  pupil- 
laris  visible; — mouth  closed; — fingers  completely  separated; — inferior  extremities  of 
greater  length  than  rudimentary  tail; — clitoris  and  penis  very  long; — thymus  as  well  as 
supra-renal  capsules  present; — coecum  placed  below  the  umbilicus; — cerebrum  5  lines, 
cerebellum  4  lines,  medulla  oblongata  1£  line,  and  medulla  spinalis  £  of  a  line,  in  dia- 
meter;— two  ventricles  of  heart  distinct. — The  decidua  reflexa  and  decidua  uterina  in 
contact; — funis  contains  umbilical  vessels  and  a  little  of  the  gelatin  of  Warthon ; — 
placenta  completely  isolated; — umbilical  vesicle,  allantois,  and  omphalo-mesenteric 
vessels  have  disappeared. 

Foetus  of  4  months. — Length  5  to  6  inches ; — weight  2^  to  3  oz. ; — skin  rosy,  tolerably 
dense; — mouth  very  large  and  open; — membrana  pupillaris  very  evident;  nails  begin  to 
appear; — genital  organs  and  sex  distinct; — coscum  placed  near  the  right  kidney; — gall- 
bladder appearing;— meconium  in  duodenum;  ccecal  valve  visible;  umbilicus  placed 
near  pubis; — ossicula  auditoria  ossified; — points  of  ossification  in  superior  part  of 
sacrum  ; — membrane  forming  at  a  point  of  insertion  of  placenta  on  uterus  ; — complete 
contact  of  chorion  with  amnion. 

Foetus  of  5  months. — Length  6  to  7  inches;  weight  5  to  7  oz. ; — volume  of  head  still 
comparatively  great; — nails  very  distinct; — hair  beginning  to  appear; — skin  without 
sebaceous  covering; — white  substance  in  cerebellum;  heart  and  kidneys  very  volumi- 
nous;—coecum  situated  at  inferior  part  of  right  kidney ;— gall-bladder  distinct; — germs 
of  permanent  teeth  appear; — points  of  ossification  in  pubis  and  calcaneum; — meconium 
has  a  yellowish-green  tint,  and  occupies  commencement  of  large  intestine. 

Foetus  of  6  months. — Length  9  to  10  inches; — weight  1  lb.; — skin  presents  some  ap- 
pearance of  fibrous  structure;— eyelids  still  agglutinated,  and  membrana  pupillaris 
remains; — sacculi  begin  to  appear  in  colon;  funis  inserted  a  little  above  pubis; — face 
of  a  purplish  red  ; — hair  white  or  silvery; — sebaceous  covering  begins  to  present  itself; 
— meconium  in  large  intestine  ;— liver  of  dark  red; — gall-bladder  contains  serous  fluid 
destitute  of  bitterness  ; — testes  near  kidneys  ; — points  of  ossification  in  four  divisions  of 
sternum; — middle  point  at  lower  end  of  sternum. 

Foetus  of  7  months. — Length  13  to  15  inches; — weight  3  to  4  Ibs. ; — skin  of  rosy  hue, 
thick,  and  fibrous; — sebaceous  covering  begins  to  appear; — nails  do  not  yet  reach  ex- 
tremities of  fingers; — eyelids  no  longer  adherent; — membrana  pupillaris  disappearing; 
— a  point  of  ossification  in  the  astragalus  ;  meconium  occupies  nearly  the  whole  of  large 
intestine; — valvula?  conniventes  beginning  to  appear; — co?cum  placed  in  right  iliac 
fossa; — left  lobe  of  liver  almost  as  large  as  right; — gall-bladder  contains  bile; — brain 
possesses  more  consistency; — testicles  more  distant  from  kidneys; — middle  point  at  a 
little  below  end  of  sternum. 

Foetus  of  8  months. — Length  14  to  16  inches; — weight  4  or  5  Ibs. ;— skin  covered  with 
well-marked  sebaceous  envelop;  nails  reach  extremities  of  fingers ; — membrana  pupil- 
laris becomes  invisible  during  this  month; — a  point  of  ossification  in  last  vertebra  of 
sacrum; — cartilage  of  inferior  extremity  of  femur  presents  no  centre  of  ossification; — 
brain  has  some  indications  of  convolutions; — testicles  descend  into  internal  ring; — 
middle  point  nearer  the  umbilicus  than  the  sternum. 

Foetus  of  9  months,  the  full  term.— Length  from  17  to  21  inches; — weight  from  5  to  9 
Ibs.,  the  average  probably  about  6|  Ibs. ;— head  covered  with  hair  in  greater  or  less  quan- 

ty,  of  from  9  to  12  lines  in  length; — skin  covered  with  sebaceous  matter,  especially  at 
nds  of  joints  ; — membrana  pupillaris  no  longer  exists; — external  auditory  meatus  still 
cartilaginous  ; — four  portions  of  occipital  bone  remain  distinct; — os  hyoides  not  yet  ossi- 
fied ; — point  of  ossification  in  the  centre  of  cartilage  at  lower  extremity  of  femur ; — white 
and  gray  substances  of  brain  become  distinct; — liver  descends  to  umbilicus;— testes 
have  passed  inguinal  ring,  and  are  frequently  found  in  scrotum; — meconium  at  termi- 
nation of  large  intestine; — middle  point  of  body  at  umbilicus,  or  a  little  below  it. 

770.  Even  at  Birth,  there  is  a  manifest  difference  in  the  physical  conditions 
of  Infants  of  different  sexes ;  for  in  the  average  of  a  large  number,  there  is  a 
decided  preponderance  on  the  sides  of  the  Males,  both  as  to  the  Length  and 
the  Weight  of  the  body.  The  Length  of  the  body  in  fifty  new-born  infants  of 
each  sex,  as  ascertained  by  Quetelet,*  was  as  follows  : — 

*  Sur  L'Homme,  torn.  ii.  p.  8. 


PROPORTION  OF  THE  SEXES.  623 

Males.  Females.  otal. 

From  16  to  17  inches*  (French)           .2  4  6 

-  17  to  18            ....       8  19  27 

-  18  to  19            ....     28  18  46 

-  19  to  20            ....     12  8  20 

-  20  to  21                                        .       0  1  i 

From  these  observations,  the  mean  and  the  extremes  of  the  Lengths  of  the 
Male  and  Female  respectively,  were  calculated  to  be, — 

Males.  Females. 

Minimum    .         .     16  inches,  2  lines  16  inches,  2  lines 

Mean  .     18  6  18  1£ 

Maximum  19  8  20  6 

Notwithstanding  that  the  maximum  is  here  on  the  side  of  the  Female  (this 
being  an  accidental  result,  which  would  probably  have  been  otherwise,  had  a 
larger  number  been  examined),  the  average  shows  a  difference  of  4  5  lines  in 
favour  of  the  Male. — The  inequality  in  the  Weight  of  the  two  is  even  more 
remarkable ;  the  observations  of  M.  Quetelett  were  made  upon  63  male  and 
56  female  infants. 

Infants  weighing  from.  Males.  Females.        Total. 

1  to  H  kilog4             ...       0  1  1 
1|  to  2 0  1  1 

2  to  2£ 3  7  10 

2£  to  3 13  14  27 

3  to  3£       .         .      "  .         .         .28  23  51 
3£  to  4 14  7 •  •          21 

4  to  4£ 5  3  8 

The  extremes  and  means  were  as  follows  :~ 

Males.  Females. 
Minimum       ....     2-34  kilog.  1-12 

Mean 3-20  2-91 

Maximum       ....     4-50  4-25 

The  average  weight  of  infants  of  both  sexes,  as  determined  by  these  inquiries, 
is  3-05  kilog.  or  6-7  Ibs. ;  and  this  corresponds  almost  exactly  with  the  state- 
ment of  Chaussier,  whose  observations  were  made  upon  more  than  20,000 
infants.  The  mean  obtained  by  him,  without  reference  to  distinction  of  sex, 
was  6-75  Ibs. ;  the  maximum  being  11-3  Ibs.,  and  the  minimum  3*2  lbs.§  The 
average  in  this  country  is  probably  rather  higher ;  according  to  Dr.  Joseph 
Clarke, ||  whose  inquiries  were  made  on  60  males  and  60  females,  the  average 
of  Male  children  is  7|  Ibs. :  and  that  of  Females  6§  Ibs.  He  adds  that  children 
which  at  the  full  time  weigh  less  than  5  Ibs.  rarely  thrive ;  being  generally 
feeble  in  their  actions,  and  dying  within  a  short  time.  Several  instances  are 
on  record,  of  infants  whose  weight  at  birth  exceeded  15  Ibs.  It  appears  that 
healthy  females,  living  in  the  country,  and  engaged  in  active  but  not  over- 
fatiguing  occupations,  have  generally  the  largest  children ;  and  this  is  what 
might  be  expected  a  priori,  from  the  superior  activity  of  their  nutritive 
functions. 

*  The  French  inch  is  about  one-fifteenth  more  than  the  English, 
f  Op.  cit.  torn.  ii.  p.  35. 

*  The  kilogramme  is  equal  to  2£  Ibs.  avoirdupois. 

§  These  numbers  have  been  erroneously  stated  in  many  Physiological  works;  owing 
to  the  difference  between  the  French  and  English  pound  not  having  been  allowed  for. 
||  Philosophical  Transactions,  vol.  Ixxvi. 


634  OF  REPRODUCTION. 

771.  Notwithstanding  that,  in  any  ordinary  population,  there  is  a  decided 
preponderance  in  the  number  of  Females,  the  number  of  Male  births  is  con- 
siderably greater  than  that  of  females.     Taking  the  average  of  the  whole  of 
Europe,  the  proportion  is  about  106  Males  to  100  Females.     It  is  curious, 
however,  that  this  proportion  is  considerably  different  for  legitimate  and  for 
illegitimate  births ;  the  average  of  the  latter  being  only  102£  to  100,  in  the 
places  where  that  of  the  former  was  105!  to  100.     This  is  probably  to  be 
accounted  for  by  the  fact,  which  is  one  of  the  most  remarkable  contributions 
that  have  yet  been  made  by  Statistics  to  Physiology,  that  the  Sex  of  the 
offspring  is  influenced  by  the  relative  ages  of  the  parents.     The  following 
table  expresses  the  average  results  obtained  by  M.  Hofacker*  in  Germany,  and 
by  Mr.  Sadlert  in  Britain ;  between  which  it  will  be  seen  that  there  is  a 
manifest  correspondence,  although  both  were  drawn  from  a  too  limited  series 
of  observations.     The  numbers  indicate  the  proportion  of  Male  births  to  100 
Females,  under  the  several  conditions  mentioned  in  the  first  column. 

Hofacker.  Sadler. 

Father  younger  than  mother         90-6  Father  younger  than  mother  86-5 

Father  and  Mother  of  equal  age    90-0  Father  and  Mother  of  equal  age    94-8 

Father  older  by  1  to  6  years       103-4  Father  older  by  1  to  6  years  103-7 

6  to  9                 124-7          .           .»        6  to  11  126-7 

9  to  18               143-7          .           .        11  to  16  147-7 

18  and  more        200-0          .           .         16  and  more  163-2 

From  this  it  appears,  that  the  more  advanced  age  of  the  Male  parent  has  a 
very  decided  influence  in  occasioning  a  preponderance  in  the  number  of  Male 
infants  ;  and,  as  the  state  of  society  generally  involves  a  condition  of  this  kind 
in  regard  to  marriages,  whilst  in  the  case  of  illegitimate  children  the  same 
does  not  hold  good,  the  difference  in  the  proportional  number  of  male  births  is 
accounted  for.  We  are  not  likely  to  obtain  data  equally  satisfactory  in  regard 
to  the  influence  of  more  advanced  age  on  the  part  of  the  Female  parent ;  as  a 
difference  of  10  or  15  years  on  that  side  is  not  so  common.  If  it  exist  to  the 
same  extent,  it  is  probable  that  the  same  law  would  be  found  to  prevail  in 
regard  to  Female  children  born  under  such  circumstances,  as  has  been  stated 
with  respect  to  the  Male  ; — namely,  that  the  mortality  is  greater  during  em- 
bryonic life  and  early  infancy,  so  that  the  preponderance  is  reduced. 

772.  There  appears  to  be,  from  the  first,  a  difference  in  the  viability  (or 
probability  of  life)  of  Male  and  Female  children :  for,  out  of  the  total  number 
born  dead,  there  are  3  Males  to  2  Females :  this  proportion  gradually  lessens, 
r/owever,  during  early  infancy  ;  being  about  4  to  3  during  the  first  two  months, 
and  about  4  to  5  during  the  next  three  months  ;  after  which  time  the  deaths 
are  nearly  in  proportion  to  the  numbers  of  the  two  sexes  respectively,  until 
the  age  of  puberty.     The  viability  of  the  two  sexes  continues  to  increase 
during  childhood ;  and  attains  its  maximum  between  the  13th  and  14th  years. 
For  a  short  time  after  this  epoch  has  been  passed,  the  rate  of  mortality  is 
higher  in  Females  than  in  Males ;  but  from  about  the  age  of  18  to  28,  the 
mortality  is  much  greater  in  Males,  being  at  its  maximum  at  25,  when  the 
viability  is  only  half  what  it  is  at  puberty.     This  fact  is  a  very  striking  one  ; 
and  shows  most  forcibly  that  the  indulgence  of  the  passions  not  only  weakens 
the  health,  but  in  a  great  number  of  instances  is  the  cause  of  a  very  premature 
death.     From  the  age  of  28  to  that  of  50,  the  mortality  is  greater,  and  the 
viability  less,  on  the  side  of  the  Female  ;  this  is  what  would  be  anticipated 
from  the  increased  risk  to  which  she  is  liable  during  the  parturient  period. 

*  Annales  d'Hygiene,  Oct.,  1829. 
f  Law  of  Population,  vol.  ii.  p.  343. 


PROPORTION  OF  THE  SEXES. 


625 


After  the  age  of  50,  the  mortality  is  nearly  the  same  for  both. — These  facts 
have  been  expressed  by  Quetelet  in  a  form  which  brings  them  prominently 
before  the  eye  (Fig.  188).  The  relative  viability  of  the  Male  at  different  ages 
is  represented  by  a  curved  line  ;  the  elevation  of  which  indicates  its  degree, 
at  the  respective  periods  marked  along  the  base  line.  The  dotted  line  which 
follows  a  different  curve,  represents  the  viability  of  the  Female.  Starting 
from  a,  the  period  of  birth,  we  arrive  at  the  maximum  of  viability  for  both  at 
/; ;  from  this  point,  the  Female  curve  steadily  descends  towards  n,  at  first  very 
rapidly,  but  afterwards  more  gradually ;  whilst  the  Male  curve  does  not  quite 
descend  so  soon,  but  afterwards  falls  much  lower,  its  minimum  being  c,  which 
corresponds  with  the  age  of  25  years.  It  afterwards  ascends  to  d,  which  is 
the  maximum  of  viability  subsequently  to  the  age  of  puberty ;  this  point  is 
attained  at  the  age  of  30  years,  from  which  period,  up  to  50,  the  probability 
of  life  is  greater  in  the  Male  than  in  the  Female.  In  the  decline  of  life  there 
seems  little  difference  for  the  two  sexes. 

Fig.  188. 


Diagram  representing  the  comparative  Viability  of  the  Male  and  Female  at  different  ages.  (After  Quetelet.) 

773.  Similar  diagrams  have  been  constructed  by  Gluetelet,  to  indicate  the 
relative  Heights  and  Weights  of  the  two  sexes  (Fig.  189).  In  regard  to 
Height  it  may  be  observed,  that  the  increase  is  most  rapid  in  the  first  year, 
and  that  it  afterwards  diminishes  gradually ;  between  the  ages  of  5  and  1(> 
years,  the  annual  increase  is  very  regular.  The  difference  between  the 
Height  of  the  Male  and  Female,  which  has  been  already  stated  to  present 
itself  at  birth,  continues  to  increase  during  infancy  and  youth  ;  it  is  not  very 
decided,  however,  until  about  the  15th  year,  after  which  the  growth  of  the 
Female  proceeds  at  a  much  diminished  rate,  whilst  that  of  the  Male  continues 
53 


626 


OF  REPRODUCTION. 


in  nearly  the  same  degree,  until  about  the  age  of  19  years.  It  appears,  then, 
that  the  Female  comes  to  her  full  development*  in  regard  to  Height,  earlier 
than  does  the  Male.  It  seems  probable,  from  the  observations  of  Gluetelet, 
that  the  full  Height  of  the  Male  is  not  generally  attained  until  the  age  of  25 
years.  At  about  the  age  of  50,  both  Male  and  Female  undergo  a  diminution 
of  their  stature,  which  continues  during  the  latter  part  of  life. — The  propor- 
tional Weight  of  the  two  sexes  at  different  periods,  corresponds  pretty  closely 
with  their  height.  Starting  from  birth,  the  predominance  then  exhibited  by 
the  Male  gradually  increases  during  the  first  few  years ;  but  towards  the 
period  of  puberty,  the  proportional  weight  of  the  Female  increases  ;  and  at 
the  age  of  12  years,  there  is  no  difference  between  the  two  sexes  in  this 
respect.  The  weight  of  the  Male,  however,  then  increases  much  more 
rapidly  than  that  of  the  Female,  especially  between  the  ages  of  15  and  20 
years ;  after  the  latter  period,  there  is  no  considerable  increase  on  the  side  of 
the  Male,  though  his  maximum  is  not  attained  until  the  age  of  40 ;  and  there 
is  an  absolute  diminution  on  the  part  of  the  Female,  whose  weight  remains 
less  during  nearly  the  whole  period  of  child-bearing.  After  the  termination 
of  the  parturient  period,  the  weight  of  the  Female  again  undergoes  an  in- 
crease, and  its  maximum  is  attained  about  50.  In  old  age,  the  weight  of  both 
sexes  undergoes  a  diminution  in  nearly  the  same  degree.  The  average 
Weights  of  the  Male  and  Female,  that  have  attained  their  full  development, 
are  twenty  times  those  of  the  new-born  Infant  of  the  two  sexes  respectively. 
The  Height,  on  the  other  hand,  is  about  3|  times  as  much. 

Fig.  189. 


774.  The  chief  differences  in  the  Constitution  of  the  two  sexes  manifest 
themselves  during  the  period  when  the  Generative  function  of  each  is  in  the 
greatest  vigour.  Many  of  these  distinctions  have  been  already  alluded  to ; 
but  there  are  others  of  too  great  importance  to  be  overlooked ;  and  these 
chiefly  relate  to  the  Nervous  System  and  its  functions.  There  is  no  obvious 
structural  difference  in  the  Nervous  System  of  the  two  sexes  (putting  aside 
the  local  peculiarities  of  its  distribution  to  the  organs  of  generation) ;  save  the 
inferior  size  of  the  Cerebral  Hemispheres  in  the  Female.  This  difference, 
which  is  not  observed  in  other  parts  of  the  Encephalon,  is  readily  accounted 
for  on  the  principles  formerly  stated ;  when  we  compare  the  psychical  character 


RELATIVE  CHARACTERS  OF  SEXES.  627 

of  Woman  with  that  of  Man.  For  there  can  be  no  doubt  that — putting  aside 
the  exceptional  cases  which  now  and  then  occur— the  intellectual  powers  of 
Woman  are  inferior  to  those  of  Man.  Although  her  perceptive  faculties  are 
more  acute,  her  capability  of  sustained  mental  exertion  is  much  less ;  and 
though  her  views  are  often  peculiarly  distinguished  by  clearness  and  decision, 
they  are  generally  deficient  in  that  comprehensiveness  which  is  necessary  for 
their  stability.  With  less  of  the  volitional  powers  than  Man  possesses,  she 
has  the  emotional  and  instinctive  in  a  much  stronger  degree.  The  emotions 
therefore  predominate ;  and  more  frequently  become  the  leading  springs  of 
action  than  they  are  in  Man.  By  their  direct  influence  upon  the  bodily  frame, 
they  produce  changes  in  the  organic  functions,  which  far  surpass  in  degree 
any  thing  of  the  same  kind  that  we  ordinarily  witness  in  Man ;  and  they  thus 
not  unfrequently  occasion  symptoms  of  an  anomalous  kind,  which  are  very 
perplexing  to  the  Medical  practitioner,  but  very  interesting  to  the  Physiolo- 
gical observer.  But  they  also  act  as  powerful  motives  to  the  Will ;  and,  when 
strongly  called  forth,  produce  a  degree  of  vigour  and  determination,  which  is 
very  surprising  to  those  who  have  usually  seen  the  individual  under  a  different 
aspect.  But  this  vigour,  being  due  to  the  strong  excitement  of  the  Feelings,  and 
not  to  any  inherent  strength  of  Intellect,  is  only  sustained  during  the  persistence 
of  the  motive,  and  fails  as  soon  as  it  subsides.  The  feelings  of  Woman,  being 
frequently  called  forth  by  the  occurrences  she  witnesses  around  her,  are  natu- 
rally more  disinterested  than  those  of  Man ;  his  energy  is  more  concentrated 
upon  one  object ;  and  to  this  his  intellect  is  directed  with  an  earnestness  that 
too  frequently  either  blunts  his  feelings,  or  carries  them  along  in  the  same 
channel, — thus  rendering  them  selfish.  The  intuitive  powers  of  Woman  are 
certainly  greater  than  those  of  Man.  Her  perceptions  are  more  acute,  her 
apprehension  quicker;  and  she  has  a  remarkable  power  of  interpreting  the 
feelings  of  others,  which  gives  to  her,  not  only  a  much  more  ready  sympathy 
with  these,  but  that  power  of  guiding  her  actions  so  as  to  be  in  accordance 
with  them,  which  we  call  tact.  This  tact  bears  a  close  correspondence  with 
the  adaptiveness  to  particular  ends,  which  we  see  in  Instinctive  actions.  In 
regard  to  the  inferior  development  of  her  Intellectual  powers,  therefore,  and  in 
the  predominance  of  the  Instinctive,  Woman  must  be  considered  as  ranking 
below  Man ;  but  in  the  superior  purity  and  elevation  of  her  Feelings,  she  is 
as  highly  raised  above  him.  Her  whole  character,  Psychical  as  well  as  Cor- 
poreal, is  beautifully  adapted  to  supply  what  is  deficient  in  Man;  and  to  ele- 
vate and  refine  those  powers  which  might  otherwise  be  directed  to  low  and 
selfish  objects. 


INDEX. 


ABERRATION,  spherical,  328,  329 ;  chroma- 
tic, 328,  329 
Abducens  nerve,  248 
Abnormal  forms  of  nutritive  process,  606— 

610 

Abortion,  300,  753 
Abscess,  608 
ABSORPTION 

Nutritive,  general  account  of,  86  ;  by  in- 
testinal surface,  461 — 463  ;  by  lacteals, 
462  ;f by  blood  vessels,  463 ;  by  general 
surface,  464—469;  by  skin, 464— 466 ; 
by  lungs,  550 

Interstitial,  by  lymphatics,  467—469  ;  by 
veins,  469 

Of  gases  by  lungs,  550,  551 
Abstinence,  cases  of,  473 
Acini,  of  liver,  655  a 
Actinia,  129, 130 
Activity,  varying,  of   nutritive  processes, 

602—605 
Adaptiveness  of  movements,  no  proof  of 

sensation,  106,  180 
Addison,  Mr.,  referred   to,  525,  554,   577, 

579 

Adhesion,  595—597 
Adipose  tissue,  see  Fat-cells 
Aeration,  see  Respiration 
Afferent  nerves,  113,  119,  162 
Albumen,  composition  of,  457;  properties 

of,  552 ;  a  product  of  digestion,  454,  459 ; 

conversion  of  into  fibrin,  553,  567,  578, 

579:  diminution  of  in  blood,  591  a,  715; 

predominance  of  in  tubercular  deposits, 

610,  714. 

Albuminous  principles,  431,  457 — 459 
Albuminuria,  591  d 


The  Numbers  refer  to  the  Paragraphs. 

Alison,  Dr.,  referred  to,  173,  385,  397,  480, 
512,  588 

Allantois,  origin  and  uses  of,  764 

Anaemia,  591  c 

Anatomy  of  nerves,  important  in  determin- 
ing their  functions,  120,  121 

Andral,  M.,  on  amount  of  carbonic  acid  ex- 
creted, 534,  note  ,•  on  buffy  coat,  589  ;  on 
pathological  changes  in  blood,  590,  591 

Animal  Heat,  see  Heat 

Animal  kingdom,  primary  subdivisions  of,  17 

Animal  magnetism,  296  note 

Animals,  distinguished  from  Plants,  13—16 
early  development  of,  15 


Anterior  roots  of  spinal  nerves,  123 
Aplastic  deposits,  609,  610 
Aplysia,  25;  nervous  system  of,  138 
Apoplexy,  decrease  of  fibrin  in,  591  b 
Arciform  fibres  of  medulla  oblongata,  171 
Area  pellucida,  759 
Areolar  tissue,  611,  637 
Areas,  comparative,  of  arteries,  476 
Arnott,  Dr.,  on  stammering,  418  n,  419;  on 

the  venous  circulation,  515 
Art,  connection  of,  with  Science,  3 — 5 
Arteries,  distribution  of,  476;  area  of,  476; 
ramifications  of,  477,  479  ;  structure  and 
properties  of,  500,  639;  elasticity  of,  501 ; 
their  contractility,  proofs  of,  502,  503 ;  its 
influence,  504  ;  regulates  the  circulation, 
504;    their    tonicity,    503;    influence  of 
nerves  upon,  209,  423,  504 
Articulata,  17,  27 — 30;  segmental  division 
of,  27;  animal  powers  of,  28;  nutrition 
of,  29;  bi-lateral  symmetry  of,  27  ;  respi- 
ration and  heat  of,  29 ;  nervous  system 
of,  142—155 
Articulate  sounds, 413— 419  ;  vowels,414— 


416;  consonants,  417 — 419 
Alcock,  Dr.,  his  experiments  on  nerves  of  I  Asphyxia,  nature  of,  546;  phenomena  of, 


taste,  228 

Alcohol,  use  of  in  supporting  heat,  730,  note 
Aliment,  causes  of  demand  for,  84 ;   see 

Food 
Alimentary  materials,  714;  see  Food 


547,  548;  referred  to,  211,  389,  391,  489, 

508,  512,  543 
Assimilation,  561 

Associations  of  muscular  actions,  398 
Asthma,  spasmodic,  300,  527 


53* 


630 


INDEX 


The  Numbers  refer 

Atrophy,  604,  605 

Attention,  effects  of,  on  sensations,  313, 
314 

Auditory  nerve,  223 ;  terminations  of,  in 
ear,  352 

Automatic  actions,  249,  285 

Azote,  absorption  and  exhalation  of,  536 ; 
excretion  of,  in  urine,  93,  670,  679 ;  re- 
spiration in,  539 


B 


Barry,  Dr.  M.,  his  researches  on  the  blood- 
corpuscles  referred  to,  574,  578,  627;  his 
embryological  researches  referred  to,  424, 
559,  733,  739,  747 

Barry,  Sir  D.,  his  experiments  on  the  ve- 
nous circulation,  516 

Basement  membrane,  612 

Bat,  peculiar  sensibility  of,  320 

Batrachia,  42,  43 ;  metamorphosis  of,  43 

Beaumont,  Dr.,  his  experiments  and  obser- 
vations on  digestion,  438 — 440,443—446, 
449—453,  470 

Becquerel  on  the  heat  of  Plants,  723 ;  on 
the  heat  of  Animals,  726;  on  the  heat  of 
muscle,  726 

Bee,  perfection  of  instinct  of,  155,  279; 
uneducability  of,  279;  temperature  of, 
725 

Bell,  Sir  C.,  his  discoveries,  162,  167,  173; 
referred  to,  113,  120,  121,  185,  196  note, 
225,  240,  247,  257 

Bell,  Mr.  T.,  on  the  development  of  the 
teeth,  635  * 

Bellinger!,  on  the  Spinal  Cord,  163,  167 

Bile,  secretion  of,  660 — 665 ;  composition 
of,  662;  amount  of,  663;  formed  from, 
venous  blood,  660  ;  effects  of  non-elimi- 
nation of,  661,  664;  purposes  of,  446, 
664,  665 

Birds,  44—52;  skeleton  of,  48,  49;  respi- 
ration and  heat  of,  44 — 46 ;  covering  of, 
47;  instinctive  powers  of,  50,  280;  nu- 
tritive system  in,  51 ;  bi-lateral  symmetry 
in,  51;  development  of  young  in,  52; 
blood-corpuscles  of,  572  c,-  braifi  of,  217 

Blake,  Mr.,  his  experiments  on  the  Circula- 
tion, 491 

Blind  persons,  acuteness  of  touch  in,  319 

Blood, 

Physical  and  vital  properties  of,  570 — 
589 ;  composed  of  liquor  sanguinis  and 
corpuscles,  570 

Structure  of  red  corpuscles,  570 ;  form  of 
corpuscles,  571;  size  of  corpuscles,  in 
Mammalia,  572  a  ,•  in  Birds,  572  b ,-  in 
Batrachia,  572  c,-  chemical  constitu- 
tion of  corpuscles,  573;  origin  of,  from 
each  other,  574  ;  first  production  of,  in 
embryo,  575;  purposes  of,  in  animal 
economy,  576 
Colourless  corpuscles,  577;  their  uses  in 


to  the  Paragraphs. 

the  economy,  578,  579 ;  white  matter 
in  blood,  580 ;  milky  serum,  580,  714 
note 

Peculiarities  of  blood  in  different  parts, 
580 ;  proximate  elements  of,  in  health, 
581 ;  quantity  of,  in  body,  490,  581 
Coagulation  of,  582 ;  due  to  fibrin  alone, 
582  ;  an  act  of  vitality,  583;  causes  in- 
fluencing, 584;  proportions  of  serum 
and  clot,  585 ;  serum,  composition  of, 
586;  influence  of  changes  in  propor- 
tion of  constituents,  587;  buffy  coat, 
causes  of,  588,589;  artificially  produc- 
ible^}' retarding  coagulation,  589 
Pathological  changes  in,  590 — 592  ;,  nor- 
mal proportion  of  chief  constituents, 
590;  importance  of  accurate  analysis, 
590,  591 ;  increase  of  fibrin  in  inflam- 
mation, 591  a,  606.  717;  deficiency  of 
fibrin  in  fever  and  hemorrhagic  diseases, 
591  b,-  increase  of  corpuscles  in  pletho- 
ra, 591  c,-  diminution  in  chlorosis,  anae- 
mia, &c.,  59 1  e  ;  decrease  of  albumen  in 
Bright's  disease,  591  d;  general  depra- 
vation of,  592 ;  imperfect  elaboration  of 
in  tuberculous  cachexia,  610,  714 
Changes  produced  in,  by  respiration,  538 
— 554 ;  difference  of  arterial  and  venous 
blood,  538 ;  excretion  of  carbonic  acid 
from,  539;  comparative  analysis  of  ar- 
terial and  venous  blood,  540 ;  gases  ex- 
tracted from,  541  ;  change  of  colour, 
causes  of,  542  ;  aeration  of,  by  general 
surface,  543  ;  general  action  of  respira- 
tion on,  544 
Organization  of,  597 

Movement  of  through  vessels,  see  Circu- 
lation 
Blood-vessels,    see    Arteries,    Capillaries, 

Veins 

Bone,  structure  of,  629;  formation  of,  630  ;" 
chemical  composition  of,  630;  growth  of, 
631  ;  regeneration  of,  632 
Bowman,  Mr.,  his  observations  on  muscu- 
lar fibre,  367 — 374, 384 ;  on  mucous  mem- 
brane, 640 ;  on  structure  of  the  kidney, 
667,  668 

Brain,  see  Encephalon,  Cerebrum,  Cerebel- 
lum, &c. 

Brewster,  Sir  D.,  his  law  of  visible  direc- 
tion, 336 

Bright's  disease  of  kidney,  591  d 
Brodie,  Sir  B.,  his  experiments  on  the  Par 

Vagum,  236;  on  animal  heat,  725 
Bronchial  tubes,  contractility  of,  527, 528 
Brunner's  glands,  706 
Buchanan,  Dr.,  referred  to,  714  note,  715 
Budd,  Dr.  W.,  referred  to,  175,  590  n,  717 
Buffy  Coat,  554,  588,  589 
Bulb,  of  hair,  623 


Cacoplastic  deposits,  609,  610 


INDEX. 


631 


The  Numbers  refer  to  the  Paragraphs. 

Callus,  formation  of,  632 

Calorification  of  Animals,  see  Heat 

Cancer,  90,  561 

Capillary  vessels,  distribution  and  size  of, 


477;  origin  of,  477;  properties  of  their 
walls,  510;  absent  in  some  tissues,  479; 
independent  action  of,  495,  499;  proofs 
of,  505—507;  motion  of  blood  in,  478; 
continues  after  death,  506;  in  acardiac 
foetus,  507;  stagnation  of.  in  Asphyxia, 
&c.,  508;  influence  of  local  excitement 
on,  509;  laws  regulating,  511,  512;  con- 
nection of,  with  nervous  influence,  513 
Carbonic  acid,  excretion  of,  92,  520,  533; 
amount  of,  534,  535;  conditions  of,  537; 
contained  in  venous  blood,  538 — 541;  ex- 


with  intelligence,  279,  280;  with  the  will, 
288;  phrenological  account  of,  292,  293; 
peculiar  conditions  of,  in  sleep,  somnam- 
bulism, &c.,  295—297 


Ceruminous  glands,  703 

Chsetodon  rostratus,  290 

Change,  involved  in  idea  ofjife,  72,  73 

Cheselden's  case  of  cataract,  334,  339 

Chiasma  of  optic  nerves,  338 

Chimpanzee,  62 — 70 

Chlorosis,  591  c 

Chondrin,  composition  and  properties  of, 

625 

Chorda  dorsalis,  760 
Chordae  vocales,  402 — 408 
Chorion,  production  of,  747 


piration  of,  in  hydrogen,  539;  existence    Chossat,  his  experiments  on  inanition,  472, 
of,  shown  by  analysis,  540;  extracted  by 


air-pump,  541;  exchanged  for  oxygen, 
544;  effects  of  its  retention  in  the  system, 
546—548 

-,  absorption  of,  by  lungs,  551 


Cartilage,  structure  of,  625;    composition 
of,  625;  nutrition  of,  626;  functions  of,  626 
Catamenia,  742 

Ce/&,86,88— 91,98;  compose  bulk  of  fabric 
of  Vegetables,  556;  origin  of,  556,  557; 
similar  origin  of  in  Animals,  558,  559; 
individual  growth  of,  561;  transforma- 
tions of,  556,560,611;  individual  life 
of,  644,  645;  death  of,  644,  645;  vary- 
ing duration  of,  645,  646 
Functions  of,  general,  86,  88 — 91,  98;  in 
Absorption,  461,  462;  in  Assimilation, 
578,  579;  in  Secretion,  622,  651;  in 
Reproduction,  698,  735 
Persistence  of  in  certain  tissues,  616;  in 
pigment,  617;  in  fat,  618,  619;  in  epi- 
dermis and  epithelium,  620 — 622;  in 
cartilage,  625, 626 

Replacement  of  by  Fibres,  613,  627—643 
Cellular  Plants,  88,  556 
Cellular  tissue,  see  Areolar  tissue 
Cellulose,  vegetable,  612 
Cementum  of  teeth,  634 
Cephalic  nerves, functions  of,  219 — 242;  cha- 
racter of, 243;  embryological  development 
of,  243 

Cerebellum,  158,  161,  294;  of  Fishes,  213; 
of  Reptiles,  216;  of  Birds,  217;  of  Mam- 
malia, 218;  of  Human  embryo,  214,  217; 
relative  dimensions  of,  266,  267;  experi- 
ments on,  268,  269;  connection  of,  with 
motor  power,  270,  271;  with  sexual  in- 
stinct, 274 — 278;  pathological  changes  in, 
272,  273,  275;  phrenological  account  of, 
274—278 

Cerebrum,  158,  161,  294;  general  structure 
of,  281;  of  Fishes,  213;  of  Reptiles,  217; 
of  Birds,  217;  of  Mammalia,  218;  of 
Human  embryo,  214,  217;  functions  of, 
279 — 293;  relative  dimensions  of,  283- 
285;  experiments  on,  286;  pathological 
changes  in,  281,  282,  287;  connection  of, 


730 

Chyle,  86;  formation  of,  in  intestines,  446; 
absorption  of,  461,  462;  analysis  of,  467; 
elaboration  of,  563—569;  aspect  of,  563; 
changes  of,  in  progress  through  lacteals, 
564,  567;  globules  contained  in,  their 
nature  and  source,  566;  their  destination, 
577:  chyle  from  thoracic  duct,  568;  rela- 
tive constitution  of,  569 
Chyme,  formed  by  digestive  process,  444- 

446 
Chymification,448 — 460;  a  chemical  action, 

454—460 
Cicatricula,  759 
Cilia,  621 

Cineritious  matter,  111 
CIRCULATION, 

General  account  of,  87;  objects  of,  475; 
course  of,  in  Man,  476;  arterial  trunks, 
476;  capillaries,  477;  veins,  477;  move- 
ment of  blood  in,  478;  absence  of  ves- 
sels in  some  tissues,  479 
Action  of  Heart,  480;  connection  of  with 
nervous  system,  209,  238,  481;  rhyth- 
mical movements  of,  482,  483;  sounds 
Off  484—486;  course  of  blood  in,  487; 
differences  of  two  sides,  488,  489; 
quantity  of  blood  impelled  by,  490, 
491;  force  of  contractions,  492;  num- 
ber of  contractions,  493,  494 
Action  of  Vessels,  proofs  of  its  indepen- 
dent existence,  495 — 499;  circulation  in 
Plants,  496,  497;  in  Lower  Animals, 
498,  499 

Action  of  Arteries,  500 — 504;  their  elas- 
ticity and  contractility,  500;  influence 
of  their  elasticity,  501;  proofs  of  their 
contractility,  502,  503;  their  tonicity, 
503;  influence  of  their  contractility, 
504 

Independent  motion  in  capillaries,  505; 
proofs  of,  506,  507;  stagnation  in,  508; 
influence  of  capillaries  in  regulating 
amount  of  flow,  509;  contractility  of 
capillaries,  510;  general  principles  of 
their  action,  511—513;  influence  of 
nerves  on  capillary  circulation,  513 


632 


INDEX. 


The  Numbers  refer  to  the  Paragraphs. 


Motion  of  Blood  in  Veins,  514—516; 
structure  and  properties  of  veins,  514; 
causes  of  flow  of  blood  through,  515, 
516 

Peculiarities  of  circulation,  in  lungs,  517, 
525;  in  portal  system,  517;  in  cranium, 
418;  in  erectile  tissue,  519;  in  foetus, 
early  state  of,  763:  subsequent  condi- 
tion of,  766 

Disorders  of  circulation,  716,  717 
Clot,  of  Blood,  see  Crassamentum 

,  organization  of,  554,  597 

Coagulable  lymph,  see  Liquor  Sanguinis 
Coagulation,  of  blood,  582;  due  to  fibrin 
alone,  582;  an  act  of  vitality,  583;   cir- 
cumstances influencing,  584;  proportion 
of  serum  and  clot,  585;    of  chyle,  563, 
564;  of  lymph,  565;  of  fibrin,  553,  554 
Coathupe,  Mr.,  his  experiments  on  respira- 
tion, 532,  534;  on  products  of  combustion 
of  charcoal,  551  note 
Cochlea,  359 
Cockchafer,  30 
Coecilia,  42 
Coition,  act  of,  in  Male,  738;  in  Female, 

743 

Cold,  degree  of,  endurable  by  Man,  721;  in- 
fluence of,  on  young  animals,  728,  729 
Coloured  particles  in  blood,  see  Corpuscles 
Colourless  globules  in  blood,  566,  577 — 579 
Colours,  impressions  made  by,  345;  com- 
plementary, 345;  deficiency  of  power  of 
distinguishing,  346 

Combe,  Dr.  A.,  quoted  from,  428,  449,  768 
Commissures  of  Brain,  216 — 2 18;  deficiency 

of,  286 

Complementary  colours,  345 
Conchifera,  nervous  system  in,  133 
Concussion  of  brain,  effects  of,  386,  425 
Consciousness,  100,  289;  double,  296 
Consensual  movements,  250 — 257 
Contractility,  of  Muscle,  105,  366;  not  de- 
pendent on  nervous  agency,  380 — 385 
but  influenced  by  it,  386 — 388;  of  arte- 
ries, 500,502 — 504;  of  capillaries,  510;  o:' 
bronchial  tubes,  527,  528 
Contraction,  of  Muscle,  mode  of,  371,  372 
causes  of,  378,  379;  alternates  with  re 
laxation,  377;  after  death,  389—391;  de- 
pendent on  arterial  blood,  392;  power  of 
the  same  at  different  degrees  of  extension 
394;  energy  of,  in  Man,  395;  in  Insects 
396;  rapidity  of,  397 
Convolutions  of  Brain,  313 — 318 
Convulsive  diseases,  298—301 
Cooling  power  of  cutaneous  exhalation,  731 
Cooper,  Sir  A.,  his  experiments  on  circu 
lation    through  cranium,   118;     his    re 
searches    on    Mammary  gland   and   its 
secretion,  427,   683 — 688;    on    Thymus 
gland,  711 
Coral,  18 
Corallines,  18 
Cornea,  structure  and  nutrition  of,  626 


Corpora  Malpighiana,  666 — 668 

Olivaria,  168—172 

Pyramidalia,  168 — 172 

Quadrigemina,  214,  215,  265 

Restiformia,  168 — 172 

Striata,  169—172,  214 

Wolffiana,  37,  667  c,  699 

/orpus  Callosum,  216,  218 
Luteum,  744 


Corpuscles,  red,  of  Blood,  structure  of,  570; 
form  of,  571;  size  of,  in  Mammalia,  572  a; 
in  Birds,  572  b;  in  Reptiles,  572  c;  chemi- 
cal constitution  of,  573;  production  of,  by 
each  other,  574;  first  formation  of,  in  em- 
bryo, 575;  large  in  foetus,  575;  uses  of, 
in  animal  economy,  576;  increase  of,  in 
plethora,  591  c;  diminution  of,  in  chlo- 
rosis, 591  c 

,  colourless,  of  Blood,  566,  577; 

uses  of,  578,  579 

of  Chyle,  564,  566 

of  Lymph,  565 

of  Spleen,  580,  708 

of  Supra-Renal  Capsules,  580, 710 


Cortical  Substance,  of  Brain,  281 


-,  of  Kidney,  666,  667 


Cranium,  circulation  in,  517 
Crassamentum  of  Blood,  582 — 585 
Croup-like  convulsion,  300 
Crowing  inspiration  of  infants,  300 
Crusta  petrosa  of  teeth,  634 
Cruveilhier,  M.,  his  observations  on  heart, 

482 — 486;  on  purulent  deposits,  665 
Cryptogamia,  reproduction  in,  732 
Crystalline  lens,  627 
Currie,  Dr.,  case  of  dysphagia  related  by, 

464 
Cuttle-fish,  nerves   of  arms   in,   139,  140; 

ejection  of  ink  by,  141,  262 
Cytoblast,  557 


Dartos,  contractility  of,  375 

Davy,  Dr.  J.,  his  researches  on  animal  heat, 
720 

Death,  somatic  and  molecular,  644  ;  death 
of  individual  cells,  645  ;  by  asphyxia,  546, 
548  ;  by  syncope,  210,  386 ;  by  necraemia, 
592;  by  retention  of  secretions,  649,  661, 
570 

Decidua,  formation  of,  748 

Decomposition,  continual,  in  living  beings, 
83,  84,  92,  467,  644 

Decussation,  of  optic  nerves,  338 

Defecation,  202 

Degeneration,  of  nervous  structure,  222 ;  of 
muscular  fibre,  381,  382;  of  elements  of 
blood  into  pus,  608,  609  ;  intotubercle,  610 

Deglutition,  433;  a  reflex  action,  191; 
nerves  concerned  in,  192,  193;  actions 
preceding,  195—197;  in  Polypes,  130 

Dental  groove,  635 

Dentine,  634 


INDEX. 


633 


The  Numbers  refer  to  the  Paragraphs. 


Devergie,  M.,  his  table  of  development  of 

foetus  at  different  ages,  769 
Diabetes,  715 

Diatheses,  gouty,  714;  saccharine,  715;  tu- 
bercular, 714;  inflammatory,  717 
Diet-scale,  see  Food 
DIGESTION, 

General  account  of,  77,  85;  in  lower  Ani- 
mals, 435;  alimentary  materials,  430; 
their  respective  destinations,  431 — 
433;  inorganic  substances,  434;  re- 
lative digestibility  of  different  kinds  of 


food, 
453 


451,    452;  importance  of  bulk, 


Processes  of,  436—447;  mastication  and 
insalivation, 436 ;  deglutition,  437 ;  con- 
dition of  stomach  in,  during  health, 
438 ;  disorder  of,  439  ;  Dr.  Beaumont's 
researches  on,  438,  439,  444—453; 
sense  of  hunger,  440 — 442;  sense  of 
thirst,  443 ;  entrance  of  food  into  sto- 
mach, 444;  movements  of  stomach, 
444;  expulsion  into  duodenum,  445; 
passage  along  intestines,  446,447 ;  dis- 
charge of  faeces,  447 
Chemical  phenomena  of,  448 — 460;  pro- 
perties and  action  of  gastric  juice,  449 
453  ;  its  chemical  action,  454 ;  artificial 
solution  of  food,  455,  456;  Schwann's 
researches  on  pepsin,  455  ;  Wasmann's 
researches,  456 ;  similarity  of  azotized 
proximate  principles,  457;  reduction 
of  food  to  form  of  albumen,  457;  com- 
position of  protein,  458;  conversion  of 
saccharine  and  oleaginous  principles, 
460 

Influence  of  nerves  upon,  235,  236 
Interstitial,  according  to  Dr.  Prout,  468 

Direction,  law  of  visible,  336 

Discs  of  Blood,  see  Corpuscles 

Distance,  adaptation  of  eye  to,  329 ;  esti- 
mate of,  341 

Domesticability  of  Animals,  50,53,  280 

Donne,  M.,  his  observations  on  Milk,  685, 
689;  on  temperature  in  disease,  720 

Dorsal  vessel  of  Articulata,29 

Double  consciousness,  296 

Dreaming,  295,  296 

Dugong,  heart  of,  476 

Dulong,   his   researches  on    animal  heat, 
727 

Dumas,  his  analysis  of  fibrin,  553 

Duration  of  life  in  individual  parts,  645, 
646 

Dzondi,  on  deglutition,  437 


E 


Ear,  general  action  of,  104  ;  comparative 
structure  of,  350,  351 ;  distribution  of  au- 
'  ditory  nerve  in,  352;  uses  of  membrana 
tympani,356;  of  tympanic  cavity,  357  ; 
of  labyrinth,  358,  359 ;  of  external  ear  and 
meatus,  359,  360 


Echinodermata,  19 

Educability.of  Birds,  50,280;  of  Mamma- 
lia, 53,  280;  of  Man,  71,279 

Edwards,  Dr.,  his  experiments  on  respira- 
tion, 533,  536,  538,  539;  on  animal  heat, 
728,  730 

Efferent  nerves,  112,  116,  162 

Egg,  see  Ovum 

Egg-shell,  Membrane  of,  554 

Ehrenberg,  on  limits  of  vision,  333 

Eighth  Pair  of  Nerves,  see  Glosso-pharyn- 
geal,  Par  Vagum,  and  Spinal  Accessory 

Elasticity,  of  arterial  walls,  500,  501 

Elastic  tissues,  638 

Embryo,  early  development  of,  758—770 ; 
formation  of  germinal  mass,  758  ;  of  ger- 
minal membrane,  758,  759;  of  vertebral 
column,  760  ;  of  amnion,  761 ;  of  vascu- 
lar area  and  umbilical  vessels,  762;  of 
branchial  arches,  763;  of  allantois,  764; 
of  umbilical  cord,  765;  influence  of  mo- 
ther on,  768  ;  table  of  development,  769 ; 
size  and  weight  of  at  birth,  770 

Embryonic  development  of  brain,  214,  215, 
217;  of  cephalic  nerves,  243 ;  of  lungs, 
526;  of  blood-corpuscles,  575;  of  liver, 
655  g;  of  kidney,  667  c,-  of  heart,  762; 
of  circulating  apparatus,  766 ;  of  diges- 
tive cavity,  767 

Emissio  seminis,  108,  203,738 

Emotions,  influence  of  on  nutrition  and  se- 
cretion, 423,  425—429 

Emotional  actions,  258,  260 — 265,  288,290 

Empiricism,  rational,  11 

Enamel,  632  c,  634 

Encephalon,  comparative  anatomy  of,  215 
— 218;  proportions  of  different  parts,  in 
Fishes,  213,  214;  in  Reptiles,  216;  in 
Birds,  217;  in  Mammalia,  218;  in  Hu- 
man Embryo,  214, 215,  217;  functions  of, 
258—293 

Epidermic  tissues,  620  —  622 ;  epidermis, 
620;  nails,  620;  epithelium,  621;  nutri- 
tion of,  612,  622;  functions  of,  651 

Epilepsy,  299 

Epithelium,  621 ;  the  real  secreting  struc- 
ture, 651 

Erectile  tissue,  519 

Eustachian  tube,  uses  of,  357 

Eustachian  valve,  uses  of,  766 

Excretion,  objects  of,  92;  of  carbonic  acid, 
92,  521 ;  of  nitrogen,  93,  670,  679;  result 
of  decomposition,  468,  648;  elements  of, 
previously  in  blood,  469,  520,  648 

Excretions,  outlets  of,  guarded  by  spinal 
cord,  202,  203 

Exhalation,  by  lungs,  550;  influenced  by 
mental  state,  429  ;  from  skin,  702,  703 

Experiments  on  nerves,  fallacies  of,  122— 
124 

Expiration,  act  of,  530 

Exudation  corpuscles,  560,  596,  601,  609 

Eye,  general  action  of,  103;  an  optical  in- 
strument, 329;  adaptation  of,  to  distance, 


634 


INDEX. 


The  Numbers  refer  to  the  Paragraphs. 


329;  defects  of,  331 ;  optical  powers  of, 
332,  333 ;  consensual  movements  of,  251 
—256 


Falsetto  notes,  how  produced,  410 

Faraday,  Mr.,  optical  illusion  discovered 
by,  344 

Farre,  Dr.  A.,  discovery  of  Spermatozoa  in 
Ovum,  733 

Fat-cells,  618,  619;  contents  of,  618;  uses 
of,  619,  730;  formation  of,  433 

Feathers,  47 

Fever,  state  of  blood  in,  591  b 

Fenestra  ovalis,  351,  358 

rotunda,  351,  358 

Ferneley,  Mr.,  on  areas  of  arteries,  476 

Fibres  of  Vegetable  tissue,  origin  of,  556 

Animal  tissues,  origin  of,  554, 

555,  611,  613;  white,  637,638;  yellow, 
637,  638;  mixture  of  in  areolar  tissue, 
637;  in  serous  and  synovial  membranes, 
639  ;  in  mucous  membrane  and  skin,  641 

Muscle  and  Nerve,  see  Muscular 

Fibre,  and  Nervous  tissue 

Fibrin,  composition  of  457,  553;  properties 
of,  553—555  ;  coagulation  of,  553—555  ; 
in  chyle,  564,  567;  in  blood,  582,  583; 
increase  of,  in  inflammation,  591  a,  606, 
717 ;  diminution  of,  in  fever  and  hemor- 

.  rhagic  diseases,  591  b  ;  imperfect  elabo- 
ration of,  in  strumous  diathesis, 610,  714; 
formed  at  expense  of  albumen,  554, 567 — 
579;  effusion  of,  607;  organization  of, 
554,  555,  560,  607 

Fibro-cartilage,  625 

Fibrous  tissues,  637,  638;  origin  of,  613 

Fifth  Pair  of  Nerves,  225;  ophthalmic 
branch  of,  226;  superior  maxillary  branch 
of,  226;  inferior  maxillary  branch  of, 
226;  lingual  branch  of,  228;  develop- 
ment of,  243;  influence  of,  on  organic 
processes,  425 

^'^65,37,38;  skeleton  of,  37;  respiration 
of,  38;  air-bladder  of,  38,  351  ;  kidneys 
of,  37;  encephalon  of,  213 — 215;  circu- 
lation in,  499 

Fluids,  absorption  of,  by  intestinal  surface, 
461—463  ;  by  general  surface,  464—466 ; 
by  veins,  463,  466 ;  by  lacteals,  461,  462 ; 
by  lymphatics,  466,  469 

Fostus,  table  of  development  of,  766  ;  circu- 
lation in,  766 ;  brain  of,  compared  with 
that  of  lower  animals,  214,  215,  217 

Follicles  of  Lieberkiihn,  705 

Food,  causes  of  demand  for,  84;  different 
kinds  of,  430—434;  destination  of,  431 — 
432;  desire  for,  440—442;  relative  di- 
gestibility of  different  kinds  of,  451,452  ; 
mechanical  reduction  of,  436 ;  entrance 
of,  into  stomach,  244;  passage  of,  into 
intestine,  445;  passage  of,  through  intes- 
tinal canal,  446,  447 ;  mode  of  solution 


of,  448 — 460;  proximate  principles  con- 
tained in,  457;  production  of  albumen 
from,  456 ;  smallest  quantity  of,  on  which 
life  can  be  supported,  473;  greatest  quan- 
tity that  can  be  devoured,  474;  supply  of 
required  by  Man,  470 — 474:  sufficiency 
indicated  by  satiety,  470 ;  allowance  of, 
in  Navy,  471 ;  in  Milbank  Penitentiary, 
472;  in  Edinburgh  House  of  Refuge, 
472  ;  in  convict-ship,  472 

Form,  mode  of  acquiring  knowledge  of,  by 
touch,  317;  by  sight,  339,  340 

Fourth  pair  of  nerves,  244,  246,  247 

Fourth  ventricle,  164,  216 

Foville,  Dr.,  his  observations  on  brain,  115, 
282 

Fremy,  M.,  his  analysis  of  nervous  matter, 
643 

Frog,  42 

Functions,  75;  division  of,  into  organic  and 
animal,  76,  77;  connection  of,  77—82, 
97;  of  Animal  life,  78-80,  100—105  ;  of 
Organic  life,  83—99 


G 


Gall-bladder,  654 

Ganglia,  111;  of  Nervous  System  of  Ra- 
diata,  129;  of  Mollusca,  132,  136;  of  Ar- 
ticulata,  143,  144,  148;  of  special  sense 
in  Vertebrata,  258,  261—265,  294;  of 
Sympathetic,  110,  111 

Ganglionic  globules,  111 

Gangrene,  608 

Gases,  poisonous,  action  of,  550,  551 

Gasteropoda,  Nervous  System  of,  133 — 138 

Gastric  fluid,  secretion  of,  not  dependent  on 
nervous  influence,  235;  properties  of, 
448,  449,  et  seq. 

Gelatin,  composition  of,  615 

,  of  cartilage,  625;  of  bone,  630 


Gerber,  Prof.,  referred  to,  519,  569 
Germinal  mass,  758 

membrane,  serous  layer,  751 


mucous  and  vascular  layers,  759 

spot,  739,  et  seq. 

vesicle,  739,  et  seq. 

Gestation  in  Mammalia,  56;  signs  of,  752; 

ordinary  duration  of,  754 ;  protracted,  755 

shortest  period  of,  756 
Gills,  respiration  by,  523 
Globules  of  Chyle  and  Lymph,  563-568;  of 

Blood,  red,  570—576;  colourless,  577,  579 
Globulin,  composition  of,  573 
Glosso-pharyngeal  nerve,  functions  of,  192, 

193,  228;  development  of,  243 
Gluttony,  cases  of,  474 
Glycerine,  composition  and  properties  of, 

618 
Goodsir,  Mr.,  his  researches  on  the  Teeth, 

625;  on  Absorption,  461,  462;  on  Secre- 
tion, 631 ;  on  milk-cells,  683  b 
Gouty  diathesis,  714 


INDEX. 


635 


The  Numbers  refer 

Grainger,  Mr.,  referred  to,  163,  177,  197 
Granulation,  600,  601 
Granulation,  process  of,  600,  601 
Greenhow,  Dr.,  his  plan  of  treating  burns, 

599 
Gray  matter  of  Nervous  system,  111,  117; 

of  Brain,  281 

Gray  or  organic  fibres,  110 
Gulliver,  Mr.,  his  observations  referred  to, 

554,  563, 568,  570,  572,  575,  577,  579,  580, 

606,  613,  632 
Guy,  Dr.,  his  researches  on  the  Pulse,  493, 

494 


H 


Haemadynamometer,  492,  548 

Haematosine,  573 

Hales,  Dr.,  his  experiments  on  the  circula- 
tion, 492 

Hall,  Dr.  M.,  his  discoveries,  173,  185,  297 

referred  to,  163,204,207,  210— 

213,381,  393,417,418 

Haller,  his  doctrine  of  muscular  irritability, 
385 

Hearing,  sense  of,  104,  308,349—365;  phy- 
sical condition  of,  349,  353—355;  use  of 
tympanum,  356;  tympanic  cavity  and 
Eustachian  tube,  357;  chain  of  bones, 
358;  labyrinth,  359;  external  ear,  360; 
auditory  nerve,  352  ; — tones  produced  by 
succession  of  sounds,  362;  estimate  of 
degree,  direction,  and  distance  of  sounds, 
363;  rapidity  of  perception,  compared 
with  sight,  364 ;  uses  of,  in  regulating 
voice,  365 

Heart,  476 ;  muscular  fibre  of,  375 ;  inhe- 
rent contractility  of,  480 ;  rhythmical 
movements  of,  482,  483;  influence  of 
nerves  on,  209,  238,  481 ;  sounds  of,  484 
—486;  course  of  blood  through,  487; 
differences  of  structure  in  two  sides  of, 
488;  difference  of  valves,  489;  quantity 
of  blood  propelled  by,  490,  491 ;  force  of 
contraction  of,  492;  number  of  contrac- 
tions of,  493;  various  causes  influencing, 
493,494;  origin  of,  763;  subsequent  de- 
velopment of,  766 

Heat,  Animal, amount  of,  developed  by  Man, 
719,  720;  in  disease,  720 ;  dependence  of 
on  formation  of  carbonic  acid,  723 — 727; 
development  of,  in  Plants,  723,  724 ;  in 
lower  Animals,  725 ;  dependent  in  part 
on  skin,  726;  not  fully  to  be  accounted 
for  by  combustion,  727;  heat  of  young 
animals, 728  ;  variations  in  power  of  gen- 
erating, at  different  seasons,  729;  loss  of, 
during  inanition,  730;  provisions  against 
excess,  731 

Heat,  external,  influence  of  on  incubation 
of  Birds,  52;  influence  of  on  vital  actions 
in  general,  730;  extremes  of,  endurable 
by  Man,  721, 722;  power  of  resisting,  731 

Hemiopia,  338 


to  the  Paragraphs. 

Hering,  experiments  of,  on  circulation,  490 

Heterologous  growths,  717 

Hippuric  acid,  674 

Holland,  Dr.,  referred  to,  296  note,  315 

Horny  matter,  composition  of,  620 

Horses,  cerebella  of,  276 

Hunger,  sense  of,  440—442 

Hunter,  John,  on  functions  of  lymphatics 

469 
,  Dr.  W.,  on  formation  of  decidua, 

748 

Hydra,  130;  reproduction  of  parts  in,  596 
Hydrophobia,  212,298,  299 
Hygiene,  dependence  of  on  Physiology,  6 
Hypertrophy,  603 
Hypochondriasis,  315 
Hypoglossal  nerve,  functions  of,  241,  242  ; 

development  of,  243 
Hysteria,  299, 473 


Idiots,  actions  of,  279,  285,  286 
Immortality  of  the  Soul,  72,  78 
Impressions  on  Nervous  system,  107,  130, 
134 

,  sensory,  persistence  of,  307 ; 


of  taste,  323:  of  smell,  325;  of  sight,  344 

Improvability  of  Man,  71 

Incontinence  of  urine,  300 

Infants,  inferior  calorifying  power  of,  728 

Inflammation,  increase  of  fibrin  in,  591  a, 
606,  717;  generally  unfavourable  to  repa- 
ration, 598,  600,  601 ;  prevention  of,  after 
injuries,  599  ;  how  far  concerned  in  depo- 
sition of  tubercle,  610;  real  nature  of, 
717 

Ingestion  of  food,  actions  concerned  in,  195 
—197 

Insanity,  263,  295;  alterations  of  brain  in, 
282 

Insects,  muscular  apparatus  of,  28,  30 ; 
strength  of,  396;  instincts  of,  28,  279; 
heat  developed  by,  29,  725;  nervous  sys- 
tem of,  143 — 151 ;  reflex  actions  of,  146; 
circulation  in,  475;  respiration  in,  523 

Inspiration,  act  of,  530 

Instincts,  of  Articulata,  28,  155,  279 ;  of 
Birds,  50, 280 ;  of  Mammalia,  53  ;  of  Man, 
155,  260—264,  279;  of  Cuttle-fish,  141  ; 
of  Idiots,  279 

Intelligence  of  Vertebrata,  34 ;  of  Birds,  50, 
280  ;  of  Mammalia,  53,  280 ;  of  Man,  71, 
279;  general  absence  of,  in  Invertebrata, 
279  ;  seat  of,  in  the  Cerebrum,  279,  280, 
285 ;  degree  of,  connected  with  early  pro- 
cesses of  development,  54 

Internuncial  function  of  Nervous  system, 
102 

Tntervertebral  nerves,  243 

Intestines,  peristaltic  movements  of,  200, 
201 ;  passage  of  food  through,  446,  447; 
glandulseof,  704 — 707;  secretions  of,  447, 
707 


636 


INDEX. 


The  Numbers  refer  to  the  Paragraphs. 


Intuitive  perceptions,  288—290 

Iron,  contained  in  food,  434;  in  blood-discs, 

573;  administration  of,  in  chlorisis,  591  c 
Irritability,  of  muscular  fibre,  366  note,-  Dr. 

M.  Hall  on,  393;  see  Contractility 


Jennings,  Mr.,  on  artificial  insufflation  of 
lungs,  528 


K 


Kellie,  Dr.,  his  experiments  on  circulation 
in  cranium,  518 

Kidneys,  general  function  of,  93 ;  structure 
of,  666 — 668 ;  cortical  and  medullary  sub- 
stances, 666  ;  tubuli  uriniferi,  667;  Mal- 
pighian  bodies  in,  667  b,  669 ;  circulation 
in,  669;  embryological  development  of, 
667  c ;  see  Urine 

Kiernan,  Mr.,  on  the  liver,  655,  656 

Kiestine,  in  urine  of  pregnant  women,  690, 
751 


Labyrinth  of  ear,  uses  of,  358, 359 

Lachrymal  gland,  696 

secretion,  696 ;  influence  of  ner- 
vous system  on,  426 

Lacteals,  origin  and  distribution  of,  461 
functions  of,  462 

Lactic  acid,  a  doubtful  constituent  of  urine, 
676 

Lamina  spiralis,  352 

Lane,  Mr.,  his  investigations  on  chyle,  568 

Larynx,  structure  of,  402 — 405;  action  of 

>  muscles  of,  403, 404 ;  nervous  connections 
of,  187,  188 

Laws  of  transmission  of  nervous  influence, 
126;  of  duration  of  cells,  645 

Lecanu,  M.,  his  analysis  of  blood,  581 ;  his 
observations  on  urine,  672 

Lee,  Dr.  R.,  his  observations  on  nerves  of 
uterus,  643,  751 

Lehmann,  his  experiments  on  composition 
of  urine,  679,  680 

Leuret,  M.,  his  observations  on  Cerebellum, 
276 

Levator  palpebrae,  action  of,  249 

Liebig,  his  analysis  of  organic  compounds, 
457;  on  digestive  process,  456;  on  red 
corpuscles  of  blood,  576  ;  on  composition 
of  urine,  674—678;  on  uric  acid,  675 

Life,  idea  of,  involves  change,  73;  duration 
of,  in  individual  parts,  645,  646 

Ligaments,  structure  of,  339;  vocal,  402 — 
405,  408 

Light,  laws  of  refraction  of,  326—328 ;  ra- 
pidity of  perception  of,  compared  with 
sound,  364;  influence  of,  on  metamor- 
phosis, 43  ;  effect  of  on  pupil,  222 


Lime,  an  element  of  animal  structures,  434 

Lingual,  branch  of  fifth  pair,  228 

Lintott,  Mr.,  his  observations  on  the  teeth, 

634,  636 

Liquor  sanguinis,  570 ;  organization  of,  600 
Liver,  general  function  of,  92;  universally 
present  in  Animal  kingdom,  651;    size 
and  form  of  in  Vertebrata,  652;  general 
structure  of,  653;  distribution  of  portal 
vessels,  654  ;  of  hepatic  duct,  655  ;  of  he- 
patic artery,  656 ;  of  hepatic  vein,  657 ; 
congestion  of,  658;  cirrhosis  of,  659 ;  em- 
bryonic development  of,  660;  proportional 
size  of,  before  and  after  birth,  661 ;  secre- 
tion of  bile,  662—665  ;  see  Bile 
Locomotive  actions,  210 
Looped  terminations   of  nerves,  215,  216, 

379 

Lungs,  general  function  of,  92 ;  structure  of, 
525,  527  ;  development  of,  526:  action  of, 
in  respiration,  528 — 531;  capacity  of,  532; 
chemical  changes  in,  533,  537,  544  ;  ex- 
halation by,  549;  absorption  by,  550,  551 
Lymph,  composition  of,  434;  elaboration  of 
565;  globules  in,  566;  purposes  of,  467, 
567,  568 

Lymph,  coagulable,  see  Liquor  Sanguinis 
Lymphatics,  distribution  of,  through  the 
body,  467 ;  function  of,  466,  468,  469  ; 
specially  concerned  in  nutritive  absorp- 
tion, 469  ;  share  of,  in  interstitial  absorp- 
tion, 469 


M 


Macartney,  Dr.,  his  views  on  the  reparative 
processes,  594—600 

Macleod,  Mr.,  on  first  production  of  blood- 
corpuscles,  575  note 

Madden,  Dr.,  his  experiments  upon  absorp- 
tion, 550 

Magnetism,  Animal,  296  note 

Magnus,  his  experiments  on  the  blood,  541 

Malignant  growths,  90,  562,  645  v 

Mammalia,  53 — 61;  sub-classes  of,  55; 
skeleton  of,  57;  respiration  and  heat  of, 
58;  subdivisions  of,  59,  61;  brain  of, 
218;  blood-corpuscles  of,  572 

Mammary  gland,  683;  structure  of  glan- 
dulae,  683  bf  development  of,  683  c,- 
structure  of  in  male,  683  d;  secretion  of, 
684—692 ;  see  Milk 

Man,  characteristics  of,  62 — 72 ;  erect  atti- 
tude of,  62—67 ;  hand  of,  68 ;  other  dis- 
tinctive characters  of,  69;  sensibility  and 
locomotive  power  of,  70;  intelligence  of, 
71;  soul  of,  72;  psychical  operations  in, 
101 

Mantle,  of  Mollusca,  24 

Margarine,  composition  and  properties  of, 
618 

Mastication,  436 

Medulla  Oblongata,  161 ;  structure  and  con- 
nections  of,  168 — 172;  general  functions 


INDEX. 


637 


The  Numbers  refer 

of,  180,  264,  294;  centre  of  respiratory 
movements,  184;  centre  of  acts  of  deglu- 
tition, 194,  196 

Medullary  matter  of  nervous  system,  struc- 
ture of,  110;  functions  of,  113—116 

Melolontha  vulgaris,  30 

Memory,  291 

Metamorphosis  of  Batrachia,  42,  43 

Michaelis,  his  analyses  of  venous  and  arte- 
rial blood,  540 

Milk,  peculiarity  of,  as  alimentary  sub- 
stance, 431,  687;  general  composition  of, 
684;  microscopic  characters  of,  685; 
constituents  of,  686 ;  proportion  of  con- 
stituents in  milk  of  different  animals,  688; 
quantity  of,  692  ;  change  in  character  of, 
during  nursing,  689;  consequences  of 
retention  of,  690 ;  transference  of  secre- 
tion, 691;  foreign  substances  entering, 
692  ;  influence  of  emotions  on,  690,  691 ; 
secretion  of,  in  male,  683  note 

Milky  aspect  of  chyle,  563 

serum,  563,  580,  714  note 

Milbank  Penitentiary,  472 

Mind,  influence  of,  on  nutrition  and  secre- 
tion, 425—429 

Mitchell,  James,  case  of,  325 

Modeling  process,  598,  599 

Mullusca,  17,  22—26;  organs  of  locomotion 
in,  24;  organs  of  nutrition  in,  25;  blood 
and  respiration  of,  26;  nervous  system 
in,  132 — 141;  acephalous,  161;  circula- 
tion in,  475;  respiration  in,  523 

Montgomery,  Dr.,  on  corpus  luteum,  744 

Mother,  influence  of,  on  foetus,  768 

Motions  of  Plants,  13,  128 

Motor  Linguae,  241,  242 

oculi,  224,  249 

nerves,  determination  of,  122 

tract  of  Sir  C.  Bell,  169 ;  connections 

of,  170—172 

Movements  of  eye,  249,  251—256 

,  other  consensual,  257 

Mucous  Membrane,  640;  of  stomach,  ap- 
pearance of,  in  health,  458;  in  disease, 
439;  intestinal,  structure  of,  461;  glan- 
dulae  of,  in  stomach,  704;  in  intestines, 
705—707 

Mulder,  his  analysis  of  organic  compounds, 
457;  of  protein-oxides,  553  note,-  of  gela- 
tin, 615 

Muller  referred  to,  162,  313,  336,  345,  354, 
381,  383, 405,  410, 451, 458,  519,  538,  539, 
541,  582,  712 

Muscular  Fibre, 

Structure  of,  366 — 375;  in  muscles  of 
Animal  life,  367—374;  arrangement 
of,  in  fasciculi,  367;  composed  of  fibril- 
lae,  367;  enveloped  in  sheath,  367; 
form  and  comparative  dimensions  of, 
368 ;  structure  of  ultimate  fibrillae,  369 ; 
state  of,  in  contraction,  371, 372;  origin 
of,  374;  in  muscles  of  organic  life,  366, 
375 

54 


to  the  Paragraphs. 

Contractility  of,  366;  duration  of,  376; 
alternates  with  relaxation,  377;  increase 
in  amount  by  exercise,  377;  different 
effects  of  stimuli  on,  378  ;  influence  of 
nerves  on,  379—387 ;  loss  of,  from  sec- 
tion of  nerves,  381,  382;  restored  after 
exhaustion,  383;  an  independent  en- 
dowment, 385;  destroyed  by  sudden 
shock  to  nervous  sys'tem,  386,  387; 
energy  of,  dependent  on  arterial  blood, 
392;  difference  of,  on  two  sides  of  heart, 
393;  the  same  at  different  degrees  of 
contraction,  394;  power  generated  by, 
in  Man,  395;  in  Insects,  396 

Contraction  of,  after  death,  389—391; 
medico-legal  inquiries  respecting,  391 ; 
rapidity  of  changes,  397;  associated  in 
movements,  398  ;  influence  of,  on  Cir- 
culation, 516 

Nutrition  of,  642;  composition  of,  642; 
regeneration  of,  642 

Sensibility  of,  399 
Muscular  sense,  400 


N 


Nails,  621 

Nasmyth,  Mr.:  on  the  Teeth,  634 

Necrsemia,  592 

Nerves,  origin  and  termination  of,  112, 113, 
116;  mode  of  determining  functions  of, 
120 — 125;  termination  of,  in  sensory  or- 
gans, 322,  352;  in  muscles,  379 

Nervous  agency,  hypothesis  on  its  nature, 
126;  laws  of  its  transmission,  126;  not 
essential  to  Nutrition  and  Secretion,  91, 
96,  237;  influence  of,  on  organic  func- 
tions, 420—429 

Nervous  System,  general  functions  of,  102, 
106—109;  elementary  structure  of,  110 
— 114;  white  matter  of,  110;  gray  mat- 
ter of,  111;  arrangement  of  fibres  in 
ganglia,  112;  afferent  and  efferent  fibres 
of,  113;  use  of  plexuses  in,  114,  115; 
isolated  course  of  single  fibres,  114 ;  func- 
tions of  gray  matter,  116—118;  functions 
of  white  matter,  116;  relation  of,  with 
vascular  system,  117,  118;  simplest  idea 
of  nervous  system,  11 9;  nature  of  changes 
in,  126;  existence  of,  in  lowest  Animals, 
128,  129;  general  recapitulation  of  func- 
tions, 294;  peculiar  conditions  of,  295, 
296;  pathological  states  of,  297—301 

Nervous  tissue,  composition  of,  643;  nutri- 
tion and  regeneration  of,  643 

Nervous  system  of  Insects,  &c.,  142—147 

Newport,  Mr.,  his  observations  on  their 
respiration,  535;  on  their  temperature, 
725 

Nucleated  cells,  persistent,  616 

Nucleus,  557 

Numerical  method,  12 

NUTRITION, 

General  account  of,  88 — 91;  connection 


INDEX. 


The  Numbers  refer  to  the  Paragraphs. 


of,  with  nervous  system,  91;  simplest 
form  of,  88;  not  dependent  upon  ner- 
vous agency,  424;  but  influenced  by 
it,  425 

Essential  nature  of,  551  et  seq.;  organ- 
izable  principles,  composition  and  pro- 
perties of,  552—554;  albumen,  552; 
fibrin,  553;  its  coagulation,  554,  555 
Origin  of  cells,  560—562;  predominance 
of,  in  Vegetable  structures,  556;  mode 
of  origin,  557,  558 ;  corresponding  phe- 
nomena in  Animals,  559,  560;  growth 
of,  by  assimilation,  561;  parasitic 
growths,  562 

Origin  of  fibres,  554,  555,  611 
Fibrin  the  chief  organizable  principle, 
554;  production  of  in  chyle  and  lymph, 
563—569 ;  characters  of  crude  chyle, 
563;  changes  during  passage  through 
lacteals,  564,  567 ;  characters  of  lymph, 
565 ;  source  of  globules  in,  566 ;  nature 
of  fluid  in  thoracic  duct,  568 ;  tabular 
view  of  elaboration  of  chyle,  569 ; 
blood,  physical  and  vital  characters  of, 
570—589  (see  Blood);  pathological 
changes  in,  590—592 
Origin  of  solid  tissues,  593—601 ;  repro- 
duction of  parts  in  lower  Animals,  593 ; 
reparative  processes,  594,595;  union 
by  first  intention,  596;  organization  of 
liquor  sanguinis,  596;  organization  of 
blood,  597;  modeling  process  of  Dr. 
Macartney, 598;  circumstances  favour- 
able to,  599;  granulation,  600,  601 
Formation  of  tissues,  611 — 646;  general 
modes  of  transformation,  612;  produc- 
tion of  fibres,  613;  composition  and 
properties  of  gelatin,  615;  cellular 
structure  in  Animal  bodies,  616;  pig- 
ment-cells, 617;  fat-cells,  618, 619 ;  epi- 
dermic tissues,  620—622;  hair,  623, 
624;  cartilage,  625,  626;  humors  of 
the  eye,  627;  mode  of  their  nutrition, 
628;  bone,  629—632;  teeth,  633— 636; 
fibrous  tissues,  637 — 641 ;  areolar  tis- 
sue, 637;  elastic  tissue,  tendons,  liga- 
ments, &c.,  638;  serous  and  synovial 
membranes,  639 ;  skin  and  mucous 
membranes,  640,  641 ;  muscular  tissue, 
642;  nervous  tissue,  643 
Death  of  tissues,  644;  term  of  existence 
of  cells,  645  ;  variation  of,  at  different 
periods  of  life,  646 

Varying  activity  of  nutritive  processes, 
602—605 ;  hypertrophy,  603 ;  atrophy, 
604,  605 

Abnormal  forms  of  Nutritive  processes, 
606—610;  inflammation,  606—608; 
suppuration,  609;  tubercular  deposit, 
610 


O 


Oblique  muscles  of  orbit,  245 — 247 


Octopus,  nerves  of,  115 

Odours,  sensibility  to,  220 

Oesophagus,  descent  of  food  through,  194 

Oleaginous  principles,  430,  432,  460,  567, 
618 

Oleine,  composition  and  properties  of,  618 

Olfactory  lobes,  in  Fishes,  213, 214;  in  Rep- 
tiles, 216;  in  Birds,  217;  in  Mammalia, 
218 

Olfactive  nerves,  functions  of,  220 

Olivary  bodies,  168—172 

Omphalo-meseraic  vessels,  762,  764 

Optic  lobes,  in  Fishes,  213,  214;  in  Rep- 
tiles, 216;  in  Birds,  217;  in  Mammalia, 
218;  in  Human  embryo,  214,  215,  217; 
functions  of,  265 

Optic  Nerve,  221;  an  exciter  of  motion, 
222  ;  decussation  of,  338  ;  termination  of 
in  papillae,  332 

Optic  Thalami,  214-218 

Orang  outan  compared  with  Man,  62 — 70 

Orbicularis  muscle,  reflex  action  of,  204 

Orbit,  motor  nerves  of,  244 — 249;  muscles 
of,  245,  246 

Organic  fibres  of  nervous  system,  110,  424, 
425 

Organization,  connection  of,  with  vital  pro- 
ties,  561 ;  incipient,  in  chyle,  86,  564;  of 
liquor  sanguinis,  554;  of  blood,  597 

Organs  of  Sense,  their  mode  of  operation, 
103,  104  ;  see  Ear,  Eye,  &c. 

Ornithorhyncus,  55 

Ostrich,  47,  52 

Ovarium,  origin  of  ova  in,  740,  741 ;  corpus 
luteum  in,  744 

Ovum,  parts  of,  739  ;  origin  of,  740;  matu- 
ration of,  741 ;  arrival  of  spermatozoa  at, 
733,  743;  discharge  of,  from  ovary,  744; 
first  changes  in,  745,  746 

Owen,  Mr.,  on  blood-corpuscles  of  Siren, 
570  n;  on  formation  of  teeth,  634 


Pancreas,  structure  of,  693;  secretion  of, 
695 

Papillae,  of  skin,  316;  of  tongue,  321;  of 
optic  nerve,  322:  of  auditory  nerve,  352 

Paralysis  of  Spinal  Cord,  176—179,  261 

agitans,  300  note. 

Parturition,  203,  753 

Par  Vagum,  the  excitor  of  respiratory  move- 
ments, 1 84, 185 ;  influence  of,  on  pharynx, 
193;  influence  of,  on  stomach,  198;  chief 
exciter  of  sense  of  hunger,  199;  effects  of 
section  of,  on  lungs,  230—233  ;  on  diges- 
tion, 234—236;  on  heart,  238 

Pathology,  the  science  of  abnormal  life,  2  ; 
connection  of  with  physiology,  7 — 9; 
connection  of,  with  therapeutics,  10;  mode 
of  advancing  it,  11,  12 

Pepsin,  455,  456 

Perception,  288,  289 


INDEX. 


639 


The  Numbers  refer 

Perennibranchiate  Batrachia,  43 

Peristaltic  movements  of  intestines,  446; 
independent  of  nervous  agency,  200;  in- 
fluenced by  spinal  cord  through  sympa- 
thetic, 200,  201 

Peyerian  glands,  705,  707 

Philip,  Dr.  Wilson,  his  experiments  on  the 
Par  Vagum,  233—236;  on  connection  of 
nervous  system  with  heart,  481 ;  with  ca- 
pillaries, 513 

Phosphorus,  an  element  of  food,  434;  in 
protein  compounds,  458 ;  oxidation  of,  in 
system,  677 

Photophobia,  222 

Phrenological  doctrines  regarding  Cerebel- 
lum, 274—278  ;  regarding  Cerebrum,  292, 
293 

Physiology,  objects  of  the  science,  and  mode 
of  pursuing  it,  1  ;  science  of  normal  life, 
2;  its  relation  to  Hygiene,  6;  to  Patholo- 
gy, 7~9 

Pigment-cells,  617 

Placenta,  54, 55 ;  formation  and  structure  of, 
748 

Placental  souffle,  750 

Plants,  see  Vegetables 

Plethora,  increase  of  blood-corpuscles  in, 
591  c 

Plica  Polonica,  624 

Poisseuille,  M.,  his  experiments  on  the  cir- 
culation, 492,  501,  503,  587 

Polypes,  18,  130;  circulation  in,  498;  re- 
production of  parts  in,  593 

Porrigo  favosa,  562 

Portal  circulation,  500,  517,  655;  in  kid- 
neys, 669 

Posterior  roots  of  spinal  nerves,  123 

Pregnancy,  signs  of,  751,752,  see  Gestation 

Presbyopia,  351 

Primitive  trace,  759 

Protein,  composition  and  properties  of,  457 

Proteus,  43 

Prout,  Dr.,  his  classification  of  alimentary 
substances,  430;  his  observations  on  di- 
gestion, 460  ;  on  amount  of  carbonic  acid 
excreted,  535 ;  on  watery  exhalation  from 
the  lungs,  549;  on  urine,  675  ;  on  general 
disorders  of  secretion,  718 

Pulsation  of  heart,  482—486 

arteries,  501 

Pulse,average  frequency  of,  at  different  ages, 
493;  variations  of,  with  sex  and  posture, 
493;  with  muscular  exertion,  516;  diur- 
nal variation  of,  494  ;  respiratory,  516 

Pupil,  action  of,  205,  222,  249,  330 

Purkinje,  optical  experiment  of,  348 

Pus,  production  of,  601,  609 

Pyramids,  anterior  and  posterior,  168—172 


Quadrumana,  61 
Quickening,  752 


to  the  Paragraphs. 

Quetelet,  M.,  his  researches  on  relative  mor- 
tality at  different  seasons,  729  ;  on  length 
and  weight  of  infants  at  birth,  779;  on 
relative  viability  of  males  and  females, 
772;  on  comparative  heights  of  males 
and  females,  772 


R 


Raciborski,  his  researches  on  conception, 

742 

Radiafi,  17;  general  structure  of,  18—20; 
affinity  with  vegetables,  18, 19;  symmetry 
in,  20;  reproduction  of  parts  in,  21 ;  ner- 
vous system  in,  128 — 131 
Recti  muscles  of  orbit,  245,  248,  249 
Reeds,  vibrating,  laws  of,  407 — 409 
Reflex  action,  130,146,  162,  173,  175 

ases  of,  in  Man,  without  sensa- 


tion, 176—180,  194 
Regeneration  of  parts,  in  lower  Animals. 

21,  593 

Reid,  Dr.,  J.,  his  researches  on  glosso-pha- 
ryngeal  nerve,  123,  192,  193,  228;  on 
pneumogastric,  184,  199,  230 — 238;  on 
laryngeal  nerves,  188 ;  on  spinal  acces- 
sory, 239,  240;  on  muscular  contracti- 
lity, 38 1—385;  on  irritability  of  heart,  480; 
on  Asphyxia,  489,  548;  on  capillary  cir- 
culation, 512;  on  mucous  membrane  of 
uterus,  748 ;  on  structure  of  placenta,  749 
Reparative  processes,  594 — 605 ;  Dr.  Ma- 
cartney's views  of,  594,  595,  598,  599 ; 
union  by  first  intention,  595  ;  process  of 
organization  of  liquor  sanguinis,  596  ; 
organization  of  blood,  597;  modeling 
process,  598 ;  causes  favourable  to,  599 ; 
granulation,  600,  601 
Repetition  of  parts,  21 
REPRODUCTION, 
General  account  of,  98,  99 ;  in  Plants, 

732;  in  Animals,  733 
History  of,  in  Male,  734 — 738  ;  sperma- 
tic fluid,  734;  evolution  of  spermato- 
zoa, 735 ;  power  of,  736,  coitus,  738 
History  of,  in  Female,  739 — 756  ;  general 
account  of  ovum,  739;  first  develop- 
ment of,  740;  maturation  of,  741 ;  men- 
struation, 742  ;  aptitude  for  conception, 
742  ;  coitus,  743 ;  escape  of  ovum,  744 ; 
corpus  luteum,  744;  first  change  in 
ovum,  745,  746;  addition  of  chorion, 
747;  formation  of  decidua,  748;  for- 
mation and  structure  of  placenta,  749 ; 
sound  of,  754;  increase  of  tissue  of 
uterus,  751  ;  quickening,  752;  parturi- 
tion, 753 ;  ordinary  duration  of  gesta- 
tion, 754 ;  protracted  gestation,  755 ; 
shortest  term  of  gestation,  756  ;  super- 
fcetation,  756 

Development  of  embryo,  see  Embryo 
Reptiles,  39—43 ;  respiration  and  circulation 
in,  39, 42;  different  orders  of,  40;  con- 
nected with  Fishes  by  Batrachia,  42, 


640 


INDEX. 


The  Numbers  refer  to  the  Paragraphs. 

43;  brain  of,  216  ;  blood-corpuscles  of, 
574 

Resistance,  sense  of,  308,  317 
RESPIRATION, 

General  purposes  of,  92,  520 ;  necessity 
for,  521;  in  Plants,  522;    in  Inverte- 
brata,  523 ;  in  lower  Vertebrata,  524  ; 
in  warm-blooded  Vertebrata,  525 
Structure  and  Action  of  Lungs,  525 — 532 ; 


development  of  lungs,  526 ;  their  struc- 
ture and  properties,  527;  movements 
concerned  in  exchange  of  air,  528 — 
531  ;  capacity  of  lungs,  532 
Chemical  phenomena,  533 — 537  ;  carbo- 
nic acid  excreted,  533 ;  amount  of,  534  ; 
variations  in,  535;  oxygen  absorbed, 
533  ;  azote  absorbed  and  exhaled,  536 ; 
principles  governing,  537 
Effects  on  the  blood,  538 — 544;  carbonic 
acid  in  venous  blood,  538—541 ;  exha- 
lation of,  in  hydrogen  and  azote,  539 ; 
comparative  analysis  of  arterial  and 
venous  blood,  540 ;  oxygen  in  arterial 
blood,  540 ;  extraction  of  gases  from 
blood,  541 ;  cause  of  change  of  colour, 
542  ;  aeration  by  general  surface,  543  ; 
general  conclusions,  544 
To  be  regarded  as  an  Excretion,  545 
consequences  of  retention  of  carbonic 
acid,  546—548 ;  phenomena  of  As- 
phyxia, 547;  its  immediate  causes,  548 
Movements  of,  dependent  on  Nervous 
agency,  183 — 190;  centre  of,  in  me- 
dulla oblongata,  184:  nerves  concerned 
in,  184—189  ;  independent  of  will  and 
of  consciousness,  186;  guard  to  en- 
trances to  lungs,  187;  influence  of,  on 
pulse,  515  ;  number  of,  530  ;  share  of 
lungs  and  air-passages  in,  527,  528 ; 
various  influences  affecting,  529 — 531 
Respiratory  circulation,  476  ;  peculiarity  of, 

517 

Respiratory  pulse,  516 
Rete  mucosum,  620 
Retina,  structure  of,  322 ;  the  recipient  of 
visual  impressions,  329  ;  inversion  of  pic- 
tures upon,  336  ;  diminution  of  force  ol 
impressions  on,  345;  vanishing  of  images 
on,  347 ;  visual  representation  of,  348 
Retractor  muscle  of  orbit,  245 
Rigor  mortis,  389-391 
Ritchie,  Dr.,  his  researches  on  menstrua- 
tion, 742  ;  on  the  corpus  luteum,  744 
Robinson,  Mr.,  on  effusion  of  fibrin,  607 


S 


Saccharine  principles,  430,  432,  460 

Salamander,  42 

Salivary  glands,  structure  of,  693 ;  secre 
tion  of,  694 ;  influence  of  nervous  sys 
tern  on,  426  ;  incorporation  of,  with  food 
436 


Sarcolemma,  367—374 

?avart,  M.,  his  researches  upon  sound,  362 

scharling,  Prof.,  his  researches  on  respira- 
tion, 544 

Schleiden,  his  researches  on  the  develop- 
ment of  cells  in  Plants,  557 

Schwann,his  experiments  on  muscular  con- 
traction, 394 ;  on  digestion,  455  ;  his  ob- 
servations on  Animal  structures,  559,  611 


Science,  applied  to  Medical  practice,  11 
,  connection  of  with  art,  3— 5 

Sciences,  connection  of  the  Medical,  1—12 

Seasons,  influence  of  on  Calorification,  729 

Sebaceous  glands,  703 

SECRETION,  general  nature  of,  95,  96,  647  ; 
structures  adapted  for,  649,  650;  essenti- 
ally composed  of  cells,  651 ;  disorders  of, 
connected  with  nutritive  processes,  718  ; 
not  dependent  on  nervous  agency,  96, 
424;  influence  of  nervous  system  on,  235, 
236,  424—429. 

Secretions,  amount  of,  647 ;  sources  of,  648; 
elements  of,  preexisting  in  the  blood,  649  ; 
some  used  in  the  system,  95 ;  see  Bile, 
Urine,  Milk,  &c. 

Selecting  power,  of  lacteals,  462 

Semicircular  canals,  359 

Seminal  secretion,  700,  734;  influenced  by 
state  of  feeling,  426  n 

SENSATION,  180,  302 ;  why  associated  with 
reflex  actions,  181,  182;  dependent  on 
capillary  circulation,  118,  303  ;  the  guide 
of  consensual  movements,  257 

Sensations,  nature  of,  289,  302;  different 
kinds  of,  308,  309 ;  pain  or  pleasure  con- 
nected with,  305;  influence  of  habit  on, 
305 — 307;  special,  308;  common,  309; 
subjective  and  objective,  310;  transfer- 
ence  of,  311  influence  of  attention  on, 
313—315;  peculiarities  of,  318;  know- 
ledge gained  Irom,  308,  317 

Sense,  muscular,  397 

Sensibility  in  different  parts,  303,  304,  316  ; 
of  muscles,  399 

Sensory  nerves,  115, 124, 302;  terminations 
of,  115 

tract  of  Sir  C.  Bell,  115,  169;  con- 


nections of,  170, 172 

Serous  membranes,  639 

Serum,  of  blood,  composition  of,  586:  pro- 
portion of,  to  clot,  585;  milky,  580,  714, 
note 

Seventh  pair,  portio  mollis  of,  223;  portio 
dura  of,  227 

Sexual  instinct,  736,  738  ;  its  supposed  loca- 
tion in  the  cerebellum,  274 — 278 

Siege  of  Landau,  768 

Sight,  sense  of,  see  Vision 

Single  vision  with  two  eyes,  253,337 — 340 

Size,  mode  of  estimating,  342 

Skin,  structure  of,  640,  641 ;  absorbing 
power  of,  464—466,  468;  respiratory 
power  of,  543;  exhaling  apparatus  in, 
701;  transpiration  from,  702 ;  sebaceous 


INDEX. 


641 


The  Numbers  refer  to  the  Paragraphs. 

and  ceruminous  glands  in,  703 ;  exuda- 
tion from,  increased  by  heat,  731 
Sleep,  295,  296 


Smell,  sense  of,  324,  325;  seat  of,  220,  324 ; 
conditions  of,  324;  acuteness  of,  in  some 
animals  and  men,  325;  modifications  of, 
325 

Sneezing,  act  of,  206 

Somnambulism,  296 

Sound,  laws  of  propagation  of,  353 — 355  ; 
successive  pulses  of,  362  ;  mode  of  esti- 
mating direction,  distance,  and  intensity 
of,  363 ;  rapidity  of  perception  of,  com- 
pared with  that  of  light,  364 

Sounds  of  heart,  484—486 

Spasmodic  diseases,  298 — 301 

Spencer,  Earl,  on  the  duration  of  gestation 
in  Cattle,  755 

Spermatic  fluid,  700,  734 

Spermatozoa,  734  ;  function  of,  733  ;  deve- 
lopment of,  735 

Sphinx  ligustri,  nervous  system  of,  143, 148 

Spinal  accessory  nerve,  239,  240 

Spinal  Cord,  of  Vertebrata,  157,  161,  164— 
168;  its  comparative  anatomy,  164;  it 
divisions,  165;  its  connections,  166; 
functions  of  several  parts  of,  167;  gene- 
ral functions  of,  173—183,  294:  absence 
of  proper  sensibility  in,  174 — 182;  pro- 
tecting agency  of,  204 — 206;  maintenance 
of  contractility  through,  208 ;  influence  of, 
on  heart,  209;  power  of  sustaining  loco- 
motive actions,  210;  influence  of,  on  or- 
ganic functions,  421,  422 

Spinal  nerves,  double  roots  of,  162 

Spleen,  structure  of,  708;  functions  of,  709 

Sponges,  13,  19 

Staminal  principles,  Dr.  Prout's  division  of 
450 

Stammering,  causes  of,  418;  treatment  of 
419 

Star-fish,  structure  of,  20;  nervous  system 
of,  129 

Stearine,  composition  and  properties  of 
618 

Stereoscope,  252,  340 
Stomach,  presence  of,  characteristic  of  Ani 
rnals,  14, 430  ;  general  characters  of,  435 
state  of,  in  health,  438  ;  in  disease,  439 
sense  of  hunger  referred  to,  440  ;  move 
ments  of,  444,  445;  influenced  by  nerves 
200;  secretions  of,  449,  704;  influence  o 
nerves  on,  440,  441 ;  effects  of  blows  on 
386,  425 

Stomato-gastric  system,  135,  150 
Strabismus,  253 
Strangury,  300 

Strings,  vibrating,  laws  of,  405 

Strumous  diathesis,  619;  see  Tubercle 

Subjective  sensations,  310,  315 

Suction,  197 

Sulphur,  contained  in  food,  434;  in  protein 

compounds,  458;  oxidation  of,  in  system 

677 


uperfoetation,  756 
uppuration,  601,  608,  609 
Supra-renal  capsules,  710 


Symmetry,  radiate,  20;  bilateral,  27 


absence  of,  in  Mollusca,  24 


Sympathetic  system,  136,  137,  151,  156,  159, 
160;  influence  of,  on  movements  of  in- 
testinal canal,  200,  201  ;  on  ureter  and 
muscular  coat  of  bladder,  202;  on  uterus 
and  Fallopian  tubes,  203;  on  heart  and 
vessels,  209,  423;  onductuscholedochus, 
209;  on  processes  of  organic  life,  421— 
425 

Sympathies,  motor,  421,422;  organic,  425 
—429,  717 

Syncope,  210,  386 


Taliacotian  operation,  313 

Taste,  sense  of,  308,  321 — 323;  nerves  con- 
cerned in,  228 ;  conditions  of,  321  ;  partly 
dependent  on  smeii,  322;  educability  of, 
623;  purposes  of,  322 

Teeth,  of  Mammalia,  59,60;  development 
of,  in  Human  infant,  635;  in  lower  ani- 
mals, 636  ;  structure  of,  633,  634  ;  a  test 
of  age,  635,  k,  I,  m 

Temperature,  sense  of,  308,  310;  extremes 
of,  sustainable  by  Man,  721,  722;  see 
Heat 

Tenesmus,  300 

Tetanus,  212,  298,  299 

Testis,  structure  of,  697,  698 ;  development 
of,  699 

Tessier's  experiments  on  duration  of  gesta- 
tion, 755 

Thackrah,  Mr.,  his  observations  on  coagu- 
lation of  blood,  585 

Thaumatrope,  344 

Therapeutics,  connection  of  with  Pathology, 
10 

Third  pair  of  cranial  nerves,  244,  249 

ventricle  of  Brain,  214 

Thirst,  sense  of,  439 

Thorax,  movements  of,  in  respiration,  328 
—531 

Thymus  gland,  711,  712 

Thyroid  gland,  713 

Tone,  of  Muscular  System,  dependent  on 
Spinal  cord,  207 

Tonicity,  of  arteries,  505 

Touch,  sense  of,  308,  316—320;  varying 
acuteness  of,  in  different  parts,  316 ;  ideas 
derived  from,  317;  peculiarities  of,  318; 
improvability  of,  319  ;  modifications  of, 
in  different  animals,  320;  connection  of, 
with  vision,  335,  336 

Toynbee,  Mr.,  his  researches  on  non-vascu- 
lar tissues,  479,  625—627 

Trifacial  nerve,  see  Fifth  Pair 

Tubercula  Quadrigemina,  see  CdrporaQua- 
drigemina 


642 


INDEX. 


The  Numbers  refer 

Tubercular  matter,  610;  tendency  in  the 

system  to  deposit,  714 
Tympanum,  membrane  of,  356  ;  cavity  of, 

357,  358 

U 

Umbilical  cord,  765 

vesicle,  762,  765 

Unguiculaled  Mammalia,  60 

Ungulated  Mammalia,  59 

Urea,  composition  of,  673 

Uric  acid,  composition  of,  673 ;  pathological 
changes  in, 675 

Urine,  nature  and  purposes  of  its  secretion, 
670  ;  effects  of  its  retention,  670  ;  com- 
position of,  in  health,  671 ;  amount  of 
urea  contained  in,  672  ;  uric  acid  in,  673  ; 
hippuric  acid  in,  675 ;  lactic  acid  in,  676 ; 
saline  compounds  in,  677 ;  comparative 
constitution  of  urine  and  bile,  677 ; 
amount  of  azotized  matter  in,  679  ;  in- 
fluence of  diet  on,  669,680  ;  transference 
of  secretion,  681  ;  excretion  of  saline 
matter  with,  682 

Uterus,  changes  of,  preparatory  to  gestation, 
749  ;  increase  in  substance  during  gesta- 
tion, 751  ;  contractions  of,  how  far  de- 
pendent on  nervous  agency,  203 


Vagus  nerve,  see  Par  Vagum 

Valentin,  his  researches  on  Spinal  Cord, 
167;  on  respiratory  nerves,  189;  on  the 
Sympathetic,  200,  202,  203,212;  on  Ol- 
factory nerve,  222 ;  on  Portio  Dura,  227 ; 
on  Spinal  Accessory,  239  ;  on  Hypoglos- 
sal,  241  ;  on  nerves  and  motions  of  eye- 
ball, 249—251,  255;  on  quantity  of  blood 
in  system,  581  ;  on  circulation  in  nerve- 
tubes,  642 

Valves  of  heart,  action  of,  487 — 489;  sounds 
produced  by,  484—486 

Vapour,  exhalation  of,  from  lungs,  549 

Varicose  nerve-tubes,  110 

Vascular  area,  763 

plants,  88 

Vegetable  proximate  principles,  457 

Vegetables,  distinguished  from  animals,  13 — 
16;  food  of,  14;  movements  of,  13;  early 
development  of,  15 ;  formation  of  cells  in, 
556 — 558;  general  functions  of,  76;  di- 
vision of  into  cellular  and  vascular,  88  ; 
circulation  in,  496,  497 ;  respiration  in, 
522  ;  reproduction  in,  732 

Veins,  distribution  of,  514;  movement  of 
blood  in,  515,  516  ;  absorbent  power  of, 
462,  463,  466,  469 

Ventricles  of  heart,  contraction  of,  480,  481 
— 486 ;  force  of,  487 ;  thickness  of,  488  ; 
capacity*of,  490 

Ventricles  of  brain,  third,  214;  fourth,  216 


to  the  Paragraphs. 

Vertebra,  32  ;  origin  of,  760 
Vertebral  columns  in  Fishes,  33 
Vertebrata,  17,31—36  ;  skeleton  of,  31—33; 
extremities  of,  33 ;  predominance  of  ner- 
vous system  in,  31,  34 ;  organs  of  animal 
and  vegetative  life  in,  36;  symmetry  in, 
36;  intelligence  of,  34;  nervous  system 
of,  17  et  seq. 

Vesicles  of  Brain  in  Embryo,  214 
Viability  of  Infant,  earliest  period  of,  755 
Villi  of  mucous  membrane,  461,462 
Visceral  system  of  nerves,  156,  159,  160; 
see  Sympathetic 

arches,  760 

Visible  direction,  law  of,  336 
Vision,  sense  of,  326—348;  optical  condi- 
tions of,  326 — 330  ;  defective,  331 ;  limits 
of,  332,  333 ;  mental  conditions  of,  334, 
335,  343  ;  connection  of,  with  touch,  334 
—336;  single,  337,338;  appreciation  of 
form  by,  339,  340  ;  of  distance,  341  ;  of 
size,  342 ;  persistence  of  impressions,  344; 
complementary  colours,   345 ;    want  of 
power  to  distinguish  colours,  346;  vanish- 
ing of  images,  347;  visual  perception  of 
retina,  348 
Vis  nervosa,  126 
Vital  Action  involves  change,  73 

-,  dependence  of,  on  conditions, 


74 

Vital  Actions,  classification  of  into  Func- 
tions, 75 

Vitalization,  561  ;  dependent  on  cell-life, 
578,  579 

Vitality,  duration  of,  in  individual  parts, 
645,  646 

of  general  system,  destroyed  by 

sudden  shock,  386,  387,  583 

Vital  properties,  561 ;  retention  of,  83 

Vitreous  humour,  627 

Voice,  401—412;  conformation  of  larynx, 
402—405;  sounds  resembling,  produced 
by  strings,  405 ;  by  flute-pipes,  406 ;  by 
reeds,  407;  action  of  chordae  vocales,  408  ; 
artificial  larynx,  408;  pitch,  how  regu- 
lated, 409 ;  falsetto  notes,  how  produced, 
410;  influence  of  air-passages  on,  412; 
movements  concerned  in,  how  directed, 
412 

Voluntary  actions,  distinguished  from  auto- 
matic, 285;  originate  in  cerebrum,  288 

Vomiting,  301 

Vowel  sounds,  414 — 416 


W 


Wagner,  his  account  of  development  of 

Spermatozoa,  735 

Wasmann,  his  researches  on  pepsin,  456 
Whale,  Spermaceti,  peculiar  sensibility  of, 

320 

Wheatstone,  Prof.,  his  Stereoscope,  253, 340 
White  globules  of  blood,  577—579 


INDEX. 


643 


The  Numbers  refer  to  the  Paragraphs. 


White  matter  of  nervous  system,  110,  281 
Williams,  Dr.,  on  contractility  of  bronchi, 
527;  on  Necreemia,  592;  on  Inflamma- 
tion, 606 

Willis,  Mr.,  his  researches  on  the  Voice,  408 
Wings  of  Insects,  interlacement  of  nerves 
supplying,  113,  147;  rapidity  of  motioa 
of,  397 


Young  animals,  low  calorifying  power  of, 
728  ;  influence  of  cold  upon,  728 


Zona  pellucida,  739 


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NEW  EDITION—  NOW  READY. 

SPECIAL  ANATOMY  AND   HISTOLOGY. 

WILLIAM  E.  HORNER,  M.D., 


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Seventh  edition. 

With  many  improvements  and  additions.    In  two  octavo  volumes,  with  illustration 

on  wood. 

This  standard  work  has  been  so  long  before  the  profession,  and  has  been  so  ex- 
tensively used,  that,  in  announcing  the  new  edition,  it  is  only  necessary  to  state,  that 
it  has  undergone  a  most  careful  revision  ;  the  author  has  introduced  many  illustra- 
tions relating  to  Microscopical  Anatomy,  and  has  added  a  large  amount  of  text  on 
these  various  points  of  investigation  that  are  rapidly  advancing  and  attracting  so 
much  attention.  This  new  edition  has  been  arranged  to  refer  conveniently  to  the 
illustrations  in  Smith  and  Horner's  Anatomical  Atlas. 

"  A  comparison  of  the  present  edition  with  its  antecedents,  will,  therefore,  the 
Author  hopes,  show  to  the  student  an  improved  state,  in  many  respects,  in  regard 
both  to  Descriptive  Anatomy  and  to  Histology  ;  much  of  the  latter,  especially,  having 
been  remodelled  and  written  anew  since  the  last  edition. 

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best  authorities,  through  numerous  figures  inserted  in  its  pages  ;  and  it  is  placed  in 
a  more  immediate  relation  with  the  plates*  of  Dr.  H.  H.  Smith's  Anatomical  Atlas, 
they  having  been  selected  expressly  as  an  elucidation  of  its  text.  This  connection 
has  been  made  by  specific  references  at  the  foot  of  the  page  to  the  plates  in  question. 

"  That  all  has  been  said  that  belongs  to  the  science  of  Anatomy,  no  one  fully 
acquainted  with  the  subject  will  admit;  but  the  author  trusts  that  no  well-established 
fact  of  leading  importance  has  been  omitted  ;  and  that  a  sufficient  expansion  has  been 
given  to  the  subject  to  realize  the  principal  object,  that  of  furnishing  an  elementary 
Text  Book  for  the  use  of  students  of  Medicine."—  Preface  to  Seventh  Edition,  Sept.  1846 


HORNSR'S   DISSECTOR. 


BEING  A   NEW  EDITION,  WITH   EXTENSIVE   MODIFICATIONS, 
AND  ALMOST  REWRITTEN,  OF 


"IIORJVEMVS 

IN  ONE  VERY  NEAT  VOLUME,  ROYAL  12MO. 

With  many  Illustrations  on  Wood. 

The  numerous  alterations  and  additions  which  this  work  has  undergone,  the  im- 
provements which  have  been  made  in  it,  and  the  numerous  wood-cuts  which  have 
been  introduced,  render  it  almost  a  new  work. 

It  is  the  standard  work  for  the  Students  in  the  University  of  Pennsylvania. 


NEW  WORKS  AND  NEW  EDITIONS  JUST  PUBLISHED  BY  LEA  AND  BLANC«ARD. 

NOW  READY,— A  NEW  EDITION  OP  DMGLISON'S  PHYSIOLOGY^ 

HUMAN   PHYSIOLOGY 

WITH  THREE  HUNDRED  AND  SEVENTY  ILLUSTRATIONS. 
BY  ROBLEY  DUNGLISON,  M.D., 

PROFESSOR  OF  THE  INSTITUTES  OF  MEDICINE  IN  THE  JEFFERSON  MEDICAL  COLLEGE,  PHILADELPHIA,  ETC.,  ETC. 

Sixth  edition,  greatly  improved. — In  two  large  octavo  volumes,  containing  nearly  1350  pages. 

"  It  is  but  necessary  for  the  Author  to  say,  that  all  the  cares  that  were  bestowed  on  the  preparation 
of  the  fifth  edition  have  been  extended  to  the  sixth,  and  even  to  a  greater  amount.  Nothing  of  import- 
ance that  has  been  recorded  since  its  publication,  has,  he  believes,  escaped  his  attention.  Upwards 
of  seventy  illustrations  have  been  added  ;  and  many  of  the  former  cuts  have  been  replaced  by  others. 
The  work,  he  trusts,  will  be  found  entirely  on  a  level  with  the  existing  advanced  state  of  physiological 
science." 

In  mechanical  and  artistical  execution,  this  edition  is  far  in  advance  of  any  former 
one.  The  illustrations  have  been  subjected  to  a  thorough  revision,  many  have  been 
rejected  and  their  places  supplied  with  superior  ones,  while  numerous  new  wood- 
cuts have  been  added  wherever  perspicuity  or  novelty  seemed  to  require  them. 

"Those  who  have  been  accustomed  to  consult  the  former  editions  of  this  work,  know  with  how 
much  care  and  accuracy  every  fact  and  opinion  of  weight,  on  the  various  subjects  embraced  in  a 
treatise  on  Physiology,  are  collected  and  arranged,  so  as  to  present  the  latest  and  best  account  of  the 
science.  To  such  we  need  hardly  say,  that,  in  this  respect,  the  present  edition  is  not  less  distinguished 
than  those  which  have  preceded  it.  In  the  two  years  and  a  half  which  have  elapsed  since  the  last  or 
fifth  edition  appeared,  nothing  of  consequence  that  has  been  recorded  seems  to  have  been  omitted. 
Upwards  of  seventy  illustrations  have  been  added,  and  many  of  the  former  cuts  have  been  replaced 
by  others  of  better  execution.  These  mostly  represent  the  minute  structures  as  seen  through  the 
microscope,  and  are  necessary  for  a  proper  comprehension  of  the  modern  discoveries  in  this  depart- 
ment.— The  Medical  Examiner. 


NOW    READY. 
THE  SIXTH  EDITION  OF  DIJNGLISON'S  MEDICAL  DICTIONARY, 

M  E  D  I  0  A  L~L  E  X I  <3  0  W . 

A   Dictionary  of 

MEDICAL     SCIENCE, 

CONTAINING  A  CONCISE  ACCOUNT  OF  THE  VARIOUS  SUBJECTS  AND  TERMS;  WITH 
THE    FRENCH    AND   OTHER   SYNONYMES;   NOTICES   OF  CLIMATES  AND  OF 
CELEBRATED  MINERAL  WATERS;  FORMULAE  FOR  VARIOUS  OFFICI- 
NAL AND  EMPIRICAL  PREPARATIONS,  &c. 

BY  ROBLEY  DUNGLISON,  M.  D.; 

PROFESSOR  OF  THE  INSTITUTES  OF  MEDICINE,  ETC.,  IN  JEFFERSON  MEDICAL  COLLEGE,  PHILADELPHIA. 

Sixth  edition,  revised  and  greatly  enlarged.  In  one  royal  octavo  volume  of  over  800  very  large 
pages,  double  columns.  Strongly  bound  in  the  best  leather,  raised  bands. 

"We  think  that  'the  author's  anxious  wish  to  render  the  work  a  satisfactory  and  desirable— if  not 
indispensable — Lexicon,  in  which  the  student  may  search  without  disappointment  for  every  term 
that  has  been  legitimated  in  the  nomenclature  of  the  science,'  has  been  fully  accomplished.  Such  a 
work  is  much  needed  by  all  medical  students  and  young  physicians,  and  will  doubtless  continue  in 
extensive  demand.  It  is  a  lasting  monument  of  the  industry  and  literary  attainments  of  the  author, 
who  has  long  occupied  the  highest  rank  among  the  medical  teachers  of  America." — The  New  Orleans 
Mvtical  and  Surgical  Journal. 

"  The  simple  announcement  of  the  fact  that  Dr.  Dunglison's  Dictionary  has  reached  a  sixth  edition, 
is  almost  as  high  praise  as  could  be  bestowed  upon  it  by  an  elaborate  notice.  It  is  one  of  those  standard 
work?  that  have  been  '  weighed  in  the  balance  and  (not)  been  found  wanting.'  It  has  stood  the  test  of 
experience,  and  the  frequent  calls  for  new  editions,  prove  conclusively  that  it  is  held  by  the  profession 
and  by  students  in  the  highest  estimation.  The  present  edition  is  not  a  mere  reprint  of  former  ones; 
the  author  has  for  some  time  been  laboriously  engaged  in  revising  and  making  such  alterations  and 
additions  as  are  required  by  the  rapid  progress  of  our  science,  and  the  introduction  of  new  terms  into 
our  vocabulary.  In  proof  of  this  it  is  stated  '  that  the  present  edition  comprises  nearly  two  thousand 
five  hundred  subjects  and  terms  not  contained  in  the  last.  Many  of  these  had  been  introduced  into 
medical  terminology  in  consequence  of  the  progress  of  the  science,  and  others  had  escaped  notice  in 
previous  revisions.'  We  think  that  the  earnest  wish  of  the  author  has  been  accomplished  ;  and  that 
he  has  succeeded  in  rendering  the  work  'a  satisfactory  and  desirable — if  not  indispensable — Lexicon, 
in  which  the  student  may  search,  without  disappointment,  for  every  term  that  has  been  legitimated  in 
the  nomenclature  of  the  science.'  This  desideratum  he  has  been  enabled  to  attempt  in  successive 
editions,  by  reason  of  the  work  not  being  stereotyped ;  and  the  present  edition  certainly  offers  stronger 
claims  to  the  attention  of  the  practitioner  and  student,  than  any  of  its  predecessors.  The  work  is  got 
up  in  the  usual  good  taste  of  the  publishers,  and  we  recommend  it  in  full  confidence  to  all  who  have 
not  yet  supplied  themselves  with  so  indispensable  an  addition  to  their  libraries."—  The  Ntw  York  Jour- 
nal of  Medicine. 


NEW  WORKS  AND  NEW  EDITIONS  LATELY  PUBLISHED  BY  LEA  AND  BLANCHARD.  5 

Now   Ready,  — Carpenter's   New   Work. 

A  KAWUAIi,  OR,  ELEMENTS  OF  PHYSIOLOGY, 
IJTCLUDIJirG    PHYSIOLOGICAL    JLJTJL  TO  JUT  **, 

FOR  THE  USE  OF  THE  MEDICAL  STUDENT. 

BY  WILLIAM  B.  CARPENTER,  M.D.,  F.R.S., 

FCLLBRIAN  PROFESSOR  OF  PHYSIOLOGY  IN  THE  ROYAL  INSTITUTION  OF  GREAT  BRITAIN,  ETC., 

With  one  hundred  and  eighty  illustrations.    In  one  octavo  volume  of  566'  pages.    Elegantly  printed 
to  match  his  a  Principles  of  Human  Physiology." 

This  work,  though  but  a  very  short  time  published,  has  attracted  much  attention  from  all  engaged 
in  teaching  the  science  of  medicine,  and  lias  been  adopted  as  a  text  book  by  many  schools  throughout 
the  country.  The  clearness  and  conciseness  with  which  all  the  latest  investigations  are  enunciated 
render  it  peculiarly  well  suited  for  those  commencing  the  study  of  medicine.  It  is  profusely  illustrated 
with  beautiful  wood  engravings,  and  is  confidently  presented  as  among  the  best  elementary  text 
books  on  Physiology  in  the  language. 

"The  author  has  shown  singular  skill  in  preserving  so  marked  a  line  of  distinction  between  the 
present  Manual  and  the  '  Principles  of  1 physiology'  previously  published  by  him.  They  are  both  on 
precisely  the  same  subject;  but  the  one  is  neither  a  copy,  nor  an  abstract,  nor  an  abridgment  of  the 
other.  In  one  thing,  however,  they  are  exactly  alike— in  their  general  excellence,  and  in  thejir  per- 
fect adaptation  to  their  respective  purposes.  The  reputation  of  Dr.  Carpenter  as  a  phj  siologist  is  too 
well  established  throughout  the  whole  medical  world  to  admit  of  increase  from  any  commendation  01" 
ours;  but  we  should  be  doing  injustice  to  our  own  feelings  if  we  did  not  here  express  our  admiration 
of  his  great  intellectual  powers,  of  his  extensive  learning,  of  the  comprehensiveness  of  his  views,  of 
the  quickness  with  which  he  seizes  the  important  points  and  bearings  of  each  subject,  of  the  logical 
order  in  which  he  arranges  his  facts,  and  of  the  clearness  and  precision  with  which  he  explains  and 
exposes  his  doctrines.  Dr.  Carpenter's  various  treatises  are  in  fact  models  in  their  respective  depart- 
ments. It  is  their  great  and  varied  excellence  which  accounts  for  their  unrivalled  popularity.  We 
can  pay  no  higher  compliment  to  the  work  before  us?  than  to  say,  that  it  is  equal  in  merit  to  the  former 
productions  of  the  author.  This  is  equivalent  to  saying  that  it  is,  without  question,  the  best  manual  or 
short  treatise  on  physiology  extant.  Although  designed  for  the  student,  and  framed  expressly  to  meet 
his  wants,  it  is  a  work,  we  will  venture  to  say,  that  may  be  consulted  with  advantage  by  most  physi- 
cians and  surgeons,  however  learned."—  The  British,  and  Foreign  Medical  Review. 

The  merits  of  this  work  are  of  such  a  high  order,  and  its  arrangement  and  discussion  of  subjects  so 
admirably  adapted  to  the  want  of  students,  that  we  unhesitatingly  commend  it  to  their  favorable  no- 
tice. This  work  studied  first,  and  then  followed  by  the  more  elaborate  treatise  of  Dunglison.  or  Muller. 
or  others  of  similar  character,  is  decidedly  the  best  course  for  the  student  of  physiology." — The  Westtrn 


Simon's  Chemistry  of  IMCan. 
A3TXXKAX.    CHEMISTRY. 

WITH  REFERENCE  TO  THE  PHYSIOLOGY  AND  PATHOLOGY  OF  MAN. 

BY  DR.  J.  FRANZ  SIMON. 
Translated  and  edited  by  GEORGE  E.  DAY,  M.  A.  &  L.  M.,  CANTAB.,  &c. 

With  plates.    In  one  octavo  volume  of  over  seven  hundred  pages,  sheep,  or  in  two  parts  boards. 

This  important  work  is  now  complete  and  may  be  had  in  one  large  octavo  volume,  Those  who 
obtained  the  first  part  can  procure  the  second  separate.  The  very  low  price  at  which  this  is  offered, 
in  comparison  with  the  cost  of  the  English  edition,  should  secure  for  it  a  large  demand. 

"This  excellent  work,  the  most  complete  on  animal  chemistry  that  has  ever  appeared,  has  recently 
been  issued  by  the  publishing  house  of  Lea  and  Blanchard,  after  the  Sydenhara  edition  of  London.  No 
physician,  who  desires  to  keep  pace  with  the  improvements  in  our  science,  or  to  be  prepared  at  all 
points  for  the  successful  treatment  of  disease,  can  remain  ignorant  of  physiological  and  pathological 
chemistry ;  and  he  will  seek  in  vain  for  as  complete  and  accurate  work  on  the  subject,  as  he  will  fand 
in  the  elaborate  and  finished  treatise  of  Dr.  Simon  The  work  is  replete  with  facts  of  U>e  highest  inlerett, 
calculated  to  reflect  a  broad  blaze  of  light  on  the  pathology  and  treatment  of  many  diseases  hithert< 
involved  in  obscurity.  We  trust  it  may  have  a  universal  circulation  among  the  profession  m  this 
country. — The  New  York  Journal  of  Medicine. 


Now  Ready— A  New  Edition  of 

CONDIE   ON   CHILDREN. 

BROUGHT  UP  TO  1847. 
In  one  octavo  volume  of  over  650  pages. 


6  NEW  WORKS  AND  NEW  EDITIONS  LATELY  PUBLISHED  EY  LEA  AND  BLANCHARD.  ' 

A  NEW  EDITION— JUST,  READY. 

Dunglison  on  New  Remedies. 

JTJSfP    REMEDIES, 

BY   ROBLEY   DUNGLISON,  M.D.,&c.,&c. 

Fifth  edition,  with  extensive  additions.    In  one  neat  octavo  volume. 

The  numerous  valuable  therapeutical  agents  which  have  of  late  years  been  introduced  into  the 
Materia  Medica,  render  it  a  difficult  matter  for  the  practitioner  to  keep  up  with  the  advancement  of 
the  science,  especially  as  the  descriptions  of  them  are  difficult  of  access,  being  scattered  so  widely 
through  transactions  of  learned  societies,  journals,  monographs.  &c.  &c.  To  obviate  this  difficulty, 
and  to  place  within  reach  of  the  profession  this  important  information  in  a  compendious  form,  is  the 
object  of  the  present  volume,  and  the  number  of  editions  through  which  it  has  passed  show  that  its 
utility  has  not  been  underrated. 

The  author  has  taken  particular  care  that  this  edition  shall  be  completely  brought  up  to  the  present 
day.  The  therapeutical  agents  added,  which  may  b«  regarded  as  newly  introduced  into  the  Materia 
Medica,  together  with  old  agents  brought  forward  with  novel  applications,  and  which  may  therefore 
be  esteemed  as  "New  Remedies,"  are  the  following : — Benzole  Acid,  Chromic  Acid,  Gallic  Acid,  Nitric 
Acid,  Phosphate  of  Ammonia,  Binelli  Water,  Brocchieri  Water,  Atropia.  Beerberia,  Chloride  of  Car- 
bon (Chloroform,)  Digitalia,  Electro-Magnetism,  Ergotin,  Ox-gall,  Glycerin,  Hsemospasy,  Haemostasia, 
Hagenia  Abyssinica,  Honey  Bte,  Protochloride  of  Mercury  and  Quinia,  lodoform,  Carbonate  of  Lithia, 
Sulphate  of  Manganese,  Maticp,  Double  Iodide  of  Mercury  and  Morphia,  lodhydrate  of  Morphia, 
Iodide  of  lodhydrate  of  Morphia,  Muriate  of  Morphia  and  Codeia,  Naphthalin,  Piscidia  Erythrina, 
Chloride  of  Lead,  Nitrate  of  Potassa,  Arseniate  of  Quinia,  Iodide  of  Quinia,  Iodide  of  Cinchonia, 
Iodide  of  lodhydrate  of  Quinia,  Lactate  of  Quinia,  Pyroacetic  Acid,  (Naphtha,  Acetone)  Hyposulphate 
of  Soda,  Phosphate  of  Soda,  Iodide  of  lodhydrate  of  Strychnia,  Double  Iodide  of  Zinc  and  Strychnia, 
Double  Iodide  of  Zinc  and  Morphia,  and  Valerianate  of  Zinc. 


Hasse's  Pathological  Anatomy. 

AN  ANATOMICAL  DESCRIPTION  OF  THE  DISEASES  OF  THE 
ORGANS  OF  CIRCULATION  AND  RESPIRATION. 

BY  CHARLES  EWALD  HASSE, 

Professor  of  Pathology  and  Clinical  Medicine  in  the  University  of  Zurich,  SfC. 

Translated  and  edited  by  W.  E.  Swaine,  M.  D.,  &c. 
In  one  octavo  volume.    A  new  work,  just  ready, — October,  1846. 

"  The  advantages  which  Professor  Hasse  has  possessed  for  the  preparation  of  such  a  work  as  the 
present,  appear  to  have  been  considerable,  and  of"  these  he  has  manifestly  availed  himself  to  the 
utmost.  As  a  diligent  student  in  the  hospitals  of  Paris  and  Vienna,  and  subsequently  as  clinical 
assistant  to  Professor  Carus,  and  pathological  prosector  in  the  principal  hospital  at  Leipsic,  he  pos- 
sessed the  means  of  observing  and  collecting  materials  for  himself,  whilst  at  the  same  time  he  was 
forming  that 'pathological  collection,' which,  under  his  auspices,  has  grown  into  a  most  interesting 
and  valuable  museum.  The  present  treatise,  therefore,  differs  essentially  from  what  is  commonly 
called  a  compilation.  For  although  he  has  '  not  relied  solely  on  his  own  investigations,  but  has 
largely  availed  himself  of  facts  recorded  by  others,'  he  has  been  chary  in  making  use  of  other  men's 
experience.  The  estimation  in  which  the  book  is  held  in  Germany,  is  sufficiently  attested  by  the  fact 
that  since  its  publication  the  author  has  had  the  offer  of  the  chair  of  Clinical  Medicine  in  five  Universi- 
ties, and  holds  that  vacated  by  Professor  Schoenlein,  at  Zurich." — TheMedico-Chirurgical  Review. 


A  NEW  WORK.— PHILLIPS  ON  SCROFULA.— JUST  READY. 


£> 

TS   NATURE,    ITS    PREVALENCK,    ITS    CAUSES,    AND   THE    PRINCI 
PLES   OF   ITS   TREATMENT. 

BY   BENJAMIN   PHILLIPS,    M.D.,   F.  R.  S.,  ETC. 

In  one  neat  octavo  volume,  with  a  plate. 

"  The  work  of  Mr.  Phillips  is  immensely  in  advance  of  all  others  that  have  ever  been  written  on 
Scrofula. 

"  The  author  has  extended  his  researches  over  a  wide  and  most  interesting  field.  It  has  been  a 
fault  with  preceding  writers,  that  they  have  riot  enjoyed  a  very  extensive  sphere  of  observation,  or 
extended  their  inquiries  so  as  to  comprise  the  influence  of  the  many  causes  which  are  supposed  to  be 
capable  of  producing  the  disease. 

"  He  has  even  extended  his  inquiries  to  Russia,  Austria,  Prussia,  Bavaria,  Portugal,  Holland, 
France,  Switzerland,  Belgium  and  America,  to  China  and  the  East  Indies,  Egypt,  Syria  and  Greece  ; 
in  short,  we  have  fully  presented  to  us,  a  body  of  authentic  statistics  bearing  upon  this  disease, — col- 
lected with  care,  and  arranged  and  classified  in  a  philosophical  manner." — The  N.  Y.  Journal  of 
Medicine. 


NEW  WORKS  AND  NEW  EDITIONS  LATELY  PUBLISHED  BY  LEA  AND  BLANCHARD. 

Ellis's   Medical  Formulary, 

NEW    AND    IMPROVED    EDITION. 

THE  MEDICAL,  FORMULARY; 

Being  a  collection  of  Prescriptions,  derived  from  the  writings  and  practice  of  many  of  the  moat 
eminent  physicians  of  America  and  Europe.  To  which  is  added  an  APPENDIX,  containing  the  usual 
dietetic  preparations  and  antidotes  for  poisons.  The  whole  accompanied  with  a  few  brief  pharraa- 
ceutic  and  medical  observations. 

BY  BENJAMIN  ELLIS,  M.  D.} 

LATE  PROFESSOR  OF  MATERIA  MEDICA  AND  PHARMACY  IN  THE  PHILADELPHIA  COLLEGE  OF  PHARMACY. 

Eighth  edition,  with  extensive  alterations  and  additions.    By  SAMUEL  GEORGE  MORTON,  M.  D. 
In  one  neat  octavo  volume. 

This  popular  work  has  been  too  extensively  and  favorably  known  to  the  profession  in  the  United 
States  to  require  any  remarks  in  introducing  a  new  edition,  except  to  state  that  the  improvements  in 
it  will  be  found  to  be  numerous  and  important.  Great  care  has  been  taken  in  its  passage  through  the 
press  to  insure  the  utmost  accuracy,  and  it  is  confidently  presented  as  worthy  the  increased  confidence 
of  physicians  and  apothecaries. 


HOPE  ON  THE  HEART.—  New  Edition,  just  published. 

A  TREATISE  ON  THE  DISEASES 

OF  THE  HEART  AND  GREAT  VESSELS, 

AND  ON  THE  AFFECTIONS  WHICH  MAY  BE  MISTAKEN  FOR  THEM. 

Comprising  the  author's  view  of  the  Physiology  of  the  Heart's  Action  and  Sounds  as  demonstrated  by 
his  experiments  on  the  Motions  and  Sounds  in  1830,  and  on  the  Sounds  in  1834—5. 

BY  J.  HOPE,  M.D.,  F.  R.S.,  &c.  &c. 
Second  American  from  the  third  London  edition.    With  Notes  and  a  Detail  of  Recent  Experiments. 

BY  C.  W.  PENNOCK,  M.D.,&c. 
In  one  octavo  volume  of  nearly  six  hundred  pages,  with  lithographic  plates. 


Under  the  title  of"  Small  Books  on  Great  Subjects,"  there  has  lately  appeared  in  London  a  series  of 
works  which  have  attracted  much  attention  from  their  originality,  strength  and  conciseness.  Not- 
withstanding their  very  high  price,  they  have  commanded  a  large  circulation  in  England,  while  that 
cause  has  limited  the  demand  in  this  country.  In  placing  them,  therefore,  before  the  American  publie 
in  a  neat  form,  and  at  the  very  low  price  of  twenty-five  cents  each,  the  American  publishers  hope  to 
meet  with  an  extended  sale.  The  following  have  appeared  : — 

No.  1.  Philosophical  Theories  and  Philosophical  Experience;  No.  2.  On  the  Connection  between 
Physiology  and  Intellectual  Science;  No.  3.  On  Man's  Power  over  himself  to  Prevent  or  Control 
Insanity ;  No.  4.  An  Introduction  to  Practical  Organic  Chemistry,  with  reference  to  the  works  of 
Davy,  Brande,  Liebig,  &c.;  No.  5.  A  Brief  View  of  Greek  Philosophy,  up  to  the  age  of  Pericles;  No. 
6.  A  Brief  View  of  Greek  Philosophy,  from  the  Age  of  Socrates  to  the  Coming  of  Christ ;  No.  7.  Chris- 
tian Doctrine  and  Practice  in  the  Second  Century;  No.  8.  An  Exposition  of  Vulgar  and  Common 
Errors  adapted  to  the  year  of  Grace  MDCCCXLV;  No  9  An  Introduction  to  Vegetable  Physiology, 
with  References  to  the  Works  of  De  Candolle,  Lindley,  &c.  No  10.  On  the  Principles  of  Criminal 
Law.  No.  11.  Christian  Sects  in  the  Nineteenth  century. 

To  be  Continued. 


NOW  READY.— PHILOLOGY  OF  THE  EXPLORING  EXPEDITION. 

The  Ethnography  and  Philology 
OF  THE  U.  S.  EXPLORING  EXPEDITION, 

Under  the  Command  of  Captain  Wilkes,  during  the  years  1838,  1839,  1840,  1841  and  1842. 

BY  HORATIO  HALE,  Philologist  to  the  Expedition. 
In  one  large  imperial  quarto  volume,  done  up  with  great  strength  in  extra  cloth,  price  only  $10. 

This  is  the  only  edition  of  this  volume,  of  which  but  few  copies  have  been  printed  Early  ap- 
plication is  therefore  necessary  to  secure  it.  It  is  printed  and  arranged  to  match  the  Congress 
copies  of  the  "  Narrative,"  and  is  confidently  presented  as  the  most  beautiful  specimen  of  typo- 
graphy ever  executed  in  this  country. 

This  work  forms  the  seventh  volume  of  the  Publications  of  the  Exploring  Expedition.  The  next 
volume,  by  Professor  Dana,  on  Corals,  with  an  Atlas  of  colored  plates,  will  shortly  be  ready,  to  be 
followed  by  the  remainder  of  the  scientific  portion. 


8  LEA  &  BLANCHARD'S  NEW  PUBLICATIONS. 

THE   GREAT   SURGICAL   LIBRARY 

(NEARLY    COMPLETED). 

CHELIUS1   SYSTEM    OF   SURGERY. 

A  SYSTEM  OF  SURGERY. 

BY  J.  M.  CHELIUS, 

Doctor  in  Medicine  and  Surgery,  Public  Professor  of  General  and  Ophthalmic  Surgery,  etc.  etc.  in  the 

University  of  Heidelberg. 

TRANSLATED  FROM  THE  GERMAN, 
AND  ACCOMPANIED  WITH  ADDITIONAL  NOTES  AND  OBSERVATIONS, 

BY  JOHN  F.  SOUTH, 

SURGEON  TO   ST.  THOMAS'    HOSPITAL. 

(£&iteb,  mill)  Hefmnce  to  American  OVnttjorities, 

BY  GEORGE  W.  NORRIS,  M.D. 

To  be  complete  in  Three  large  Octavo  Volumes  of  about  Six  Hundred  very  large  pages  each,  or 
in  Seventeen  Numbers  at  Fifty  Cents. 

The  completion  of  this  great  work  has  been  delayed  by  the  very  numerous  and  important 
additions  of  the  translator:  it  is  now,  however,  in  a  state  to  enable  the  publishers  to  pro- 
mise its  conclusion  by  the  first  of  March,  1847. 

It  is  unnecessary  to  call  the  attention  of  the  profession  to  this  important  work.  The 
names  which  are  associated  in  it,  and  the  unanimous  testimony  borne  by  the  medical  press 
to  its  excellence  are  sufficient  to  prove  its  great  value.  For  fullness  and  completeness  it  is 
unapproached  by  any  work  of  the  kind  now  before  the  profession,  and  it  may,  indeed,  be 
said  to  be  the  only  real  SYSTEM  OF  SURGERY,  embracing  both  the  Principles  and  Practice,  that 
has  appeared  since  the  days  of  Hunter.  The  consideration  which  it  has  long  enjoyed  abroad 
may  be  estimated  from  the  fact  of  its  having  passed  through  six  editions  in  Germany,  and  its 
having  been  translated  into  no  less  than  seven  languages. 

"Judging  from  a  single  number  only  of  this  work,  we  have  no  hesitation  in  saying  that,  if  the  re- 
maining portions  correspond  at  all  with  the  first,  it  will  be  by  far  the  most  complete  and  scientific  Sys- 
tem of  Surgery  in  the  English  language.  We  have,  indeed,  seen  no  work  which  so  nearly  comes  up 
to  our  idea  of  what  such  a  production  should  be,  both  as  a  practical  guide  and  as  a  work  of  reference, 
•as  this;  and  the  fact  that  it  has  passed  through  six  editions  in  Germany,  and  been  translated  into  seven 
languages,  is  sufficiently  convincing  proof  of  its  value.  It  is  methodical  and  concise,  clear  and  accu- 
rate; omitting  all  minor  details  and  fruitless  speculations,  it  gives  us  all  the  information  we  want  in 
he  shortest  and  simplest  form." — New  York  Journal  of  Medicine. 


DRUITT'S  SURGERY.    New  Edition— Now  Ready. 

THE 

PRINCIPLES  AND  PRACTICE  OF  MODERN  SURGERY, 

BY  ROBERT  DRUITT,  SURGEON. 

THIRD  AMERICAN  FROM  THE  THIRD  LONDON  EDITION. 
ILLUSTRATED  WITH  ONE  HUNDRED  AND  FIFTY-THREE  WOOD  ENGRAVINGS. 

WITH  NOTES  AND  COMMENTS 
BY  JOSHUA  B.  FLINT,  M.D.,  M.M.,  S.S.,  &c.  &c. 

In  One  very  neat  Octavo  Volume  of  about  Five  Hundred  and  Fifty  Pages. 

In  presenting  this  work  to  the  American  profession  for  the  third  time,  but  little  need  be 
said  to  solicit  for  it  a  continuation  of  the  favor  with  which  it  has  been  received.  The  me- 
rits which  have  procured  it  this  favor,  its  clearness,  conciseness,  and  its  excellent  arrange- 
ment, will  continue  to  render  it  the  favorite  text-book  of  the  student  who  wishes  in  a 
moderate  space  a  compend  of  the  principles  and  practice  of  Surgery. 


LEA  &  BLANCHARD'S  NEW  PUBLICATIONS.  9 

JONES  ON  THE  EYE.    Now  Ready. 

THE  PRINCIPLES  AND  PRACTICE 
OF  OPHTHALMIC  MEDICINE  AND  SURGERY. 

BY  T.  WHARTON  JONES,  F.R.S.,  &c.  &c. 

WITH    ONE    HUNDRED    AND    TEN    ILLUSTRATIONS. 

EDITED  BY  ISAAC  HAYS,  M.  D.;  &c. 

In  One  very  neat  Volume,  large  royal  12mo.,  with  Four  Plates,  plain  or  colored,  and 

Ninety-eight  well  executed  Woodcuts. 

This  volume  will  be  found  to  occupy  a  place  hitherto  unfilled  in  this  department  of  medi- 
cal science.  The  aim  of  the  author  has  been  to  produce  a  work  which  should,  in  a  mode- 
rate compass,  be  sufficient  to  serve  both  as  a  convenient  text-book  for  students  and  a  book 
of  reference  for  practitioners.  Thus,  by  great  attention  to  conciseness  of  expression,  a 
strict  adherence  to  arrangement,  and  the  aid  of  numerous  pictorial  illustrations,  he  has  been 
enabled  to  embody  in  it  the  principles  of  ophthalmic  medicine,  and  to  point  out  their  prac- 
tical application  more  fully  than  has  been  done  in  any  other  publication  of  the  same  size. 
The  execution  of  the  work  will  be  found  to  correspond  with  its  merit,  the  illustrations  have 
been  engraved  and  printed  with  care,  and  the  whole  is  confidently  presented  as  in  every 
way  worthy  the  attention  of  the  profession. 

- 


VOGEL'S  PATHOLOGICAL   ANATOMY. 


PATHOLOGICAL  ANATOMY  OF  THE  HUMAN  BODY, 

BY  JULIUS  VOGEL,  M.D.,  &c. 
TRANSLATED  FROM  THE  GERMAN,  WITH  ADDITIONS, 

BY  GEORGE  E.  DAY,  M.D.,  &c. 

Xllustrateti  ftp  u^toartis  of  ©ne  ^untireU  $lafn  anO  ColowlJ  Hnfltabfnfls. 
In  One  neat  Octavo  Volume. 

The  entire  absence  of  any  English  work  on  Morbid  Anatomy,  embracing  the  recent  dis- 
coveries effected  by  chemistry  and  the  microscope,  affords  a  sufficient  reason  for  the  ap- 
pearance, in  the  present  form,  of  "  Vbgel's  Pathological  Anatomy  of  the  Human  Body." 
It  forms  in  itself  a  complete  treatise  on  General  Morbid  Anatomy,  and  will  shortly  be  fol- 
lowed by  a  second  volume  devoted  to  the  consideration  of  pathological  changes  affecting 
special  organs.  This  translation  has  been  made  with  the  approbation  and  assistance  of  the 
author,  who  has  examined  a  considerable  portion  of  the  volume  and  expressed  his  satisfac- 
tion at  the  manner  in  which  it  was  executed. 

A  PKACTICAL  TREATISE 


ON 

,   TTT.nTCBiTTfW  4  NT)  TlMl 


INFLAMMATION,  ULCERATION  AND  INDURATION  OF  THE  NECK  OF  THE  UTERUS: 

WITH  REMARKS  ON  THE  VALUE  OF  LEUCORRHO2A  AND  PROLAPSUS 

UTERI  AS  SYMPTOMS  OF  THIS  FORM  OF  DISEASE. 

BY  J.  HENRY  BENNET,  M.D., 

In  One  Duodecimo  Volume,  cloth. 

"The  descriptions  of  disease  are  throughout  clear  and  concise,  the  arrangement  of  the  subject  i» 
judicious  and  the  remarks  are  thoroughly  practical,  and  calculated  to  improve  the  treatment  ot  a 
ouent  and  troublesome  class  of  diseases.    In  recommending  Dr.  Beimel's  volume,  therefore,  to  our 
readers  as  an  excellent  essay  upon  the  subject,  we  only  convey  the  impression  which  us  perusal  hag 
left  upon  us."— Dublin  Medical  Press. 


10  LEA  &  BLANCHARD'S  NEW  PUBLICATIONS. 

ROYLE'S   MATERIA  MEDICA, 
MATERIA  MEDICA  AND  THERAPEUTICS; 

INCLUDING   THE   PREPARATIONS    OF    THE    PHARMACOPOEIAS    OF 
LONDON,  EDINBURGH,  DUBLIN,  (AND  OF  THE  UNITED  STATES.) 

WITH    MANY    NEW    MEDICINES. 

BY  J.  FORBES  ROYLE,  M.D.,  F.  R.  S., 

Late  of  the  Medical  Staff  in  the  Bengal  Army,  Professor  of  Materia  Medica  and  Therapeutics, 
King's  College   London,  &c.  &c. 

EDITED  BY  JOSEPH  CARSON,  M.D., 

Professor  of  Materia  Medica  in  the  Philadelphia  College  of  Pharmacy,  &c.  &c. 
WITH  NINETY-EIGHT  ILLUSTRATIONS. 

In  one  large  octavo  volume  of  about  700  pages. 
Being  one  of  the  most  beautiful  Medical  works  published  in  this  Country. 

No  apology  is  requisite  for  re-issuing  the  book  in  this  country.  By  the  student  attending 
upon  lectures,  as  well  as  by  practitioners,  a  full  and  large  manual  like  this  cannot  but  be  re- 
ceived with  favor,  and  notwithstanding  the  large  and  valuable  works  that  have  of  late  been 
presented  to  the  profession,  its  merit  will  insure  for  it  a  favorable  reception.  The  illustrations 
are  superior  to  those  heretofore  given  in  works  of  the  kind,  every  care  having  been  taken 
both  in  the  engraving  and  printing.  The  labors  of  the  editor  have  been  confined  to  the  su- 
pervision of  the  work  in  passing  it  through  the  press,  and  the  addition  of  such  matter  in  con- 
nection with  the  Pharmacopoeia  and  indigenous  Materia  Medica  of  the  United  States,  as 
would  render  the  work  fitted  for  American  students  and  practitioners. 

WILSON'S  ANATOMY.    New  Edition— Now  Ready. 

A  SYSTEM  OF   HUMAN  ANATOMY, 
GENERAL   AND  SPECIAL. 

BY  ERASMUS  WILSON,  M.D., 

Lecturer  on  Anatomy,  London. 
THIRD  AMERICAN  FROM  THE  THIRD  LONDON  EDITION. 

EDITED  BY  P.  B.   GODDARD,  A.M.,  M.D., 

Professor  of  Anatomy  in  the  Franklin  Medical  College  of  Philadelphia. 

WITH  TWO  HUNDRED  AND  THIRTY-FIVE  ILLUSTRATIONS  BY  GILBERT. 
In  one  beautiful  octavo  volume  of  over  SIX.  HUNDRED  JLarg-e  fag-et, 

Strongly  Bound  and  sold  at  a  low  price. 

Since  the  publication  of  the  second  American  edition  of  this  work,  the  author  has  issued 
a  third  in  London,  in  which  he  has  carefully  brought  up  his  work  to  a  level  with  the  most 
advanced  science  of  the  day.  All  the  elementary  chapters  have  been  rewritten,  and  such 
alterations  made  through  the  body  of  the  work,  by  the  introduction  of  all  new  facts  of  inte- 
rest, illustrated  by  appropriate  engravings,  as  much  increase  its  value.  The  present 
edition  is  a  careful  and  exact  reprint  of  the  English  volume,  with  the  addition  of  such  other 
illustrations  as  were  deemed  necessary  to  a  more  complete  elucidation  of  the  text;  and 
the  insertion  of  such  of  the  notes  appended  to  the  last  American  edition  as  had  not  been 
adopted  by  the  author  and  embodied  in  his  text;  together  with  such  additional  information 
as  appeared  calculated  to  enhance  the  value  of  the  work.  It  may  also  be  stated  that  the 
utmost  care  has  been  taken  in  the  revision  of  the  letter-press,  and  in  obtaining  clear  and 
distinct  impressions  of  the  accompanying  cuts. 

It  will  thus  be  seen,  that  every  effort  has  been  used  to  render  this  text-book  worthy  of  a 
continuance  of  the  great  favor  with  which  it  has  been  everywhere  received.  Professors 
desirous  of  adopting  it  for  their  classes  may  rely  on  being  always  able  to  procure  editions 
brought  up  to  the  day. 

This  book  is  well  known  for  the  beauty  and  accuracy  of  its  mechanical  execution.  The 
present  edition  is  an  improvement  over  the  last,  both  in  the  number  and  clearness  of  its 
embellishments  ;  it  is  bound  in  the  best  manner  in  strong  sheep,  and  is  sold  at  a  price 
which  renders  it  accessible  to  all. 


/ 


LEA  &  BLANCHARD'S  NEW  PUBLICATIONS.  \\ 


SUPPLEMENT  TO  THE  ENCYCLOPEDIA  AMERICANA,  UP  TO  THE  YEAR  1847, 

ENCYCLOPEDIA  AMERICANA-Supplementary  Vol. 
A  POPULAR  DICTIONARY 

OF  ARTS,  SCIENCES,  LITERATURE,  HISTORY,  POLITICS 
AND  BIOGRAPHY. 

VOL.  XIV. 

EDITED  BY  HENRY  VETHAKE,  LL.D., 

Vice-Provost  and  Professor  of  Mathematics  in  the  Universi^of  Pennsylvania,  Author  of  "A  Treatise 

on  Political  Economy." 

In  One  large  Octavo  Volume  of  over  Six  Hundred  and  Fifty  double  columned  pages. 

The  numerous  subscribers  who  have  been  waiting  the  completion  of  this  volume  can  now 
perfect  their  sets,  and  all  who  want  a  Register  of  the  Events  of  the  last  Fifteen  Years,  for 
the  Whole  World,  particularly  embracing  interesting  scientific  investigations  and  discover- 
ies, can  obtain  this  volume  separately,  price  Two  Dollars  uncut  in  cloth,  or  Two  Dollars 
and  Fifty  Cents  in  leather,  to  match  the  styles  in  which  the  publishers  have  been  selling  sets. 

Subscribers  in  the  large  cities  can  be  supplied  on  application  at  any  of  the  principal  book- 
stores; and  persons  residing  in  the  country  can  have  their  sets  matched  by  sending  a  volume 
in  charge  of  friends  visiting  the  city. 

Complete  sets  furnished  at  very  low  prices  in  various  bindings. 

"The  Conversations  Lexikon  (Encyclopaedia  Americana)  has  become  a  household  book  in  all  th 
intelligent  families  in  America,  and  is  undoubtedly  the  best  depository  of  biographical,  historical,  geo- 
graphical and  political  information  of  that  kind  which  discriminating  readers  require.  There  is  in  the 
present  volume  much  matter  purely  scientific,  which  was  all  the  more  acceptable  to  us  that  it  was 
unexpected." — Silliman's  Journal. 

THE  CHEMISTRY  OF  THE  FOUR  SEASONS— A  NEW  WORE. 
THE  CHEMISTRY  OF  THE  FOUR  SEASONS, 

SPRING,  SUMMER,  AUTUMN  AND  WINTER. 

AN  ESSAY   PRINCIPALLY   CONCERNING    NATURAL    PHENOMENA    ADMITTING    OF 

ILLUSTRATION  BY  CHEMICAL  SCIENCE,  AND  ILLUSTRATING  PASSAGES 

OF  SCRIPTURE. 

BY  THOMAS  GRIFFITHS, 

Professor  of  Chemistry  in  the  Medical  College  of  St.  Bartholomew's  Hospital,  Ac. 

In  One  very  neat  Volume,  royal  12mo.,  of  Four  Hundred  and  Fifty  large  pages,  extra  ckth, 

illustrated  unth  numerous  Woodcuts. 

"The  title-page  copied  at  the  head  of  this  article  sufficiently  expresses  the  objects  of  the  work,  and 
the  subjects  of  which  it  treats.  It  is  a  token  from  the  laboratory,  designed  for  the  parlor.  The  dis- 
courses are  adapted  to  the  comprehension  of  those  not  familiar  with  the  technicalities  and  details  of 
chemistry,  and  are  written  in  a  pleasing  style.  The  mechanical  execution  of  the  work  is  neat  and 
tasteful.  Altogether  it  is  a  beautiful  volume."— Buffalo  Med.  Journal. 

YOUATT    ON    THE    DOG. 

THE    DOG. 

BY   WILLIAM   YOUATT. 

WITH  NUMEROUS  AND  BEAUTIFUL  ILLUSTRATIONS. 
EDITED  BY  E.  J.  LEWIS,  M.D.,  &c.  &c. 

In  One  beautifully  printed  Volume.  Crown  Octavo,  with  Twenty-four  Plates,  done  up  in 

rich  crimson  extra  cloth. 

"With  this  explanation  of  his  connection  with  the  work  he  leaves  it,  in  the  hope  that  it 
may  prove  of  value  to  the  sportsman  from  its  immediate  relation  to  his  stirring  pursuits;  to 
the  general  reader  from  the  large  amount  of  curious  information  collected  in  its  pages;  and 
to  the  medical  student  from  the  light  it  sheds  on  the  pathology  and  disease*  of  the  dog,  by 
which  he  will  be  surprised  to  learn  how  many  ills  that  animal  shares  in  common  with  the 
human  race."— EDITOR'S  PREFACE. 


12  VALUABLE  WORKS  PUBLISHED  BY  LEA  AND  BLANCHARD. 

Valuable  Works  for  Sportsmen,  &c, 
THE    11ORSE, 

BY     WILLIAM     YOUATT. 

A  NEW  EDITION,  WITH  NUMEROUS  ILLUSTRATIONS.    TOGETHER  WITH  A 


A    DISSERTATION    ONTHE    AMERICAN    TROTTING    HORSE 

HOW  TRAINED  AND  JOCKEYED.      AN  ACCOUNT  OF  HIS  REMARKABLE  PERFORMANCES  J 
AND  AN  ESSAY  ON  THE  ASS  AND  THE  MULE, 

BY    J     S.    SKINNER, 

ASSISTANT  POST-MASTER  GENERAL,  AND  EDITOR  OF  THE  TURF  REGISTER. 

This  edition  of  Youatt's  well-known  and  standard  work  on  the  Management,  Diseases  and 
Treatment  of  the  Horse,  has  already  obtained  such  a  wide  circulation  throughout  the  country; 
that  the  Publishers  need  say  nothing  to  attract  to  it  the  attention  and  confidence  of  all  who 
keep  Horses  or  are  interested  in  their  improvement. 


STABLE  TALK  AND  TABLE  TALK, 

OR  SPECTACLES  FOR  YOUNG  SPORTSMEN. 

BY  HARRY  HIEOVER. 
In  one  very  neat  duodecimo  volume,  extra  cloth. 


THE    SPORTSMAN'S   LIBRARY, 

OR  HINTS  ON  HUNTERS,  HUNTING,  HOUNDS,  SHOOTING,  GAME,  DOGS,  GUNS,  FISHING, 

COURSING,  &c.,  &c. 
In  one  well  printed  volume,  duodecimo,  extra  cloth. 


EVERY  MAN  HIS  OWN  FARRIER; 

CONTAINING  THE  CAUSES,  SYMPTOMS  AND  MOST  APPROVED  METHODS  OF  CURE  OF  THE 

DISEASES  OF  HORSES. 

BY    FRANCIS    CLATER, 

AUTHOR  OF  "  EVERY  MAN  HIS  OWN  CATTLE  DOCTOR." 

AND  HIS  SON  JOHN  CLATER. 

First  American  from  the  twenty-eighth  London  edition,  with  notes  and  additions,  by  J.  S.  SKINNER.    In  one 

12mo.  volume,  cloth. 


EVERY  MAN  HIS  OWN  CATTLE  DOCTOR. 

CONTAINING  THE  CAUSES,  SYMPTOMS  AND  TREATMENT  OF  ALL  DISEASES  INCIDENT  TO 
OXEN,  SHEEP  AND  SWINE;  AND  A  SKETCH  OF  THE  ANATOMY  AND  PHYSI- 
OLOGY OF  NEAT  CATTLE.-BY  FRANCIS  CLATER. 

Edited,  Revised,  and  almost  Rewritten,  by  WILLIAM  YOUATT.    With  numerous  Additions,  embracingan  Essay 

on  the  Use  of  Oxen,  and  the  Improvement  in  the  Breed  of  Sheep,  by  J.  S.  SKINNER,  Asst.  P.  M  General. 

In  one  duodecimo  volume,  cloth,  with  numerous  illustrations. 

Kirby  and  Spence's  Entomology,  for  Popular  Use, 
AN  INTRODUCTION~TO  ENTOMOLOGY; 

OR,  ELEMENTS  OF  THE  NATURAL  HISTORY  OF  INSECTS;  COMPRISING  AN  ACCOUNT  OF 
NOXIOUS  AND  USEFUL  INSECTS,  OF  THEIR  METAMORPHOSES,  FOOD,  STRATAGEMS, 
HABITATIONS,  SOCIETIES,  MOTIONS,  NOISES,  HYBERNATION,  INSTINCT,  &c.,  &c. 

With  Plates,  Plain  or  Colored. 
BY  WILLIAM  KIRBY,  M.  A.,  F.  R.  S.    AND  WILLIAM  SPENCE,  ESQ,,  F.  R.  S. 

From  the  sixth  London  edition,  which  was  corrected  and  considerably  enlarged.  In  one 
large  octavo  volume,  extra  cloth. 

We  have  been  greatly  interested  in  running  over  the  pages  of  this  treatise.  There  is  scarcely,  in  the  wide 
range  of  natural  science,  a  more  interesting  or  instructive  study  than  that  of  fnsects,  or  one  that  is  calculated 
to  excite  more  curiosity  or  wonder. 

The  popular  form  of  letters  is  adopted  by  the  authors  in  imparting  a  knowledge  of  the  subject,  which  ren- 
ders the  work  peculiarly  fitted  for  our  district  school  libraries,  which  are  open  to  all  ages  and  classes.— Hunfs 
Merchants'  Magazine. 


VALUABLE  WORKS  PUBLISHED  BY  LEA  AND  BLANCH ARD.  13 

CAMPBELL'S  LORD  CHANCELLORS. 

JUST  PUBLISHED. 

LIVES  OF  THE  LORD  CHANCELLORS  AND  KEEPERS  OF  THE 

GREAT  SEAL  OF  ENGLAND, 

FROM  THE  EARLIEST  TIMES  TO  THE  REIGN  OF  KING  GEORGE  IV., 
BY  JOHN  LORD  CAMPBELL,  A.  M.,  F.  R.  S.  E. 

First  Series,  forming  three  neat  volumes  in  demy  octavo,  extra  cloth. 

Bringing  the  work  to  the  time  of  Lord  Jeffries. 
The  second  series  will  shortly  follow  in  three  volumes  to  match. 

It  is  sufficient  for  us  to  thank  Lord  Campbell  for  tne  honest  industry  with  which  he  has 
thus  far  prosecuted  his  large  task,  the  general  candor  and  liberality  with  which  he  has 
analyzed  the  lives  and  characters  of  a  long  succession  of  influential  magistrates  and  min- 
isters, and  the  manly  style  of  his  narrative.  We  need  hardly  say  that  we  shall  expect  with 
great  interest  the  continuation  of  this  performance.  But  the  present  series  of  itself  is  more 
than  sufficient  to  give  Lord  Campbell  a  high  station  among  the  English  authors  of  his  age. 
—  Quarterly  Rev. 

The  volumes  teem  with  exciting  incidents,  abound  in  portraits,  sketches  and  anecdotes, 
and  are  at  once  interesting  and  instructive.  The  work  is  not  only  historical  and  biographi- 
cal, but  it  is  anecdotal  and  philosophical.  Many  of  the  chapters  embody  thrilling  incidents, 
while  as  a  whole,  the  publication  may  be  regarded  as  of  a  high  intellectual  order. — Inquirer. 

A  work  in  three  handsome  octavo  volumes,  which  we  shall  regard  as  both  an  ornament 
and  an  honor  to  our  library.  A  History  of  the  Lord  Chancellors  of  England  from  the  insti- 
tution of  the  office,  is  necessarily  a  History  of  the  Constitution,  the  Court,  and  the  Jurispru- 
dence of  the  Kingdom,  and  these  volumes  teem  with  a  world  of  collateral  matter  of  the  live- 
liest character  for  the  general  reader,  as  well  as  with  much  of  the  deepest  interest  for  the  pro- 
fessional or  philosophical  mind. — Saturday  Courier. 

A  work  of  enduring  interest,  as  well  from  the  signal  ability  with  which  it  is  written,  as 
from  the  great  names  whose  personal  history  and  official  acts  it  enumerates. — Richmond 
Whig. 

HAWKER   ON^SHOOTING. 

INSTRUCTIONS   TO   YOUNG    SPORTSMEN   IN   ALL    THAT    RE- 
LATES   TO    GUNS    AND    SHOOTING. 

BY  LIEUT.  COL.  P.  HAWKER. 

From  the  enlarged  and  improved  ninth  London  edition. 

To  which  is  added  the  Hunting  and  Shooting  of  North  America^  with  Descriptions  of  Animals  and  Birds. 
Carefully  collated  from  authentic  sources. 

BY  W.  T.  PORTER,   ESQ.,  EDITOR  OF  THE  N.  Y.  SPIRIT  OF  THE  TIMES. 

In  one  large  octavo  volume,  rich  extra  cloth,  with  numerous  Illustrations. 

"  Here  is  a  book,  a  hand-book,  or  rather  a  text-book—one  that  contains  the  whole  routine  of  the  science.  It  is 
the  Primer,  the  Lexicon,  and  the  Homer.  Every  thing  is  here,  from  the  minutest  portion  of  a  gun-lock,  to  a 
dead  Buffalo.  The  sportsman  who  reads  this  book  understandingly,  may  pass  an  examination.  He  will  know 
the  science,  and  may  give  advice  to  others.  Every  sportsman,  and  sportsmen  are  plentiful,  should  own  this 
work.  It  should  be  a  "  vade  mecum."  He  should  be  examined  on  its  contents,  and  estimated  by  his  abilities 
to  answer.  We  have  not  been  without  treatises  on  the  art,  but  hitherto  they  have  not  descended  into  all  II 
minutiae  of  equipments  and  qualifications  to  proceed  to  the  completion.  This  work  supplies  deficiencies,  and 
completes  the  sportsman's  library." — 17.  S.  Gazette. 


PHILOSOPHY  IN  SPORT  MADE  SCIENCE  IN  EARNEST, 

BEING  AN  ATTEMPT  TO  ILLUSTRATE  THE  FIRST  PRINCIPLES  OF  NATURAL 

PHILOSOPHY,  BY  THE  AID  OF  THE  POPULAR  TOYS 

AND  SPORTS  OF  YOUTH. 

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PUBLISHED   BY   LEA   &    BLANCHARP. 
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EN  C  YD  LOP/EDJjl  AMERICANA, 

THE  ENCYCLOP/EDIA  AMERICANA: 

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OF  ARTS,  SCIENCES,  LITERATURE,  HISTORY,  POLITICS  &  BIOGRAPHY. 

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THE   SUPPLEMENTARY   VOLUME, 

(VOL  XIV.) 

Bringing  the  -work  up  to  1847. 
EDITED  BY  HENRY  VETHAKE,  LL.D., 

Vice  Provost  and  Professor  of  Mathematics  in  the  University  of  Pennsylvania,  &c.;  Author  of  a  Treatise  on 

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MURRAY'S  ENCYCLOPEDIA  OF  GEOGRAPHY. 


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•  Renewals  and  recharges  may  be  made 
4  days  prior  to  due  date 

DUE  AS  STAMPED  BELOW 
MAR  0  4  2006 


DD20   12M   1-05 

lm-4,'29    I 


OP 


